branch: add branch.<name>.deleteMerged opt-out

Setting branch.<name>.deleteMerged=false exempts that branch from
"git branch --delete-merged", which is useful for a topic you want
to keep developing after an early round of it has been merged
upstream. Unless --quiet is given, each skip is reported so the
user knows why their topic was kept.

Explicit deletion with "git branch -d" still uses the normal merge
check and ignores this setting.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/branch.adoc

@@ -102,3 +102,10 @@ for details).
 	`git branch --edit-description`. Branch description is
 	automatically added to the `format-patch` cover letter or
 	`request-pull` summary.
+
+`branch.<name>.deleteMerged`::
+	If set to `false`, branch _<name>_ is exempt from
+	`git branch --delete-merged`.  Useful for a topic branch you
+	intend to develop further after an initial round has been
+	merged upstream.  Defaults to true.  Explicit deletion via
+	`git branch -d` is unaffected.

Documentation/git-branch.adoc

@@ -216,11 +216,12 @@ A branch is not deleted when:
 +
 --
 * its configured upstream ref no longer exists,
-* it is checked out in any worktree, or
+* it is checked out in any worktree,
 * pushing it by name to the remote configured by
   `branch.<name>.remote` would update its upstream, so it cannot be
   distinguished from a branch that just looks "fully merged" right
-  after a pull.
+  after a pull, or
+* `branch.<name>.deleteMerged` is set to `false`.
 --
 +
 A branch whose work has not yet been merged into its upstream is

builtin/branch.c

@@ -786,6 +786,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
 	struct ref_array candidates = { 0 };
 	struct strset deletable_branch_names = STRSET_INIT;
 	struct strvec branches_to_delete = STRVEC_INIT;
+	struct strbuf key = STRBUF_INIT;
 	struct hashmap_iter iter;
 	struct strmap_entry *entry;
 	int ret = 0;
@@ -804,6 +805,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
 		const char *branch_name;
 		struct branch *branch;
 		const char *upstream_refname;
+		int opt_out;
 
 		if (!skip_prefix(branch_refname, "refs/heads/", &branch_name))
 			BUG("filter returned non-branch ref '%s'", branch_refname);
@@ -821,6 +823,17 @@ static int delete_merged_branches(const struct strvec *upstreams,
 					FILTER_REFS_BRANCHES, DELETE_BRANCH_SKIP_UNMERGED))
 			continue;
 
+		strbuf_reset(&key);
+		strbuf_addf(&key, "branch.%s.deletemerged", branch_name);
+		if (!repo_config_get_bool(the_repository, key.buf, &opt_out) &&
+		    !opt_out) {
+			if (!(flags & DELETE_BRANCH_QUIET))
+				fprintf(stderr,
+					_("Skipping '%s' (branch.%s.deleteMerged is false)\n"),
+					branch_name, branch_name);
+			continue;
+		}
+
 		strset_add(&deletable_branch_names, branch_name);
 	}
 
@@ -836,6 +849,7 @@ static int delete_merged_branches(const struct strvec *upstreams,
 				      DELETE_BRANCH_NO_HEAD_FALLBACK |
 				      flags);
 
+	strbuf_release(&key);
 	strvec_clear(&branches_to_delete);
 	strset_clear(&deletable_branch_names);
 	ref_array_clear(&candidates);

t/t3200-branch.sh

@@ -2038,4 +2038,40 @@ test_expect_success '--delete-merged requires a value' '
 	test_must_fail git -C forked branch --delete-merged 2>err &&
 	test_grep "requires a value" err
 '
+
+test_expect_success '--delete-merged honours branch.<name>.deleteMerged=false' '
+	setup_repo_for_delete_merged &&
+	create_merged_branch deleted &&
+	create_merged_branch kept &&
+	(
+		cd repo &&
+		git config branch.kept.deleteMerged false &&
+		git checkout --detach &&
+
+		git branch --delete-merged origin/next 2>err &&
+
+		test_grep "Skipping .kept." err &&
+		check_branches <<-\EOF
+		kept
+		main
+		EOF
+	)
+'
+
+test_expect_success "branch -d still deletes a deleteMerged=false branch" '
+	setup_repo_for_delete_merged &&
+	create_merged_branch kept &&
+	(
+		cd repo &&
+		git config branch.kept.deleteMerged false &&
+		git checkout --detach &&
+
+		git branch -d kept &&
+
+		check_branches <<-\EOF
+		main
+		EOF
+	)
+'
+
 test_done