[PATCH 1/9] commit-graph: add --changed-paths option to write

["Garima Singh via GitGitGadget" <gitgitgadget@gmail.com>]

From: Garima Singh <garima.singh@microsoft.com>

Add --changed-paths option to git commit-graph write. This option will
soon allow users to compute bloom filters for the paths changed between
a commit and its first significant parent, and write this information
into the commit-graph file.

Note: This commit does not change any behavior. It only introduces
the option and passes down the appropriate flag to the commit-graph.

RFC Notes:
1. We named the option --changed-paths to capture what the option does,
   instead of how it does it. The current implementation does this
   using bloom filters. We believe using --changed-paths however keeps
   the implementation open to other data structures.
   All thoughts and suggestions for the name and this approach are
   welcome

2. Currently, a subsequent commit in this series will add tests that
   exercise this option. I plan to split that test commit across the
   series as appropriate.

Helped-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Garima Singh <garima.singh@microsoft.com>
---
 Documentation/git-commit-graph.txt | 5 +++++
 builtin/commit-graph.c             | 9 +++++++--
 commit-graph.h                     | 3 ++-
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index bcd85c1976..1efe6e5c5a 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -54,6 +54,11 @@ or `--stdin-packs`.)
 With the `--append` option, include all commits that are present in the
 existing commit-graph file.
 +
+With the `--changed-paths` option, compute and write information about the
+paths changed between a commit and it's first parent. This operation can
+take a while on large repositories. It provides significant performance gains
+for getting file based history logs with `git log`
++
 With the `--split` option, write the commit-graph as a chain of multiple
 commit-graph files stored in `<dir>/info/commit-graphs`. The new commits
 not already in the commit-graph are added in a new "tip" file. This file
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index e0c6fc4bbf..9bd1e11161 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -9,7 +9,7 @@
 
 static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
-	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
+	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--changed-paths] [--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -19,7 +19,7 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 };
 
 static const char * const builtin_commit_graph_write_usage[] = {
-	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
+	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--changed-paths] [--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -32,6 +32,7 @@ static struct opts_commit_graph {
 	int split;
 	int shallow;
 	int progress;
+	int enable_bloom_filters;
 } opts;
 
 static int graph_verify(int argc, const char **argv)
@@ -110,6 +111,8 @@ static int graph_write(int argc, const char **argv)
 			N_("start walk at commits listed by stdin")),
 		OPT_BOOL(0, "append", &opts.append,
 			N_("include all commits already in the commit-graph file")),
+		OPT_BOOL(0, "changed-paths", &opts.enable_bloom_filters,
+			N_("enable computation for changed paths")),
 		OPT_BOOL(0, "progress", &opts.progress, N_("force progress reporting")),
 		OPT_BOOL(0, "split", &opts.split,
 			N_("allow writing an incremental commit-graph file")),
@@ -143,6 +146,8 @@ static int graph_write(int argc, const char **argv)
 		flags |= COMMIT_GRAPH_WRITE_SPLIT;
 	if (opts.progress)
 		flags |= COMMIT_GRAPH_WRITE_PROGRESS;
+	if (opts.enable_bloom_filters)
+		flags |= COMMIT_GRAPH_WRITE_BLOOM_FILTERS;
 
 	read_replace_refs = 0;
 
diff --git a/commit-graph.h b/commit-graph.h
index 7f5c933fa2..952a4b83be 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -76,7 +76,8 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),
 	COMMIT_GRAPH_WRITE_SPLIT      = (1 << 2),
 	/* Make sure that each OID in the input is a valid commit OID. */
-	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
+	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3),
+	COMMIT_GRAPH_WRITE_BLOOM_FILTERS = (1 << 4)
 };
 
 struct split_commit_graph_opts {
-- 
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