[PATCH v2 0/3] Output fixes for --remerge-diff

Philippe Blain found and reported a couple issues with the output of --remerge-diff[1]. After digging in, I think one of them actually counts as two separate issues, so here's a series with three patches to fix these issues. Each includes testcases to keep us from regressing.

Changes since v1:

 * Added a new diff_filepair_is_phoney() function to make the code more
   self-documenting, as suggested by Junio.
 * Note: Patch 2, as called out in its commit message, disables
   TEST_PASSES_SANITIZE_LEAK for t4069. This is not because I introduce any
   memory leaks, but because I add new testcases invoking additional parts
   of the code (pickaxe stuff) which already had pre-existing leaks. This is
   not a change since v1, but this somehow accidentally got munged out of
   Junio's application of my v1.

Note: The issue fixed by the third commit for --remerge-diff is also an
issue exhibited by 'git log --cc $FILTER_RULES $COMMIT' (or by -c instead of
--cc). However, as far as I can tell the causes are different and come from
separate codepaths; this series focuses on --remerge-diff and hence makes no
attempt to fix independent (even if similar) --cc or -c issues.

[1] https://lore.kernel.org/git/43cf2a1d-058a-fd79-befe-7d9bc62581ed@gmail.com/

Elijah Newren (3):
  diff: have submodule_format logic avoid additional diff headers
  diff: fix filtering of additional headers under --remerge-diff
  diff: fix filtering of merge commits under --remerge-diff

 diff.c                  | 17 ++++++++++++++---
 t/t4069-remerge-diff.sh | 30 +++++++++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 4 deletions(-)

base-commit: 6c8e4ee870332d11e4bba84901654b355a9ff016
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1342%2Fnewren%2Fremerge-diff-output-fixes-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1342/newren/remerge-diff-output-fixes-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1342

Range-diff vs v1:

 1:  e4414cf630d ! 1:  aea0bbc1c6a diff: have submodule_format logic avoid additional diff headers
     @@ Commit message
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
       ## diff.c ##
     +@@ diff.c: static void add_formatted_headers(struct strbuf *msg,
     + 				     line_prefix, meta, reset);
     + }
     + 
     ++static int diff_filepair_is_phoney(struct diff_filespec *one,
     ++				   struct diff_filespec *two)
     ++{
     ++	return !DIFF_FILE_VALID(one) && !DIFF_FILE_VALID(two);
     ++}
     ++
     + static void builtin_diff(const char *name_a,
     + 			 const char *name_b,
     + 			 struct diff_filespec *one,
      @@ diff.c: static void builtin_diff(const char *name_a,
       
       	if (o->submodule_format == DIFF_SUBMODULE_LOG &&
       	    (!one->mode || S_ISGITLINK(one->mode)) &&
      -	    (!two->mode || S_ISGITLINK(two->mode))) {
      +	    (!two->mode || S_ISGITLINK(two->mode)) &&
     -+	    (one->mode || two->mode)) {
     ++	    (!diff_filepair_is_phoney(one, two))) {
       		show_submodule_diff_summary(o, one->path ? one->path : two->path,
       				&one->oid, &two->oid,
       				two->dirty_submodule);
     @@ diff.c: static void builtin_diff(const char *name_a,
       		   (!one->mode || S_ISGITLINK(one->mode)) &&
      -		   (!two->mode || S_ISGITLINK(two->mode))) {
      +		   (!two->mode || S_ISGITLINK(two->mode)) &&
     -+		   (one->mode || two->mode)) {
     ++		   (!diff_filepair_is_phoney(one, two))) {
       		show_submodule_inline_diff(o, one->path ? one->path : two->path,
       				&one->oid, &two->oid,
       				two->dirty_submodule);
     +@@ diff.c: static void builtin_diff(const char *name_a,
     + 	b_two = quote_two(b_prefix, name_b + (*name_b == '/'));
     + 	lbl[0] = DIFF_FILE_VALID(one) ? a_one : "/dev/null";
     + 	lbl[1] = DIFF_FILE_VALID(two) ? b_two : "/dev/null";
     +-	if (!DIFF_FILE_VALID(one) && !DIFF_FILE_VALID(two)) {
     ++	if (diff_filepair_is_phoney(one, two)) {
     + 		/*
     + 		 * We should only reach this point for pairs from
     + 		 * create_filepairs_for_header_only_notifications().  For
      
       ## t/t4069-remerge-diff.sh ##
      @@ t/t4069-remerge-diff.sh: test_expect_success 'remerge-diff w/ diff-filter=U: all conflict headers, no dif
 2:  feac9749460 = 2:  3bd622d5b45 diff: fix filtering of additional headers under --remerge-diff
 3:  46ea0d7dd65 = 3:  7903f8380dc diff: fix filtering of merge commits under --remerge-diff