commit-graph: add new config for changed-paths & recommend it in scalar

The changed-path Bloom filters feature has proven stable and reliable
over several years of use, delivering significant performance
improvement for file history computation in large monorepos. Currently
a user can opt-in to writing the changed-path Bloom filters using the
"--changed-paths" option to "git commit-graph write". The filters will
be persisted until the user drops the filters using the
"--no-changed-paths" option. For this functionality, refer to 0087a87ba8
(commit-graph: persist existence of changed-paths, 2020-07-01).

Large monorepos using Git's background maintenance to build and update
commit-graph files could use an easy switch to enable this feature
without a foreground computation. In this commit, we're proposing a new
config option "commitGraph.changedPaths":

* If "true", "git commit-graph write" will write Bloom filters,
  equivalent to passing "--changed-paths";
* If "false" or "unset", Bloom filters will be written during "git
  commit-graph write" only if the filters already exist in the current
  commit-graph file. This matches the default behaviour of "git
  commit-graph write" without any "--[no-]changed-paths" option. Note
  "false" can disable a previous "true" config value but doesn't imply
  "--no-changed-paths".

This config will always respect the precedence of command line option
"--[no-]changed-paths".

We also set this new config as optional recommended config in scalar to
turn on this feature for large repos.

Helped-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Emily Yang <emilyyang.git@gmail.com>
Acked-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 0b3404f58f..98c6910963 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -946,4 +946,48 @@ test_expect_success 'stale commit cannot be parsed when traversing graph' '
 	)
 '
 
+test_expect_success 'config commitGraph.changedPaths acts like --changed-paths' '
+	git init config-changed-paths &&
+	(
+		cd config-changed-paths &&
+
+		# commitGraph.changedPaths is not set and it should not write Bloom filters
+		test_commit first &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --reachable --progress 2>error &&
+		test_grep ! "Bloom filters" error &&
+
+		# Set commitGraph.changedPaths to true and it should write Bloom filters
+		test_commit second &&
+		git config commitGraph.changedPaths true &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --reachable --progress 2>error &&
+		test_grep "Bloom filters" error &&
+
+		# Add one more config commitGraph.changedPaths as false to disable the previous true config value
+		# It should still write Bloom filters due to existing filters
+		test_commit third &&
+		git config --add commitGraph.changedPaths false &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --reachable --progress 2>error &&
+		test_grep "Bloom filters" error &&
+
+		# commitGraph.changedPaths is still false and command line options should take precedence
+		test_commit fourth &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --no-changed-paths --reachable --progress 2>error &&
+		test_grep ! "Bloom filters" error &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --reachable --progress 2>error &&
+		test_grep ! "Bloom filters" error &&
+
+		# commitGraph.changedPaths is all cleared and then set to false again, command line options should take precedence
+		test_commit fifth &&
+		git config --unset-all commitGraph.changedPaths &&
+		git config commitGraph.changedPaths false &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --changed-paths --reachable --progress 2>error &&
+		test_grep "Bloom filters" error &&
+
+		# commitGraph.changedPaths is still false and it should write Bloom filters due to existing filters
+		test_commit sixth &&
+		GIT_PROGRESS_DELAY=0 git commit-graph write --reachable --progress 2>error &&
+		test_grep "Bloom filters" error
+	)
+'
+
 test_done