When we're going to run an external diff, we have to make the contents
of the pre- and post-images available either by dumping them to a
tempfile, or by pointing at a valid file in the worktree. The logic of
this is all handled by prepare_temp_file(), and we just pass in the
filename and the diff_filespec.
But there's a gotcha here. The "filename" we have is a logical filename
and not necessarily a path on disk or in the repository. This matters in
at least one case: when using "--relative", we may have a name like
"foo", even though the file content is found at "subdir/foo". As a
result, we look for the wrong path, fail to find "foo", and claim that
the file has been deleted (passing "/dev/null" to the external diff,
rather than the correct worktree path).
We can fix this by passing the pathname from the diff_filespec, which
should always be a full repository path (and that's what we want even if
reusing a worktree file, since we're always operating from the top-level
of the working tree).
The breakage seems to go all the way back to cd676a5136 (diff
--relative: output paths as relative to the current subdirectory,
2008-02-12). As far as I can tell, before then "name" would always have
been the same as the filespec's "path".
There are two related cases I looked at that aren't buggy:
1. the only other caller of prepare_temp_file() is run_textconv(). But
it always passes the filespec's path field, so it's OK.
2. I wondered if file renames/copies might cause similar confusion.
But they don't, because run_external_diff() receives two names in
that case: "name" and "other", which correspond to the two sides of
the diff. And we did correctly pass "other" when handling the
post-image side. Barring the use of "--relative", that would always
match "two->path", the path of the second filespec (and the rename
destination).
So the only bug is just the interaction with external diff drivers and
--relative.
Reported-by: Carl Baldwin <carl@xxxxxxxxxxxxx>
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
diff.c | 2 +-
t/t4045-diff-relative.sh | 29 +++++++++++++++++++++++++++++
2 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/diff.c b/diff.c
index 9b14543e6e..59039773a1 100644
--- a/diff.c
+++ b/diff.c
@@ -4281,7 +4281,7 @@ static void add_external_diff_name(struct repository *r,
const char *name,
struct diff_filespec *df)
{
- struct diff_tempfile *temp = prepare_temp_file(r, name, df);
+ struct diff_tempfile *temp = prepare_temp_file(r, df->path, df);
strvec_push(argv, temp->name);
strvec_push(argv, temp->hex);
strvec_push(argv, temp->mode);
diff --git a/t/t4045-diff-relative.sh b/t/t4045-diff-relative.sh
index 198dfc9190..9b46c4c1be 100755
--- a/t/t4045-diff-relative.sh
+++ b/t/t4045-diff-relative.sh
@@ -164,6 +164,35 @@ check_diff_relative_option subdir file2 true --no-relative --relative
check_diff_relative_option . file2 false --no-relative --relative=subdir
check_diff_relative_option . file2 true --no-relative --relative=subdir
+test_expect_success 'external diff with --relative' '
+ test_when_finished "git reset --hard" &&
+ echo changed >file1 &&
+ echo changed >subdir/file2 &&
+
+ write_script mydiff <<-\EOF &&
+ # hacky pretend diff; the goal here is just to make sure we got
+ # passed sensible input that we _could_ diff, without relying on
+ # the specific output of a system diff tool.
+ echo "diff a/$1 b/$1" &&
+ echo "--- a/$1" &&
+ echo "+++ b/$1" &&
+ echo "@@ -1 +0,0 @@" &&
+ sed "s/^/-/" "$2" &&
+ sed "s/^/+/" "$5"
+ EOF
+
+ cat >expect <<-\EOF &&
+ diff a/file2 b/file2
+ --- a/file2
+ +++ b/file2
+ @@ -1 +0,0 @@
+ -other content
+ +changed
+ EOF
+ GIT_EXTERNAL_DIFF=./mydiff git diff --relative=subdir >actual &&
+ test_cmp expect actual
+'
+
test_expect_success 'setup diff --relative unmerged' '
test_commit zero file0 &&
test_commit base subdir/file0 &&
--
2.39.0.463.g3774f23bc9
