Redirect STDERR to /dev/null in process spawn

src/common/process.cpp

@@ -127,6 +127,8 @@ Process::StringResult Process::spawn_get_stdout_line() {
     posix_spawn_file_actions_t actions;
     posix_spawn_file_actions_init(&actions);
     posix_spawn_file_actions_adddup2(&actions, output_pipe[1], STDOUT_FILENO);
+    posix_spawn_file_actions_addopen(&actions, STDERR_FILENO, "/dev/null",
+                                     O_WRONLY | O_APPEND, 0);
     posix_spawn_file_actions_addclose(&actions, output_pipe[0]);
     posix_spawn_file_actions_addclose(&actions, output_pipe[1]);
 

src/common/process.h

@@ -158,10 +158,11 @@ class Process {
     inline void environment(ProcessEnvironment env) { env_ = std::move(env); }
 
     /**
-     * Spawn the process, leave STDIN and STDERR alone, and return the first
+     * Spawn the process, leave STDIN, redirect STDERR to `/dev/null`, and
-     * line (without the trailing linefeed) of STDOUT. The first output line
+     * return the first line (without the trailing linefeed) of STDOUT. The
-     * will still be returned even if the process exits with a non-zero exit
+     * first output line will still be returned even if the process exits with a
-     * code. Uses `posix_spawn()`, leaves file descriptors in tact.
+     * non-zero exit code. Uses `posix_spawn()`, leaves file descriptors in
+     * tact.
      */
     StringResult spawn_get_stdout_line();