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
    }
  ]

7 files changed, 77 insertions, 46 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,
diff --git a/src/libstore/derived-path.cc b/src/libstore/derived-path.cc
index 7fe9b9648..88b59f615 100644
--- a/src/libstore/derived-path.cc
+++ b/src/libstore/derived-path.cc
@@ -53,28 +53,13 @@ StorePathSet BuiltPath::outPaths() const
     );
 }
 
-template<typename T>
-nlohmann::json stuffToJSON(const std::vector<T> & ts, ref<Store> store) {
-    auto res = nlohmann::json::array();
-    for (const T & t : ts) {
-        std::visit([&res, store](const auto & t) {
-            res.push_back(t.toJSON(store));
-        }, t.raw());
-    }
-    return res;
-}
-
-nlohmann::json builtPathsToJSON(const BuiltPaths & buildables, ref<Store> store)
-{ return stuffToJSON<BuiltPath>(buildables, store); }
-nlohmann::json derivedPathsToJSON(const DerivedPaths & paths, ref<Store> store)
-{ return stuffToJSON<DerivedPath>(paths, store); }
-
-
-std::string DerivedPath::Opaque::to_string(const Store & store) const {
+std::string DerivedPath::Opaque::to_string(const Store & store) const
+{
     return store.printStorePath(path);
 }
 
-std::string DerivedPath::Built::to_string(const Store & store) const {
+std::string DerivedPath::Built::to_string(const Store & store) const
+{
     return store.printStorePath(drvPath)
         + "!"
         + (outputs.empty() ? std::string { "*" } : concatStringsSep(",", outputs));
diff --git a/src/libstore/derived-path.hh b/src/libstore/derived-path.hh
index b2d0956b8..878696136 100644
--- a/src/libstore/derived-path.hh
+++ b/src/libstore/derived-path.hh
@@ -125,7 +125,4 @@ struct BuiltPath : _BuiltPathRaw {
 typedef std::vector<DerivedPath> DerivedPaths;
 typedef std::vector<BuiltPath> BuiltPaths;
 
-nlohmann::json builtPathsToJSON(const BuiltPaths & buildables, ref<Store> store);
-nlohmann::json derivedPathsToJSON(const DerivedPaths & , ref<Store> store);
-
 }
diff --git a/src/nix/app.cc b/src/nix/app.cc
index 48de8fb82..5658f2a52 100644
--- a/src/nix/app.cc
+++ b/src/nix/app.cc
@@ -37,11 +37,13 @@ struct InstallableDerivedPath : Installable
  * Return the rewrites that are needed to resolve a string whose context is
  * included in `dependencies`.
  */
-StringPairs resolveRewrites(Store & store, const BuiltPaths dependencies)
+StringPairs resolveRewrites(
+    Store & store,
+    const std::vector<BuiltPathWithResult> & dependencies)
 {
     StringPairs res;
     for (auto & dep : dependencies)
-        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep))
+        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep.path))
             for (auto & [ outputName, outputPath ] : drvDep->outputs)
                 res.emplace(
                     downstreamPlaceholder(store, drvDep->drvPath, outputName),
@@ -53,7 +55,10 @@ StringPairs resolveRewrites(Store & store, const BuiltPaths dependencies)
 /**
  * Resolve the given string assuming the given context.
  */
-std::string resolveString(Store & store, const std::string & toResolve, const BuiltPaths dependencies)
+std::string resolveString(
+    Store & store,
+    const std::string & toResolve,
+    const std::vector<BuiltPathWithResult> & dependencies)
 {
     auto rewrites = resolveRewrites(store, dependencies);
     return rewriteStrings(toResolve, rewrites);
diff --git a/src/nix/build.cc b/src/nix/build.cc
index 2b91f8e0a..94b169167 100644
--- a/src/nix/build.cc
+++ b/src/nix/build.cc
@@ -10,6 +10,37 @@
 
 using namespace nix;
 
+nlohmann::json derivedPathsToJSON(const DerivedPaths & paths, ref<Store> store)
+{
+    auto res = nlohmann::json::array();
+    for (auto & t : paths) {
+        std::visit([&res, store](const auto & t) {
+            res.push_back(t.toJSON(store));
+        }, t.raw());
+    }
+    return res;
+}
+
+nlohmann::json builtPathsWithResultToJSON(const std::vector<BuiltPathWithResult> & buildables, ref<Store> store)
+{
+    auto res = nlohmann::json::array();
+    for (auto & b : buildables) {
+        std::visit([&](const auto & t) {
+            auto j = t.toJSON(store);
+            if (b.result) {
+                j["startTime"] = b.result->startTime;
+                j["stopTime"] = b.result->stopTime;
+                if (b.result->cpuUser)
+                    j["cpuUser"] = ((double) b.result->cpuUser->count()) / 1000000;
+                if (b.result->cpuSystem)
+                    j["cpuSystem"] = ((double) b.result->cpuSystem->count()) / 1000000;
+            }
+            res.push_back(j);
+        }, b.path.raw());
+    }
+    return res;
+}
+
 struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
 {
     Path outLink = "result";
@@ -78,7 +109,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             Realise::Outputs,
             installables, buildMode);
 
-        if (json) logger->cout("%s", builtPathsToJSON(buildables, store).dump());
+        if (json) logger->cout("%s", builtPathsWithResultToJSON(buildables, store).dump());
 
         if (outLink != "")
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
@@ -98,7 +129,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                                 store2->addPermRoot(output.second, absPath(symlink));
                             }
                         },
-                    }, buildable.raw());
+                    }, buildable.path.raw());
                 }
 
         if (printOutputPaths) {
@@ -113,11 +144,14 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                             std::cout << store->printStorePath(output.second) << std::endl;
                         }
                     },
-                }, buildable.raw());
+                }, buildable.path.raw());
             }
         }
 
-        updateProfile(buildables);
+        BuiltPaths buildables2;
+        for (auto & b : buildables)
+            buildables2.push_back(b.path);
+        updateProfile(buildables2);
     }
 };
 
diff --git a/src/nix/profile.cc b/src/nix/profile.cc
index 3814e7d5a..11910523d 100644
--- a/src/nix/profile.cc
+++ b/src/nix/profile.cc
@@ -253,11 +253,11 @@ struct ProfileManifest
 
 static std::map<Installable *, BuiltPaths>
 builtPathsPerInstallable(
-    const std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> & builtPaths)
+    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);
+        res[installable.get()].push_back(builtPath.path);
     return res;
 }