From de6629754d45d21ad5d81b2b95a631a8e3073add Mon Sep 17 00:00:00 2001
From: eldritch horrors <pennae@lix.systems>
Date: Mon, 17 Mar 2025 15:45:27 +0100
Subject: [PATCH] libutil: add generic redirections runProgram2

explicit stderr redirection makes mergeStderrToStdout unnecessary also.

Change-Id: I63de929e6dc53f6c5ceb2d43c2ce288bfc04d872
---
 src/libfetchers/git.cc                | 5 +++--
 src/libstore/build/derivation-goal.cc | 2 +-
 src/libstore/globals.cc               | 3 ++-
 src/libstore/ssh.cc                   | 3 ++-
 src/libutil/processes.cc              | 8 +++++---
 src/libutil/processes.hh              | 7 ++++++-
 6 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 29eaf8b78..74275d8e7 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -17,6 +17,7 @@
 #include <string.h>
 #include <sys/time.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 using namespace std::string_literals;
 
@@ -163,7 +164,7 @@ WorkdirInfo getWorkdirInfo(const Input & input, const Path & workdir)
         .program = "git",
         .args = { "-C", workdir, "--git-dir", gitDir, "rev-parse", "--verify", "--no-revs", "HEAD^{commit}" },
         .environment = env,
-        .mergeStderrToStdout = true
+        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
     });
     auto exitCode = WEXITSTATUS(result.first);
     auto errorMessage = result.second;
@@ -625,7 +626,7 @@ struct GitInputScheme : InputScheme
         auto result = runProgram(RunOptions {
             .program = "git",
             .args = { "-C", repoDir, "--git-dir", gitDir, "cat-file", "commit", input.getRev()->gitRev() },
-            .mergeStderrToStdout = true
+            .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
         });
         if (WEXITSTATUS(result.first) == 128
             && result.second.find("bad file") != std::string::npos)
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 4180654ab..50f39ddbc 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -917,7 +917,7 @@ void runPostBuildHook(
         .program = settings.postBuildHook,
         .environment = hookEnvironment,
         .captureStdout = true,
-        .mergeStderrToStdout = true,
+        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
     });
     Finally const _wait([&] { proc.waitAndCheck(); });
 
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 6cfa3ffac..a06743f4c 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -233,7 +233,8 @@ StringSet Settings::getDefaultExtraPlatforms()
     // x86_64 in aarch64 environments or vice versa since they can
     // always exec with their own binary preferences.
     if (std::string{SYSTEM} == "aarch64-darwin" &&
-        runProgram(RunOptions {.program = "arch", .args = {"-arch", "x86_64", "/usr/bin/true"}, .mergeStderrToStdout = true}).first == 0)
+        runProgram(RunOptions {.program = "arch", .args = {"-arch", "x86_64", "/usr/bin/true"},
+            .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}}}).first == 0)
         extraPlatforms.insert("x86_64-darwin");
 #endif
 
diff --git a/src/libstore/ssh.cc b/src/libstore/ssh.cc
index 8386b0e0a..02ae81989 100644
--- a/src/libstore/ssh.cc
+++ b/src/libstore/ssh.cc
@@ -4,6 +4,7 @@
 #include "finally.hh"
 #include "logging.hh"
 #include "strings.hh"
+#include <unistd.h>
 
 namespace nix {
 
@@ -49,7 +50,7 @@ bool SSHMaster::isMasterRunning() {
     Strings args = {"-O", "check", host};
     addCommonSSHOpts(args);
 
-    auto res = runProgram(RunOptions {.program = "ssh", .args = args, .mergeStderrToStdout = true});
+    auto res = runProgram(RunOptions {.program = "ssh", .args = args, .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}}});
     return res.first == 0;
 }
 
diff --git a/src/libutil/processes.cc b/src/libutil/processes.cc
index 46cbb66da..6fb903d9a 100644
--- a/src/libutil/processes.cc
+++ b/src/libutil/processes.cc
@@ -329,9 +329,11 @@ RunningProgram runProgram2(const RunOptions & options)
             replaceEnv(*options.environment);
         if (options.captureStdout && 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");
+        for (auto redirection : options.redirections) {
+            if (dup2(redirection.to, redirection.from) == -1) {
+                throw SysError("dupping fd %i to %i", redirection.from, redirection.to);
+            }
+        }
 
         if (options.chdir && chdir((*options.chdir).c_str()) == -1)
             throw SysError("chdir failed");
diff --git a/src/libutil/processes.hh b/src/libutil/processes.hh
index 3566aa3cf..a48fea3b9 100644
--- a/src/libutil/processes.hh
+++ b/src/libutil/processes.hh
@@ -76,6 +76,11 @@ std::string runProgram(Path program, bool searchPath = false,
 
 struct RunOptions
 {
+    struct Redirection
+    {
+        int from, to;
+    };
+
     Path program;
     bool searchPath = true;
     Strings args;
@@ -84,8 +89,8 @@ struct RunOptions
     std::optional<Path> chdir;
     std::optional<std::map<std::string, std::string>> environment;
     bool captureStdout = false;
-    bool mergeStderrToStdout = false;
     bool isInteractive = false;
+    std::vector<Redirection> redirections;
 };
 
 struct [[nodiscard("you must call RunningProgram::wait()")]] RunningProgram