3 files changed, 26 insertions, 1 deletions
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)