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merge-recursive: add a bunch of FIXME comments documenting known bugs

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The plan is to just delete merge-recursive, but not until everyone is
comfortable with merge-ort as a replacement.  Given that I haven't
switched all callers of merge-recursive over yet (e.g. git-am still uses
merge-recursive), maybe there's some value documenting known bugs in the
algorithm in case we end up keeping it or someone wants to dig it up in
the future.

Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2021-03-20 00:03:53 +00:00 committed by Junio C Hamano
parent 5291828df8
commit 816147e7ba
1 changed files with 37 additions and 0 deletions
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37
merge-recursive.c
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@ -1075,6 +1075,11 @@ static int merge_3way(struct merge_options *opt,
read_mmblob(&src1, &a->oid);
read_mmblob(&src2, &b->oid);
/*
* FIXME: Using a->path for normalization rules in ll_merge could be
* wrong if we renamed from a->path to b->path. We should use the
* target path for where the file will be written.
*/
merge_status = ll_merge(result_buf, a->path, &orig, base,
&src1, name1, &src2, name2,
opt->repo->index, &ll_opts);
@ -1154,6 +1159,8 @@ static void print_commit(struct commit *commit)
struct strbuf sb = STRBUF_INIT;
struct pretty_print_context ctx = {0};
ctx.date_mode.type = DATE_NORMAL;
/* FIXME: Merge this with output_commit_title() */
assert(!merge_remote_util(commit));
format_commit_message(commit, " %h: %m %s", &sb, &ctx);
fprintf(stderr, "%s\n", sb.buf);
strbuf_release(&sb);
@ -1177,6 +1184,11 @@ static int merge_submodule(struct merge_options *opt,
int search = !opt->priv->call_depth;
/* store a in result in case we fail */
/* FIXME: This is the WRONG resolution for the recursive case when
* we need to be careful to avoid accidentally matching either side.
* Should probably use o instead there, much like we do for merging
* binaries.
*/
oidcpy(result, a);
/* we can not handle deletion conflicts */
@ -1301,6 +1313,13 @@ static int merge_mode_and_contents(struct merge_options *opt,
if ((S_IFMT & a->mode) != (S_IFMT & b->mode)) {
result->clean = 0;
/*
* FIXME: This is a bad resolution for recursive case; for
* the recursive case we want something that is unlikely to
* accidentally match either side. Also, while it makes
* sense to prefer regular files over symlinks, it doesn't
* make sense to prefer regular files over submodules.
*/
if (S_ISREG(a->mode)) {
result->blob.mode = a->mode;
oidcpy(&result->blob.oid, &a->oid);
@ -1349,6 +1368,7 @@ static int merge_mode_and_contents(struct merge_options *opt,
free(result_buf.ptr);
if (ret)
return ret;
/* FIXME: bug, what if modes didn't match? */
result->clean = (merge_status == 0);
} else if (S_ISGITLINK(a->mode)) {
result->clean = merge_submodule(opt, &result->blob.oid,
@ -2664,6 +2684,14 @@ static int process_renames(struct merge_options *opt,
struct string_list b_by_dst = STRING_LIST_INIT_NODUP;
const struct rename *sre;
/*
* FIXME: As string-list.h notes, it's O(n^2) to build a sorted
* string_list one-by-one, but O(n log n) to build it unsorted and
* then sort it. Note that as we build the list, we do not need to
* check if the existing destination path is already in the list,
* because the structure of diffcore_rename guarantees we won't
* have duplicates.
*/
for (i = 0; i < a_renames->nr; i++) {
sre = a_renames->items[i].util;
string_list_insert(&a_by_dst, sre->pair->two->path)->util
@ -3602,6 +3630,15 @@ static int merge_recursive_internal(struct merge_options *opt,
return err(opt, _("merge returned no commit"));
}
/*
* FIXME: Since merge_recursive_internal() is only ever called by
* places that ensure the index is loaded first
* (e.g. builtin/merge.c, rebase/sequencer, etc.), in the common
* case where the merge base was unique that means when we get here
* we immediately discard the index and re-read it, which is a
* complete waste of time. We should only be discarding and
* re-reading if we were forced to recurse.
*/
discard_index(opt->repo->index);
if (!opt->priv->call_depth)
repo_read_index(opt->repo);