run-command: add env_array, an optional argv_array for env

Similar to args, add a struct argv_array member to struct child_process
that simplifies specifying the environment for children.  It is freed
automatically by finish_command() or if start_command() encounters an
error.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-run-command.txt

@@ -169,6 +169,11 @@ string pointers (NULL terminated) in .env:
 . If the string does not contain '=', it names an environment
   variable that will be removed from the child process's environment.
 
+If the .env member is NULL, `start_command` will point it at the
+.env_array `argv_array` (so you may use one or the other, but not both).
+The memory in .env_array will be cleaned up automatically during
+`finish_command` (or during `start_command` when it is unsuccessful).
+
 To specify a new initial working directory for the sub-process,
 specify it in the .dir member.
 

run-command.c

@@ -12,6 +12,7 @@ void child_process_init(struct child_process *child)
 {
 	memset(child, 0, sizeof(*child));
 	argv_array_init(&child->args);
+	argv_array_init(&child->env_array);
 }
 
 struct child_to_clean {
@@ -287,6 +288,8 @@ int start_command(struct child_process *cmd)
 
 	if (!cmd->argv)
 		cmd->argv = cmd->args.argv;
+	if (!cmd->env)
+		cmd->env = cmd->env_array.argv;
 
 	/*
 	 * In case of errors we must keep the promise to close FDs
@@ -338,6 +341,7 @@ int start_command(struct child_process *cmd)
 			error("cannot create %s pipe for %s: %s",
 				str, cmd->argv[0], strerror(failed_errno));
 			argv_array_clear(&cmd->args);
+			argv_array_clear(&cmd->env_array);
 			errno = failed_errno;
 			return -1;
 		}
@@ -524,6 +528,7 @@ int start_command(struct child_process *cmd)
 		else if (cmd->err)
 			close(cmd->err);
 		argv_array_clear(&cmd->args);
+		argv_array_clear(&cmd->env_array);
 		errno = failed_errno;
 		return -1;
 	}
@@ -550,6 +555,7 @@ int finish_command(struct child_process *cmd)
 {
 	int ret = wait_or_whine(cmd->pid, cmd->argv[0]);
 	argv_array_clear(&cmd->args);
+	argv_array_clear(&cmd->env_array);
 	return ret;
 }
 

run-command.h

@@ -10,6 +10,7 @@
 struct child_process {
 	const char **argv;
 	struct argv_array args;
+	struct argv_array env_array;
 	pid_t pid;
 	/*
 	 * Using .in, .out, .err:
@@ -44,7 +45,7 @@ struct child_process {
 	unsigned clean_on_exit:1;
 };
 
-#define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT }
+#define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
 void child_process_init(struct child_process *);
 
 int start_command(struct child_process *);