diff: use filespec path to set up tempfiles for ext-diff

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@ecbaldwin.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diff.c b/diff.c
index 1054a4b7329d0b70ed62311a728b5257df3a8143..c78ea27033f961a99489cba52c86a5be2b5d27c2 100644 (file)
--- 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 fab351b48a1f52b450f3911aa6edafae70015613..5e1bbb57e725f08f347ba5baaf93c159c364bb97 100755 (executable)
--- a/t/t4045-diff-relative.sh
+++ b/t/t4045-diff-relative.sh
@@ -162,6 +162,35 @@ 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 &&