nix flake check: Show which outputs failed or succeeded

src/libexpr/eval-cache.cc

@@ -379,14 +379,19 @@ std::vector<Symbol> AttrCursor::getAttrPath(Symbol name) const
     return attrPath;
 }
 
+std::string toAttrPathStr(EvalState & state, const AttrPath & attrPath)
+{
+    return dropEmptyInitThenConcatStringsSep(".", state.symbols.resolve(attrPath));
+}
+
 std::string AttrCursor::getAttrPathStr() const
 {
-    return dropEmptyInitThenConcatStringsSep(".", root->state.symbols.resolve(getAttrPath()));
+    return toAttrPathStr(root->state, getAttrPath());
 }
 
 std::string AttrCursor::getAttrPathStr(Symbol name) const
 {
-    return dropEmptyInitThenConcatStringsSep(".", root->state.symbols.resolve(getAttrPath(name)));
+    return toAttrPathStr(root->state, getAttrPath(name));
 }
 
 Value & AttrCursor::forceValue()

src/libexpr/include/nix/expr/eval-cache.hh

@@ -13,6 +13,10 @@ namespace nix::eval_cache {
 struct AttrDb;
 class AttrCursor;
 
+using AttrPath = std::vector<Symbol>;
+
+std::string toAttrPathStr(EvalState & state, const AttrPath & attrPath);
+
 struct CachedEvalError : EvalError
 {
     const ref<AttrCursor> cursor;

src/libstore/include/nix/store/derived-path.hh

@@ -234,10 +234,6 @@ struct DerivedPath : _DerivedPathRaw
         return static_cast<const Raw &>(*this);
     }
 
-    bool operator==(const DerivedPath &) const = default;
-    // TODO libc++ 16 (used by darwin) missing `std::set::operator <=>`, can't do yet.
-    // auto operator <=> (const DerivedPath &) const = default;
-
     /**
      * Get the store path this is ultimately derived from (by realising
      * and projecting outputs).

src/nix/flake.cc

@@ -18,6 +18,7 @@
 #include "nix/store/local-fs-store.hh"
 #include "nix/store/globals.hh"
 #include "nix/expr/parallel-eval.hh"
+#include "nix/util/exit.hh"
 
 #include <filesystem>
 #include <nlohmann/json.hpp>
@@ -385,7 +386,9 @@ struct CmdFlakeCheck : FlakeCommand
             }
         };
 
-        Sync<StringSet> omittedSystems;
+        Sync<std::vector<DerivedPath>> drvPaths_;
+        Sync<std::set<std::string>> omittedSystems;
+        Sync<std::map<DerivedPath, std::vector<eval_cache::AttrPath>>> derivedPathToAttrPaths_;
 
         // FIXME: rewrite to use EvalCache.
 
@@ -434,8 +437,6 @@ struct CmdFlakeCheck : FlakeCommand
             return std::nullopt;
         };
 
-        std::vector<DerivedPath> drvPaths;
-
         FutureVector futures(*state->executor);
 
         auto checkApp = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
@@ -633,11 +634,13 @@ struct CmdFlakeCheck : FlakeCommand
                                                 *attr2.value,
                                                 attr2.pos);
                                             if (drvPath && attr_name == settings.thisSystem.get()) {
-                                                auto path = DerivedPath::Built{
+                                                auto derivedPath = DerivedPath::Built{
                                                     .drvPath = makeConstantStorePathRef(*drvPath),
                                                     .outputs = OutputsSpec::All{},
                                                 };
-                                                drvPaths.push_back(std::move(path));
+                                                (*derivedPathToAttrPaths_.lock())[derivedPath].push_back(
+                                                    {state->symbols.create("checks"), attr.name, attr2.name});
+                                                drvPaths_.lock()->push_back(std::move(derivedPath));
                                             }
                                         }
                                     }
@@ -806,7 +809,10 @@ struct CmdFlakeCheck : FlakeCommand
         futures.spawn(1, checkFlake);
         futures.finishAll();
 
-        if (build && !drvPaths.empty()) {
+        auto drvPaths(drvPaths_.lock());
+        auto derivedPathToAttrPaths(derivedPathToAttrPaths_.lock());
+
+        if (build && !drvPaths->empty()) {
             // TODO: This filtering of substitutable paths is a temporary workaround until
             // https://github.com/NixOS/nix/issues/5025 (union stores) is implemented.
             //
@@ -819,32 +825,68 @@ struct CmdFlakeCheck : FlakeCommand
             // via substitution, as `nix flake check` only needs to verify buildability,
             // not actually produce the outputs.
             state->waitForAllPaths();
-            auto missing = store->queryMissing(drvPaths);
+            auto missing = store->queryMissing(*drvPaths);
 
             std::vector<DerivedPath> toBuild;
+            std::set<DerivedPath> toBuildSet;
             for (auto & path : missing.willBuild) {
-                toBuild.emplace_back(
-                    DerivedPath::Built{
-                        .drvPath = makeConstantStorePathRef(path),
-                        .outputs = OutputsSpec::All{},
-                    });
+                auto derivedPath = DerivedPath::Built{
+                    .drvPath = makeConstantStorePathRef(path),
+                    .outputs = OutputsSpec::All{},
+                };
+                toBuild.emplace_back(derivedPath);
+                toBuildSet.insert(std::move(derivedPath));
             }
 
+            for (auto & [derivedPath, attrPaths] : *derivedPathToAttrPaths)
+                if (!toBuildSet.contains(derivedPath))
+                    for (auto & attrPath : attrPaths)
+                        notice(
+                            "✅ " ANSI_BOLD "%s" ANSI_NORMAL ANSI_ITALIC ANSI_FAINT " (previously built)" ANSI_NORMAL,
+                            eval_cache::toAttrPathStr(*state, attrPath));
+
             // FIXME: should start building while evaluating.
             Activity act(*logger, lvlInfo, actUnknown, fmt("running %d flake checks", toBuild.size()));
-            store->buildPaths(toBuild);
+            auto buildResults = store->buildPathsWithResults(toBuild);
+            assert(buildResults.size() == toBuild.size());
+
+            // Report successes first.
+            for (auto & buildResult : buildResults)
+                if (buildResult.tryGetSuccess())
+                    for (auto & attrPath : (*derivedPathToAttrPaths)[buildResult.path])
+                        notice("✅ " ANSI_BOLD "%s" ANSI_NORMAL, eval_cache::toAttrPathStr(*state, attrPath));
+
+            // Then cancelled builds.
+            for (auto & buildResult : buildResults)
+                if (buildResult.isCancelled())
+                    for (auto & attrPath : (*derivedPathToAttrPaths)[buildResult.path])
+                        notice(
+                            "❓ " ANSI_BOLD "%s" ANSI_NORMAL ANSI_FAINT " (cancelled)",
+                            eval_cache::toAttrPathStr(*state, attrPath));
+
+            // Then failures.
+            for (auto & buildResult : buildResults)
+                if (auto failure = buildResult.tryGetFailure(); failure && !buildResult.isCancelled())
+                    try {
+                        hasErrors = true;
+                        for (auto & attrPath : (*derivedPathToAttrPaths)[buildResult.path])
+                            printError("❌ " ANSI_RED "%s" ANSI_NORMAL, eval_cache::toAttrPathStr(*state, attrPath));
+                        failure->rethrow();
+                    } catch (Error & e) {
+                        logError(e.info());
+                    }
         }
 
-        if (hasErrors)
-            throw Error("some errors were encountered during the evaluation");
-
         if (!omittedSystems.lock()->empty()) {
             // TODO: empty system is not visible; render all as nix strings?
             warn(
                 "The check omitted these incompatible systems: %s\n"
                 "Use '--all-systems' to check all.",
                 concatStringsSep(", ", *omittedSystems.lock()));
-        };
+        }
+
+        if (hasErrors)
+            throw Exit(1);
     };
 };