Merge pull request #7484 from edolstra/fix-7417

 InstallableFlake::toDerivedPaths(): Support paths and store paths

12 files changed, 263 insertions, 179 deletions

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 79361e94e..c0db2a715 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -358,7 +358,7 @@ void completeFlakeRef(ref<Store> store, std::string_view prefix)
     }
 }
 
-DerivedPath Installable::toDerivedPath()
+DerivedPathWithInfo Installable::toDerivedPath()
 {
     auto buildables = toDerivedPaths();
     if (buildables.size() != 1)
@@ -422,21 +422,9 @@ struct InstallableStorePath : Installable
         return req.to_string(*store);
     }
 
-    DerivedPaths toDerivedPaths() override
+    DerivedPathsWithInfo toDerivedPaths() override
     {
-        return { req };
-    }
-
-    StorePathSet toDrvPaths(ref<Store> store) override
-    {
-        return std::visit(overloaded {
-            [&](const DerivedPath::Built & bfd) -> StorePathSet {
-                return { bfd.drvPath };
-            },
-            [&](const DerivedPath::Opaque & bo) -> StorePathSet {
-                return { getDeriver(store, *this, bo.path) };
-            },
-        }, req.raw());
+        return {{.path = req, .info = {} }};
     }
 
     std::optional<StorePath> getStorePath() override
@@ -452,34 +440,6 @@ struct InstallableStorePath : Installable
     }
 };
 
-DerivedPaths InstallableValue::toDerivedPaths()
-{
-    DerivedPaths res;
-
-    std::map<StorePath, std::set<std::string>> drvsToOutputs;
-    RealisedPath::Set drvsToCopy;
-
-    // Group by derivation, helps with .all in particular
-    for (auto & drv : toDerivations()) {
-        for (auto & outputName : drv.outputsToInstall)
-            drvsToOutputs[drv.drvPath].insert(outputName);
-        drvsToCopy.insert(drv.drvPath);
-    }
-
-    for (auto & i : drvsToOutputs)
-        res.push_back(DerivedPath::Built { i.first, i.second });
-
-    return res;
-}
-
-StorePathSet InstallableValue::toDrvPaths(ref<Store> store)
-{
-    StorePathSet res;
-    for (auto & drv : toDerivations())
-        res.insert(drv.drvPath);
-    return res;
-}
-
 struct InstallableAttrPath : InstallableValue
 {
     SourceExprCommand & cmd;
@@ -509,40 +469,45 @@ struct InstallableAttrPath : InstallableValue
         return {vRes, pos};
     }
 
-    virtual std::vector<InstallableValue::DerivationInfo> toDerivations() override;
-};
+    DerivedPathsWithInfo toDerivedPaths() override
+    {
+        auto v = toValue(*state).first;
 
-std::vector<InstallableValue::DerivationInfo> InstallableAttrPath::toDerivations()
-{
-    auto v = toValue(*state).first;
+        Bindings & autoArgs = *cmd.getAutoArgs(*state);
 
-    Bindings & autoArgs = *cmd.getAutoArgs(*state);
+        DrvInfos drvInfos;
+        getDerivations(*state, *v, "", autoArgs, drvInfos, false);
 
-    DrvInfos drvInfos;
-    getDerivations(*state, *v, "", autoArgs, drvInfos, false);
+        // Backward compatibility hack: group results by drvPath. This
+        // helps keep .all output together.
+        std::map<StorePath, DerivedPath::Built> byDrvPath;
 
-    std::vector<DerivationInfo> res;
-    for (auto & drvInfo : drvInfos) {
-        auto drvPath = drvInfo.queryDrvPath();
-        if (!drvPath)
-            throw Error("'%s' is not a derivation", what());
+        for (auto & drvInfo : drvInfos) {
+            auto drvPath = drvInfo.queryDrvPath();
+            if (!drvPath)
+                throw Error("'%s' is not a derivation", what());
 
-        std::set<std::string> outputsToInstall;
+            std::set<std::string> outputsToInstall;
 
-        if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
-            outputsToInstall = *outputNames;
-        else
-            for (auto & output : drvInfo.queryOutputs(false, std::get_if<DefaultOutputs>(&outputsSpec)))
-                outputsToInstall.insert(output.first);
+            if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
+                outputsToInstall = *outputNames;
+            else
+                for (auto & output : drvInfo.queryOutputs(false, std::get_if<DefaultOutputs>(&outputsSpec)))
+                    outputsToInstall.insert(output.first);
 
-        res.push_back(DerivationInfo {
-            .drvPath = *drvPath,
-            .outputsToInstall = std::move(outputsToInstall)
-        });
-    }
+            auto derivedPath = byDrvPath.emplace(*drvPath, DerivedPath::Built { .drvPath = *drvPath }).first;
 
-    return res;
-}
+            for (auto & output : outputsToInstall)
+                derivedPath->second.outputs.insert(output);
+        }
+
+        DerivedPathsWithInfo res;
+        for (auto & [_, info] : byDrvPath)
+            res.push_back({ .path = { info } });
+
+        return res;
+    }
+};
 
 std::vector<std::string> InstallableFlake::getActualAttrPaths()
 {
@@ -630,7 +595,7 @@ InstallableFlake::InstallableFlake(
         throw UsageError("'--arg' and '--argstr' are incompatible with flakes");
 }
 
-std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableFlake::toDerivation()
+DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
 {
     Activity act(*logger, lvlTalkative, actUnknown, fmt("evaluating derivation '%s'", what()));
 
@@ -638,8 +603,38 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
 
     auto attrPath = attr->getAttrPathStr();
 
-    if (!attr->isDerivation())
-        throw Error("flake output attribute '%s' is not a derivation", attrPath);
+    if (!attr->isDerivation()) {
+
+        // FIXME: use eval cache?
+        auto v = attr->forceValue();
+
+        if (v.type() == nPath) {
+            PathSet context;
+            auto storePath = state->copyPathToStore(context, Path(v.path));
+            return {{
+                .path = DerivedPath::Opaque {
+                    .path = std::move(storePath),
+                }
+            }};
+        }
+
+        else if (v.type() == nString) {
+            PathSet context;
+            auto s = state->forceString(v, context, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
+            auto storePath = state->store->maybeParseStorePath(s);
+            if (storePath && context.count(std::string(s))) {
+                return {{
+                    .path = DerivedPath::Opaque {
+                        .path = std::move(*storePath),
+                    }
+                }};
+            } else
+                throw Error("flake output attribute '%s' evaluates to the string '%s' which is not a store path", attrPath, s);
+        }
+
+        else
+            throw Error("flake output attribute '%s' is not a derivation or path", attrPath);
+    }
 
     auto drvPath = attr->forceDerivation();
 
@@ -674,20 +669,19 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
     if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
         outputsToInstall = *outputNames;
 
-    auto drvInfo = DerivationInfo {
-        .drvPath = std::move(drvPath),
-        .outputsToInstall = std::move(outputsToInstall),
-        .priority = priority,
-    };
-
-    return {attrPath, getLockedFlake()->flake.lockedRef, std::move(drvInfo)};
-}
-
-std::vector<InstallableValue::DerivationInfo> InstallableFlake::toDerivations()
-{
-    std::vector<DerivationInfo> res;
-    res.push_back(std::get<2>(toDerivation()));
-    return res;
+    return {{
+        .path = DerivedPath::Built {
+            .drvPath = std::move(drvPath),
+            .outputs = std::move(outputsToInstall),
+        },
+        .info = {
+            .priority = priority,
+            .originalRef = flakeRef,
+            .resolvedRef = getLockedFlake()->flake.lockedRef,
+            .attrPath = attrPath,
+            .outputsSpec = outputsSpec,
+        }
+    }};
 }
 
 std::pair<Value *, PosIdx> InstallableFlake::toValue(EvalState & state)
@@ -895,13 +889,19 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
     if (mode == Realise::Nothing)
         settings.readOnlyMode = true;
 
+    struct Aux
+    {
+        ExtraPathInfo info;
+        std::shared_ptr<Installable> installable;
+    };
+
     std::vector<DerivedPath> pathsToBuild;
-    std::map<DerivedPath, std::vector<std::shared_ptr<Installable>>> backmap;
+    std::map<DerivedPath, std::vector<Aux>> backmap;
 
     for (auto & i : installables) {
         for (auto b : i->toDerivedPaths()) {
-            pathsToBuild.push_back(b);
-            backmap[b].push_back(i);
+            pathsToBuild.push_back(b.path);
+            backmap[b.path].push_back({.info = b.info, .installable = i});
         }
     }
 
@@ -914,7 +914,7 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
         printMissing(store, pathsToBuild, lvlError);
 
         for (auto & path : pathsToBuild) {
-            for (auto & installable : backmap[path]) {
+            for (auto & aux : backmap[path]) {
                 std::visit(overloaded {
                     [&](const DerivedPath::Built & bfd) {
                         OutputPathMap outputs;
@@ -943,10 +943,14 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
                                     output, *drvOutput->second);
                             }
                         }
-                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Built { bfd.drvPath, outputs },
+                            .info = aux.info}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Opaque { bo.path },
+                            .info = aux.info}});
                     },
                 }, path.raw());
             }
@@ -962,16 +966,22 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
             if (!buildResult.success())
                 buildResult.rethrow();
 
-            for (auto & installable : backmap[buildResult.path]) {
+            for (auto & aux : backmap[buildResult.path]) {
                 std::visit(overloaded {
                     [&](const DerivedPath::Built & bfd) {
                         std::map<std::string, StorePath> outputs;
                         for (auto & path : buildResult.builtOutputs)
                             outputs.emplace(path.first.outputName, path.second.outPath);
-                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }, .result = buildResult}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Built { bfd.drvPath, outputs },
+                            .info = aux.info,
+                            .result = buildResult}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }, .result = buildResult}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Opaque { bo.path },
+                            .info = aux.info,
+                            .result = buildResult}});
                     },
                 }, buildResult.path.raw());
             }
@@ -1056,7 +1066,7 @@ StorePathSet Installable::toDerivations(
                 [&](const DerivedPath::Built & bfd) {
                     drvPaths.insert(bfd.drvPath);
                 },
-            }, b.raw());
+            }, b.path.raw());
 
     return drvPaths;
 }
diff --git a/src/libcmd/installables.hh b/src/libcmd/installables.hh
index 02ea351d3..250cf7e83 100644
--- a/src/libcmd/installables.hh
+++ b/src/libcmd/installables.hh
@@ -52,26 +52,42 @@ enum class OperateOn {
     Derivation
 };
 
+struct ExtraPathInfo
+{
+    std::optional<NixInt> priority;
+    std::optional<FlakeRef> originalRef;
+    std::optional<FlakeRef> resolvedRef;
+    std::optional<std::string> attrPath;
+    // FIXME: merge with DerivedPath's 'outputs' field?
+    std::optional<OutputsSpec> outputsSpec;
+};
+
+/* A derived path with any additional info that commands might
+   need from the derivation. */
+struct DerivedPathWithInfo
+{
+    DerivedPath path;
+    ExtraPathInfo info;
+};
+
 struct BuiltPathWithResult
 {
     BuiltPath path;
+    ExtraPathInfo info;
     std::optional<BuildResult> result;
 };
 
+typedef std::vector<DerivedPathWithInfo> DerivedPathsWithInfo;
+
 struct Installable
 {
     virtual ~Installable() { }
 
     virtual std::string what() const = 0;
 
-    virtual DerivedPaths toDerivedPaths() = 0;
-
-    virtual StorePathSet toDrvPaths(ref<Store> store)
-    {
-        throw Error("'%s' cannot be converted to a derivation path", what());
-    }
+    virtual DerivedPathsWithInfo toDerivedPaths() = 0;
 
-    DerivedPath toDerivedPath();
+    DerivedPathWithInfo toDerivedPath();
 
     UnresolvedApp toApp(EvalState & state);
 
@@ -146,19 +162,6 @@ struct InstallableValue : Installable
     ref<EvalState> state;
 
     InstallableValue(ref<EvalState> state) : state(state) {}
-
-    struct DerivationInfo
-    {
-        StorePath drvPath;
-        std::set<std::string> outputsToInstall;
-        std::optional<NixInt> priority;
-    };
-
-    virtual std::vector<DerivationInfo> toDerivations() = 0;
-
-    DerivedPaths toDerivedPaths() override;
-
-    StorePathSet toDrvPaths(ref<Store> store) override;
 };
 
 struct InstallableFlake : InstallableValue
@@ -186,9 +189,7 @@ struct InstallableFlake : InstallableValue
 
     Value * getFlakeOutputs(EvalState & state, const flake::LockedFlake & lockedFlake);
 
-    std::tuple<std::string, FlakeRef, DerivationInfo> toDerivation();
-
-    std::vector<DerivationInfo> toDerivations() override;
+    DerivedPathsWithInfo toDerivedPaths() override;
 
     std::pair<Value *, PosIdx> toValue(EvalState & state) override;
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 72c2b104f..978b0f0e2 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -2166,7 +2166,7 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         if (canonicalizePath)
             path = canonPath(*path);
         if (copyToStore)
-            path = copyPathToStore(context, std::move(path).toOwned());
+            path = store->printStorePath(copyPathToStore(context, std::move(path).toOwned()));
         return path;
     }
 
@@ -2215,26 +2215,26 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
 }
 
 
-std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
+StorePath EvalState::copyPathToStore(PathSet & context, const Path & path)
 {
     if (nix::isDerivation(path))
         error("file names are not allowed to end in '%1%'", drvExtension).debugThrow<EvalError>();
 
-    Path dstPath;
-    auto i = srcToStore.find(path);
-    if (i != srcToStore.end())
-        dstPath = store->printStorePath(i->second);
-    else {
-        auto p = settings.readOnlyMode
+    auto dstPath = [&]() -> StorePath
+    {
+        auto i = srcToStore.find(path);
+        if (i != srcToStore.end()) return i->second;
+
+        auto dstPath = settings.readOnlyMode
             ? store->computeStorePathForPath(std::string(baseNameOf(path)), checkSourcePath(path)).first
             : store->addToStore(std::string(baseNameOf(path)), checkSourcePath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
-        dstPath = store->printStorePath(p);
-        allowPath(p);
-        srcToStore.insert_or_assign(path, std::move(p));
-        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
-    }
+        allowPath(dstPath);
+        srcToStore.insert_or_assign(path, dstPath);
+        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, store->printStorePath(dstPath));
+        return dstPath;
+    }();
 
-    context.insert(dstPath);
+    context.insert(store->printStorePath(dstPath));
     return dstPath;
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 9b3d160ea..4e0c4db95 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -379,7 +379,7 @@ public:
         bool canonicalizePath = true,
         std::string_view errorCtx = "");
 
-    std::string copyPathToStore(PathSet & context, const Path & path);
+    StorePath copyPathToStore(PathSet & context, const Path & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 5dc453b2e..c35c876e3 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -1,6 +1,7 @@
 #include "value-to-json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
+#include "store-api.hh"
 
 #include <cstdlib>
 #include <iomanip>
@@ -35,7 +36,7 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nPath:
             if (copyToStore)
-                out = state.copyPathToStore(context, v.path);
+                out = state.store->printStorePath(state.copyPathToStore(context, v.path));
             else
                 out = v.path;
             break;
diff --git a/src/nix/app.cc b/src/nix/app.cc
index 5658f2a52..a8d7e115b 100644
--- a/src/nix/app.cc
+++ b/src/nix/app.cc
@@ -19,12 +19,11 @@ struct InstallableDerivedPath : Installable
     {
     }
 
-
     std::string what() const override { return derivedPath.to_string(*store); }
 
-    DerivedPaths toDerivedPaths() override
+    DerivedPathsWithInfo toDerivedPaths() override
     {
-        return {derivedPath};
+        return {{derivedPath}};
     }
 
     std::optional<StorePath> getStorePath() override
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 94b169167..12b22d999 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -94,13 +94,15 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
         if (dryRun) {
             std::vector<DerivedPath> pathsToBuild;
 
-            for (auto & i : installables) {
-                auto b = i->toDerivedPaths();
-                pathsToBuild.insert(pathsToBuild.end(), b.begin(), b.end());
-            }
+            for (auto & i : installables)
+                for (auto & b : i->toDerivedPaths())
+                    pathsToBuild.push_back(b.path);
+
             printMissing(store, pathsToBuild, lvlError);
+
             if (json)
                 logger->cout("%s", derivedPathsToJSON(pathsToBuild, store).dump());
+
             return;
         }
 
diff --git a/src/nix/log.cc b/src/nix/log.cc
index 72d02ef11..a0598ca13 100644
--- a/src/nix/log.cc
+++ b/src/nix/log.cc
@@ -49,7 +49,7 @@ struct CmdLog : InstallableCommand
                 [&](const DerivedPath::Built & bfd) {
                     return logSub.getBuildLog(bfd.drvPath);
                 },
-            }, b.raw());
+            }, b.path.raw());
             if (!log) continue;
             stopProgressBar();
             printInfo("got build log for '%s' from '%s'", installable->what(), logSub.getUri());
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 11910523d..22ee51ab9 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -32,12 +32,14 @@ struct ProfileElementSource
     }
 };
 
+const int defaultPriority = 5;
+
 struct ProfileElement
 {
     StorePathSet storePaths;
     std::optional<ProfileElementSource> source;
     bool active = true;
-    int priority = 5;
+    int priority = defaultPriority;
 
     std::string describe() const
     {
@@ -251,13 +253,20 @@ struct ProfileManifest
     }
 };
 
-static std::map<Installable *, BuiltPaths>
+static std::map<Installable *, std::pair<BuiltPaths, ExtraPathInfo>>
 builtPathsPerInstallable(
     const std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> & builtPaths)
 {
-    std::map<Installable *, BuiltPaths> res;
-    for (auto & [installable, builtPath] : builtPaths)
-        res[installable.get()].push_back(builtPath.path);
+    std::map<Installable *, std::pair<BuiltPaths, ExtraPathInfo>> res;
+    for (auto & [installable, builtPath] : builtPaths) {
+        auto & r = res[installable.get()];
+        /* Note that there could be conflicting info
+           (e.g. meta.priority fields) if the installable returned
+           multiple derivations. So pick one arbitrarily. FIXME:
+           print a warning? */
+        r.first.push_back(builtPath.path);
+        r.second = builtPath.info;
+    }
     return res;
 }
 
@@ -297,28 +306,25 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
         for (auto & installable : installables) {
             ProfileElement element;
 
+            auto & [res, info] = builtPaths[installable.get()];
 
-
-            if (auto installable2 = std::dynamic_pointer_cast<InstallableFlake>(installable)) {
-                // FIXME: make build() return this?
-                auto [attrPath, resolvedRef, drv] = installable2->toDerivation();
+            if (info.originalRef && info.resolvedRef && info.attrPath && info.outputsSpec) {
                 element.source = ProfileElementSource {
-                    installable2->flakeRef,
-                    resolvedRef,
-                    attrPath,
-                    installable2->outputsSpec
+                    .originalRef = *info.originalRef,
+                    .resolvedRef = *info.resolvedRef,
+                    .attrPath = *info.attrPath,
+                    .outputs = *info.outputsSpec,
                 };
-
-                if(drv.priority) {
-                    element.priority = *drv.priority;
-                }
             }
 
-            if(priority) { // if --priority was specified we want to override the priority of the installable
-                element.priority = *priority;
-            };
+            // If --priority was specified we want to override the
+            // priority of the installable.
+            element.priority =
+                priority
+                ? *priority
+                : info.priority.value_or(defaultPriority);
 
-            element.updateStorePaths(getEvalStore(), store, builtPaths[installable.get()]);
+            element.updateStorePaths(getEvalStore(), store, res);
 
             manifest.elements.push_back(std::move(element));
         }
@@ -476,18 +482,22 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                     Strings{},
                     lockFlags);
 
-                auto [attrPath, resolvedRef, drv] = installable->toDerivation();
+                auto derivedPaths = installable->toDerivedPaths();
+                if (derivedPaths.empty()) continue;
+                auto & info = derivedPaths[0].info;
+
+                assert(info.resolvedRef && info.attrPath);
 
-                if (element.source->resolvedRef == resolvedRef) continue;
+                if (element.source->resolvedRef == info.resolvedRef) continue;
 
                 printInfo("upgrading '%s' from flake '%s' to '%s'",
-                    element.source->attrPath, element.source->resolvedRef, resolvedRef);
+                    element.source->attrPath, element.source->resolvedRef, *info.resolvedRef);
 
                 element.source = ProfileElementSource {
-                    installable->flakeRef,
-                    resolvedRef,
-                    attrPath,
-                    installable->outputsSpec
+                    .originalRef = installable->flakeRef,
+                    .resolvedRef = *info.resolvedRef,
+                    .attrPath = *info.attrPath,
+                    .outputs = installable->outputsSpec,
                 };
 
                 installables.push_back(installable);
@@ -515,7 +525,7 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
         for (size_t i = 0; i < installables.size(); ++i) {
             auto & installable = installables.at(i);
             auto & element = manifest.elements[indices.at(i)];
-            element.updateStorePaths(getEvalStore(), store, builtPaths[installable.get()]);
+            element.updateStorePaths(getEvalStore(), store, builtPaths[installable.get()].first);
         }
 
         updateProfile(manifest.build(store));
diff --git a/src/nix/store-copy-log.cc b/src/nix/store-copy-log.cc
index 2e288f743..d5fab5f2f 100644
--- a/src/nix/store-copy-log.cc
+++ b/src/nix/store-copy-log.cc
@@ -33,13 +33,7 @@ struct CmdCopyLog : virtual CopyCommand, virtual InstallablesCommand
         auto dstStore = getDstStore();
         auto & dstLogStore = require<LogStore>(*dstStore);
 
-        StorePathSet drvPaths;
-
-        for (auto & i : installables)
-            for (auto & drvPath : i->toDrvPaths(getEvalStore()))
-                drvPaths.insert(drvPath);
-
-        for (auto & drvPath : drvPaths) {
+        for (auto & drvPath : Installable::toDerivations(getEvalStore(), installables, true)) {
             if (auto log = srcLogStore.getBuildLog(drvPath))
                 dstLogStore.addBuildLog(drvPath, *log);
             else
diff --git a/tests/flakes/build-paths.sh b/tests/flakes/build-paths.sh
new file mode 100644
index 000000000..08b4d1763
--- /dev/null
+++ b/tests/flakes/build-paths.sh
@@ -0,0 +1,66 @@
+source ./common.sh
+
+flake1Dir=$TEST_ROOT/flake1
+flake2Dir=$TEST_ROOT/flake2
+
+mkdir -p $flake1Dir $flake2Dir
+
+writeSimpleFlake $flake2Dir
+tar cfz $TEST_ROOT/flake.tar.gz -C $TEST_ROOT flake2
+hash=$(nix hash path $flake2Dir)
+
+dep=$(nix store add-path ./common.sh)
+
+cat > $flake1Dir/flake.nix <<EOF
+{
+  inputs.flake2.url = "file://$TEST_ROOT/flake.tar.gz";
+
+  outputs = { self, flake2 }: {
+
+    a1 = builtins.fetchTarball {
+      #type = "tarball";
+      url = "file://$TEST_ROOT/flake.tar.gz";
+      sha256 = "$hash";
+    };
+
+    a2 = ./foo;
+
+    a3 = ./.;
+
+    a4 = self.outPath;
+
+    # FIXME
+    a5 = self;
+
+    a6 = flake2.outPath;
+
+    # FIXME
+    a7 = "${flake2}/config.nix";
+
+    # This is only allowed in impure mode.
+    a8 = builtins.storePath $dep;
+
+    a9 = "$dep";
+  };
+}
+EOF
+
+echo bar > $flake1Dir/foo
+
+nix build --json --out-link $TEST_ROOT/result $flake1Dir#a1
+[[ -e $TEST_ROOT/result/simple.nix ]]
+
+nix build --json --out-link $TEST_ROOT/result $flake1Dir#a2
+[[ $(cat $TEST_ROOT/result) = bar ]]
+
+nix build --json --out-link $TEST_ROOT/result $flake1Dir#a3
+
+nix build --json --out-link $TEST_ROOT/result $flake1Dir#a4
+
+nix build --json --out-link $TEST_ROOT/result $flake1Dir#a6
+[[ -e $TEST_ROOT/result/simple.nix ]]
+
+nix build --impure --json --out-link $TEST_ROOT/result $flake1Dir#a8
+diff common.sh $TEST_ROOT/result
+
+(! nix build --impure --json --out-link $TEST_ROOT/result $flake1Dir#a9)
diff --git a/tests/local.mk b/tests/local.mk
index 2489baecf..5ac1ede32 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -9,6 +9,7 @@ nix_tests = \
   flakes/check.sh \
   flakes/unlocked-override.sh \
   flakes/absolute-paths.sh \
+  flakes/build-paths.sh \
   ca/gc.sh \
   gc.sh \
   remote-store.sh \