@matheusbsbs / matheus-bagliano / commits / a0f83e7776

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>

Jeff King committed Jan 6, 2023 at 06:03 UTC a0f83e777660dbf7d9526c05d94fc920e459aed9

2 files changed +30 -1

diff.c

+1 -1

@@ -4281,7 +4281,7 @@ static void add_external_diff_name(struct repository *r,

4281 const char *name,

4282 struct diff_filespec *df)

4283 {

4284 - struct diff_tempfile *temp = prepare_temp_file(r, name, df);

4284 + struct diff_tempfile *temp = prepare_temp_file(r, df->path, df);

4285 strvec_push(argv, temp->name);

4286 strvec_push(argv, temp->hex);

4287 strvec_push(argv, temp->mode);

t/t4045-diff-relative.sh

+29

@@ -162,6 +162,35 @@ check_diff_relative_option subdir file2 true --no-relative --relative

162 check_diff_relative_option . file2 false --no-relative --relative=subdir

163 check_diff_relative_option . file2 true --no-relative --relative=subdir

164

165 +test_expect_success 'external diff with --relative' '

166 + test_when_finished "git reset --hard" &&

167 + echo changed >file1 &&

168 + echo changed >subdir/file2 &&

169 +

170 + write_script mydiff <<-\EOF &&

171 + # hacky pretend diff; the goal here is just to make sure we got

172 + # passed sensible input that we _could_ diff, without relying on

173 + # the specific output of a system diff tool.

174 + echo "diff a/$1 b/$1" &&

175 + echo "--- a/$1" &&

176 + echo "+++ b/$1" &&

177 + echo "@@ -1 +0,0 @@" &&

178 + sed "s/^/-/" "$2" &&

179 + sed "s/^/+/" "$5"

180 + EOF

181 +

182 + cat >expect <<-\EOF &&

183 + diff a/file2 b/file2

184 + --- a/file2

185 + +++ b/file2

186 + @@ -1 +0,0 @@

187 + -other content

188 + +changed

189 + EOF

190 + GIT_EXTERNAL_DIFF=./mydiff git diff --relative=subdir >actual &&

191 + test_cmp expect actual

192 +'

193 +

194 test_expect_success 'setup diff --relative unmerged' '

195 test_commit zero file0 &&

196 test_commit base subdir/file0 &&