run_command: return exit code as positive value

As a general guideline, functions in git's code return zero to indicate
success and negative values to indicate failure. The run_command family of
functions followed this guideline. But there are actually two different
kinds of failure:

- failures of system calls;

- non-zero exit code of the program that was run.

Usually, a non-zero exit code of the program is a failure and means a
failure to the caller. Except that sometimes it does not. For example, the
exit code of merge programs (e.g. external merge drivers) conveys
information about how the merge failed, and not all exit calls are
actually failures.

Furthermore, the return value of run_command is sometimes used as exit
code by the caller.

This change arranges that the exit code of the program is returned as a
positive value, which can now be regarded as the "result" of the function.
System call failures continue to be reported as negative values.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 7 insertions, 19 deletions

diff --git a/builtin-merge.c b/builtin-merge.c
index af9adab300..96ecaf4e48 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -594,7 +594,7 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 		discard_cache();
 		if (read_cache() < 0)
 			die("failed to read the cache");
-		return -ret;
+		return ret;
 	}
 }
 
diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index 6ec1d056e6..6235903552 100644
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -143,8 +143,8 @@ static int run_status(int code, const char *cmd_name)
 	case -ERR_RUN_COMMAND_WAITPID_NOEXIT:
 		return error("%s died strangely", cmd_name);
 	default:
-		error("%s exited with error code %d", cmd_name, -code);
-		return -code;
+		error("%s exited with error code %d", cmd_name, code);
+		return code;
 	}
 }
 
diff --git a/convert.c b/convert.c
index 1816e977b7..491e7141b4 100644
--- a/convert.c
+++ b/convert.c
@@ -267,7 +267,7 @@ static int filter_buffer(int fd, void *data)
 
 	status = finish_command(&child_process);
 	if (status)
-		error("external filter %s failed %d", params->cmd, -status);
+		error("external filter %s failed %d", params->cmd, status);
 	return (write_err || status);
 }
 
diff --git a/git.c b/git.c
index 65ed733fda..d223eab62f 100644
--- a/git.c
+++ b/git.c
@@ -418,9 +418,9 @@ static void execv_dashed_external(const char **argv)
 	 */
 	status = run_command_v_opt(argv, 0);
 	if (status != -ERR_RUN_COMMAND_EXEC) {
-		if (IS_RUN_COMMAND_ERR(status))
+		if (status < 0)
 			die("unable to run '%s'", argv[0]);
-		exit(-status);
+		exit(status);
 	}
 	errno = ENOENT; /* as if we called execvp */
 
diff --git a/ll-merge.c b/ll-merge.c
index a2c13c4c08..31c74578f6 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -192,10 +192,6 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 
 	args[2] = cmd.buf;
 	status = run_command_v_opt(args, 0);
-	if (status < -ERR_RUN_COMMAND_FORK)
-		; /* failure in run-command */
-	else
-		status = -status;
 	fd = open(temp[1], O_RDONLY);
 	if (fd < 0)
 		goto bad;
diff --git a/run-command.c b/run-command.c
index eb2efc3307..a4e309eeb9 100644
--- a/run-command.c
+++ b/run-command.c
@@ -241,14 +241,7 @@ static int wait_or_whine(pid_t pid)
 		if (!WIFEXITED(status))
 			return -ERR_RUN_COMMAND_WAITPID_NOEXIT;
 		code = WEXITSTATUS(status);
-		switch (code) {
-		case 127:
-			return -ERR_RUN_COMMAND_EXEC;
-		case 0:
-			return 0;
-		default:
-			return -code;
-		}
+		return code == 127 ? -ERR_RUN_COMMAND_EXEC : code;
 	}
 }
 
diff --git a/run-command.h b/run-command.h
index e345502843..0211e1d471 100644
--- a/run-command.h
+++ b/run-command.h
@@ -10,7 +10,6 @@ enum {
 	ERR_RUN_COMMAND_WAITPID_SIGNAL,
 	ERR_RUN_COMMAND_WAITPID_NOEXIT,
 };
-#define IS_RUN_COMMAND_ERR(x) (-(x) >= ERR_RUN_COMMAND_FORK)
 
 struct child_process {
 	const char **argv;