@@ -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.

@@ -215,10 +215,11 @@ A branch is not deleted when:
 +
 --
 * its upstream remote-tracking branch no longer exists,
-* it is checked out in any worktree, or
+* it is checked out in any worktree,
 * its push destination (`<branch>@{push}`) equals its upstream
   (`<branch>@{upstream}`), so it cannot be distinguished from a
-  branch that just looks "fully merged" right after a pull.
+  branch that just looks "fully merged" right after a pull, or
+* `branch.<name>.deleteMerged` is set to `false`.
 --
 +
 A branch whose work has not yet been merged into its upstream is

@@ -758,6 +758,8 @@ static int delete_merged_branches(int argc, const char **argv,
 	struct ref_array candidates = { 0 };
 	struct strset deletable = STRSET_INIT;
 	struct strvec to_delete = STRVEC_INIT;
+	struct strbuf key = STRBUF_INIT;
+	bool quiet = flags & DELETE_BRANCH_QUIET;
 	int i, ret = 0;
 
 	if (!argc)

@@ -775,6 +777,7 @@ static int delete_merged_branches(int argc, const char **argv,
 		const char *short_name;
 		struct branch *branch;
 		const char *upstream, *push;
+		int opt_out;
 
 		if (!skip_prefix(full_name, "refs/heads/", &short_name))
 			BUG("filter returned non-branch ref '%s'", full_name);

@@ -793,6 +796,17 @@ static int delete_merged_branches(int argc, const char **argv,
 					FILTER_REFS_BRANCHES, DELETE_BRANCH_SKIP_UNMERGED))
 			continue;
 
+		strbuf_reset(&key);
+		strbuf_addf(&key, "branch.%s.deletemerged", short_name);
+		if (!repo_config_get_bool(the_repository, key.buf, &opt_out) &&
+		    !opt_out) {
+			if (!quiet)
+				fprintf(stderr,
+					_("Skipping '%s' (branch.%s.deleteMerged is false)\n"),
+					short_name, short_name);
+			continue;
+		}
+
 		strset_add(&deletable, short_name);
 	}
 

@@ -814,6 +828,7 @@ static int delete_merged_branches(int argc, const char **argv,
 				      DELETE_BRANCH_NO_HEAD_FALLBACK |
 				      flags);
 
+	strbuf_release(&key);
 	strvec_clear(&to_delete);
 	strset_clear(&deletable);
 	ref_array_clear(&candidates);

@@ -1990,4 +1990,30 @@ test_expect_success '--delete-merged keeps a chain of upstreams of a kept branch
 	test_cmp expect actual
 '
 
+test_expect_success '--delete-merged honours branch.<name>.deleteMerged=false' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo_for_delete_merged &&
+	merged_branch deleted origin/next &&
+	merged_branch kept origin/next &&
+	git -C repo config branch.kept.deleteMerged false &&
+	git -C repo checkout --detach &&
+
+	git -C repo branch --delete-merged origin/next 2>err &&
+
+	test_grep "Skipping .kept." err &&
+	test_must_fail git -C repo rev-parse --verify refs/heads/deleted &&
+	git -C repo rev-parse --verify refs/heads/kept
+'
+
+test_expect_success "branch -d still deletes a deleteMerged=false branch" '
+	test_when_finished "rm -rf repo" &&
+	setup_repo_for_delete_merged &&
+	merged_branch kept origin/next &&
+	git -C repo config branch.kept.deleteMerged false &&
+	git -C repo checkout --detach &&
+
+	git -C repo branch -d kept &&
+	test_must_fail git -C repo rev-parse --verify refs/heads/kept
+'
+
 test_done