clean: optimize and document cases where we recurse into subdirectories

Commit 6b1db43109 ("clean: teach clean -d to preserve ignored paths", 2017-05-23) added the following code block (among others) to git-clean: if (remove_directories) dir.flags |= DIR_SHOW_IGNORED_TOO | DIR_KEEP_UNTRACKED_CONTENTS; The reason for these flags is well documented in the commit message, but isn't obvious just from looking at the code. Add some explanations to the code to make it clearer. Further, it appears git-2.26 did not correctly handle this combination of flags from git-clean. With both these flags and without DIR_SHOW_IGNORED_TOO_MODE_MATCHING set, git is supposed to recurse into all untracked AND ignored directories. git-2.26.0 clearly was not doing that. I don't know the full reasons for that or whether git < 2.27.0 had additional unknown bugs because of that misbehavior, because I don't feel it's worth digging into. As per the huge changes and craziness documented in commit 8d92fb2927 ("dir: replace exponential algorithm with a linear one", 2020-04-01), the old algorithm was a mess and was thrown out. What I can say is that git-2.27.0 correctly recurses into untracked AND ignored directories with that combination. However, in clean's case we don't need to recurse into ignored directories; that is just a waste of time. Thus, when git-2.27.0 started correctly handling those flags, we got a performance regression report. Rather than relying on other bugs in fill_directory()'s former logic to provide the behavior of skipping ignored directories, make use of the DIR_SHOW_IGNORED_TOO_MODE_MATCHING value specifically added in commit eec0f7f2b7 ("status: add option to show ignored files differently", 2017-10-30) for this purpose. Reported-by: Brian Malehorn <bmalehorn@gmail.com> Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Elijah Newren committed Jun 11, 2020 at 06:59 UTC 7233f17577c63c95da0b4a23eefc26125e4971d1

1 file changed +31 -2

builtin/clean.c

+31 -2

@@ -955,8 +955,37 @@ int cmd_clean(int argc, const char **argv, const char *prefix)

955 remove_directories = 1;

956 }

957

958 - if (remove_directories && !ignored_only)

959 - dir.flags |= DIR_SHOW_IGNORED_TOO | DIR_KEEP_UNTRACKED_CONTENTS;

958 + if (remove_directories && !ignored_only) {

959 + /*

960 + * We need to know about ignored files too:

961 + *

962 + * If (ignored), then we will delete ignored files as well.

963 + *

964 + * If (!ignored), then even though we not are doing

965 + * anything with ignored files, we need to know about them

966 + * so that we can avoid deleting a directory of untracked

967 + * files that also contains an ignored file within it.

968 + *

969 + * For the (!ignored) case, since we only need to avoid

970 + * deleting ignored files, we can set

971 + * DIR_SHOW_IGNORED_TOO_MODE_MATCHING in order to avoid

972 + * recursing into a directory which is itself ignored.

973 + */

974 + dir.flags |= DIR_SHOW_IGNORED_TOO;

975 + if (!ignored)

976 + dir.flags |= DIR_SHOW_IGNORED_TOO_MODE_MATCHING;

977 +

978 + /*

979 + * Let the fill_directory() machinery know that we aren't

980 + * just recursing to collect the ignored files; we want all

981 + * the untracked ones so that we can delete them. (Note:

982 + * we could also set DIR_KEEP_UNTRACKED_CONTENTS when

983 + * ignored_only is true, since DIR_KEEP_UNTRACKED_CONTENTS

984 + * only has effect in combination with DIR_SHOW_IGNORED_TOO. It makes

985 + * the code clearer to exclude it, though.

986 + */

987 + dir.flags |= DIR_KEEP_UNTRACKED_CONTENTS;

988 + }

989

990 if (read_cache() < 0)

991 die(_("index file corrupt"));