15 files changed, 677 insertions, 469 deletions

diff --git a/src/libexpr/attr-set.cc b/src/libexpr/attr-set.cc
index b6091c955..52ac47e9b 100644
--- a/src/libexpr/attr-set.cc
+++ b/src/libexpr/attr-set.cc
@@ -7,26 +7,19 @@
 namespace nix {
 
 
+
 /* Allocate a new array of attributes for an attribute set with a specific
    capacity. The space is implicitly reserved after the Bindings
    structure. */
 Bindings * EvalState::allocBindings(size_t capacity)
 {
+    if (capacity == 0)
+        return &emptyBindings;
     if (capacity > std::numeric_limits<Bindings::size_t>::max())
         throw Error("attribute set of size %d is too big", capacity);
-    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings((Bindings::size_t) capacity);
-}
-
-
-void EvalState::mkAttrs(Value & v, size_t capacity)
-{
-    if (capacity == 0) {
-        v = vEmptySet;
-        return;
-    }
-    v.mkAttrs(allocBindings(capacity));
     nrAttrsets++;
     nrAttrsInAttrsets += capacity;
+    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings((Bindings::size_t) capacity);
 }
 
 
@@ -41,15 +34,36 @@ Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
 }
 
 
-Value * EvalState::allocAttr(Value & vAttrs, const std::string & name)
+Value * EvalState::allocAttr(Value & vAttrs, std::string_view name)
 {
     return allocAttr(vAttrs, symbols.create(name));
 }
 
 
+Value & BindingsBuilder::alloc(const Symbol & name, ptr<Pos> pos)
+{
+    auto value = state.allocValue();
+    bindings->push_back(Attr(name, value, pos));
+    return *value;
+}
+
+
+Value & BindingsBuilder::alloc(std::string_view name, ptr<Pos> pos)
+{
+    return alloc(state.symbols.create(name), pos);
+}
+
+
 void Bindings::sort()
 {
-    std::sort(begin(), end());
+    if (size_) std::sort(begin(), end());
+}
+
+
+Value & Value::mkAttrs(BindingsBuilder & bindings)
+{
+    mkAttrs(bindings.finish());
+    return *this;
 }
 
 
diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
index 7d6ffc9f3..82c348287 100644
--- a/src/libexpr/attr-set.hh
+++ b/src/libexpr/attr-set.hh
@@ -113,5 +113,45 @@ public:
     friend class EvalState;
 };
 
+/* A wrapper around Bindings that ensures that its always in sorted
+   order at the end. The only way to consume a BindingsBuilder is to
+   call finish(), which sorts the bindings. */
+class BindingsBuilder
+{
+    Bindings * bindings;
+
+public:
+
+    EvalState & state;
+
+    BindingsBuilder(EvalState & state, Bindings * bindings)
+        : bindings(bindings), state(state)
+    { }
+
+    void insert(Symbol name, Value * value, ptr<Pos> pos = ptr(&noPos))
+    {
+        insert(Attr(name, value, pos));
+    }
+
+    void insert(const Attr & attr)
+    {
+        bindings->push_back(attr);
+    }
+
+    Value & alloc(const Symbol & name, ptr<Pos> pos = ptr(&noPos));
+
+    Value & alloc(std::string_view name, ptr<Pos> pos = ptr(&noPos));
+
+    Bindings * finish()
+    {
+        bindings->sort();
+        return bindings;
+    }
+
+    Bindings * alreadySorted()
+    {
+        return bindings;
+    }
+};
 
 }
diff --git a/src/libexpr/common-eval-args.cc b/src/libexpr/common-eval-args.cc
index fb0932c00..fffca4ac5 100644
--- a/src/libexpr/common-eval-args.cc
+++ b/src/libexpr/common-eval-args.cc
@@ -73,17 +73,16 @@ MixEvalArgs::MixEvalArgs()
 
 Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
 {
-    Bindings * res = state.allocBindings(autoArgs.size());
+    auto res = state.buildBindings(autoArgs.size());
     for (auto & i : autoArgs) {
-        Value * v = state.allocValue();
+        auto v = state.allocValue();
         if (i.second[0] == 'E')
             state.mkThunk_(*v, state.parseExprFromString(string(i.second, 1), absPath(".")));
         else
-            mkString(*v, string(i.second, 1));
-        res->push_back(Attr(state.symbols.create(i.first), v));
+            v->mkString(((std::string_view) i.second).substr(1));
+        res.insert(state.symbols.create(i.first), v);
     }
-    res->sort();
-    return res;
+    return res.finish();
 }
 
 Path lookupFileArg(EvalState & state, string s)
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index a95726f5f..61bccd6e2 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -36,6 +36,19 @@
 namespace nix {
 
 
+static char * allocString(size_t size)
+{
+    char * t;
+#if HAVE_BOEHMGC
+    t = (char *) GC_MALLOC_ATOMIC(size);
+#else
+    t = malloc(size);
+#endif
+    if (!t) throw std::bad_alloc();
+    return t;
+}
+
+
 static char * dupString(const char * s)
 {
     char * t;
@@ -145,7 +158,7 @@ void printValue(std::ostream & str, std::set<const Value *> & active, const Valu
         str << v.fpoint;
         break;
     default:
-        throw Error("invalid value");
+        abort();
     }
 
     active.erase(&v);
@@ -413,6 +426,7 @@ EvalState::EvalState(
     , sSelf(symbols.create("self"))
     , sEpsilon(symbols.create(""))
     , repair(NoRepair)
+    , emptyBindings(0)
     , store(store)
     , buildStore(buildStore ? buildStore : store)
     , regexCache(makeRegexCache())
@@ -454,8 +468,6 @@ EvalState::EvalState(
         }
     }
 
-    vEmptySet.mkAttrs(allocBindings(0));
-
     createBaseEnv();
 }
 
@@ -613,7 +625,7 @@ Value * EvalState::addPrimOp(const string & name,
         auto vPrimOp = allocValue();
         vPrimOp->mkPrimOp(new PrimOp { .fun = primOp, .arity = 1, .name = sym });
         Value v;
-        mkApp(v, *vPrimOp, *vPrimOp);
+        v.mkApp(vPrimOp, vPrimOp);
         return addConstant(name, v);
     }
 
@@ -635,7 +647,7 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
         auto vPrimOp = allocValue();
         vPrimOp->mkPrimOp(new PrimOp(std::move(primOp)));
         Value v;
-        mkApp(v, *vPrimOp, *vPrimOp);
+        v.mkApp(vPrimOp, vPrimOp);
         return addConstant(primOp.name, v);
     }
 
@@ -766,15 +778,14 @@ LocalNoInline(void addErrorTrace(Error & e, const Pos & pos, const char * s, con
 }
 
 
-void mkString(Value & v, const char * s)
+void Value::mkString(std::string_view s)
 {
-    v.mkString(dupString(s));
+    mkString(dupStringWithLen(s.data(), s.size()));
 }
 
 
-Value & mkString(Value & v, std::string_view s, const PathSet & context)
+static void copyContextToValue(Value & v, const PathSet & context)
 {
-    v.mkString(dupStringWithLen(s.data(), s.size()));
     if (!context.empty()) {
         size_t n = 0;
         v.string.context = (const char * *)
@@ -783,13 +794,24 @@ Value & mkString(Value & v, std::string_view s, const PathSet & context)
             v.string.context[n++] = dupString(i.c_str());
         v.string.context[n] = 0;
     }
-    return v;
 }
 
+void Value::mkString(std::string_view s, const PathSet & context)
+{
+    mkString(s);
+    copyContextToValue(*this, context);
+}
 
-void mkPath(Value & v, const char * s)
+void Value::mkStringMove(const char * s, const PathSet & context)
 {
-    v.mkPath(dupString(s));
+    mkString(s);
+    copyContextToValue(*this, context);
+}
+
+
+void Value::mkPath(std::string_view s)
+{
+    mkPath(dupStringWithLen(s.data(), s.size()));
 }
 
 
@@ -882,13 +904,13 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 void EvalState::mkPos(Value & v, ptr<Pos> pos)
 {
     if (pos->file.set()) {
-        mkAttrs(v, 3);
-        mkString(*allocAttr(v, sFile), pos->file);
-        mkInt(*allocAttr(v, sLine), pos->line);
-        mkInt(*allocAttr(v, sColumn), pos->column);
-        v.attrs->sort();
+        auto attrs = buildBindings(3);
+        attrs.alloc(sFile).mkString(pos->file);
+        attrs.alloc(sLine).mkInt(pos->line);
+        attrs.alloc(sColumn).mkInt(pos->column);
+        v.mkAttrs(attrs);
     } else
-        mkNull(v);
+        v.mkNull();
 }
 
 
@@ -1067,8 +1089,8 @@ void ExprPath::eval(EvalState & state, Env & env, Value & v)
 
 void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 {
-    state.mkAttrs(v, attrs.size() + dynamicAttrs.size());
-    Env *dynamicEnv = &env;
+    v.mkAttrs(state.buildBindings(attrs.size() + dynamicAttrs.size()).finish());
+    auto dynamicEnv = &env;
 
     if (recursive) {
         /* Create a new environment that contains the attributes in
@@ -1259,14 +1281,14 @@ void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
         if (vAttrs->type() != nAttrs ||
             (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
         {
-            mkBool(v, false);
+            v.mkBool(false);
             return;
         } else {
             vAttrs = j->value;
         }
     }
 
-    mkBool(v, true);
+    v.mkBool(true);
 }
 
 
@@ -1341,7 +1363,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                     /* Nope, so show the first unexpected argument to the
                        user. */
                     for (auto & i : *args[0]->attrs)
-                        if (lambda.formals->argNames.find(i.name) == lambda.formals->argNames.end())
+                        if (!lambda.formals->argNames.count(i.name))
                             throwTypeError(pos, "%1% called with unexpected argument '%2%'", lambda, i.name);
                     abort(); // can't happen
                 }
@@ -1484,22 +1506,20 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
         return;
     }
 
-    Value * actualArgs = allocValue();
-    mkAttrs(*actualArgs, std::max(static_cast<uint32_t>(fun.lambda.fun->formals->formals.size()), args.size()));
+    auto attrs = buildBindings(std::max(static_cast<uint32_t>(fun.lambda.fun->formals->formals.size()), args.size()));
 
     if (fun.lambda.fun->formals->ellipsis) {
         // If the formals have an ellipsis (eg the function accepts extra args) pass
         // all available automatic arguments (which includes arguments specified on
         // the command line via --arg/--argstr)
-        for (auto& v : args) {
-            actualArgs->attrs->push_back(v);
-        }
+        for (auto & v : args)
+            attrs.insert(v);
     } else {
         // Otherwise, only pass the arguments that the function accepts
         for (auto & i : fun.lambda.fun->formals->formals) {
             Bindings::iterator j = args.find(i.name);
             if (j != args.end()) {
-                actualArgs->attrs->push_back(*j);
+                attrs.insert(*j);
             } else if (!i.def) {
                 throwMissingArgumentError(i.pos, R"(cannot evaluate a function that has an argument without a value ('%1%')
 
@@ -1512,9 +1532,7 @@ https://nixos.org/manual/nix/stable/#ss-functions.)", i.name);
         }
     }
 
-    actualArgs->attrs->sort();
-
-    callFunction(fun, *actualArgs, res, noPos);
+    callFunction(fun, allocValue()->mkAttrs(attrs), res, noPos);
 }
 
 
@@ -1549,7 +1567,7 @@ void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpNot::eval(EvalState & state, Env & env, Value & v)
 {
-    mkBool(v, !state.evalBool(env, e));
+    v.mkBool(!state.evalBool(env, e));
 }
 
 
@@ -1557,7 +1575,7 @@ void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    mkBool(v, state.eqValues(v1, v2));
+    v.mkBool(state.eqValues(v1, v2));
 }
 
 
@@ -1565,25 +1583,25 @@ void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    mkBool(v, !state.eqValues(v1, v2));
+    v.mkBool(!state.eqValues(v1, v2));
 }
 
 
 void ExprOpAnd::eval(EvalState & state, Env & env, Value & v)
 {
-    mkBool(v, state.evalBool(env, e1, pos) && state.evalBool(env, e2, pos));
+    v.mkBool(state.evalBool(env, e1, pos) && state.evalBool(env, e2, pos));
 }
 
 
 void ExprOpOr::eval(EvalState & state, Env & env, Value & v)
 {
-    mkBool(v, state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
+    v.mkBool(state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
 }
 
 
 void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
 {
-    mkBool(v, !state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
+    v.mkBool(!state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
 }
 
 
@@ -1598,7 +1616,7 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
     if (v1.attrs->size() == 0) { v = v2; return; }
     if (v2.attrs->size() == 0) { v = v1; return; }
 
-    state.mkAttrs(v, v1.attrs->size() + v2.attrs->size());
+    auto attrs = state.buildBindings(v1.attrs->size() + v2.attrs->size());
 
     /* Merge the sets, preferring values from the second set.  Make
        sure to keep the resulting vector in sorted order. */
@@ -1607,17 +1625,19 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 
     while (i != v1.attrs->end() && j != v2.attrs->end()) {
         if (i->name == j->name) {
-            v.attrs->push_back(*j);
+            attrs.insert(*j);
             ++i; ++j;
         }
         else if (i->name < j->name)
-            v.attrs->push_back(*i++);
+            attrs.insert(*i++);
         else
-            v.attrs->push_back(*j++);
+            attrs.insert(*j++);
     }
 
-    while (i != v1.attrs->end()) v.attrs->push_back(*i++);
-    while (j != v2.attrs->end()) v.attrs->push_back(*j++);
+    while (i != v1.attrs->end()) attrs.insert(*i++);
+    while (j != v2.attrs->end()) attrs.insert(*j++);
+
+    v.mkAttrs(attrs.alreadySorted());
 
     state.nrOpUpdateValuesCopied += v.attrs->size();
 }
@@ -1664,13 +1684,34 @@ void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const Po
 void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 {
     PathSet context;
-    std::ostringstream s;
+    std::vector<std::string> s;
+    size_t sSize = 0;
     NixInt n = 0;
     NixFloat nf = 0;
 
     bool first = !forceString;
     ValueType firstType = nString;
 
+    const auto str = [&] {
+        std::string result;
+        result.reserve(sSize);
+        for (const auto & part : s) result += part;
+        return result;
+    };
+    /* c_str() is not str().c_str() because we want to create a string
+       Value. allocating a GC'd string directly and moving it into a
+       Value lets us avoid an allocation and copy. */
+    const auto c_str = [&] {
+        char * result = allocString(sSize + 1);
+        char * tmp = result;
+        for (const auto & part : s) {
+            memcpy(tmp, part.c_str(), part.size());
+            tmp += part.size();
+        }
+        *tmp = 0;
+        return result;
+    };
+
     for (auto & [i_pos, i] : *es) {
         Value vTmp;
         i->eval(state, env, vTmp);
@@ -1700,26 +1741,29 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
                 nf += vTmp.fpoint;
             } else
                 throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp));
-        } else
+        } else {
+            if (s.empty()) s.reserve(es->size());
             /* skip canonization of first path, which would only be not
             canonized in the first place if it's coming from a ./${foo} type
             path */
-            s << state.coerceToString(i_pos, vTmp, context, false, firstType == nString, !first);
+            s.emplace_back(
+                state.coerceToString(i_pos, vTmp, context, false, firstType == nString, !first));
+            sSize += s.back().size();
+        }
 
         first = false;
     }
 
     if (firstType == nInt)
-        mkInt(v, n);
+        v.mkInt(n);
     else if (firstType == nFloat)
-        mkFloat(v, nf);
+        v.mkFloat(nf);
     else if (firstType == nPath) {
         if (!context.empty())
             throwEvalError(pos, "a string that refers to a store path cannot be appended to a path");
-        auto path = canonPath(s.str());
-        mkPath(v, path.c_str());
+        v.mkPath(canonPath(str()));
     } else
-        mkString(v, s.str(), context);
+        v.mkStringMove(c_str(), context);
 }
 
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 15925a6b4..850c5bae6 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -44,8 +44,6 @@ struct Env
 };
 
 
-Value & mkString(Value & v, std::string_view s, const PathSet & context = PathSet());
-
 void copyContext(const Value & v, PathSet & context);
 
 
@@ -93,7 +91,7 @@ public:
        mode. */
     std::optional<PathSet> allowedPaths;
 
-    Value vEmptySet;
+    Bindings emptyBindings;
 
     /* Store used to materialise .drv files. */
     const ref<Store> store;
@@ -339,12 +337,16 @@ public:
     Env & allocEnv(size_t size);
 
     Value * allocAttr(Value & vAttrs, const Symbol & name);
-    Value * allocAttr(Value & vAttrs, const std::string & name);
+    Value * allocAttr(Value & vAttrs, std::string_view name);
 
     Bindings * allocBindings(size_t capacity);
 
+    BindingsBuilder buildBindings(size_t capacity)
+    {
+        return BindingsBuilder(*this, allocBindings(capacity));
+    }
+
     void mkList(Value & v, size_t length);
-    void mkAttrs(Value & v, size_t capacity);
     void mkThunk_(Value & v, Expr * expr);
     void mkPos(Value & v, ptr<Pos> pos);
 
@@ -353,7 +355,10 @@ public:
     /* Print statistics. */
     void printStats();
 
-    void realiseContext(const PathSet & context);
+    /* Realise the given context, and return a mapping from the placeholders
+     * used to construct the associated value to their final store path
+     */
+    [[nodiscard]] StringMap realiseContext(const PathSet & context);
 
 private:
 
@@ -394,6 +399,8 @@ private:
     friend struct ExprSelect;
     friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
     friend void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v);
+
+    friend struct Value;
 };
 
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index b15878d5c..190a128d7 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -251,6 +251,10 @@ static Flake getFlake(
             forceTrivialValue(state, *setting.value, *setting.pos);
             if (setting.value->type() == nString)
                 flake.config.settings.insert({setting.name, state.forceStringNoCtx(*setting.value, *setting.pos)});
+            else if (setting.value->type() == nPath) {
+                PathSet emptyContext = {};
+                flake.config.settings.insert({setting.name, state.coerceToString(*setting.pos, *setting.value, emptyContext, false, true, true)});
+            }
             else if (setting.value->type() == nInt)
                 flake.config.settings.insert({setting.name, state.forceInt(*setting.value, *setting.pos)});
             else if (setting.value->type() == nBool)
@@ -344,7 +348,8 @@ LockedFlake lockFlake(
             const InputPath & inputPathPrefix,
             std::shared_ptr<const Node> oldNode,
             const LockParent & parent,
-            const Path & parentPath)>
+            const Path & parentPath,
+            bool trustLock)>
             computeLocks;
 
         computeLocks = [&](
@@ -353,7 +358,8 @@ LockedFlake lockFlake(
             const InputPath & inputPathPrefix,
             std::shared_ptr<const Node> oldNode,
             const LockParent & parent,
-            const Path & parentPath)
+            const Path & parentPath,
+            bool trustLock)
         {
             debug("computing lock file node '%s'", printInputPath(inputPathPrefix));
 
@@ -464,14 +470,20 @@ LockedFlake lockFlake(
                                         .isFlake = (*lockedNode)->isFlake,
                                     });
                                 } else if (auto follows = std::get_if<1>(&i.second)) {
-                                    auto o = input.overrides.find(i.first);
-                                    // If the override disappeared, we have to refetch the flake,
-                                    // since some of the inputs may not be present in the lockfile.
-                                    if (o == input.overrides.end()) {
-                                        mustRefetch = true;
-                                        // There's no point populating the rest of the fake inputs,
-                                        // since we'll refetch the flake anyways.
-                                        break;
+                                    if (! trustLock) {
+                                        // It is possible that the flake has changed,
+                                        // so we must confirm all the follows that are in the lockfile are also in the flake.
+                                        auto overridePath(inputPath);
+                                        overridePath.push_back(i.first);
+                                        auto o = overrides.find(overridePath);
+                                        // If the override disappeared, we have to refetch the flake,
+                                        // since some of the inputs may not be present in the lockfile.
+                                        if (o == overrides.end()) {
+                                            mustRefetch = true;
+                                            // There's no point populating the rest of the fake inputs,
+                                            // since we'll refetch the flake anyways.
+                                            break;
+                                        }
                                     }
                                     fakeInputs.emplace(i.first, FlakeInput {
                                         .follows = *follows,
@@ -482,14 +494,14 @@ LockedFlake lockFlake(
 
                         LockParent newParent {
                             .path = inputPath,
-                            .absolute = false
+                            .absolute = true
                         };
 
                         computeLocks(
                             mustRefetch
                             ? getFlake(state, oldLock->lockedRef, false, flakeCache).inputs
                             : fakeInputs,
-                            childNode, inputPath, oldLock, newParent, parentPath);
+                            childNode, inputPath, oldLock, newParent, parentPath, !mustRefetch);
 
                     } else {
                         /* We need to create a new lock file entry. So fetch
@@ -546,7 +558,7 @@ LockedFlake lockFlake(
                                 ? std::dynamic_pointer_cast<const Node>(oldLock)
                                 : LockFile::read(
                                     inputFlake.sourceInfo->actualPath + "/" + inputFlake.lockedRef.subdir + "/flake.lock").root,
-                                newParent, localPath);
+                                newParent, localPath, false);
                         }
 
                         else {
@@ -574,7 +586,7 @@ LockedFlake lockFlake(
 
         computeLocks(
             flake.inputs, newLockFile.root, {},
-            lockFlags.recreateLockFile ? nullptr : oldLockFile.root, parent, parentPath);
+            lockFlags.recreateLockFile ? nullptr : oldLockFile.root, parent, parentPath, false);
 
         for (auto & i : lockFlags.inputOverrides)
             if (!overridesUsed.count(i.first))
@@ -674,7 +686,7 @@ void callFlake(EvalState & state,
     auto vTmp1 = state.allocValue();
     auto vTmp2 = state.allocValue();
 
-    mkString(*vLocks, lockedFlake.lockFile.to_string());
+    vLocks->mkString(lockedFlake.lockFile.to_string());
 
     emitTreeAttrs(
         state,
@@ -684,7 +696,7 @@ void callFlake(EvalState & state,
         false,
         lockedFlake.flake.forceDirty);
 
-    mkString(*vRootSubdir, lockedFlake.flake.lockedRef.subdir);
+    vRootSubdir->mkString(lockedFlake.flake.lockedRef.subdir);
 
     if (!state.vCallFlake) {
         state.vCallFlake = allocRootValue(state.allocValue());
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index ed4c47fbb..25fd9b949 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -254,15 +254,14 @@ bool DrvInfo::queryMetaBool(const string & name, bool def)
 void DrvInfo::setMeta(const string & name, Value * v)
 {
     getMeta();
-    Bindings * old = meta;
-    meta = state->allocBindings(1 + (old ? old->size() : 0));
+    auto attrs = state->buildBindings(1 + (meta ? meta->size() : 0));
     Symbol sym = state->symbols.create(name);
-    if (old)
-        for (auto i : *old)
+    if (meta)
+        for (auto i : *meta)
             if (i.name != sym)
-                meta->push_back(i);
-    if (v) meta->push_back(Attr(sym, v));
-    meta->sort();
+                attrs.insert(i);
+    if (v) attrs.insert(sym, v);
+    meta = attrs.finish();
 }
 
 
diff --git a/src/libexpr/json-to-value.cc b/src/libexpr/json-to-value.cc
index 9ca5ac86d..88716250c 100644
--- a/src/libexpr/json-to-value.cc
+++ b/src/libexpr/json-to-value.cc
@@ -37,10 +37,10 @@ class JSONSax : nlohmann::json_sax<json> {
         ValueMap attrs;
         std::unique_ptr<JSONState> resolve(EvalState & state) override
         {
-            Value & v = parent->value(state);
-            state.mkAttrs(v, attrs.size());
+            auto attrs2 = state.buildBindings(attrs.size());
             for (auto & i : attrs)
-                v.attrs->push_back(Attr(i.first, i.second));
+                attrs2.insert(i.first, i.second);
+            parent->value(state).mkAttrs(attrs2.alreadySorted());
             return std::move(parent);
         }
         void add() override { v = nullptr; }
@@ -76,45 +76,51 @@ class JSONSax : nlohmann::json_sax<json> {
     EvalState & state;
     std::unique_ptr<JSONState> rs;
 
-    template<typename T, typename... Args> inline bool handle_value(T f, Args... args)
-    {
-        f(rs->value(state), args...);
-        rs->add();
-        return true;
-    }
-
 public:
     JSONSax(EvalState & state, Value & v) : state(state), rs(new JSONState(&v)) {};
 
     bool null()
     {
-        return handle_value(mkNull);
+        rs->value(state).mkNull();
+        rs->add();
+        return true;
     }
 
     bool boolean(bool val)
     {
-        return handle_value(mkBool, val);
+        rs->value(state).mkBool(val);
+        rs->add();
+        return true;
     }
 
     bool number_integer(number_integer_t val)
     {
-        return handle_value(mkInt, val);
+        rs->value(state).mkInt(val);
+        rs->add();
+        return true;
     }
 
     bool number_unsigned(number_unsigned_t val)
     {
-        return handle_value(mkInt, val);
+        rs->value(state).mkInt(val);
+        rs->add();
+        return true;
     }
 
     bool number_float(number_float_t val, const string_t & s)
     {
-        return handle_value(mkFloat, val);
+        rs->value(state).mkFloat(val);
+        rs->add();
+        return true;
     }
 
     bool string(string_t & val)
     {
-        return handle_value<void(Value&, const char*)>(mkString, val.c_str());
+        rs->value(state).mkString(val);
+        rs->add();
+        return true;
     }
+
 #if NLOHMANN_JSON_VERSION_MAJOR >= 3 && NLOHMANN_JSON_VERSION_MINOR >= 8
     bool binary(binary_t&)
     {
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index c013f5deb..0a60057e5 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -94,7 +94,7 @@ struct ExprInt : Expr
 {
     NixInt n;
     Value v;
-    ExprInt(NixInt n) : n(n) { mkInt(v, n); };
+    ExprInt(NixInt n) : n(n) { v.mkInt(n); };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };
@@ -103,7 +103,7 @@ struct ExprFloat : Expr
 {
     NixFloat nf;
     Value v;
-    ExprFloat(NixFloat nf) : nf(nf) { mkFloat(v, nf); };
+    ExprFloat(NixFloat nf) : nf(nf) { v.mkFloat(nf); };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };
@@ -112,7 +112,7 @@ struct ExprString : Expr
 {
     Symbol s;
     Value v;
-    ExprString(const Symbol & s) : s(s) { mkString(v, s); };
+    ExprString(const Symbol & s) : s(s) { v.mkString(s); };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };
@@ -368,6 +368,13 @@ struct StaticEnv
             [](const Vars::value_type & a, const Vars::value_type & b) { return a.first < b.first; });
     }
 
+    void deduplicate()
+    {
+        const auto last = std::unique(vars.begin(), vars.end(),
+            [] (const Vars::value_type & a, const Vars::value_type & b) { return a.first == b.first; });
+        vars.erase(last, vars.end());
+    }
+
     Vars::const_iterator find(const Symbol & name) const
     {
         Vars::value_type key(name, 0);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 852317aa3..b819918ad 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -35,9 +35,10 @@ namespace nix {
 InvalidPathError::InvalidPathError(const Path & path) :
     EvalError("path '%s' is not valid", path), path(path) {}
 
-void EvalState::realiseContext(const PathSet & context)
+StringMap EvalState::realiseContext(const PathSet & context)
 {
     std::vector<DerivedPath::Built> drvs;
+    StringMap res;
 
     for (auto & i : context) {
         auto [ctxS, outputName] = decodeContext(i);
@@ -46,10 +47,12 @@ void EvalState::realiseContext(const PathSet & context)
             throw InvalidPathError(store->printStorePath(ctx));
         if (!outputName.empty() && ctx.isDerivation()) {
             drvs.push_back({ctx, {outputName}});
+        } else {
+            res.insert_or_assign(ctxS, ctxS);
         }
     }
 
-    if (drvs.empty()) return;
+    if (drvs.empty()) return {};
 
     if (!evalSettings.enableImportFromDerivation)
         throw Error(
@@ -61,19 +64,53 @@ void EvalState::realiseContext(const PathSet & context)
     for (auto & d : drvs) buildReqs.emplace_back(DerivedPath { d });
     store->buildPaths(buildReqs);
 
+    /* Get all the output paths corresponding to the placeholders we had */
+    for (auto & [drvPath, outputs] : drvs) {
+        auto outputPaths = store->queryDerivationOutputMap(drvPath);
+        for (auto & outputName : outputs) {
+            if (outputPaths.count(outputName) == 0)
+                throw Error("derivation '%s' does not have an output named '%s'",
+                        store->printStorePath(drvPath), outputName);
+            res.insert_or_assign(
+                downstreamPlaceholder(*store, drvPath, outputName),
+                store->printStorePath(outputPaths.at(outputName))
+            );
+        }
+    }
+
     /* Add the output of this derivations to the allowed
        paths. */
     if (allowedPaths) {
-        for (auto & [drvPath, outputs] : drvs) {
-            auto outputPaths = store->queryDerivationOutputMap(drvPath);
-            for (auto & outputName : outputs) {
-                if (outputPaths.count(outputName) == 0)
-                    throw Error("derivation '%s' does not have an output named '%s'",
-                            store->printStorePath(drvPath), outputName);
-                allowPath(outputPaths.at(outputName));
-            }
+        for (auto & [_placeholder, outputPath] : res) {
+            allowPath(store->toRealPath(outputPath));
         }
     }
+
+    return res;
+}
+
+struct RealisePathFlags {
+    // Whether to check whether the path is a valid absolute path
+    bool requireAbsolutePath = true;
+    // Whether to check that the path is allowed in pure eval mode
+    bool checkForPureEval = true;
+};
+
+static Path realisePath(EvalState & state, const Pos & pos, Value & v, const RealisePathFlags flags = {})
+{
+    PathSet context;
+
+    Path path = flags.requireAbsolutePath
+        ? state.coerceToPath(pos, v, context)
+        : state.coerceToString(pos, v, context, false, false);
+
+    StringMap rewrites = state.realiseContext(context);
+
+    auto realPath = state.toRealPath(rewriteStrings(path, rewrites), context);
+
+    return flags.checkForPureEval
+        ? state.checkSourcePath(realPath)
+        : realPath;
 }
 
 /* Add and attribute to the given attribute map from the output name to
@@ -88,13 +125,15 @@ void EvalState::realiseContext(const PathSet & context)
    the actual path.
 
    The 'drv' and 'drvPath' outputs must correspond. */
-static void mkOutputString(EvalState & state, Value & v,
-    const StorePath & drvPath, const BasicDerivation & drv,
-    std::pair<string, DerivationOutput> o)
+static void mkOutputString(
+    EvalState & state,
+    BindingsBuilder & attrs,
+    const StorePath & drvPath,
+    const BasicDerivation & drv,
+    const std::pair<string, DerivationOutput> & o)
 {
     auto optOutputPath = o.second.path(*state.store, drv.name, o.first);
-    mkString(
-        *state.allocAttr(v, state.symbols.create(o.first)),
+    attrs.alloc(o.first).mkString(
         optOutputPath
             ? state.store->printStorePath(*optOutputPath)
             /* Downstream we would substitute this for an actual path once
@@ -109,11 +148,9 @@ static void mkOutputString(EvalState & state, Value & v,
    argument. */
 static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vScope, Value & v)
 {
-    PathSet context;
-    Path path = state.coerceToPath(pos, vPath, context);
-
+    Path path;
     try {
-        state.realiseContext(context);
+        path = realisePath(state, pos, vPath);
     } catch (InvalidPathError & e) {
         throw EvalError({
             .msg = hintfmt("cannot import '%1%', since path '%2%' is not valid", path, e.path),
@@ -124,8 +161,6 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
         throw;
     }
 
-    Path realPath = state.checkSourcePath(state.toRealPath(path, context));
-
     // FIXME
     auto isValidDerivationInStore = [&]() -> std::optional<StorePath> {
         if (!state.store->isStorePath(path))
@@ -139,23 +174,19 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
     if (auto optStorePath = isValidDerivationInStore()) {
         auto storePath = *optStorePath;
         Derivation drv = state.store->readDerivation(storePath);
-        Value & w = *state.allocValue();
-        state.mkAttrs(w, 3 + drv.outputs.size());
-        Value * v2 = state.allocAttr(w, state.sDrvPath);
-        mkString(*v2, path, {"=" + path});
-        v2 = state.allocAttr(w, state.sName);
-        mkString(*v2, drv.env["name"]);
-        Value * outputsVal =
-            state.allocAttr(w, state.symbols.create("outputs"));
-        state.mkList(*outputsVal, drv.outputs.size());
-        unsigned int outputs_index = 0;
-
-        for (const auto & o : drv.outputs) {
-            mkOutputString(state, w, storePath, drv, o);
-            outputsVal->listElems()[outputs_index] = state.allocValue();
-            mkString(*(outputsVal->listElems()[outputs_index++]), o.first);
+        auto attrs = state.buildBindings(3 + drv.outputs.size());
+        attrs.alloc(state.sDrvPath).mkString(path, {"=" + path});
+        attrs.alloc(state.sName).mkString(drv.env["name"]);
+        auto & outputsVal = attrs.alloc(state.sOutputs);
+        state.mkList(outputsVal, drv.outputs.size());
+
+        for (const auto & [i, o] : enumerate(drv.outputs)) {
+            mkOutputString(state, attrs, storePath, drv, o);
+            (outputsVal.listElems()[i] = state.allocValue())->mkString(o.first);
         }
-        w.attrs->sort();
+
+        auto w = state.allocValue();
+        w->mkAttrs(attrs);
 
         if (!state.vImportedDrvToDerivation) {
             state.vImportedDrvToDerivation = allocRootValue(state.allocValue());
@@ -165,7 +196,7 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
         }
 
         state.forceFunction(**state.vImportedDrvToDerivation, pos);
-        mkApp(v, **state.vImportedDrvToDerivation, w);
+        v.mkApp(*state.vImportedDrvToDerivation, w);
         state.forceAttrs(v, pos);
     }
 
@@ -177,7 +208,7 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
 
     else {
         if (!vScope)
-            state.evalFile(realPath, v);
+            state.evalFile(path, v);
         else {
             state.forceAttrs(*vScope);
 
@@ -195,8 +226,8 @@ static void import(EvalState & state, const Pos & pos, Value & vPath, Value * vS
             // No need to call staticEnv.sort(), because
             // args[0]->attrs is already sorted.
 
-            printTalkative("evaluating file '%1%'", realPath);
-            Expr * e = state.parseExprFromFile(resolveExprPath(realPath), staticEnv);
+            printTalkative("evaluating file '%1%'", path);
+            Expr * e = state.parseExprFromFile(resolveExprPath(path), staticEnv);
 
             e->eval(state, *env, v);
         }
@@ -281,22 +312,19 @@ extern "C" typedef void (*ValueInitializer)(EvalState & state, Value & v);
 /* Load a ValueInitializer from a DSO and return whatever it initializes */
 void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    PathSet context;
-    Path path = state.coerceToPath(pos, *args[0], context);
-
+    Path path;
     try {
-        state.realiseContext(context);
+        path = realisePath(state, pos, *args[0]);
     } catch (InvalidPathError & e) {
         throw EvalError({
-            .msg = hintfmt(
-                "cannot import '%1%', since path '%2%' is not valid",
-                path, e.path),
+            .msg = hintfmt("cannot import '%1%', since path '%2%' is not valid", path, e.path),
             .errPos = pos
         });
+    } catch (Error & e) {
+        e.addTrace(pos, "while importing '%s'", path);
+        throw;
     }
 
-    path = state.checkSourcePath(path);
-
     string sym = state.forceStringNoCtx(*args[1], pos);
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
@@ -338,7 +366,7 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
     for (unsigned int i = 1; i < args[0]->listSize(); ++i)
         commandArgs.emplace_back(state.coerceToString(pos, *elems[i], context, false, false));
     try {
-        state.realiseContext(context);
+        auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
         throw EvalError({
             .msg = hintfmt("cannot execute '%1%', since path '%2%' is not valid",
@@ -384,7 +412,7 @@ static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Valu
         case nFloat: t = "float"; break;
         case nThunk: abort();
     }
-    mkString(v, state.symbols.create(t));
+    v.mkString(state.symbols.create(t));
 }
 
 static RegisterPrimOp primop_typeOf({
@@ -402,7 +430,7 @@ static RegisterPrimOp primop_typeOf({
 static void prim_isNull(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nNull);
+    v.mkBool(args[0]->type() == nNull);
 }
 
 static RegisterPrimOp primop_isNull({
@@ -422,7 +450,7 @@ static RegisterPrimOp primop_isNull({
 static void prim_isFunction(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nFunction);
+    v.mkBool(args[0]->type() == nFunction);
 }
 
 static RegisterPrimOp primop_isFunction({
@@ -438,7 +466,7 @@ static RegisterPrimOp primop_isFunction({
 static void prim_isInt(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nInt);
+    v.mkBool(args[0]->type() == nInt);
 }
 
 static RegisterPrimOp primop_isInt({
@@ -454,7 +482,7 @@ static RegisterPrimOp primop_isInt({
 static void prim_isFloat(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nFloat);
+    v.mkBool(args[0]->type() == nFloat);
 }
 
 static RegisterPrimOp primop_isFloat({
@@ -470,7 +498,7 @@ static RegisterPrimOp primop_isFloat({
 static void prim_isString(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nString);
+    v.mkBool(args[0]->type() == nString);
 }
 
 static RegisterPrimOp primop_isString({
@@ -486,7 +514,7 @@ static RegisterPrimOp primop_isString({
 static void prim_isBool(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nBool);
+    v.mkBool(args[0]->type() == nBool);
 }
 
 static RegisterPrimOp primop_isBool({
@@ -502,7 +530,7 @@ static RegisterPrimOp primop_isBool({
 static void prim_isPath(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nPath);
+    v.mkBool(args[0]->type() == nPath);
 }
 
 static RegisterPrimOp primop_isPath({
@@ -657,7 +685,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
 
         /* Call the `operator' function with `e' as argument. */
         Value call;
-        mkApp(call, *op->value, *e);
+        call.mkApp(op->value, e);
         state.forceList(call, pos);
 
         /* Add the values returned by the operator to the work set. */
@@ -733,7 +761,7 @@ static RegisterPrimOp primop_addErrorContext(RegisterPrimOp::Info {
 static void prim_ceil(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto value = state.forceFloat(*args[0], args[0]->determinePos(pos));
-    mkInt(v, ceil(value));
+    v.mkInt(ceil(value));
 }
 
 static RegisterPrimOp primop_ceil({
@@ -752,7 +780,7 @@ static RegisterPrimOp primop_ceil({
 static void prim_floor(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto value = state.forceFloat(*args[0], args[0]->determinePos(pos));
-    mkInt(v, floor(value));
+    v.mkInt(floor(value));
 }
 
 static RegisterPrimOp primop_floor({
@@ -772,16 +800,16 @@ static RegisterPrimOp primop_floor({
  * else => {success=false; value=false;} */
 static void prim_tryEval(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.mkAttrs(v, 2);
+    auto attrs = state.buildBindings(2);
     try {
         state.forceValue(*args[0], pos);
-        v.attrs->push_back(Attr(state.sValue, args[0]));
-        mkBool(*state.allocAttr(v, state.symbols.create("success")), true);
+        attrs.insert(state.sValue, args[0]);
+        attrs.alloc("success").mkBool(true);
     } catch (AssertionError & e) {
-        mkBool(*state.allocAttr(v, state.sValue), false);
-        mkBool(*state.allocAttr(v, state.symbols.create("success")), false);
+        attrs.alloc(state.sValue).mkBool(false);
+        attrs.alloc("success").mkBool(false);
     }
-    v.attrs->sort();
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_tryEval({
@@ -809,7 +837,7 @@ static RegisterPrimOp primop_tryEval({
 static void prim_getEnv(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     string name = state.forceStringNoCtx(*args[0], pos);
-    mkString(v, evalSettings.restrictEval || evalSettings.pureEval ? "" : getEnv(name).value_or(""));
+    v.mkString(evalSettings.restrictEval || evalSettings.pureEval ? "" : getEnv(name).value_or(""));
 }
 
 static RegisterPrimOp primop_getEnv({
@@ -1235,11 +1263,11 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         drvHashes.lock()->insert_or_assign(drvPath, h);
     }
 
-    state.mkAttrs(v, 1 + drv.outputs.size());
-    mkString(*state.allocAttr(v, state.sDrvPath), drvPathS, {"=" + drvPathS});
+    auto attrs = state.buildBindings(1 + drv.outputs.size());
+    attrs.alloc(state.sDrvPath).mkString(drvPathS, {"=" + drvPathS});
     for (auto & i : drv.outputs)
-        mkOutputString(state, v, drvPath, drv, i);
-    v.attrs->sort();
+        mkOutputString(state, attrs, drvPath, drv, i);
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_derivationStrict(RegisterPrimOp::Info {
@@ -1257,7 +1285,7 @@ static RegisterPrimOp primop_derivationStrict(RegisterPrimOp::Info {
    ‘out’. */
 static void prim_placeholder(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkString(v, hashPlaceholder(state.forceStringNoCtx(*args[0], pos)));
+    v.mkString(hashPlaceholder(state.forceStringNoCtx(*args[0], pos)));
 }
 
 static RegisterPrimOp primop_placeholder({
@@ -1282,7 +1310,7 @@ static void prim_toPath(EvalState & state, const Pos & pos, Value * * args, Valu
 {
     PathSet context;
     Path path = state.coerceToPath(pos, *args[0], context);
-    mkString(v, canonPath(path), context);
+    v.mkString(canonPath(path), context);
 }
 
 static RegisterPrimOp primop_toPath({
@@ -1326,7 +1354,7 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
     context.insert(state.store->printStorePath(path2));
-    mkString(v, path, context);
+    v.mkString(path, context);
 }
 
 static RegisterPrimOp primop_storePath({
@@ -1349,10 +1377,14 @@ static RegisterPrimOp primop_storePath({
 
 static void prim_pathExists(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    PathSet context;
-    Path path = state.coerceToPath(pos, *args[0], context);
+    Path path;
     try {
-        state.realiseContext(context);
+        // We don’t check the path right now, because we don’t want to throw if
+        // the path isn’t allowed, but just return false
+        // (and we can’t just catch the exception here because we still want to
+        // throw if something in the evaluation of `*args[0]` tries to access an
+        // unauthorized path)
+        path = realisePath(state, pos, *args[0], { .checkForPureEval = false });
     } catch (InvalidPathError & e) {
         throw EvalError({
             .msg = hintfmt(
@@ -1363,13 +1395,13 @@ static void prim_pathExists(EvalState & state, const Pos & pos, Value * * args,
     }
 
     try {
-        mkBool(v, pathExists(state.checkSourcePath(path)));
+        v.mkBool(pathExists(state.checkSourcePath(path)));
     } catch (SysError & e) {
         /* Don't give away info from errors while canonicalising
            ‘path’ in restricted mode. */
-        mkBool(v, false);
+        v.mkBool(false);
     } catch (RestrictedPathError & e) {
-        mkBool(v, false);
+        v.mkBool(false);
     }
 }
 
@@ -1388,7 +1420,7 @@ static RegisterPrimOp primop_pathExists({
 static void prim_baseNameOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    mkString(v, baseNameOf(state.coerceToString(pos, *args[0], context, false, false)), context);
+    v.mkString(baseNameOf(state.coerceToString(pos, *args[0], context, false, false)), context);
 }
 
 static RegisterPrimOp primop_baseNameOf({
@@ -1409,7 +1441,7 @@ static void prim_dirOf(EvalState & state, const Pos & pos, Value * * args, Value
 {
     PathSet context;
     Path dir = dirOf(state.coerceToString(pos, *args[0], context, false, false));
-    if (args[0]->type() == nPath) mkPath(v, dir.c_str()); else mkString(v, dir, context);
+    if (args[0]->type() == nPath) v.mkPath(dir); else v.mkString(dir, context);
 }
 
 static RegisterPrimOp primop_dirOf({
@@ -1426,20 +1458,23 @@ static RegisterPrimOp primop_dirOf({
 /* Return the contents of a file as a string. */
 static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    PathSet context;
-    Path path = state.coerceToPath(pos, *args[0], context);
+    Path path;
     try {
-        state.realiseContext(context);
+        path = realisePath(state, pos, *args[0]);
     } catch (InvalidPathError & e) {
         throw EvalError({
             .msg = hintfmt("cannot read '%1%', since path '%2%' is not valid", path, e.path),
             .errPos = pos
         });
     }
-    string s = readFile(state.checkSourcePath(state.toRealPath(path, context)));
+    string s = readFile(path);
     if (s.find((char) 0) != string::npos)
         throw Error("the contents of the file '%1%' cannot be represented as a Nix string", path);
-    mkString(v, s.c_str());
+    auto refs = state.store->isInStore(path) ?
+        state.store->queryPathInfo(state.store->toStorePath(path).first)->references :
+        StorePathSet{};
+    auto context = state.store->printStorePathSet(refs);
+    v.mkString(s, context);
 }
 
 static RegisterPrimOp primop_readFile({
@@ -1475,11 +1510,10 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
             pos
         );
 
-        PathSet context;
-        string path = state.coerceToString(pos, *i->value, context, false, false);
+        Path path;
 
         try {
-            state.realiseContext(context);
+            path = realisePath(state, pos, *i->value, { .requireAbsolutePath = false });
         } catch (InvalidPathError & e) {
             throw EvalError({
                 .msg = hintfmt("cannot find '%1%', since path '%2%' is not valid", path, e.path),
@@ -1492,7 +1526,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
 
     string path = state.forceStringNoCtx(*args[1], pos);
 
-    mkPath(v, state.checkSourcePath(state.findFile(searchPath, path, pos)).c_str());
+    v.mkPath(state.checkSourcePath(state.findFile(searchPath, path, pos)));
 }
 
 static RegisterPrimOp primop_findFile(RegisterPrimOp::Info {
@@ -1512,15 +1546,14 @@ static void prim_hashFile(EvalState & state, const Pos & pos, Value * * args, Va
             .errPos = pos
         });
 
-    PathSet context;
-    Path path = state.coerceToPath(pos, *args[1], context);
+    Path path;
     try {
-        state.realiseContext(context);
+        path = realisePath(state, pos, *args[1]);
     } catch (InvalidPathError & e) {
         throw EvalError("cannot read '%s' since path '%s' is not valid, at %s", path, e.path, pos);
     }
 
-    mkString(v, hashFile(*ht, state.checkSourcePath(state.toRealPath(path, context))).to_string(Base16, false));
+    v.mkString(hashFile(*ht, path).to_string(Base16, false));
 }
 
 static RegisterPrimOp primop_hashFile({
@@ -1537,10 +1570,9 @@ static RegisterPrimOp primop_hashFile({
 /* Read a directory (without . or ..) */
 static void prim_readDir(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    PathSet ctx;
-    Path path = state.coerceToPath(pos, *args[0], ctx);
+    Path path;
     try {
-        state.realiseContext(ctx);
+        path = realisePath(state, pos, *args[0]);
     } catch (InvalidPathError & e) {
         throw EvalError({
             .msg = hintfmt("cannot read '%1%', since path '%2%' is not valid", path, e.path),
@@ -1548,21 +1580,21 @@ static void prim_readDir(EvalState & state, const Pos & pos, Value * * args, Val
         });
     }
 
-    DirEntries entries = readDirectory(state.checkSourcePath(path));
-    state.mkAttrs(v, entries.size());
+    DirEntries entries = readDirectory(path);
+
+    auto attrs = state.buildBindings(entries.size());
 
     for (auto & ent : entries) {
-        Value * ent_val = state.allocAttr(v, state.symbols.create(ent.name));
         if (ent.type == DT_UNKNOWN)
             ent.type = getFileType(path + "/" + ent.name);
-        ent_val->mkString(
+        attrs.alloc(ent.name).mkString(
             ent.type == DT_REG ? "regular" :
             ent.type == DT_DIR ? "directory" :
             ent.type == DT_LNK ? "symlink" :
             "unknown");
     }
 
-    v.attrs->sort();
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_readDir({
@@ -1598,7 +1630,7 @@ static void prim_toXML(EvalState & state, const Pos & pos, Value * * args, Value
     std::ostringstream out;
     PathSet context;
     printValueAsXML(state, true, false, *args[0], out, context, pos);
-    mkString(v, out.str(), context);
+    v.mkString(out.str(), context);
 }
 
 static RegisterPrimOp primop_toXML({
@@ -1706,7 +1738,7 @@ static void prim_toJSON(EvalState & state, const Pos & pos, Value * * args, Valu
     std::ostringstream out;
     PathSet context;
     printValueAsJSON(state, true, *args[0], pos, out, context);
-    mkString(v, out.str(), context);
+    v.mkString(out.str(), context);
 }
 
 static RegisterPrimOp primop_toJSON({
@@ -1780,7 +1812,7 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
        result, since `storePath' itself has references to the paths
        used in args[1]. */
 
-    mkString(v, storePath, {storePath});
+    v.mkString(storePath, {storePath});
 }
 
 static RegisterPrimOp primop_toFile({
@@ -1875,7 +1907,8 @@ static void addPath(
     try {
         // FIXME: handle CA derivation outputs (where path needs to
         // be rewritten to the actual output).
-        state.realiseContext(context);
+        auto rewrites = state.realiseContext(context);
+        path = state.toRealPath(rewriteStrings(path, rewrites), context);
 
         StorePathSet refs;
 
@@ -1896,10 +1929,10 @@ static void addPath(
             /* Call the filter function.  The first argument is the path,
                the second is a string indicating the type of the file. */
             Value arg1;
-            mkString(arg1, path);
+            arg1.mkString(path);
 
             Value arg2;
-            mkString(arg2,
+            arg2.mkString(
                 S_ISREG(st.st_mode) ? "regular" :
                 S_ISDIR(st.st_mode) ? "directory" :
                 S_ISLNK(st.st_mode) ? "symlink" :
@@ -1926,7 +1959,7 @@ static void addPath(
         } else
             dstPath = state.store->printStorePath(*expectedStorePath);
 
-        mkString(v, dstPath, {dstPath});
+        v.mkString(dstPath, {dstPath});
 
         state.allowPath(dstPath);
 
@@ -2100,7 +2133,7 @@ static void prim_attrNames(EvalState & state, const Pos & pos, Value * * args, V
 
     size_t n = 0;
     for (auto & i : *args[0]->attrs)
-        mkString(*(v.listElems()[n++] = state.allocValue()), i.name);
+        (v.listElems()[n++] = state.allocValue())->mkString(i.name);
 
     std::sort(v.listElems(), v.listElems() + n,
               [](Value * v1, Value * v2) { return strcmp(v1->string.s, v2->string.s) < 0; });
@@ -2184,7 +2217,7 @@ static void prim_unsafeGetAttrPos(EvalState & state, const Pos & pos, Value * *
     state.forceAttrs(*args[1], pos);
     Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
     if (i == args[1]->attrs->end())
-        mkNull(v);
+        v.mkNull();
     else
         state.mkPos(v, i->pos);
 }
@@ -2200,7 +2233,7 @@ static void prim_hasAttr(EvalState & state, const Pos & pos, Value * * args, Val
 {
     string attr = state.forceStringNoCtx(*args[0], pos);
     state.forceAttrs(*args[1], pos);
-    mkBool(v, args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
+    v.mkBool(args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
 }
 
 static RegisterPrimOp primop_hasAttr({
@@ -2218,7 +2251,7 @@ static RegisterPrimOp primop_hasAttr({
 static void prim_isAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nAttrs);
+    v.mkBool(args[0]->type() == nAttrs);
 }
 
 static RegisterPrimOp primop_isAttrs({
@@ -2245,11 +2278,12 @@ static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args,
     /* Copy all attributes not in that set.  Note that we don't need
        to sort v.attrs because it's a subset of an already sorted
        vector. */
-    state.mkAttrs(v, args[0]->attrs->size());
+    auto attrs = state.buildBindings(args[0]->attrs->size());
     for (auto & i : *args[0]->attrs) {
         if (!names.count(i.name))
-            v.attrs->push_back(i);
+            attrs.insert(i);
     }
+    v.mkAttrs(attrs.alreadySorted());
 }
 
 static RegisterPrimOp primop_removeAttrs({
@@ -2277,7 +2311,7 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
 {
     state.forceList(*args[0], pos);
 
-    state.mkAttrs(v, args[0]->listSize());
+    auto attrs = state.buildBindings(args[0]->listSize());
 
     std::set<Symbol> seen;
 
@@ -2303,11 +2337,11 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
                 v2->attrs,
                 pos
             );
-            v.attrs->push_back(Attr(sym, j2->value, j2->pos));
+            attrs.insert(sym, j2->value, j2->pos);
         }
     }
 
-    v.attrs->sort();
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_listToAttrs({
@@ -2340,13 +2374,15 @@ static void prim_intersectAttrs(EvalState & state, const Pos & pos, Value * * ar
     state.forceAttrs(*args[0], pos);
     state.forceAttrs(*args[1], pos);
 
-    state.mkAttrs(v, std::min(args[0]->attrs->size(), args[1]->attrs->size()));
+    auto attrs = state.buildBindings(std::min(args[0]->attrs->size(), args[1]->attrs->size()));
 
     for (auto & i : *args[0]->attrs) {
         Bindings::iterator j = args[1]->attrs->find(i.name);
         if (j != args[1]->attrs->end())
-            v.attrs->push_back(*j);
+            attrs.insert(*j);
     }
+
+    v.mkAttrs(attrs.alreadySorted());
 }
 
 static RegisterPrimOp primop_intersectAttrs({
@@ -2400,7 +2436,7 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
 {
     state.forceValue(*args[0], pos);
     if (args[0]->isPrimOpApp() || args[0]->isPrimOp()) {
-        state.mkAttrs(v, 0);
+        v.mkAttrs(&state.emptyBindings);
         return;
     }
     if (!args[0]->isLambda())
@@ -2410,18 +2446,15 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
         });
 
     if (!args[0]->lambda.fun->hasFormals()) {
-        state.mkAttrs(v, 0);
+        v.mkAttrs(&state.emptyBindings);
         return;
     }
 
-    state.mkAttrs(v, args[0]->lambda.fun->formals->formals.size());
-    for (auto & i : args[0]->lambda.fun->formals->formals) {
+    auto attrs = state.buildBindings(args[0]->lambda.fun->formals->formals.size());
+    for (auto & i : args[0]->lambda.fun->formals->formals)
         // !!! should optimise booleans (allocate only once)
-        Value * value = state.allocValue();
-        v.attrs->push_back(Attr(i.name, value, ptr(&i.pos)));
-        mkBool(*value, i.def);
-    }
-    v.attrs->sort();
+        attrs.alloc(i.name, ptr(&i.pos)).mkBool(i.def);
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_functionArgs({
@@ -2446,15 +2479,17 @@ static void prim_mapAttrs(EvalState & state, const Pos & pos, Value * * args, Va
 {
     state.forceAttrs(*args[1], pos);
 
-    state.mkAttrs(v, args[1]->attrs->size());
+    auto attrs = state.buildBindings(args[1]->attrs->size());
 
     for (auto & i : *args[1]->attrs) {
         Value * vName = state.allocValue();
         Value * vFun2 = state.allocValue();
-        mkString(*vName, i.name);
-        mkApp(*vFun2, *args[0], *vName);
-        mkApp(*state.allocAttr(v, i.name), *vFun2, *i.value);
+        vName->mkString(i.name);
+        vFun2->mkApp(args[0], vName);
+        attrs.alloc(i.name).mkApp(vFun2, i.value);
     }
+
+    v.mkAttrs(attrs.alreadySorted());
 }
 
 static RegisterPrimOp primop_mapAttrs({
@@ -2472,6 +2507,91 @@ static RegisterPrimOp primop_mapAttrs({
     .fun = prim_mapAttrs,
 });
 
+static void prim_zipAttrsWith(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    // we will first count how many values are present for each given key.
+    // we then allocate a single attrset and pre-populate it with lists of
+    // appropriate sizes, stash the pointers to the list elements of each,
+    // and populate the lists. after that we replace the list in the every
+    // attribute with the merge function application. this way we need not
+    // use (slightly slower) temporary storage the GC does not know about.
+
+    std::map<Symbol, std::pair<size_t, Value * *>> attrsSeen;
+
+    state.forceFunction(*args[0], pos);
+    state.forceList(*args[1], pos);
+    const auto listSize = args[1]->listSize();
+    const auto listElems = args[1]->listElems();
+
+    for (unsigned int n = 0; n < listSize; ++n) {
+        Value * vElem = listElems[n];
+        try {
+            state.forceAttrs(*vElem);
+            for (auto & attr : *vElem->attrs)
+                attrsSeen[attr.name].first++;
+        } catch (TypeError & e) {
+            e.addTrace(pos, hintfmt("while invoking '%s'", "zipAttrsWith"));
+            throw;
+        }
+    }
+
+    auto attrs = state.buildBindings(attrsSeen.size());
+    for (auto & [sym, elem] : attrsSeen) {
+        auto & list = attrs.alloc(sym);
+        state.mkList(list, elem.first);
+        elem.second = list.listElems();
+    }
+    v.mkAttrs(attrs.alreadySorted());
+
+    for (unsigned int n = 0; n < listSize; ++n) {
+        Value * vElem = listElems[n];
+        for (auto & attr : *vElem->attrs)
+            *attrsSeen[attr.name].second++ = attr.value;
+    }
+
+    for (auto & attr : *v.attrs) {
+        auto name = state.allocValue();
+        name->mkString(attr.name);
+        auto call1 = state.allocValue();
+        call1->mkApp(args[0], name);
+        auto call2 = state.allocValue();
+        call2->mkApp(call1, attr.value);
+        attr.value = call2;
+    }
+}
+
+static RegisterPrimOp primop_zipAttrsWith({
+    .name = "__zipAttrsWith",
+    .args = {"f", "list"},
+    .doc = R"(
+      Transpose a list of attribute sets into an attribute set of lists,
+      then apply `mapAttrs`.
+
+      `f` receives two arguments: the attribute name and a non-empty
+      list of all values encountered for that attribute name.
+
+      The result is an attribute set where the attribute names are the
+      union of the attribute names in each element of `list`. The attribute
+      values are the return values of `f`.
+
+      ```nix
+      builtins.zipAttrsWith
+        (name: values: { inherit name values; })
+        [ { a = "x"; } { a = "y"; b = "z"; } ]
+      ```
+
+      evaluates to
+
+      ```
+      {
+        a = { name = "a"; values = [ "x" "y" ]; };
+        b = { name = "b"; values = [ "z" ]; };
+      }
+      ```
+    )",
+    .fun = prim_zipAttrsWith,
+});
+
 
 /*************************************************************
  * Lists
@@ -2482,7 +2602,7 @@ static RegisterPrimOp primop_mapAttrs({
 static void prim_isList(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    mkBool(v, args[0]->type() == nList);
+    v.mkBool(args[0]->type() == nList);
 }
 
 static RegisterPrimOp primop_isList({
@@ -2580,8 +2700,8 @@ static void prim_map(EvalState & state, const Pos & pos, Value * * args, Value &
     state.mkList(v, args[1]->listSize());
 
     for (unsigned int n = 0; n < v.listSize(); ++n)
-        mkApp(*(v.listElems()[n] = state.allocValue()),
-            *args[0], *args[1]->listElems()[n]);
+        (v.listElems()[n] = state.allocValue())->mkApp(
+            args[0], args[1]->listElems()[n]);
 }
 
 static RegisterPrimOp primop_map({
@@ -2650,7 +2770,7 @@ static void prim_elem(EvalState & state, const Pos & pos, Value * * args, Value
             res = true;
             break;
         }
-    mkBool(v, res);
+    v.mkBool(res);
 }
 
 static RegisterPrimOp primop_elem({
@@ -2683,7 +2803,7 @@ static RegisterPrimOp primop_concatLists({
 static void prim_length(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceList(*args[0], pos);
-    mkInt(v, args[0]->listSize());
+    v.mkInt(args[0]->listSize());
 }
 
 static RegisterPrimOp primop_length({
@@ -2740,12 +2860,12 @@ static void anyOrAll(bool any, EvalState & state, const Pos & pos, Value * * arg
         state.callFunction(*args[0], *elem, vTmp, pos);
         bool res = state.forceBool(vTmp, pos);
         if (res == any) {
-            mkBool(v, any);
+            v.mkBool(any);
             return;
         }
     }
 
-    mkBool(v, !any);
+    v.mkBool(!any);
 }
 
 
@@ -2792,9 +2912,9 @@ static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Val
     state.mkList(v, len);
 
     for (unsigned int n = 0; n < (unsigned int) len; ++n) {
-        Value * arg = state.allocValue();
-        mkInt(*arg, n);
-        mkApp(*(v.listElems()[n] = state.allocValue()), *args[0], *arg);
+        auto arg = state.allocValue();
+        arg->mkInt(n);
+        (v.listElems()[n] = state.allocValue())->mkApp(args[0], arg);
     }
 }
 
@@ -2888,21 +3008,21 @@ static void prim_partition(EvalState & state, const Pos & pos, Value * * args, V
             wrong.push_back(vElem);
     }
 
-    state.mkAttrs(v, 2);
+    auto attrs = state.buildBindings(2);
 
-    Value * vRight = state.allocAttr(v, state.sRight);
+    auto & vRight = attrs.alloc(state.sRight);
     auto rsize = right.size();
-    state.mkList(*vRight, rsize);
+    state.mkList(vRight, rsize);
     if (rsize)
-        memcpy(vRight->listElems(), right.data(), sizeof(Value *) * rsize);
+        memcpy(vRight.listElems(), right.data(), sizeof(Value *) * rsize);
 
-    Value * vWrong = state.allocAttr(v, state.sWrong);
+    auto & vWrong = attrs.alloc(state.sWrong);
     auto wsize = wrong.size();
-    state.mkList(*vWrong, wsize);
+    state.mkList(vWrong, wsize);
     if (wsize)
-        memcpy(vWrong->listElems(), wrong.data(), sizeof(Value *) * wsize);
+        memcpy(vWrong.listElems(), wrong.data(), sizeof(Value *) * wsize);
 
-    v.attrs->sort();
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_partition({
@@ -2944,14 +3064,16 @@ static void prim_groupBy(EvalState & state, const Pos & pos, Value * * args, Val
         vector->second.push_back(vElem);
     }
 
-    state.mkAttrs(v, attrs.size());
+    auto attrs2 = state.buildBindings(attrs.size());
 
     for (auto & i : attrs) {
-        Value * list = state.allocAttr(v, i.first);
+        auto & list = attrs2.alloc(i.first);
         auto size = i.second.size();
-        state.mkList(*list, size);
-        memcpy(list->listElems(), i.second.data(), sizeof(Value *) * size);
+        state.mkList(list, size);
+        memcpy(list.listElems(), i.second.data(), sizeof(Value *) * size);
     }
+
+    v.mkAttrs(attrs2.alreadySorted());
 }
 
 static RegisterPrimOp primop_groupBy({
@@ -3030,9 +3152,9 @@ static void prim_add(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        mkFloat(v, state.forceFloat(*args[0], pos) + state.forceFloat(*args[1], pos));
+        v.mkFloat(state.forceFloat(*args[0], pos) + state.forceFloat(*args[1], pos));
     else
-        mkInt(v, state.forceInt(*args[0], pos) + state.forceInt(*args[1], pos));
+        v.mkInt(state.forceInt(*args[0], pos) + state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_add({
@@ -3049,9 +3171,9 @@ static void prim_sub(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        mkFloat(v, state.forceFloat(*args[0], pos) - state.forceFloat(*args[1], pos));
+        v.mkFloat(state.forceFloat(*args[0], pos) - state.forceFloat(*args[1], pos));
     else
-        mkInt(v, state.forceInt(*args[0], pos) - state.forceInt(*args[1], pos));
+        v.mkInt(state.forceInt(*args[0], pos) - state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_sub({
@@ -3068,9 +3190,9 @@ static void prim_mul(EvalState & state, const Pos & pos, Value * * args, Value &
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     if (args[0]->type() == nFloat || args[1]->type() == nFloat)
-        mkFloat(v, state.forceFloat(*args[0], pos) * state.forceFloat(*args[1], pos));
+        v.mkFloat(state.forceFloat(*args[0], pos) * state.forceFloat(*args[1], pos));
     else
-        mkInt(v, state.forceInt(*args[0], pos) * state.forceInt(*args[1], pos));
+        v.mkInt(state.forceInt(*args[0], pos) * state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_mul({
@@ -3095,7 +3217,7 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
         });
 
     if (args[0]->type() == nFloat || args[1]->type() == nFloat) {
-        mkFloat(v, state.forceFloat(*args[0], pos) / state.forceFloat(*args[1], pos));
+        v.mkFloat(state.forceFloat(*args[0], pos) / state.forceFloat(*args[1], pos));
     } else {
         NixInt i1 = state.forceInt(*args[0], pos);
         NixInt i2 = state.forceInt(*args[1], pos);
@@ -3106,7 +3228,7 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
                 .errPos = pos
             });
 
-        mkInt(v, i1 / i2);
+        v.mkInt(i1 / i2);
     }
 }
 
@@ -3121,7 +3243,7 @@ static RegisterPrimOp primop_div({
 
 static void prim_bitAnd(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0], pos) & state.forceInt(*args[1], pos));
+    v.mkInt(state.forceInt(*args[0], pos) & state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_bitAnd({
@@ -3135,7 +3257,7 @@ static RegisterPrimOp primop_bitAnd({
 
 static void prim_bitOr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0], pos) | state.forceInt(*args[1], pos));
+    v.mkInt(state.forceInt(*args[0], pos) | state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_bitOr({
@@ -3149,7 +3271,7 @@ static RegisterPrimOp primop_bitOr({
 
 static void prim_bitXor(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    mkInt(v, state.forceInt(*args[0], pos) ^ state.forceInt(*args[1], pos));
+    v.mkInt(state.forceInt(*args[0], pos) ^ state.forceInt(*args[1], pos));
 }
 
 static RegisterPrimOp primop_bitXor({
@@ -3166,7 +3288,7 @@ static void prim_lessThan(EvalState & state, const Pos & pos, Value * * args, Va
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     CompareValues comp{state};
-    mkBool(v, comp(args[0], args[1]));
+    v.mkBool(comp(args[0], args[1]));
 }
 
 static RegisterPrimOp primop_lessThan({
@@ -3193,7 +3315,7 @@ static void prim_toString(EvalState & state, const Pos & pos, Value * * args, Va
 {
     PathSet context;
     string s = state.coerceToString(pos, *args[0], context, true, false);
-    mkString(v, s, context);
+    v.mkString(s, context);
 }
 
 static RegisterPrimOp primop_toString({
@@ -3237,7 +3359,7 @@ static void prim_substring(EvalState & state, const Pos & pos, Value * * args, V
             .errPos = pos
         });
 
-    mkString(v, (unsigned int) start >= s.size() ? "" : string(s, start, len), context);
+    v.mkString((unsigned int) start >= s.size() ? "" : string(s, start, len), context);
 }
 
 static RegisterPrimOp primop_substring({
@@ -3264,7 +3386,7 @@ static void prim_stringLength(EvalState & state, const Pos & pos, Value * * args
 {
     PathSet context;
     string s = state.coerceToString(pos, *args[0], context);
-    mkInt(v, s.size());
+    v.mkInt(s.size());
 }
 
 static RegisterPrimOp primop_stringLength({
@@ -3291,7 +3413,7 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
     PathSet context; // discarded
     string s = state.forceString(*args[1], context, pos);
 
-    mkString(v, hashString(*ht, s).to_string(Base16, false));
+    v.mkString(hashString(*ht, s).to_string(Base16, false));
 }
 
 static RegisterPrimOp primop_hashString({
@@ -3330,7 +3452,7 @@ void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
 
         std::smatch match;
         if (!std::regex_match(str, match, regex->second)) {
-            mkNull(v);
+            v.mkNull();
             return;
         }
 
@@ -3339,9 +3461,9 @@ void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
         state.mkList(v, len);
         for (size_t i = 0; i < len; ++i) {
             if (!match[i+1].matched)
-                mkNull(*(v.listElems()[i] = state.allocValue()));
+                (v.listElems()[i] = state.allocValue())->mkNull();
             else
-                mkString(*(v.listElems()[i] = state.allocValue()), match[i + 1].str().c_str());
+                (v.listElems()[i] = state.allocValue())->mkString(match[i + 1].str());
         }
 
     } catch (std::regex_error &e) {
@@ -3416,7 +3538,6 @@ static void prim_split(EvalState & state, const Pos & pos, Value * * args, Value
         const size_t len = std::distance(begin, end);
         state.mkList(v, 2 * len + 1);
         size_t idx = 0;
-        Value * elem;
 
         if (len == 0) {
             v.listElems()[idx++] = args[1];
@@ -3428,28 +3549,26 @@ static void prim_split(EvalState & state, const Pos & pos, Value * * args, Value
             std::smatch match = *i;
 
             // Add a string for non-matched characters.
-            elem = v.listElems()[idx++] = state.allocValue();
-            mkString(*elem, match.prefix().str().c_str());
+            (v.listElems()[idx++] = state.allocValue())->mkString(match.prefix().str());
 
             // Add a list for matched substrings.
             const size_t slen = match.size() - 1;
-            elem = v.listElems()[idx++] = state.allocValue();
+            auto elem = v.listElems()[idx++] = state.allocValue();
 
             // Start at 1, beacause the first match is the whole string.
             state.mkList(*elem, slen);
             for (size_t si = 0; si < slen; ++si) {
                 if (!match[si + 1].matched)
-                    mkNull(*(elem->listElems()[si] = state.allocValue()));
+                    (elem->listElems()[si] = state.allocValue())->mkNull();
                 else
-                    mkString(*(elem->listElems()[si] = state.allocValue()), match[si + 1].str().c_str());
+                    (elem->listElems()[si] = state.allocValue())->mkString(match[si + 1].str());
             }
 
             // Add a string for non-matched suffix characters.
-            if (idx == 2 * len) {
-                elem = v.listElems()[idx++] = state.allocValue();
-                mkString(*elem, match.suffix().str().c_str());
-            }
+            if (idx == 2 * len)
+                (v.listElems()[idx++] = state.allocValue())->mkString(match.suffix().str());
         }
+
         assert(idx == 2 * len + 1);
 
     } catch (std::regex_error &e) {
@@ -3521,7 +3640,7 @@ static void prim_concatStringsSep(EvalState & state, const Pos & pos, Value * *
         res += state.coerceToString(pos, *elem, context);
     }
 
-    mkString(v, res, context);
+    v.mkString(res, context);
 }
 
 static RegisterPrimOp primop_concatStringsSep({
@@ -3590,7 +3709,7 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
         }
     }
 
-    mkString(v, res, context);
+    v.mkString(res, context);
 }
 
 static RegisterPrimOp primop_replaceStrings({
@@ -3619,10 +3738,10 @@ static void prim_parseDrvName(EvalState & state, const Pos & pos, Value * * args
 {
     string name = state.forceStringNoCtx(*args[0], pos);
     DrvName parsed(name);
-    state.mkAttrs(v, 2);
-    mkString(*state.allocAttr(v, state.sName), parsed.name);
-    mkString(*state.allocAttr(v, state.symbols.create("version")), parsed.version);
-    v.attrs->sort();
+    auto attrs = state.buildBindings(2);
+    attrs.alloc(state.sName).mkString(parsed.name);
+    attrs.alloc("version").mkString(parsed.version);
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_parseDrvName({
@@ -3643,7 +3762,7 @@ static void prim_compareVersions(EvalState & state, const Pos & pos, Value * * a
 {
     string version1 = state.forceStringNoCtx(*args[0], pos);
     string version2 = state.forceStringNoCtx(*args[1], pos);
-    mkInt(v, compareVersions(version1, version2));
+    v.mkInt(compareVersions(version1, version2));
 }
 
 static RegisterPrimOp primop_compareVersions({
@@ -3671,11 +3790,8 @@ static void prim_splitVersion(EvalState & state, const Pos & pos, Value * * args
         components.emplace_back(std::move(component));
     }
     state.mkList(v, components.size());
-    unsigned int n = 0;
-    for (auto & component : components) {
-        auto listElem = v.listElems()[n++] = state.allocValue();
-        mkString(*listElem, std::move(component));
-    }
+    for (const auto & [n, component] : enumerate(components))
+        (v.listElems()[n] = state.allocValue())->mkString(std::move(component));
 }
 
 static RegisterPrimOp primop_splitVersion({
@@ -3725,37 +3841,37 @@ void EvalState::createBaseEnv()
     Value v;
 
     /* `builtins' must be first! */
-    mkAttrs(v, 128);
+    v.mkAttrs(buildBindings(128).finish());
     addConstant("builtins", v);
 
-    mkBool(v, true);
+    v.mkBool(true);
     addConstant("true", v);
 
-    mkBool(v, false);
+    v.mkBool(false);
     addConstant("false", v);
 
-    mkNull(v);
+    v.mkNull();
     addConstant("null", v);
 
     if (!evalSettings.pureEval) {
-        mkInt(v, time(0));
+        v.mkInt(time(0));
         addConstant("__currentTime", v);
 
-        mkString(v, settings.thisSystem.get());
+        v.mkString(settings.thisSystem.get());
         addConstant("__currentSystem", v);
     }
 
-    mkString(v, nixVersion);
+    v.mkString(nixVersion);
     addConstant("__nixVersion", v);
 
-    mkString(v, store->storeDir);
+    v.mkString(store->storeDir);
     addConstant("__storeDir", v);
 
     /* Language version.  This should be increased every time a new
        language feature gets added.  It's not necessary to increase it
        when primops get added, because you can just use `builtins ?
        primOp' to check. */
-    mkInt(v, 6);
+    v.mkInt(6);
     addConstant("__langVersion", v);
 
     // Miscellaneous
@@ -3768,11 +3884,10 @@ void EvalState::createBaseEnv()
     mkList(v, searchPath.size());
     int n = 0;
     for (auto & i : searchPath) {
-        auto v2 = v.listElems()[n++] = allocValue();
-        mkAttrs(*v2, 2);
-        mkString(*allocAttr(*v2, symbols.create("path")), i.second);
-        mkString(*allocAttr(*v2, symbols.create("prefix")), i.first);
-        v2->attrs->sort();
+        auto attrs = buildBindings(2);
+        attrs.alloc("path").mkString(i.second);
+        attrs.alloc("prefix").mkString(i.first);
+        (v.listElems()[n++] = allocValue())->mkAttrs(attrs);
     }
     addConstant("__nixPath", v);
 
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
index 20545afd0..a239c06da 100644
--- a/src/libexpr/primops/context.cc
+++ b/src/libexpr/primops/context.cc
@@ -7,8 +7,7 @@ namespace nix {
 static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    string s = state.coerceToString(pos, *args[0], context);
-    mkString(v, s, PathSet());
+    v.mkString(state.coerceToString(pos, *args[0], context));
 }
 
 static RegisterPrimOp primop_unsafeDiscardStringContext("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
@@ -18,7 +17,7 @@ static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args,
 {
     PathSet context;
     state.forceString(*args[0], context, pos);
-    mkBool(v, !context.empty());
+    v.mkBool(!context.empty());
 }
 
 static RegisterPrimOp primop_hasContext("__hasContext", 1, prim_hasContext);
@@ -39,7 +38,7 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & po
     for (auto & p : context)
         context2.insert(p.at(0) == '=' ? string(p, 1) : p);
 
-    mkString(v, s, context2);
+    v.mkString(s, context2);
 }
 
 static RegisterPrimOp primop_unsafeDiscardOutputDependency("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
@@ -103,27 +102,26 @@ static void prim_getContext(EvalState & state, const Pos & pos, Value * * args,
         }
     }
 
-    state.mkAttrs(v, contextInfos.size());
+    auto attrs = state.buildBindings(contextInfos.size());
 
     auto sPath = state.symbols.create("path");
     auto sAllOutputs = state.symbols.create("allOutputs");
     for (const auto & info : contextInfos) {
-        auto & infoVal = *state.allocAttr(v, state.symbols.create(info.first));
-        state.mkAttrs(infoVal, 3);
+        auto infoAttrs = state.buildBindings(3);
         if (info.second.path)
-            mkBool(*state.allocAttr(infoVal, sPath), true);
+            infoAttrs.alloc(sPath).mkBool(true);
         if (info.second.allOutputs)
-            mkBool(*state.allocAttr(infoVal, sAllOutputs), true);
+            infoAttrs.alloc(sAllOutputs).mkBool(true);
         if (!info.second.outputs.empty()) {
-            auto & outputsVal = *state.allocAttr(infoVal, state.sOutputs);
+            auto & outputsVal = infoAttrs.alloc(state.sOutputs);
             state.mkList(outputsVal, info.second.outputs.size());
-            size_t i = 0;
-            for (const auto & output : info.second.outputs)
-                mkString(*(outputsVal.listElems()[i++] = state.allocValue()), output);
+            for (const auto & [i, output] : enumerate(info.second.outputs))
+                (outputsVal.listElems()[i] = state.allocValue())->mkString(output);
         }
-        infoVal.attrs->sort();
+        attrs.alloc(info.first).mkAttrs(infoAttrs);
     }
-    v.attrs->sort();
+
+    v.mkAttrs(attrs);
 }
 
 static RegisterPrimOp primop_getContext("__getContext", 1, prim_getContext);
@@ -187,7 +185,7 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
         }
     }
 
-    mkString(v, orig, context);
+    v.mkString(orig, context);
 }
 
 static RegisterPrimOp primop_appendContext("__appendContext", 2, prim_appendContext);
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index c23480853..42214c207 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -70,19 +70,19 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     // FIXME: use name
     auto [tree, input2] = input.fetch(state.store);
 
-    state.mkAttrs(v, 8);
+    auto attrs2 = state.buildBindings(8);
     auto storePath = state.store->printStorePath(tree.storePath);
-    mkString(*state.allocAttr(v, state.sOutPath), storePath, PathSet({storePath}));
+    attrs2.alloc(state.sOutPath).mkString(storePath, {storePath});
     if (input2.getRef())
-        mkString(*state.allocAttr(v, state.symbols.create("branch")), *input2.getRef());
+        attrs2.alloc("branch").mkString(*input2.getRef());
     // Backward compatibility: set 'rev' to
     // 0000000000000000000000000000000000000000 for a dirty tree.
     auto rev2 = input2.getRev().value_or(Hash(htSHA1));
-    mkString(*state.allocAttr(v, state.symbols.create("rev")), rev2.gitRev());
-    mkString(*state.allocAttr(v, state.symbols.create("shortRev")), std::string(rev2.gitRev(), 0, 12));
+    attrs2.alloc("rev").mkString(rev2.gitRev());
+    attrs2.alloc("shortRev").mkString(rev2.gitRev().substr(0, 12));
     if (auto revCount = input2.getRevCount())
-        mkInt(*state.allocAttr(v, state.symbols.create("revCount")), *revCount);
-    v.attrs->sort();
+        attrs2.alloc("revCount").mkInt(*revCount);
+    v.mkAttrs(attrs2);
 
     state.allowPath(tree.storePath);
 }
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index 079513873..6647bd35c 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -21,49 +21,48 @@ void emitTreeAttrs(
 {
     assert(input.isImmutable());
 
-    state.mkAttrs(v, 8);
+    auto attrs = state.buildBindings(8);
 
     auto storePath = state.store->printStorePath(tree.storePath);
 
-    mkString(*state.allocAttr(v, state.sOutPath), storePath, PathSet({storePath}));
+    attrs.alloc(state.sOutPath).mkString(storePath, {storePath});
 
     // FIXME: support arbitrary input attributes.
 
     auto narHash = input.getNarHash();
     assert(narHash);
-    mkString(*state.allocAttr(v, state.symbols.create("narHash")),
-        narHash->to_string(SRI, true));
+    attrs.alloc("narHash").mkString(narHash->to_string(SRI, true));
 
     if (input.getType() == "git")
-        mkBool(*state.allocAttr(v, state.symbols.create("submodules")),
+        attrs.alloc("submodules").mkBool(
             fetchers::maybeGetBoolAttr(input.attrs, "submodules").value_or(false));
 
     if (!forceDirty) {
 
         if (auto rev = input.getRev()) {
-            mkString(*state.allocAttr(v, state.symbols.create("rev")), rev->gitRev());
-            mkString(*state.allocAttr(v, state.symbols.create("shortRev")), rev->gitShortRev());
+            attrs.alloc("rev").mkString(rev->gitRev());
+            attrs.alloc("shortRev").mkString(rev->gitShortRev());
         } else if (emptyRevFallback) {
             // Backwards compat for `builtins.fetchGit`: dirty repos return an empty sha1 as rev
             auto emptyHash = Hash(htSHA1);
-            mkString(*state.allocAttr(v, state.symbols.create("rev")), emptyHash.gitRev());
-            mkString(*state.allocAttr(v, state.symbols.create("shortRev")), emptyHash.gitShortRev());
+            attrs.alloc("rev").mkString(emptyHash.gitRev());
+            attrs.alloc("shortRev").mkString(emptyHash.gitShortRev());
         }
 
         if (auto revCount = input.getRevCount())
-            mkInt(*state.allocAttr(v, state.symbols.create("revCount")), *revCount);
+            attrs.alloc("revCount").mkInt(*revCount);
         else if (emptyRevFallback)
-            mkInt(*state.allocAttr(v, state.symbols.create("revCount")), 0);
+            attrs.alloc("revCount").mkInt(0);
 
     }
 
     if (auto lastModified = input.getLastModified()) {
-        mkInt(*state.allocAttr(v, state.symbols.create("lastModified")), *lastModified);
-        mkString(*state.allocAttr(v, state.symbols.create("lastModifiedDate")),
+        attrs.alloc("lastModified").mkInt(*lastModified);
+        attrs.alloc("lastModifiedDate").mkString(
             fmt("%s", std::put_time(std::gmtime(&*lastModified), "%Y%m%d%H%M%S")));
     }
 
-    v.attrs->sort();
+    v.mkAttrs(attrs);
 }
 
 std::string fixURI(std::string uri, EvalState & state, const std::string & defaultScheme = "file")
@@ -248,7 +247,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     state.allowPath(storePath);
 
     auto path = state.store->printStorePath(storePath);
-    mkString(v, path, PathSet({path}));
+    v.mkString(path, PathSet({path}));
 }
 
 static void prim_fetchurl(EvalState & state, const Pos & pos, Value * * args, Value & v)
diff --git a/src/libexpr/primops/fromTOML.cc b/src/libexpr/primops/fromTOML.cc
index 4c6682dfd..80c7e0b82 100644
--- a/src/libexpr/primops/fromTOML.cc
+++ b/src/libexpr/primops/fromTOML.cc
@@ -1,86 +1,76 @@
 #include "primops.hh"
 #include "eval-inline.hh"
 
-#include "../../cpptoml/cpptoml.h"
+#include "../../toml11/toml.hpp"
 
 namespace nix {
 
-static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Value & v)
+static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Value & val)
 {
-    using namespace cpptoml;
-
     auto toml = state.forceStringNoCtx(*args[0], pos);
 
     std::istringstream tomlStream(toml);
 
-    std::function<void(Value &, std::shared_ptr<base>)> visit;
+    std::function<void(Value &, toml::value)> visit;
 
-    visit = [&](Value & v, std::shared_ptr<base> t) {
+    visit = [&](Value & v, toml::value t) {
 
-        if (auto t2 = t->as_table()) {
+        switch(t.type())
+        {
+            case toml::value_t::table:
+                {
+                    auto table = toml::get<toml::table>(t);
 
-            size_t size = 0;
-            for (auto & i : *t2) { (void) i; size++; }
+                    size_t size = 0;
+                    for (auto & i : table) { (void) i; size++; }
 
-            state.mkAttrs(v, size);
+                    auto attrs = state.buildBindings(size);
 
-            for (auto & i : *t2) {
-                auto & v2 = *state.allocAttr(v, state.symbols.create(i.first));
+                    for(auto & elem : table)
+                        visit(attrs.alloc(elem.first), elem.second);
 
-                if (auto i2 = i.second->as_table_array()) {
-                    size_t size2 = i2->get().size();
-                    state.mkList(v2, size2);
-                    for (size_t j = 0; j < size2; ++j)
-                        visit(*(v2.listElems()[j] = state.allocValue()), i2->get()[j]);
+                    v.mkAttrs(attrs);
                 }
-                else
-                    visit(v2, i.second);
-            }
-
-            v.attrs->sort();
-        }
-
-        else if (auto t2 = t->as_array()) {
-            size_t size = t2->get().size();
-
-            state.mkList(v, size);
-
-            for (size_t i = 0; i < size; ++i)
-                visit(*(v.listElems()[i] = state.allocValue()), t2->get()[i]);
-        }
-
-        // Handle cases like 'a = [[{ a = true }]]', which IMHO should be
-        // parsed as a array containing an array containing a table,
-        // but instead are parsed as an array containing a table array
-        // containing a table.
-        else if (auto t2 = t->as_table_array()) {
-            size_t size = t2->get().size();
-
-            state.mkList(v, size);
-
-            for (size_t j = 0; j < size; ++j)
-                visit(*(v.listElems()[j] = state.allocValue()), t2->get()[j]);
-        }
+                break;;
+            case toml::value_t::array:
+                {
+                    auto array = toml::get<std::vector<toml::value>>(t);
+
+                    size_t size = array.size();
+                    state.mkList(v, size);
+                    for (size_t i = 0; i < size; ++i)
+                        visit(*(v.listElems()[i] = state.allocValue()), array[i]);
+                }
+                break;;
+            case toml::value_t::boolean:
+                v.mkBool(toml::get<bool>(t));
+                break;;
+            case toml::value_t::integer:
+                v.mkInt(toml::get<int64_t>(t));
+                break;;
+            case toml::value_t::floating:
+                v.mkFloat(toml::get<NixFloat>(t));
+                break;;
+            case toml::value_t::string:
+                v.mkString(toml::get<std::string>(t));
+                break;;
+            case toml::value_t::local_datetime:
+            case toml::value_t::offset_datetime:
+            case toml::value_t::local_date:
+            case toml::value_t::local_time:
+                // We fail since Nix doesn't have date and time types
+                throw std::runtime_error("Dates and times are not supported");
+                break;;
+            case toml::value_t::empty:
+                v.mkNull();
+                break;;
 
-        else if (t->is_value()) {
-            if (auto val = t->as<int64_t>())
-                mkInt(v, val->get());
-            else if (auto val = t->as<NixFloat>())
-                mkFloat(v, val->get());
-            else if (auto val = t->as<bool>())
-                mkBool(v, val->get());
-            else if (auto val = t->as<std::string>())
-                mkString(v, val->get());
-            else
-                throw EvalError("unsupported value type in TOML");
         }
-
-        else abort();
     };
 
     try {
-        visit(v, parser(tomlStream).parse());
-    } catch (std::runtime_error & e) {
+        visit(val, toml::parse(tomlStream, "fromTOML" /* the "filename" */));
+    } catch (std::exception & e) { // TODO: toml::syntax_error
         throw EvalError({
             .msg = hintfmt("while parsing a TOML string: %s", e.what()),
             .errPos = pos
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 6b4f3c0ae..1896c7563 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -10,6 +10,8 @@
 
 namespace nix {
 
+class BindingsBuilder;
+
 
 typedef enum {
     tInt = 1,
@@ -235,6 +237,17 @@ public:
         string.context = context;
     }
 
+    void mkString(std::string_view s);
+
+    void mkString(std::string_view s, const PathSet & context);
+
+    void mkStringMove(const char * s, const PathSet & context);
+
+    inline void mkString(const Symbol & s)
+    {
+        mkString(((const std::string &) s).c_str());
+    }
+
     inline void mkPath(const char * s)
     {
         clearValue();
@@ -242,6 +255,8 @@ public:
         path = s;
     }
 
+    void mkPath(std::string_view s);
+
     inline void mkNull()
     {
         clearValue();
@@ -255,6 +270,8 @@ public:
         attrs = a;
     }
 
+    Value & mkAttrs(BindingsBuilder & bindings);
+
     inline void mkList(size_t size)
     {
         clearValue();
@@ -383,45 +400,6 @@ public:
 };
 
 
-
-// TODO: Remove these static functions, replace call sites with v.mk* instead
-static inline void mkInt(Value & v, NixInt n)
-{
-    v.mkInt(n);
-}
-
-static inline void mkFloat(Value & v, NixFloat n)
-{
-    v.mkFloat(n);
-}
-
-static inline void mkBool(Value & v, bool b)
-{
-    v.mkBool(b);
-}
-
-static inline void mkNull(Value & v)
-{
-    v.mkNull();
-}
-
-static inline void mkApp(Value & v, Value & left, Value & right)
-{
-    v.mkApp(&left, &right);
-}
-
-static inline void mkString(Value & v, const Symbol & s)
-{
-    v.mkString(((const string &) s).c_str());
-}
-
-
-void mkString(Value & v, const char * s);
-
-
-void mkPath(Value & v, const char * s);
-
-
 #if HAVE_BOEHMGC
 typedef std::vector<Value *, traceable_allocator<Value *> > ValueVector;
 typedef std::map<Symbol, Value *, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, Value *> > > ValueMap;