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diffcore-rename: provide basic implementation of idx_possible_rename()

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Add a new struct dir_rename_info with various values we need inside our
idx_possible_rename() function introduced in the previous commit.  Add a
basic implementation for this function showing how we plan to use the
variables, but which will just return early with a value of -1 (not
found) when those variables are not set up.

Future commits will do the work necessary to set up those other
variables so that idx_possible_rename() does not always return -1.

Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2021-02-27 00:30:40 +00:00 committed by Junio C Hamano
parent 37a2514364
commit bde8b9f34c
1 changed files with 94 additions and 6 deletions
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100
diffcore-rename.c
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@ -367,6 +367,19 @@ static int find_exact_renames(struct diff_options *options)
return renames;
}
struct dir_rename_info {
struct strintmap idx_map;
struct strmap dir_rename_guess;
struct strmap *dir_rename_count;
unsigned setup;
};
static char *get_dirname(const char *filename)
{
char *slash = strrchr(filename, '/');
return slash ? xstrndup(filename, slash - filename) : xstrdup("");
}
static const char *get_basename(const char *filename)
{
/*
@ -379,14 +392,86 @@ static const char *get_basename(const char *filename)
return base ? base + 1 : filename;
}
static int idx_possible_rename(char *filename)
static int idx_possible_rename(char *filename, struct dir_rename_info *info)
{
/* Unconditionally return -1, "not found", for now */
return -1;
/*
* Our comparison of files with the same basename (see
* find_basename_matches() below), is only helpful when after exact
* rename detection we have exactly one file with a given basename
* among the rename sources and also only exactly one file with
* that basename among the rename destinations. When we have
* multiple files with the same basename in either set, we do not
* know which to compare against. However, there are some
* filenames that occur in large numbers (particularly
* build-related filenames such as 'Makefile', '.gitignore', or
* 'build.gradle' that potentially exist within every single
* subdirectory), and for performance we want to be able to quickly
* find renames for these files too.
*
* The reason basename comparisons are a useful heuristic was that it
* is common for people to move files across directories while keeping
* their filename the same. If we had a way of determining or even
* making a good educated guess about which directory these non-unique
* basename files had moved the file to, we could check it.
* Luckily...
*
* When an entire directory is in fact renamed, we have two factors
* helping us out:
* (a) the original directory disappeared giving us a hint
* about when we can apply an extra heuristic.
* (a) we often have several files within that directory and
* subdirectories that are renamed without changes
* So, rules for a heuristic:
* (0) If there basename matches are non-unique (the condition under
* which this function is called) AND
* (1) the directory in which the file was found has disappeared
* (i.e. dirs_removed is non-NULL and has a relevant entry) THEN
* (2) use exact renames of files within the directory to determine
* where the directory is likely to have been renamed to. IF
* there is at least one exact rename from within that
* directory, we can proceed.
* (3) If there are multiple places the directory could have been
* renamed to based on exact renames, ignore all but one of them.
* Just use the destination with the most renames going to it.
* (4) Check if applying that directory rename to the original file
* would result in a destination filename that is in the
* potential rename set. If so, return the index of the
* destination file (the index within rename_dst).
* (5) Compare the original file and returned destination for
* similarity, and if they are sufficiently similar, record the
* rename.
*
* This function, idx_possible_rename(), is only responsible for (4).
* The conditions/steps in (1)-(3) will be handled via setting up
* dir_rename_count and dir_rename_guess in a future
* initialize_dir_rename_info() function. Steps (0) and (5) are
* handled by the caller of this function.
*/
char *old_dir, *new_dir;
struct strbuf new_path = STRBUF_INIT;
int idx;
if (!info->setup)
return -1;
old_dir = get_dirname(filename);
new_dir = strmap_get(&info->dir_rename_guess, old_dir);
free(old_dir);
if (!new_dir)
return -1;
strbuf_addstr(&new_path, new_dir);
strbuf_addch(&new_path, '/');
strbuf_addstr(&new_path, get_basename(filename));
idx = strintmap_get(&info->idx_map, new_path.buf);
strbuf_release(&new_path);
return idx;
}
static int find_basename_matches(struct diff_options *options,
int minimum_score)
int minimum_score,
struct dir_rename_info *info)
{
/*
* When I checked in early 2020, over 76% of file renames in linux
@ -494,7 +579,7 @@ static int find_basename_matches(struct diff_options *options,
dst_index = strintmap_get(&dests, base);
if (src_index == -1 || dst_index == -1) {
src_index = i;
dst_index = idx_possible_rename(filename);
dst_index = idx_possible_rename(filename, info);
}
if (dst_index == -1)
continue;
@ -677,8 +762,10 @@ void diffcore_rename(struct diff_options *options)
int num_destinations, dst_cnt;
int num_sources, want_copies;
struct progress *progress = NULL;
struct dir_rename_info info;
trace2_region_enter("diff", "setup", options->repo);
info.setup = 0;
want_copies = (detect_rename == DIFF_DETECT_COPY);
if (!minimum_score)
minimum_score = DEFAULT_RENAME_SCORE;
@ -774,7 +861,8 @@ void diffcore_rename(struct diff_options *options)
/* Utilize file basenames to quickly find renames. */
trace2_region_enter("diff", "basename matches", options->repo);
rename_count += find_basename_matches(options,
min_basename_score);
min_basename_score,
&info);
trace2_region_leave("diff", "basename matches", options->repo);
/*