Re: [PATCH v2 1/3] am: add --show-current-patch

[Duy Nguyen <pclouds@gmail.com>]

On Wed, Jan 31, 2018 at 02:59:32PM -0800, Junio C Hamano wrote:
> Eric Sunshine <sunshine@sunshineco.com> writes:
> 
> > On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy <pclouds@gmail.com> wrote:
> >> Pointing the user to $GIT_DIR/rebase-apply may encourage them to mess
> >> around in there, which is not a good thing. With this, the user does
> >> not have to keep the path around somewhere (because after a couple of
> >> commands, the path may be out of scrollback buffer) when they need to
> >> look at the patch.
> >>
> >> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> >> ---
> >> diff --git a/builtin/am.c b/builtin/am.c
> >> @@ -2121,6 +2120,22 @@ static void am_abort(struct am_state *state)
> >> +static int show_patch(struct am_state *state)
> >> +{
> >> +       struct strbuf sb = STRBUF_INIT;
> >> +       int len;
> >> +
> >> +       len = strbuf_read_file(&sb, am_path(state, msgnum(state)), 0);
> >> +       if (len < 0)
> >> +               die_errno(_("failed to read '%s'"),
> >> +                         am_path(state, msgnum(state)));
> >
> > Isn't this am_path() invocation inside die_errno() likely to clobber
> > the 'errno' from strbuf_read_file() which you want to be reporting?
> 
> True.

Thanks both. Good catch. Of course I will fix this in the re-roll, but
should we also do something for the current code base with the
following patch?

I think this is something coccinelle can help catch, but my
coccinelle-foo is way too low to come up with something like
"die_errno() must not take any arguments as function calls, except _()
and N_()".

-- 8< --
Subject: [PATCH] Preserve errno in case case before calling sth_errno()

All these locations do something like this

    sth_errno(..., somefunc(...));

where somefunc() can potentially change errno, which will be read by
sth_errno(). Call somefunc separately with errno preserved to avoid
this.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/am.c      |  8 +++++++-
 builtin/commit.c  |  8 ++++++--
 builtin/init-db.c |  9 ++++++---
 rerere.c          |  9 ++++++---
 shallow.c         | 27 ++++++++++++++++++---------
 5 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/builtin/am.c b/builtin/am.c
index acfe9d3c8c..ba67e187a4 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -244,6 +244,9 @@ static int am_in_progress(const struct am_state *state)
 static int read_state_file(struct strbuf *sb, const struct am_state *state,
 			const char *file, int trim)
 {
+	int saved_errno;
+	const char *path;
+
 	strbuf_reset(sb);
 
 	if (strbuf_read_file(sb, am_path(state, file), 0) >= 0) {
@@ -256,7 +259,10 @@ static int read_state_file(struct strbuf *sb, const struct am_state *state,
 	if (errno == ENOENT)
 		return -1;
 
-	die_errno(_("could not read '%s'"), am_path(state, file));
+	saved_errno = errno;
+	path = am_path(state, file);
+	errno = saved_errno;
+	die_errno(_("could not read '%s'"), path);
 }
 
 /**
diff --git a/builtin/commit.c b/builtin/commit.c
index 4610e3d8e3..39836b3734 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -780,8 +780,12 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	}
 
 	s->fp = fopen_for_writing(git_path_commit_editmsg());
-	if (s->fp == NULL)
-		die_errno(_("could not open '%s'"), git_path_commit_editmsg());
+	if (s->fp == NULL) {
+		int saved_errno = errno;
+		const char *path = git_path_commit_editmsg();
+		errno = saved_errno;
+		die_errno(_("could not open '%s'"), path);
+	}
 
 	/* Ignore status.displayCommentPrefix: we do need comments in COMMIT_EDITMSG. */
 	old_display_comment_prefix = s->display_comment_prefix;
diff --git a/builtin/init-db.c b/builtin/init-db.c
index c9b7946bad..e384749f73 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -570,9 +570,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			set_git_work_tree(work_tree);
 		else
 			set_git_work_tree(git_work_tree_cfg);
-		if (access(get_git_work_tree(), X_OK))
-			die_errno (_("Cannot access work tree '%s'"),
-				   get_git_work_tree());
+		if (access(get_git_work_tree(), X_OK)) {
+			int saved_errno = errno;
+			const char *path = get_git_work_tree();
+			errno = saved_errno;
+			die_errno(_("Cannot access work tree '%s'"), path);
+		}
 	}
 	else {
 		if (work_tree)
diff --git a/rerere.c b/rerere.c
index 1ce440f4bb..f19a53ff2c 100644
--- a/rerere.c
+++ b/rerere.c
@@ -683,9 +683,12 @@ static int merge(const struct rerere_id *id, const char *path)
 	 * A successful replay of recorded resolution.
 	 * Mark that "postimage" was used to help gc.
 	 */
-	if (utime(rerere_path(id, "postimage"), NULL) < 0)
-		warning_errno("failed utime() on %s",
-			      rerere_path(id, "postimage"));
+	if (utime(rerere_path(id, "postimage"), NULL) < 0) {
+		int saved_errno = errno;
+		const char *path = rerere_path(id, "postimage");
+		errno = saved_errno;
+		warning_errno("failed utime() on %s", path);
+	}
 
 	/* Update "path" with the resolution */
 	f = fopen(path, "w");
diff --git a/shallow.c b/shallow.c
index df4d44ea7a..9da82f5292 100644
--- a/shallow.c
+++ b/shallow.c
@@ -295,9 +295,12 @@ const char *setup_temporary_shallow(const struct oid_array *extra)
 		temp = xmks_tempfile(git_path("shallow_XXXXXX"));
 
 		if (write_in_full(temp->fd, sb.buf, sb.len) < 0 ||
-		    close_tempfile_gently(temp) < 0)
-			die_errno("failed to write to %s",
-				  get_tempfile_path(temp));
+		    close_tempfile_gently(temp) < 0) {
+			int saved_errno = errno;
+			const char *path = get_tempfile_path(temp);
+			errno = saved_errno;
+			die_errno("failed to write to %s", path);
+		}
 		strbuf_release(&sb);
 		return get_tempfile_path(temp);
 	}
@@ -319,9 +322,12 @@ void setup_alternate_shallow(struct lock_file *shallow_lock,
 				       LOCK_DIE_ON_ERROR);
 	check_shallow_file_for_update();
 	if (write_shallow_commits(&sb, 0, extra)) {
-		if (write_in_full(fd, sb.buf, sb.len) < 0)
-			die_errno("failed to write to %s",
-				  get_lock_file_path(shallow_lock));
+		if (write_in_full(fd, sb.buf, sb.len) < 0) {
+			int saved_errno = errno;
+			const char *path = get_lock_file_path(shallow_lock);
+			errno = saved_errno;
+			die_errno("failed to write to %s", path);
+		}
 		*alternate_shallow_file = get_lock_file_path(shallow_lock);
 	} else
 		/*
@@ -366,9 +372,12 @@ void prune_shallow(int show_only)
 				       LOCK_DIE_ON_ERROR);
 	check_shallow_file_for_update();
 	if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
-		if (write_in_full(fd, sb.buf, sb.len) < 0)
-			die_errno("failed to write to %s",
-				  get_lock_file_path(&shallow_lock));
+		if (write_in_full(fd, sb.buf, sb.len) < 0) {
+			int saved_errno = errno;
+			const char *path = get_lock_file_path(&shallow_lock);
+			errno = saved_errno;
+			die_errno("failed to write to %s", path);
+		}
 		commit_lock_file(&shallow_lock);
 	} else {
 		unlink(git_path_shallow());
-- 
2.16.1.205.g271f633410

-- 8< --