6 files changed, 98 insertions, 3 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index a28619ab907d..4bec37e0f7ba 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1629,6 +1629,61 @@ void DerivationGoal::buildDone()
            being valid. */
         registerOutputs();
 
+        if (settings.postBuildHook != "") {
+            Activity act(*logger, lvlInfo, actPostBuildHook,
+                fmt("running post-build-hook '%s'", settings.postBuildHook),
+                Logger::Fields{drvPath});
+            PushActivity pact(act.id);
+            auto outputPaths = drv->outputPaths();
+            std::map<std::string, std::string> hookEnvironment = getEnv();
+
+            hookEnvironment.emplace("DRV_PATH", drvPath);
+            hookEnvironment.emplace("OUT_PATHS", chomp(concatStringsSep(" ", outputPaths)));
+
+            RunOptions opts(settings.postBuildHook, {});
+            opts.environment = hookEnvironment;
+
+            struct LogSink : Sink {
+                Activity & act;
+                std::string currentLine;
+
+                LogSink(Activity & act) : act(act) { }
+
+                void operator() (const unsigned char * data, size_t len) override {
+                    for (size_t i = 0; i < len; i++) {
+                        auto c = data[i];
+
+                        if (c == '\n') {
+                            flushLine();
+                        } else {
+                            currentLine += c;
+                        }
+                    }
+                }
+
+                void flushLine() {
+                    if (settings.verboseBuild) {
+                        printError("post-build-hook: " + currentLine);
+                    } else {
+                        act.result(resPostBuildLogLine, currentLine);
+                    }
+                    currentLine.clear();
+                }
+
+                ~LogSink() {
+                    if (currentLine != "") {
+                        currentLine += '\n';
+                        flushLine();
+                    }
+                }
+            };
+            LogSink sink(act);
+
+            opts.standardOut = &sink;
+            opts.mergeStderrToStdout = true;
+            runProgram2(opts);
+        }
+
         if (buildMode == bmCheck) {
             done(BuildResult::Built);
             return;
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 0c0a9ec544ea..13effb507b81 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -315,6 +315,9 @@ public:
         "pre-build-hook",
         "A program to run just before a build to set derivation-specific build settings."};
 
+    Setting<std::string> postBuildHook{this, "", "post-build-hook",
+        "A program to run just after each succesful build."};
+
     Setting<std::string> netrcFile{this, fmt("%s/%s", nixConfDir, "netrc"), "netrc-file",
         "Path to the netrc file used to obtain usernames/passwords for downloads."};
 
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index 5f221944594b..5df03da74e00 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -26,6 +26,7 @@ typedef enum {
     actVerifyPaths = 107,
     actSubstitute = 108,
     actQueryPathInfo = 109,
+    actPostBuildHook = 110,
 } ActivityType;
 
 typedef enum {
@@ -36,6 +37,7 @@ typedef enum {
     resSetPhase = 104,
     resProgress = 105,
     resSetExpected = 106,
+    resPostBuildLogLine = 107,
 } ResultType;
 
 typedef uint64_t ActivityId;
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 17aee2d5c3d0..44fa72482552 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -84,6 +84,15 @@ void clearEnv()
         unsetenv(name.first.c_str());
 }
 
+void replaceEnv(std::map<std::string, std::string> newEnv)
+{
+    clearEnv();
+    for (auto newEnvVar : newEnv)
+    {
+        setenv(newEnvVar.first.c_str(), newEnvVar.second.c_str(), 1);
+    }
+}
+
 
 Path absPath(Path path, Path dir)
 {
@@ -1019,10 +1028,22 @@ void runProgram2(const RunOptions & options)
     if (options.standardOut) out.create();
     if (source) in.create();
 
+    ProcessOptions processOptions;
+    // vfork implies that the environment of the main process and the fork will
+    // be shared (technically this is undefined, but in practice that's the
+    // case), so we can't use it if we alter the environment
+    if (options.environment)
+        processOptions.allowVfork = false;
+
     /* Fork. */
     Pid pid = startProcess([&]() {
+        if (options.environment)
+            replaceEnv(*options.environment);
         if (options.standardOut && dup2(out.writeSide.get(), STDOUT_FILENO) == -1)
             throw SysError("dupping stdout");
+        if (options.mergeStderrToStdout)
+            if (dup2(STDOUT_FILENO, STDERR_FILENO) == -1)
+                throw SysError("cannot dup stdout into stderr");
         if (source && dup2(in.readSide.get(), STDIN_FILENO) == -1)
             throw SysError("dupping stdin");
 
@@ -1047,7 +1068,7 @@ void runProgram2(const RunOptions & options)
             execv(options.program.c_str(), stringsToCharPtrs(args_).data());
 
         throw SysError("executing '%1%'", options.program);
-    });
+    }, processOptions);
 
     out.writeSide = -1;
 
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index fce3cab8def5..b538a0b41ce8 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -270,12 +270,14 @@ struct RunOptions
     std::optional<uid_t> uid;
     std::optional<uid_t> gid;
     std::optional<Path> chdir;
+    std::optional<std::map<std::string, std::string>> environment;
     Path program;
     bool searchPath = true;
     Strings args;
     std::optional<std::string> input;
     Source * standardIn = nullptr;
     Sink * standardOut = nullptr;
+    bool mergeStderrToStdout = false;
     bool _killStderr = false;
 
     RunOptions(const Path & program, const Strings & args)
diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index b1c1d87de1a2..c0bcfb0c91bc 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -170,6 +170,14 @@ public:
                 name, sub);
         }
 
+        if (type == actPostBuildHook) {
+            auto name = storePathToName(getS(fields, 0));
+            if (hasSuffix(name, ".drv"))
+                name.resize(name.size() - 4);
+            i->s = fmt("post-build " ANSI_BOLD "%s" ANSI_NORMAL, name);
+            i->name = DrvName(name).name;
+        }
+
         if (type == actQueryPathInfo) {
             auto name = storePathToName(getS(fields, 0));
             i->s = fmt("querying " ANSI_BOLD "%s" ANSI_NORMAL " on %s", name, getS(fields, 1));
@@ -228,14 +236,18 @@ public:
             update(*state);
         }
 
-        else if (type == resBuildLogLine) {
+        else if (type == resBuildLogLine || type == resPostBuildLogLine) {
             auto lastLine = trim(getS(fields, 0));
             if (!lastLine.empty()) {
                 auto i = state->its.find(act);
                 assert(i != state->its.end());
                 ActInfo info = *i->second;
                 if (printBuildLogs) {
-                    log(*state, lvlInfo, ANSI_FAINT + info.name.value_or("unnamed") + "> " + ANSI_NORMAL + lastLine);
+                    auto suffix = "> ";
+                    if (type == resPostBuildLogLine) {
+                        suffix = " (post)> ";
+                    }
+                    log(*state, lvlInfo, ANSI_FAINT + info.name.value_or("unnamed") + suffix + ANSI_NORMAL + lastLine);
                 } else {
                     state->activities.erase(i->second);
                     info.lastLine = lastLine;