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diff: replace diff_options.dry_run flag with NULL file 

We introduced a dry_run flag to diff_options in b55e6d36eb (diff: ensure
consistent diff behavior with ignore options, 2025-08-08), with the idea
that the lower-level diff code could skip output when it is set.

As we saw with the bugs fixed by 3ed5d8bd73 (diff: stop output garbled
message in dry run mode, 2025-10-20), it is easy to miss spots. In the
end, we located all of them by checking where diff_options.file is used.

That suggests another possible approach: we can replace the dry_run
boolean with a NULL pointer for "file", as we know that using "file" in
dry_run mode would always be an error. This turns any missed spots from
producing extra output[1] into a segfault. Which is less forgiving, but
that is the point: this is indicative of a programming error, and
complaining loudly and immediately is good.

[1] We protect ourselves against garbled output as a separate step,
    courtesy of 623f7af284 (diff: restore redirection to /dev/null for
    diff_from_contents, 2025-10-17). So in that sense this patch can
    only introduce user-visible errors (since any "bugs" were going to
    /dev/null before), but the idea is to catch them rather than quietly
    send garbage to /dev/null.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
main
Jeff King 2025-10-24 13:08:53 -04:00 committed by Junio C Hamano
parent 0152831d96
commit b2b5ad514d
2 changed files with 8 additions and 10 deletions
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16
diff.c
View File

@ -1351,7 +1351,7 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
int len = eds->len;
unsigned flags = eds->flags;

if (o->dry_run)
if (!o->file)
return;

switch (s) {
@ -3765,9 +3765,9 @@ static void builtin_diff(const char *name_a,

if (o->word_diff)
init_diff_words_data(&ecbdata, o, one, two);
if (o->dry_run) {
if (!o->file) {
/*
* Unlike the !dry_run case, we need to ignore the
* Unlike the normal output case, we need to ignore the
* return value from xdi_diff_outf() here, because
* xdi_diff_outf() takes non-zero return from its
* callback function as a sign of error and returns
@ -4423,7 +4423,7 @@ static void run_external_diff(const struct external_diff *pgm,
{
struct child_process cmd = CHILD_PROCESS_INIT;
struct diff_queue_struct *q = &diff_queued_diff;
int quiet = !(o->output_format & DIFF_FORMAT_PATCH) || o->dry_run;
int quiet = !(o->output_format & DIFF_FORMAT_PATCH) || !o->file;
int rc;

/*
@ -4621,7 +4621,7 @@ static void run_diff_cmd(const struct external_diff *pgm,
p->status == DIFF_STATUS_RENAMED)
o->found_changes = 1;
} else {
if (!o->dry_run)
if (o->file)
fprintf(o->file, "* Unmerged path %s\n", name);
o->found_changes = 1;
}
@ -6199,15 +6199,15 @@ static void diff_flush_patch(struct diff_filepair *p, struct diff_options *o)
/* return 1 if any change is found; otherwise, return 0 */
static int diff_flush_patch_quietly(struct diff_filepair *p, struct diff_options *o)
{
int saved_dry_run = o->dry_run;
FILE *saved_file = o->file;
int saved_found_changes = o->found_changes;
int ret;

o->dry_run = 1;
o->file = NULL;
o->found_changes = 0;
diff_flush_patch(p, o);
ret = o->found_changes;
o->dry_run = saved_dry_run;
o->file = saved_file;
o->found_changes |= saved_found_changes;
return ret;
}

2
diff.h
View File

@ -408,8 +408,6 @@ struct diff_options {
#define COLOR_MOVED_WS_ERROR (1<<0)
unsigned color_moved_ws_handling;

bool dry_run;

struct repository *repo;
struct strmap *additional_path_headers;