Make the Store API more type-safe

Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.

Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.

Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).

1 files changed, 64 insertions, 69 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index d693a3b20..3ef827ebc 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -44,29 +44,28 @@ std::pair<string, string> decodeContext(const string & s)
 
 
 InvalidPathError::InvalidPathError(const Path & path) :
-    EvalError(format("path '%1%' is not valid") % path), path(path) {}
+    EvalError("path '%s' is not valid", path), path(path) {}
 
 void EvalState::realiseContext(const PathSet & context)
 {
-    PathSet drvs;
+    std::vector<StorePathWithOutputs> drvs;
 
     for (auto & i : context) {
         std::pair<string, string> decoded = decodeContext(i);
-        Path ctx = decoded.first;
-        assert(store->isStorePath(ctx));
+        auto ctx = store->parseStorePath(decoded.first);
         if (!store->isValidPath(ctx))
-            throw InvalidPathError(ctx);
-        if (!decoded.second.empty() && nix::isDerivation(ctx)) {
-            drvs.insert(decoded.first + "!" + decoded.second);
+            throw InvalidPathError(store->printStorePath(ctx));
+        if (!decoded.second.empty() && ctx.isDerivation()) {
+            drvs.push_back(StorePathWithOutputs{ctx.clone(), {decoded.second}});
 
             /* Add the output of this derivation to the allowed
                paths. */
             if (allowedPaths) {
-                auto drv = store->derivationFromPath(decoded.first);
+                auto drv = store->derivationFromPath(store->parseStorePath(decoded.first));
                 DerivationOutputs::iterator i = drv.outputs.find(decoded.second);
                 if (i == drv.outputs.end())
                     throw Error("derivation '%s' does not have an output named '%s'", decoded.first, decoded.second);
-                allowedPaths->insert(i->second.path);
+                allowedPaths->insert(store->printStorePath(i->second.path));
             }
         }
     }
@@ -74,10 +73,11 @@ void EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return;
 
     if (!evalSettings.enableImportFromDerivation)
-        throw EvalError(format("attempted to realize '%1%' during evaluation but 'allow-import-from-derivation' is false") % *(drvs.begin()));
+        throw EvalError("attempted to realize '%1%' during evaluation but 'allow-import-from-derivation' is false",
+            store->printStorePath(drvs.begin()->path));
 
     /* For performance, prefetch all substitute info. */
-    PathSet willBuild, willSubstitute, unknown;
+    StorePathSet willBuild, willSubstitute, unknown;
     unsigned long long downloadSize, narSize;
     store->queryMissing(drvs, willBuild, willSubstitute, unknown, downloadSize, narSize);
     store->buildPaths(drvs);
@@ -100,8 +100,9 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 
     Path realPath = state.checkSourcePath(state.toRealPath(path, context));
 
-    if (state.store->isStorePath(path) && state.store->isValidPath(path) && isDerivation(path)) {
-        Derivation drv = readDerivation(realPath);
+    // FIXME
+    if (state.store->isStorePath(path) && state.store->isValidPath(state.store->parseStorePath(path)) && isDerivation(path)) {
+        Derivation drv = readDerivation(*state.store, realPath);
         Value & w = *state.allocValue();
         state.mkAttrs(w, 3 + drv.outputs.size());
         Value * v2 = state.allocAttr(w, state.sDrvPath);
@@ -115,7 +116,7 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 
         for (const auto & o : drv.outputs) {
             v2 = state.allocAttr(w, state.symbols.create(o.first));
-            mkString(*v2, o.second.path, {"!" + o.first + "!" + path});
+            mkString(*v2, state.store->printStorePath(o.second.path), {"!" + o.first + "!" + path});
             outputsVal->listElems()[outputs_index] = state.allocValue();
             mkString(*(outputsVal->listElems()[outputs_index++]), o.first);
         }
@@ -676,24 +677,24 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
            runs. */
         if (path.at(0) == '=') {
             /* !!! This doesn't work if readOnlyMode is set. */
-            PathSet refs;
-            state.store->computeFSClosure(string(path, 1), refs);
+            StorePathSet refs;
+            state.store->computeFSClosure(state.store->parseStorePath(std::string_view(path).substr(1)), refs);
             for (auto & j : refs) {
-                drv.inputSrcs.insert(j);
-                if (isDerivation(j))
-                    drv.inputDrvs[j] = state.store->queryDerivationOutputNames(j);
+                drv.inputSrcs.insert(j.clone());
+                if (j.isDerivation())
+                    drv.inputDrvs[j.clone()] = state.store->queryDerivationOutputNames(j);
             }
         }
 
         /* Handle derivation outputs of the form ‘!<name>!<path>’. */
         else if (path.at(0) == '!') {
             std::pair<string, string> ctx = decodeContext(path);
-            drv.inputDrvs[ctx.first].insert(ctx.second);
+            drv.inputDrvs[state.store->parseStorePath(ctx.first)].insert(ctx.second);
         }
 
         /* Otherwise it's a source file. */
         else
-            drv.inputSrcs.insert(path);
+            drv.inputSrcs.insert(state.store->parseStorePath(path));
     }
 
     /* Do we have all required attributes? */
@@ -703,10 +704,8 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         throw EvalError(format("required attribute 'system' missing, at %1%") % posDrvName);
 
     /* Check whether the derivation name is valid. */
-    checkStoreName(drvName);
     if (isDerivation(drvName))
-        throw EvalError(format("derivation names are not allowed to end in '%1%', at %2%")
-            % drvExtension % posDrvName);
+        throw EvalError("derivation names are not allowed to end in '%s', at %s", drvExtension, posDrvName);
 
     if (outputHash) {
         /* Handle fixed-output derivations. */
@@ -716,52 +715,51 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         HashType ht = outputHashAlgo.empty() ? htUnknown : parseHashType(outputHashAlgo);
         Hash h(*outputHash, ht);
 
-        Path outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
-        if (!jsonObject) drv.env["out"] = outPath;
-        drv.outputs["out"] = DerivationOutput(outPath,
-            (outputHashRecursive ? "r:" : "") + printHashType(h.type),
-            h.to_string(Base16, false));
+        auto outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
+        if (!jsonObject) drv.env["out"] = state.store->printStorePath(outPath);
+        drv.outputs.insert_or_assign("out", DerivationOutput(std::move(outPath),
+                (outputHashRecursive ? "r:" : "") + printHashType(h.type),
+                h.to_string(Base16, false)));
     }
 
     else {
-        /* Construct the "masked" store derivation, which is the final
-           one except that in the list of outputs, the output paths
-           are empty, and the corresponding environment variables have
-           an empty value.  This ensures that changes in the set of
-           output names do get reflected in the hash. */
+        /* Compute a hash over the "masked" store derivation, which is
+           the final one except that in the list of outputs, the
+           output paths are empty strings, and the corresponding
+           environment variables have an empty value.  This ensures
+           that changes in the set of output names do get reflected in
+           the hash. */
         for (auto & i : outputs) {
             if (!jsonObject) drv.env[i] = "";
-            drv.outputs[i] = DerivationOutput("", "", "");
         }
 
-        /* Use the masked derivation expression to compute the output
-           path. */
-        Hash h = hashDerivationModulo(*state.store, drv);
+        Hash h = hashDerivationModulo(*state.store, Derivation(drv), true);
 
-        for (auto & i : drv.outputs)
-            if (i.second.path == "") {
-                Path outPath = state.store->makeOutputPath(i.first, h, drvName);
-                if (!jsonObject) drv.env[i.first] = outPath;
-                i.second.path = outPath;
-            }
+        for (auto & i : outputs) {
+            auto outPath = state.store->makeOutputPath(i, h, drvName);
+            if (!jsonObject) drv.env[i] = state.store->printStorePath(outPath);
+            drv.outputs.insert_or_assign(i,
+                DerivationOutput(std::move(outPath), "", ""));
+        }
     }
 
     /* Write the resulting term into the Nix store directory. */
-    Path drvPath = writeDerivation(state.store, drv, drvName, state.repair);
+    auto drvPath = writeDerivation(state.store, drv, drvName, state.repair);
+    auto drvPathS = state.store->printStorePath(drvPath);
 
-    printMsg(lvlChatty, format("instantiated '%1%' -> '%2%'")
-        % drvName % drvPath);
+    printMsg(lvlChatty, "instantiated '%1%' -> '%2%'", drvName, drvPathS);
 
     /* Optimisation, but required in read-only mode! because in that
        case we don't actually write store derivations, so we can't
        read them later. */
-    drvHashes[drvPath] = hashDerivationModulo(*state.store, drv);
+    drvHashes.insert_or_assign(drvPath.clone(),
+        hashDerivationModulo(*state.store, Derivation(drv), false));
 
     state.mkAttrs(v, 1 + drv.outputs.size());
-    mkString(*state.allocAttr(v, state.sDrvPath), drvPath, {"=" + drvPath});
+    mkString(*state.allocAttr(v, state.sDrvPath), drvPathS, {"=" + drvPathS});
     for (auto & i : drv.outputs) {
         mkString(*state.allocAttr(v, state.symbols.create(i.first)),
-            i.second.path, {"!" + i.first + "!" + drvPath});
+            state.store->printStorePath(i.second.path), {"!" + i.first + "!" + drvPathS});
     }
     v.attrs->sort();
 }
@@ -814,7 +812,7 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
         throw EvalError(format("path '%1%' is not in the Nix store, at %2%") % path % pos);
     Path path2 = state.store->toStorePath(path);
     if (!settings.readOnlyMode)
-        state.store->ensurePath(path2);
+        state.store->ensurePath(state.store->parseStorePath(path2));
     context.insert(path2);
     mkString(v, path, context);
 }
@@ -1010,17 +1008,17 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
     string name = state.forceStringNoCtx(*args[0], pos);
     string contents = state.forceString(*args[1], context, pos);
 
-    PathSet refs;
+    StorePathSet refs;
 
     for (auto path : context) {
         if (path.at(0) != '/')
             throw EvalError(format("in 'toFile': the file '%1%' cannot refer to derivation outputs, at %2%") % name % pos);
-        refs.insert(path);
+        refs.insert(state.store->parseStorePath(path));
     }
 
-    Path storePath = settings.readOnlyMode
+    auto storePath = state.store->printStorePath(settings.readOnlyMode
         ? state.store->computeStorePathForText(name, contents, refs)
-        : state.store->addTextToStore(name, contents, refs, state.repair);
+        : state.store->addTextToStore(name, contents, refs, state.repair));
 
     /* Note: we don't need to add `context' to the context of the
        result, since `storePath' itself has references to the paths
@@ -1060,21 +1058,18 @@ static void addPath(EvalState & state, const Pos & pos, const string & name, con
         return state.forceBool(res, pos);
     }) : defaultPathFilter;
 
-    Path expectedStorePath;
-    if (expectedHash) {
-        expectedStorePath =
-            state.store->makeFixedOutputPath(recursive, expectedHash, name);
-    }
+    std::optional<StorePath> expectedStorePath;
+    if (expectedHash)
+        expectedStorePath = state.store->makeFixedOutputPath(recursive, expectedHash, name);
     Path dstPath;
-    if (!expectedHash || !state.store->isValidPath(expectedStorePath)) {
-        dstPath = settings.readOnlyMode
+    if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
+        dstPath = state.store->printStorePath(settings.readOnlyMode
             ? state.store->computeStorePathForPath(name, path, recursive, htSHA256, filter).first
-            : state.store->addToStore(name, path, recursive, htSHA256, filter, state.repair);
-        if (expectedHash && expectedStorePath != dstPath) {
-            throw Error(format("store path mismatch in (possibly filtered) path added from '%1%'") % path);
-        }
+            : state.store->addToStore(name, path, recursive, htSHA256, filter, state.repair));
+        if (expectedHash && expectedStorePath != state.store->parseStorePath(dstPath))
+            throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
     } else
-        dstPath = expectedStorePath;
+        dstPath = state.store->printStorePath(*expectedStorePath);
 
     mkString(v, dstPath, {dstPath});
 }
@@ -1091,7 +1086,7 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
     if (args[0]->type != tLambda)
         throw TypeError(format("first argument in call to 'filterSource' is not a function but %1%, at %2%") % showType(*args[0]) % pos);
 
-    addPath(state, pos, baseNameOf(path), path, args[0], true, Hash(), v);
+    addPath(state, pos, std::string(baseNameOf(path)), path, args[0], true, Hash(), v);
 }
 
 static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value & v)
@@ -2151,7 +2146,7 @@ void EvalState::createBaseEnv()
     }
 
     if (!evalSettings.pureEval) {
-        mkString(v, settings.thisSystem);
+        mkString(v, settings.thisSystem.get());
         addConstant("__currentSystem", v);
     }