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

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>

diff --git a/merge-recursive.c b/merge-recursive.c
index b052974f191cd82741475a019076c90e45d6d4de..99a197597db5c7ab83532661027774253c3abea7 100644 (file)
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -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);