nix build --json: Include build statistics

Example:

  # nix build -L --extra-experimental-features cgroups --impure --expr 'with import <nixpkgs> {}; runCommand "foo" {} "dd if=/dev/urandom bs=1M count=1024 | md5sum; mkdir $out"' --json
  [
    {
      "cpuSystem": 1.911431,
      "cpuUser": 1.214249,
      "drvPath": "/nix/store/xzdqz67xba18hljhycp0hwfigzrs2z69-foo.drv",
      "outputs": {
        "out": "/nix/store/rh9mc9l2gkpq8kn2sgzndr6ll7ffjh6l-foo"
      },
      "startTime": 1669024076,
      "stopTime": 1669024079
    }
  ]

2 files changed, 25 insertions, 15 deletions

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 5945a2578..e036b8836 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -840,20 +840,20 @@ std::shared_ptr<Installable> SourceExprCommand::parseInstallable(
     return installables.front();
 }
 
-BuiltPaths Installable::build(
+std::vector<BuiltPathWithResult> Installable::build(
     ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
     const std::vector<std::shared_ptr<Installable>> & installables,
     BuildMode bMode)
 {
-    BuiltPaths res;
-    for (auto & [_, builtPath] : build2(evalStore, store, mode, installables, bMode))
-        res.push_back(builtPath);
+    std::vector<BuiltPathWithResult> res;
+    for (auto & [_, builtPathWithResult] : build2(evalStore, store, mode, installables, bMode))
+        res.push_back(builtPathWithResult);
     return res;
 }
 
-std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::build2(
+std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Installable::build2(
     ref<Store> evalStore,
     ref<Store> store,
     Realise mode,
@@ -873,7 +873,7 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
         }
     }
 
-    std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> res;
+    std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> res;
 
     switch (mode) {
 
@@ -914,10 +914,10 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
                                     output, *drvOutput->second);
                             }
                         }
-                        res.push_back({installable, BuiltPath::Built { bfd.drvPath, outputs }});
+                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, BuiltPath::Opaque { bo.path }});
+                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }}});
                     },
                 }, path.raw());
             }
@@ -939,10 +939,10 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
                         std::map<std::string, StorePath> outputs;
                         for (auto & path : buildResult.builtOutputs)
                             outputs.emplace(path.first.outputName, path.second.outPath);
-                        res.push_back({installable, BuiltPath::Built { bfd.drvPath, outputs }});
+                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }, .result = buildResult}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, BuiltPath::Opaque { bo.path }});
+                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }, .result = buildResult}});
                     },
                 }, buildResult.path.raw());
             }
@@ -965,9 +965,12 @@ BuiltPaths Installable::toBuiltPaths(
     OperateOn operateOn,
     const std::vector<std::shared_ptr<Installable>> & installables)
 {
-    if (operateOn == OperateOn::Output)
-        return Installable::build(evalStore, store, mode, installables);
-    else {
+    if (operateOn == OperateOn::Output) {
+        BuiltPaths res;
+        for (auto & p : Installable::build(evalStore, store, mode, installables))
+            res.push_back(p.path);
+        return res;
+    } else {
         if (mode == Realise::Nothing)
             settings.readOnlyMode = true;
 
diff --git a/src/libcmd/installables.hh b/src/libcmd/installables.hh
index 948f78919..02ea351d3 100644
--- a/src/libcmd/installables.hh
+++ b/src/libcmd/installables.hh
@@ -7,6 +7,7 @@
 #include "eval.hh"
 #include "store-api.hh"
 #include "flake/flake.hh"
+#include "build-result.hh"
 
 #include <optional>
 
@@ -51,6 +52,12 @@ enum class OperateOn {
     Derivation
 };
 
+struct BuiltPathWithResult
+{
+    BuiltPath path;
+    std::optional<BuildResult> result;
+};
+
 struct Installable
 {
     virtual ~Installable() { }
@@ -91,14 +98,14 @@ struct Installable
         return FlakeRef::fromAttrs({{"type","indirect"}, {"id", "nixpkgs"}});
     }
 
-    static BuiltPaths build(
+    static std::vector<BuiltPathWithResult> build(
         ref<Store> evalStore,
         ref<Store> store,
         Realise mode,
         const std::vector<std::shared_ptr<Installable>> & installables,
         BuildMode bMode = bmNormal);
 
-    static std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> build2(
+    static std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> build2(
         ref<Store> evalStore,
         ref<Store> store,
         Realise mode,