Subject: [PATCH 2/5] repo-settings: add feature.manyCommits setting

From: "Derrick Stolee via GitGitGadget" <[email-masked]>
Date: Mon, 22 Jul 2019 10:54:22 -0700 (PDT)

From: Derrick Stolee <[email-masked]>

When a repo has many commits, it is helpful to write and read the
commit-graph file. Future changes to Git may include new config
settings that are benefitial in this scenario.

Create the 'feature.manyCommits' config setting that changes the
default values of 'core.commitGraph' and 'gc.writeCommitGraph' to
true.

Signed-off-by: Derrick Stolee <[email-masked]>
---
 Documentation/config.txt         |  2 ++
 Documentation/config/core.txt    |  3 ++-
 Documentation/config/feature.txt | 15 +++++++++++++++
 Documentation/config/gc.txt      |  4 ++--
 repo-settings.c                  |  7 +++++++
 5 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/config/feature.txt

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e3f5bc3396..77f3b1486b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -345,6 +345,8 @@ include::config/difftool.txt[]
 
 include::config/fastimport.txt[]
 
+include::config/feature.txt[]
+
 include::config/fetch.txt[]
 
 include::config/format.txt[]
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 75538d27e7..d80162681a 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -577,7 +577,8 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to false, unless
+	`feature.manyCommits` is enabled. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
new file mode 100644
index 0000000000..f74314ae90
--- /dev/null
+++ b/Documentation/config/feature.txt
@@ -0,0 +1,15 @@
+feature.*::
+	The config settings that start with `feature.` modify the defaults of
+	a group of other config settings. These groups are created by the Git
+	developer community as recommended defaults and are subject to change.
+	In particular, new config options may be added with different defaults.
+
+feature.manyCommits::
+	Enable config options that optimize for repos with many commits. This
+	setting is recommended for repos with at least 100,000 commits. The
+	new default values are:
++
+* `core.commitGraph=true` enables reading the commit-graph file.
++
+* `gc.writeCommitGraph=true` enables writing the commit-graph file during
+garbage collection.
\ No newline at end of file
diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 02b92b18b5..31a5fc4f75 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -63,8 +63,8 @@ gc.writeCommitGraph::
 	If true, then gc will rewrite the commit-graph file when
 	linkgit:git-gc[1] is run. When using `git gc --auto`
 	the commit-graph will be updated if housekeeping is
-	required. Default is false. See linkgit:git-commit-graph[1]
-	for details.
+	required. Default is false, unless `feature.manyCommits`
+	is enabled. See linkgit:git-commit-graph[1] for details.
 
 gc.logExpiry::
 	If the file gc.log exists, then `git gc --auto` will print
diff --git a/repo-settings.c b/repo-settings.c
index 13a9128f62..f328602fd7 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -3,10 +3,17 @@
 #include "config.h"
 #include "repo-settings.h"
 
+#define UPDATE_DEFAULT(s,v) do { if (s == -1) { s = v; } } while(0)
+
 static int git_repo_config(const char *key, const char *value, void *cb)
 {
 	struct repo_settings *rs = (struct repo_settings *)cb;
 
+	if (!strcmp(key, "feature.manycommits")) {
+		UPDATE_DEFAULT(rs->core_commit_graph, 1);
+		UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
+		return 0;
+	}
 	if (!strcmp(key, "core.commitgraph")) {
 		rs->core_commit_graph = git_config_bool(key, value);
 		return 0;
-- 
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