Merge pull request #5648 from edolstra/list-iter

Support range-based for loop over list values

10 files changed, 103 insertions, 79 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 1fd609bd4..b987e1888 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -119,8 +119,8 @@ void printValue(std::ostream & str, std::set<const Value *> & active, const Valu
     case tList2:
     case tListN:
         str << "[ ";
-        for (unsigned int n = 0; n < v.listSize(); ++n) {
-            printValue(str, active, *v.listElems()[n]);
+        for (auto v2 : v.listItems()) {
+            printValue(str, active, *v2);
             str << " ";
         }
         str << "]";
@@ -1155,8 +1155,8 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
 void ExprList::eval(EvalState & state, Env & env, Value & v)
 {
     state.mkList(v, elems.size());
-    for (size_t n = 0; n < elems.size(); ++n)
-        v.listElems()[n] = elems[n]->maybeThunk(state, env);
+    for (auto [n, v2] : enumerate(v.listItems()))
+        const_cast<Value * &>(v2) = elems[n]->maybeThunk(state, env);
 }
 
 
@@ -1736,8 +1736,8 @@ void EvalState::forceValueDeep(Value & v)
         }
 
         else if (v.isList()) {
-            for (size_t n = 0; n < v.listSize(); ++n)
-                recurse(*v.listElems()[n]);
+            for (auto v2 : v.listItems())
+                recurse(*v2);
         }
     };
 
@@ -1921,12 +1921,12 @@ string EvalState::coerceToString(const Pos & pos, Value & v, PathSet & context,
 
         if (v.isList()) {
             string result;
-            for (size_t n = 0; n < v.listSize(); ++n) {
-                result += coerceToString(pos, *v.listElems()[n],
+            for (auto [n, v2] : enumerate(v.listItems())) {
+                result += coerceToString(pos, *v2,
                     context, coerceMore, copyToStore);
                 if (n < v.listSize() - 1
                     /* !!! not quite correct */
-                    && (!v.listElems()[n]->isList() || v.listElems()[n]->listSize() != 0))
+                    && (!v2->isList() || v2->listSize() != 0))
                     result += " ";
             }
             return result;
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index f5be67d67..06136579e 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -257,8 +257,7 @@ static Flake getFlake(
                 flake.config.settings.insert({setting.name, state.forceBool(*setting.value, *setting.pos)});
             else if (setting.value->type() == nList) {
                 std::vector<std::string> ss;
-                for (unsigned int n = 0; n < setting.value->listSize(); ++n) {
-                    auto elem = setting.value->listElems()[n];
+                for (auto elem : setting.value->listItems()) {
                     if (elem->type() != nString)
                         throw TypeError("list element in flake configuration setting '%s' is %s while a string is expected",
                             setting.name, showType(*setting.value));
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index f774e6493..ed4c47fbb 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -102,9 +102,9 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall)
             state->forceList(*i->value, *i->pos);
 
             /* For each output... */
-            for (unsigned int j = 0; j < i->value->listSize(); ++j) {
+            for (auto elem : i->value->listItems()) {
                 /* Evaluate the corresponding set. */
-                string name = state->forceStringNoCtx(*i->value->listElems()[j], *i->pos);
+                string name = state->forceStringNoCtx(*elem, *i->pos);
                 Bindings::iterator out = attrs->find(state->symbols.create(name));
                 if (out == attrs->end()) continue; // FIXME: throw error?
                 state->forceAttrs(*out->value);
@@ -128,9 +128,9 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall)
         /* ^ this shows during `nix-env -i` right under the bad derivation */
     if (!outTI->isList()) throw errMsg;
     Outputs result;
-    for (auto i = outTI->listElems(); i != outTI->listElems() + outTI->listSize(); ++i) {
-        if ((*i)->type() != nString) throw errMsg;
-        auto out = outputs.find((*i)->string.s);
+    for (auto elem : outTI->listItems()) {
+        if (elem->type() != nString) throw errMsg;
+        auto out = outputs.find(elem->string.s);
         if (out == outputs.end()) throw errMsg;
         result.insert(*out);
     }
@@ -174,8 +174,8 @@ bool DrvInfo::checkMeta(Value & v)
 {
     state->forceValue(v);
     if (v.type() == nList) {
-        for (unsigned int n = 0; n < v.listSize(); ++n)
-            if (!checkMeta(*v.listElems()[n])) return false;
+        for (auto elem : v.listItems())
+            if (!checkMeta(*elem)) return false;
         return true;
     }
     else if (v.type() == nAttrs) {
@@ -364,10 +364,10 @@ static void getDerivations(EvalState & state, Value & vIn,
     }
 
     else if (v.type() == nList) {
-        for (unsigned int n = 0; n < v.listSize(); ++n) {
-            string pathPrefix2 = addToPath(pathPrefix, (format("%1%") % n).str());
-            if (getDerivation(state, *v.listElems()[n], pathPrefix2, drvs, done, ignoreAssertionFailures))
-                getDerivations(state, *v.listElems()[n], pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+        for (auto [n, elem] : enumerate(v.listItems())) {
+            string pathPrefix2 = addToPath(pathPrefix, fmt("%d", n));
+            if (getDerivation(state, *elem, pathPrefix2, drvs, done, ignoreAssertionFailures))
+                getDerivations(state, *elem, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
         }
     }
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 8cbeaa520..c0d59da8c 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -335,9 +335,8 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
     PathSet context;
     auto program = state.coerceToString(pos, *elems[0], context, false, false);
     Strings commandArgs;
-    for (unsigned int i = 1; i < args[0]->listSize(); ++i) {
+    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);
     } catch (InvalidPathError & e) {
@@ -616,8 +615,8 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
     state.forceList(*startSet->value, pos);
 
     ValueList workSet;
-    for (unsigned int n = 0; n < startSet->value->listSize(); ++n)
-        workSet.push_back(startSet->value->listElems()[n]);
+    for (auto elem : startSet->value->listItems())
+        workSet.push_back(elem);
 
     /* Get the operator. */
     Bindings::iterator op = getAttr(
@@ -662,9 +661,9 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         state.forceList(call, pos);
 
         /* Add the values returned by the operator to the work set. */
-        for (unsigned int n = 0; n < call.listSize(); ++n) {
-            state.forceValue(*call.listElems()[n], pos);
-            workSet.push_back(call.listElems()[n]);
+        for (auto elem : call.listItems()) {
+            state.forceValue(*elem, pos);
+            workSet.push_back(elem);
         }
     }
 
@@ -1013,8 +1012,8 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                command-line arguments to the builder. */
             else if (i->name == state.sArgs) {
                 state.forceList(*i->value, pos);
-                for (unsigned int n = 0; n < i->value->listSize(); ++n) {
-                    string s = state.coerceToString(posDrvName, *i->value->listElems()[n], context, true);
+                for (auto elem : i->value->listItems()) {
+                    string s = state.coerceToString(posDrvName, *elem, context, true);
                     drv.args.push_back(s);
                 }
             }
@@ -1044,8 +1043,8 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                         /* Require ‘outputs’ to be a list of strings. */
                         state.forceList(*i->value, posDrvName);
                         Strings ss;
-                        for (unsigned int n = 0; n < i->value->listSize(); ++n)
-                            ss.emplace_back(state.forceStringNoCtx(*i->value->listElems()[n], posDrvName));
+                        for (auto elem : i->value->listItems())
+                            ss.emplace_back(state.forceStringNoCtx(*elem, posDrvName));
                         handleOutputs(ss);
                     }
 
@@ -1460,20 +1459,19 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
 
     SearchPath searchPath;
 
-    for (unsigned int n = 0; n < args[0]->listSize(); ++n) {
-        Value & v2(*args[0]->listElems()[n]);
-        state.forceAttrs(v2, pos);
+    for (auto v2 : args[0]->listItems()) {
+        state.forceAttrs(*v2, pos);
 
         string prefix;
-        Bindings::iterator i = v2.attrs->find(state.symbols.create("prefix"));
-        if (i != v2.attrs->end())
+        Bindings::iterator i = v2->attrs->find(state.symbols.create("prefix"));
+        if (i != v2->attrs->end())
             prefix = state.forceStringNoCtx(*i->value, pos);
 
         i = getAttr(
             state,
             "findFile",
             "path",
-            v2.attrs,
+            v2->attrs,
             pos
         );
 
@@ -2239,9 +2237,9 @@ static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args,
 
     /* Get the attribute names to be removed. */
     std::set<Symbol> names;
-    for (unsigned int i = 0; i < args[1]->listSize(); ++i) {
-        state.forceStringNoCtx(*args[1]->listElems()[i], pos);
-        names.insert(state.symbols.create(args[1]->listElems()[i]->string.s));
+    for (auto elem : args[1]->listItems()) {
+        state.forceStringNoCtx(*elem, pos);
+        names.insert(state.symbols.create(elem->string.s));
     }
 
     /* Copy all attributes not in that set.  Note that we don't need
@@ -2249,7 +2247,7 @@ static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args,
        vector. */
     state.mkAttrs(v, args[0]->attrs->size());
     for (auto & i : *args[0]->attrs) {
-        if (names.find(i.name) == names.end())
+        if (!names.count(i.name))
             v.attrs->push_back(i);
     }
 }
@@ -2283,15 +2281,14 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
 
     std::set<Symbol> seen;
 
-    for (unsigned int i = 0; i < args[0]->listSize(); ++i) {
-        Value & v2(*args[0]->listElems()[i]);
-        state.forceAttrs(v2, pos);
+    for (auto v2 : args[0]->listItems()) {
+        state.forceAttrs(*v2, pos);
 
         Bindings::iterator j = getAttr(
             state,
             "listToAttrs",
             state.sName,
-            v2.attrs,
+            v2->attrs,
             pos
         );
 
@@ -2303,7 +2300,7 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
                 state,
                 "listToAttrs",
                 state.sValue,
-                v2.attrs,
+                v2->attrs,
                 pos
             );
             v.attrs->push_back(Attr(sym, j2->value, j2->pos));
@@ -2370,11 +2367,10 @@ static void prim_catAttrs(EvalState & state, const Pos & pos, Value * * args, Va
     Value * res[args[1]->listSize()];
     unsigned int found = 0;
 
-    for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
-        Value & v2(*args[1]->listElems()[n]);
-        state.forceAttrs(v2, pos);
-        Bindings::iterator i = v2.attrs->find(attrName);
-        if (i != v2.attrs->end())
+    for (auto v2 : args[1]->listItems()) {
+        state.forceAttrs(*v2, pos);
+        Bindings::iterator i = v2->attrs->find(attrName);
+        if (i != v2->attrs->end())
             res[found++] = i->value;
     }
 
@@ -2649,8 +2645,8 @@ static void prim_elem(EvalState & state, const Pos & pos, Value * * args, Value
 {
     bool res = false;
     state.forceList(*args[1], pos);
-    for (unsigned int n = 0; n < args[1]->listSize(); ++n)
-        if (state.eqValues(*args[0], *args[1]->listElems()[n])) {
+    for (auto elem : args[1]->listItems())
+        if (state.eqValues(*args[0], *elem)) {
             res = true;
             break;
         }
@@ -2709,8 +2705,8 @@ static void prim_foldlStrict(EvalState & state, const Pos & pos, Value * * args,
     if (args[2]->listSize()) {
         Value * vCur = args[1];
 
-        for (unsigned int n = 0; n < args[2]->listSize(); ++n) {
-            Value * vs []{vCur, args[2]->listElems()[n]};
+        for (auto [n, elem] : enumerate(args[2]->listItems())) {
+            Value * vs []{vCur, elem};
             vCur = n == args[2]->listSize() - 1 ? &v : state.allocValue();
             state.callFunction(*args[0], 2, vs, *vCur, pos);
         }
@@ -2740,8 +2736,8 @@ static void anyOrAll(bool any, EvalState & state, const Pos & pos, Value * * arg
     state.forceList(*args[1], pos);
 
     Value vTmp;
-    for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
-        state.callFunction(*args[0], *args[1]->listElems()[n], vTmp, pos);
+    for (auto elem : args[1]->listItems()) {
+        state.callFunction(*args[0], *elem, vTmp, pos);
         bool res = state.forceBool(vTmp, pos);
         if (res == any) {
             mkBool(v, any);
@@ -3470,9 +3466,9 @@ static void prim_concatStringsSep(EvalState & state, const Pos & pos, Value * *
     res.reserve((args[1]->listSize() + 32) * sep.size());
     bool first = true;
 
-    for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
+    for (auto elem : args[1]->listItems()) {
         if (first) first = false; else res += sep;
-        res += state.coerceToString(pos, *args[1]->listElems()[n], context);
+        res += state.coerceToString(pos, *elem, context);
     }
 
     mkString(v, res, context);
@@ -3501,14 +3497,14 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
 
     vector<string> from;
     from.reserve(args[0]->listSize());
-    for (unsigned int n = 0; n < args[0]->listSize(); ++n)
-        from.push_back(state.forceString(*args[0]->listElems()[n], pos));
+    for (auto elem : args[0]->listItems())
+        from.push_back(state.forceString(*elem, pos));
 
     vector<std::pair<string, PathSet>> to;
     to.reserve(args[1]->listSize());
-    for (unsigned int n = 0; n < args[1]->listSize(); ++n) {
+    for (auto elem : args[1]->listItems()) {
         PathSet ctx;
-        auto s = state.forceString(*args[1]->listElems()[n], ctx, pos);
+        auto s = state.forceString(*elem, ctx, pos);
         to.push_back(std::make_pair(std::move(s), std::move(ctx)));
     }
 
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
index 31cf812b4..20545afd0 100644
--- a/src/libexpr/primops/context.cc
+++ b/src/libexpr/primops/context.cc
@@ -118,9 +118,8 @@ static void prim_getContext(EvalState & state, const Pos & pos, Value * * args,
             auto & outputsVal = *state.allocAttr(infoVal, state.sOutputs);
             state.mkList(outputsVal, info.second.outputs.size());
             size_t i = 0;
-            for (const auto & output : info.second.outputs) {
+            for (const auto & output : info.second.outputs)
                 mkString(*(outputsVal.listElems()[i++] = state.allocValue()), output);
-            }
         }
         infoVal.attrs->sort();
     }
@@ -181,8 +180,8 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
                     .errPos = *i.pos
                 });
             }
-            for (unsigned int n = 0; n < iter->value->listSize(); ++n) {
-                auto name = state.forceStringNoCtx(*iter->value->listElems()[n], *iter->pos);
+            for (auto elem : iter->value->listItems()) {
+                auto name = state.forceStringNoCtx(*elem, *iter->pos);
                 context.insert("!" + name + "!" + string(i.name));
             }
         }
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 4d642c720..517da4c01 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -63,9 +63,9 @@ void printValueAsJSON(EvalState & state, bool strict,
 
         case nList: {
             auto list(out.list());
-            for (unsigned int n = 0; n < v.listSize(); ++n) {
+            for (auto elem : v.listItems()) {
                 auto placeholder(list.placeholder());
-                printValueAsJSON(state, strict, *v.listElems()[n], pos, placeholder, context);
+                printValueAsJSON(state, strict, *elem, pos, placeholder, context);
             }
             break;
         }
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 54268ece0..a875f82d7 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -122,8 +122,8 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
 
         case nList: {
             XMLOpenElement _(doc, "list");
-            for (unsigned int n = 0; n < v.listSize(); ++n)
-                printValueAsXML(state, strict, location, *v.listElems()[n], doc, context, drvsSeen, pos);
+            for (auto v2 : v.listItems())
+                printValueAsXML(state, strict, location, *v2, doc, context, drvsSeen, pos);
             break;
         }
 
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 3bb97b3c2..4b43e47ae 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <cassert>
+
 #include "symbol-table.hh"
 
 #if HAVE_BOEHMGC
@@ -350,6 +352,34 @@ public:
     bool isTrivial() const;
 
     std::vector<std::pair<Path, std::string>> getContext();
+
+    auto listItems()
+    {
+        struct ListIterable
+        {
+            typedef Value * const * iterator;
+            iterator _begin, _end;
+            iterator begin() const { return _begin; }
+            iterator end() const { return _end; }
+        };
+        assert(isList());
+        auto begin = listElems();
+        return ListIterable { begin, begin + listSize() };
+    }
+
+    auto listItems() const
+    {
+        struct ConstListIterable
+        {
+            typedef const Value * const * iterator;
+            iterator _begin, _end;
+            iterator begin() const { return _begin; }
+            iterator end() const { return _end; }
+        };
+        assert(isList());
+        auto begin = listElems();
+        return ConstListIterable { begin, begin + listSize() };
+    }
 };
 
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 4056d973d..0dd0e34a0 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -1149,10 +1149,10 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                                 } else if (v->type() == nList) {
                                     attrs2["type"] = "strings";
                                     XMLOpenElement m(xml, "meta", attrs2);
-                                    for (unsigned int j = 0; j < v->listSize(); ++j) {
-                                        if (v->listElems()[j]->type() != nString) continue;
+                                    for (auto elem : v->listItems()) {
+                                        if (elem->type() != nString) continue;
                                         XMLAttrs attrs3;
-                                        attrs3["value"] = v->listElems()[j]->string.s;
+                                        attrs3["value"] = elem->string.s;
                                         xml.writeEmptyElement("string", attrs3);
                                     }
                               } else if (v->type() == nAttrs) {
diff --git a/src/nix/repl.cc b/src/nix/repl.cc
index fd86174f2..41283c5f2 100644
--- a/src/nix/repl.cc
+++ b/src/nix/repl.cc
@@ -771,12 +771,12 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
 
         str << "[ ";
         if (maxDepth > 0)
-            for (unsigned int n = 0; n < v.listSize(); ++n) {
-                if (seen.find(v.listElems()[n]) != seen.end())
+            for (auto elem : v.listItems()) {
+                if (seen.count(elem))
                     str << "«repeated»";
                 else
                     try {
-                        printValue(str, *v.listElems()[n], maxDepth - 1, seen);
+                        printValue(str, *elem, maxDepth - 1, seen);
                     } catch (AssertionError & e) {
                         str << ANSI_RED "«error: " << e.msg() << "»" ANSI_NORMAL;
                     }