builtins + test helpers: use return instead of exit() in cmd_*

Change various cmd_* functions that claim to return an "int" to use
"return" instead of exit() to indicate an exit code. These were not
marked with NORETURN, and by directly exit()-ing we'll skip the
cleanup git.c would otherwise do (e.g. closing fd's, erroring if we
can't). See run_builtin() in git.c.

In the case of shell.c and sh-i18n--envsubst.c this was the result of
an incomplete migration to using a cmd_main() in 3f2e2297b9 (add an
extra level of indirection to main(), 2016-07-01).

This was spotted by SunCC 12.5 on Solaris 10 (gcc210 on the gccfarm).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/difftool.c

@@ -671,7 +671,7 @@ static int run_file_diff(int prompt, const char *prefix,
 		"GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
 		NULL
 	};
-	int ret = 0, i;
+	int i;
 
 	if (prompt > 0)
 		env[2] = "GIT_DIFFTOOL_PROMPT=true";
@@ -682,8 +682,7 @@ static int run_file_diff(int prompt, const char *prefix,
 	strvec_push(&args, "diff");
 	for (i = 0; i < argc; i++)
 		strvec_push(&args, argv[i]);
-	ret = run_command_v_opt_cd_env(args.v, RUN_GIT_CMD, prefix, env);
-	exit(ret);
+	return run_command_v_opt_cd_env(args.v, RUN_GIT_CMD, prefix, env);
 }
 
 int cmd_difftool(int argc, const char **argv, const char *prefix)

builtin/merge-ours.c

@@ -28,6 +28,6 @@ int cmd_merge_ours(int argc, const char **argv, const char *prefix)
 	if (read_cache() < 0)
 		die_errno("read_cache failed");
 	if (index_differs_from(the_repository, "HEAD", NULL, 0))
-		exit(2);
-	exit(0);
+		return 2;
+	return 0;
 }

builtin/mktree.c

@@ -189,5 +189,5 @@ int cmd_mktree(int ac, const char **av, const char *prefix)
 		used=0; /* reset tree entry buffer for re-use in batch mode */
 	}
 	strbuf_release(&sb);
-	exit(0);
+	return 0;
 }

sh-i18n--envsubst.c

@@ -104,12 +104,12 @@ cmd_main (int argc, const char *argv[])
   if (ferror (stderr) || fflush (stderr))
     {
       fclose (stderr);
-      exit (EXIT_FAILURE);
+      return (EXIT_FAILURE);
     }
   if (fclose (stderr) && errno != EBADF)
-    exit (EXIT_FAILURE);
+    return (EXIT_FAILURE);
 
-  exit (EXIT_SUCCESS);
+  return (EXIT_SUCCESS);
 }
 
 /* Parse the string and invoke the callback each time a $VARIABLE or

shell.c

@@ -177,7 +177,7 @@ int cmd_main(int argc, const char **argv)
 		default:
 			continue;
 		}
-		exit(cmd->exec(cmd->name, arg));
+		return cmd->exec(cmd->name, arg);
 	}
 
 	cd_to_homedir();

t/helper/test-hash-speed.c

@@ -57,5 +57,5 @@ int cmd__hash_speed(int ac, const char **av)
 		free(p);
 	}
 
-	exit(0);
+	return 0;
 }

t/helper/test-hash.c

@@ -54,5 +54,5 @@ int cmd_hash_impl(int ac, const char **av, int algo)
 		fwrite(hash, 1, algop->rawsz, stdout);
 	else
 		puts(hash_to_hex_algop(hash, algop));
-	exit(0);
+	return 0;
 }

t/helper/test-match-trees.c

@@ -23,5 +23,5 @@ int cmd__match_trees(int ac, const char **av)
 	shift_tree(the_repository, &one->object.oid, &two->object.oid, &shifted, -1);
 	printf("shifted: %s\n", oid_to_hex(&shifted));
 
-	exit(0);
+	return 0;
 }

t/helper/test-reach.c

@@ -166,5 +166,5 @@ int cmd__reach(int ac, const char **av)
 		print_sorted_commit_ids(list);
 	}
 
-	exit(0);
+	return 0;
 }