gc: enable cruft packs by default

Here is a very tiny reroll of my series to graduate gc.cruftPacks out of feature.experimental and enables it by default.

A complete summary of the topic is available in the original cover letter[1], and the changes since last time are limited to test clean-up, patch reorganization, and some touch-ups on the patch messages themselves.

As always, a range-diff is below for convenience.

Thanks for all of the review thus far, and in advance for any review on this round, too.

[1]: https://lore.kernel.org/git/[email protected]/

Taylor Blau (10):
pack-write.c: plug a leak in stage_tmp_packfiles() builtin/repack.c: fix incorrect reference to '-C' builtin/gc.c: ignore cruft packs with --keep-largest-pack t/t5304-prune.sh: prepare for gc --cruft by default t/t6501-freshen-objects.sh: prepare for gc --cruft by default t/t6500-gc.sh: refactor cruft pack tests t/t6500-gc.sh: add additional test cases t/t9300-fast-import.sh: prepare for gc --cruft by default builtin/gc.c: make gc.cruftPacks enabled by default repository.h: drop unused gc_cruft_packs

 Documentation/config/feature.txt |   3 -
 Documentation/config/gc.txt      |  12 +--
 Documentation/git-gc.txt         |  12 +--
 Documentation/gitformat-pack.txt |   4 +-
 builtin/gc.c                     |   8 +-
 builtin/repack.c                 |   2 +-
 pack-write.c                     |  14 ++--
 repo-settings.c                  |   4 +-
 repository.h                     |   1 -
 t/t5304-prune.sh                 |  28 +++----
 t/t6500-gc.sh                    | 135 ++++++++++++++++---------------
 t/t6501-freshen-objects.sh       |  10 +--
 t/t9300-fast-import.sh           |  13 +--
 13 files changed, 120 insertions(+), 126 deletions(-)

Range-diff against v1:

 1:  65ac7ed9b8 =  1:  c477b754e7 pack-write.c: plug a leak in stage_tmp_packfiles()
 2:  fbc8d15032 =  2:  52fb61fa9c builtin/repack.c: fix incorrect reference to '-C'
 3:  796df920ad !  3:  63b9ee8e2e builtin/gc.c: ignore cruft packs with `--keep-largest-pack`

@@ Commit message
- The same is true for gc.bigPackThreshold, if the size of the cruft pack exceeds the limit set by the caller.

- Ignore cruft packs in the common implementation for both of these
- options, and add a pair of tests to prevent any future regressions here.
+ In the future, it is possible that gc.bigPackThreshold could be used
+ to write a separate cruft pack containing any new unreachable objects
+ that entered the repository since the last time a cruft pack was
+ written.
+
+ There are some complexities to doing so, mainly around handling
+ pruning objects that are in an existing cruft pack that is above the
+ threshold (which would either need to be rewritten, or else delay
+ pruning). Rewriting a substantially similar cruft pack isn't ideal, but
+ it is significantly better than the status-quo.
+
+ If users have large cruft packs that they don't want to rewrite, they
+ can mark them as *.keep packs. But in general, if a repository has a
+ cruft pack that is so large it is slowing down GC's, it should probably
+ be pruned anyway.
+
+ In the meantime, ignore cruft packs in the common implementation for
+ both of these options, and add a pair of tests to prevent any future
+ regressions here.

@@ Documentation/git-gc.txt: be performed as well.
- All packs except the largest pack and those marked with a
- .keep files are consolidated into a single pack. When this
- option is used, gc.bigPackThreshold is ignored.
-+ All packs except the largest pack, any packs marked with a
-+ .keep file, and any cruft pack(s) are consolidated into a
-+ single pack. When this option is used, gc.bigPackThreshold is
-+ ignored.
++ All packs except the largest non-cruft pack, any packs marked
++ with a .keep file, and any cruft pack(s) are consolidated into
++ a single pack. When this option is used, gc.bigPackThreshold
++ is ignored.

AGGRESSIVE
----------

 4:  44006da959 =  4:  905eeb9027 t/t5304-prune.sh: prepare for `gc --cruft` by default
 8:  4ccc525c39 !  5:  fa6eafb1fe t/t6501-freshen-objects.sh: prepare for `gc --cruft` by default

@@ Commit message
cover the case of freshening loose objects not using cruft packs.

We could run this test twice, once with --cruft and once with
- --no-cruft, but doing so is unnecessary, since the object rescuing and
- freshening behavior is already extensively tested via t5329.
+ --no-cruft, but doing so is unnecessary, since we already test object
+ rescuing, freshening, and dealing with corrupt parts of the unreachable
+ object graph extensively via t5329.

 6:  56a965e517 =  6:  e6270d75fa t/t6500-gc.sh: refactor cruft pack tests
 7:  6957e54f51 !  7:  9db3fa9e36 t/t6500-gc.sh: add additional test cases

@@ Commit message
which enumerates all possible combinations of arguments that will produce (or not produce) a cruft pack.

- This prepares us for the following commit, which will change the default
+ This prepares us for a future commit which will change the default value
of gc.cruftPacks by ensuring that we understand which invocations do and do not change as a result.

@@ t/t6500-gc.sh: do
done

for argv in \
-+ "gc --no-cruft" \
++ "gc" \
+ "-c gc.cruftPacks=false gc" \
+ "-c gc.cruftPacks=true gc --no-cruft" \
"-c feature.expiremental=true -c gc.cruftPacks=false gc" \
5: 1b07eb83fe ! 8: 894cf176ea t/t9300-fast-import.sh: prepare for gc --cruft by default
@@ Metadata
## Commit message ##
t/t9300-fast-import.sh: prepare for gc --cruft by default

- In a similar fashion as the previous commit, adjust the fast-import
- tests to prepare for "git gc" generating a cruft pack by default.
+ In a similar fashion as previous commits, adjust the fast-import tests
+ to prepare for "git gc" generating a cruft pack by default.

This adjustment is slightly different, however. Instead of relying on us writing out the objects loose, and then calling git prune to remove
@@ Commit message
one git gc --prune, which handles pruning both loose objects, and objects that would otherwise be written to a cruft pack.

+ Likely this pattern of "git gc && git prune" started all the way back in
+ 03db4525d3 (Support gitlinks in fast-import., 2008-07-19), which
+ happened after deprecating git gc --prune in 9e7d501990 (builtin-gc.c:
+ deprecate --prune, it now really has no effect, 2008-05-09).
+
+ After --prune was un-deprecated in 58e9d9d472 (gc: make --prune useful
+ again by accepting an optional parameter, 2009-02-14), this script got a
+ handful of new "git gc && git prune" instances via via 4cedb78cb5
+ (fast-import: add input format tests, 2011-08-11). These could have been
+ git gc --prune, but weren't (likely taking after 03db4525d3).
+

## t/t9300-fast-import.sh ##
9: bfda40a21d ! 9: b6784ddfe2 builtin/gc.c: make gc.cruftPacks enabled by default

    @@ t/t6500-gc.sh: assert_no_cruft_packs () {
      }
      
      for argv in \
    +-	"gc --cruft" \
     +	"gc" \
    - 	"gc --cruft" \
      	"-c gc.cruftPacks=true gc" \
     -	"-c gc.cruftPacks=false gc --cruft" \
     -	"-c feature.experimental=true gc" \
    @@ t/t6500-gc.sh: assert_no_cruft_packs () {
      do
      	test_expect_success "git $argv generates a cruft pack" '
      		test_when_finished "rm -fr repo" &&
    -@@ t/t6500-gc.sh: done
    +@@ t/t6500-gc.sh: do
    + done
    + 
      for argv in \
    - 	"gc --no-cruft" \
    +-	"gc" \
    ++	"gc --no-cruft" \
      	"-c gc.cruftPacks=false gc" \
     -	"-c gc.cruftPacks=true gc --no-cruft" \
     -	"-c feature.expiremental=true -c gc.cruftPacks=false gc" \

10: fa15125454 = 10: c67ee7c2ff repository.h: drop unused gc_cruft_packs

2.40.0.362.gc67ee7c2ff