Re: diff-index --cc no longer permitted, gitk is now broken (slightly)

[Sergey Organov <sorganov@gmail.com>]

Johannes Sixt <j6t@kdbg.org> writes:

> Since 19b2517f95a0 (diff-merges: move specific diff-index "-m" handling
> to diff-index, 2021-05-21) git diff-index no longer accepts --cc. This
> breaks gitk: it invokes
>
>    git diff-index --cached -p -C --cc --no-commit-id -U3 HEAD
>
> to show the staged changes (when the line "Local changes checked in to
> index but not committed" is selected).
>
> The man page of git diff-index does not mention --cc as an option. I
> haven't fully grokked the meaning of --cc, so I cannot tell whether this
> absence has any significance (is deliberate or an omission).
>
> Is gitk wrong to add --cc unconditionally? Should it do so only when
> there are conflicts? Or not at all?
>

Here is a patch that fixes diff-index to accept --cc again:

Subject: [PATCH] diff-index: restore -c/--cc options handling

This fixes git:19b2517f95a0a908a8ada7417cf0717299e7e1aa
"diff-merges: move specific diff-index "-m" handling to diff-index"

That commit disabled handling of all diff for merges options in
diff-index on an assumption that they are unused. However, it later
appeared that -c and --cc, even though undocumented and not being
covered by tests, happen to have had particular effect on diff-index
output.

Restore original -c/--cc options handling by diff-index.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
---
 builtin/diff-index.c |  6 +++---
 diff-merges.c        | 14 ++++----------
 diff-merges.h        |  2 +-
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/builtin/diff-index.c b/builtin/diff-index.c
index cf09559e422d..5fd23ab5b6c5 100644
--- a/builtin/diff-index.c
+++ b/builtin/diff-index.c
@@ -29,10 +29,10 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	prefix = precompose_argv_prefix(argc, argv, prefix);
 
 	/*
-	 * We need no diff for merges options, and we need to avoid conflict
-	 * with our own meaning of "-m".
+	 * We need (some of) diff for merges options (e.g., --cc), and we need
+	 * to avoid conflict with our own meaning of "-m".
 	 */
-	diff_merges_suppress_options_parsing();
+	diff_merges_suppress_m_parsing();
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	for (i = 1; i < argc; i++) {
diff --git a/diff-merges.c b/diff-merges.c
index d897fd8a2933..5060ccd890bd 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -6,7 +6,7 @@ typedef void (*diff_merges_setup_func_t)(struct rev_info *);
 static void set_separate(struct rev_info *revs);
 
 static diff_merges_setup_func_t set_to_default = set_separate;
-static int suppress_parsing;
+static int suppress_m_parsing;
 
 static void suppress(struct rev_info *revs)
 {
@@ -91,9 +91,9 @@ int diff_merges_config(const char *value)
 	return 0;
 }
 
-void diff_merges_suppress_options_parsing(void)
+void diff_merges_suppress_m_parsing(void)
 {
-	suppress_parsing = 1;
+	suppress_m_parsing = 1;
 }
 
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
@@ -102,10 +102,7 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 	const char *optarg;
 	const char *arg = argv[0];
 
-	if (suppress_parsing)
-		return 0;
-
-	if (!strcmp(arg, "-m")) {
+	if (!suppress_m_parsing && !strcmp(arg, "-m")) {
 		set_to_default(revs);
 	} else if (!strcmp(arg, "-c")) {
 		set_combined(revs);
@@ -153,9 +150,6 @@ void diff_merges_set_dense_combined_if_unset(struct rev_info *revs)
 
 void diff_merges_setup_revs(struct rev_info *revs)
 {
-	if (suppress_parsing)
-		return;
-
 	if (revs->combine_merges == 0)
 		revs->dense_combined_merges = 0;
 	if (revs->separate_merges == 0)
diff --git a/diff-merges.h b/diff-merges.h
index b5d57f6563e3..19639689bb05 100644
--- a/diff-merges.h
+++ b/diff-merges.h
@@ -11,7 +11,7 @@ struct rev_info;
 
 int diff_merges_config(const char *value);
 
-void diff_merges_suppress_options_parsing(void);
+void diff_merges_suppress_m_parsing(void);
 
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv);
 
-- 
2.33.0.114.g9123bcff51bf