On 2/9/2021 6:32 AM, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@xxxxxxxxx>
>
> We want to make use of unique basenames to help inform rename detection,
> so that more likely pairings can be checked first. (src/moduleA/foo.txt
> and source/module/A/foo.txt are likely related if there are no other
> 'foo.txt' files among the deleted and added files.) Add a new function,
> not yet used, which creates a map of the unique basenames within
> rename_src and another within rename_dst, together with the indices
> within rename_src/rename_dst where those basenames show up. Non-unique
> basenames still show up in the map, but have an invalid index (-1).
>
> This function was inspired by the fact that in real world repositories,
> most renames often do not involve a basename change. Here are some
> sample repositories and the percentage of their historical renames (as of
> early 2020) that did not involve a basename change:
I found this difficult to parse. Perhaps instead
"the percentage of their renames that preserved basenames".
We might also need something stronger, though: which percentage of renames
preserved the basename but also had no other copy of that basename in the
scope of all add/deletes?
Is this reproducible from a shell command that could be documented here?
> +MAYBE_UNUSED
> +static int find_basename_matches(struct diff_options *options,
> + int minimum_score,
> + int num_src)
> +{
> + int i;
> + struct strintmap sources;
> + struct strintmap dests;
> +
> + /* Create maps of basename -> fullname(s) for sources and dests */
> + strintmap_init_with_options(&sources, -1, NULL, 0);
> + strintmap_init_with_options(&dests, -1, NULL, 0);
Initially, I was wondering why we need the map for each side, but we will need
to enforce uniqueness in each set, so OK.
> + for (i = 0; i < num_src; ++i) {
> + char *filename = rename_src[i].p->one->path;
> + char *base;
> +
> + /* exact renames removed in remove_unneeded_paths_from_src() */
> + assert(!rename_src[i].p->one->rename_used);
> +
> + base = strrchr(filename, '/');
> + base = (base ? base+1 : filename);
nit: "base + 1"
Also, this is used here and below. Perhaps it's worth pulling out as a
helper? I see similar code being duplicated in these existing spots:
* diff-no-index.c:append_basename()
* help.c:append_similar_ref()
* packfile.c:pack_basename()
* replace-object.c:register_replace_ref()
* setup.c:read_gitfile_gently()
* builtin/rebase.c:cmd_rebase()
* builtin/stash.c:do_create_stash()
* builtin/worktree.c:add_worktree()
* contrib/credential/gnome-keyring/git-credential-gnome-keyring.c:usage()
* contrib/credential/libsecret/git-credential-libsecret.c:usage()
* trace2/tr2_dst.c:tr2_dst_try_auto_path()
There are other places that use strchr(_, '/') but they seem to be related
to peeling basenames off of paths and using the leading portion of the path.
> + /* Record index within rename_src (i) if basename is unique */
> + if (strintmap_contains(&sources, base))
> + strintmap_set(&sources, base, -1);
> + else
> + strintmap_set(&sources, base, i);
> + }
> + for (i = 0; i < rename_dst_nr; ++i) {
> + char *filename = rename_dst[i].p->two->path;
> + char *base;
> +
> + if (rename_dst[i].is_rename)
> + continue; /* involved in exact match already. */
> +
> + base = strrchr(filename, '/');
> + base = (base ? base+1 : filename);
> +
> + /* Record index within rename_dst (i) if basename is unique */
> + if (strintmap_contains(&dests, base))
> + strintmap_set(&dests, base, -1);
> + else
> + strintmap_set(&dests, base, i);
> + }
> +
> + /* TODO: Make use of basenames source and destination basenames */
> +
> + strintmap_clear(&sources);
> + strintmap_clear(&dests);
> +
> + return 0;
> +}
Thanks,
-Stolee
