@@ -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>.pruneMerged`::
+	If set to `false`, branch _<name>_ is exempt from
+	`git branch --prune-merged`.
+	Useful for topic branches you intend to develop further after
+	an initial round has been merged upstream. Defaults to true.
+	Explicit deletion via `git branch -d` is unaffected.

@@ -216,16 +216,16 @@ Each _<remote>_ may be either the name of a configured remote
 	Delete the local branches that `--forked` would list for
 	the same _<remote>_ arguments, but only when the branch's
 	push destination remote-tracking branch (the branch `git push`
-	would update; see `branch_get_push` semantics) no longer
-	resolves locally. In other words: the branch was pushed
-	under some name on _<remote>_, and that name has since
-	been pruned upstream.
+	would update) no longer resolves locally. In other words:
+	the branch was pushed under some name on _<remote>_, and
+	that name has since been pruned upstream.
 +
 As a safety check, branches with commits not yet integrated into
 their upstream remote-tracking branch are refused; if the upstream
 itself is gone, the remote's default branch is consulted instead.
 With `--force` (or `-f`), delete refused branches regardless. The
-currently checked-out branch in any worktree is always preserved.
+currently checked-out branch in any worktree is always preserved,
+as is any branch with `branch.<name>.pruneMerged` set to `false`.
 
 `-v`::
 `-vv`::

@@ -864,13 +864,16 @@ static int prune_merged_branches(int argc, const char **argv, int force,
 	for_each_string_list_item(item, &candidates) {
 		const char *short_name = item->string;
 		struct strbuf full = STRBUF_INIT;
+		struct strbuf key = STRBUF_INIT;
 		struct branch *branch;
 		const char *push_ref;
 		const char *upstream;
+		int opt_out = 0;
 
 		strbuf_addf(&full, "refs/heads/%s", short_name);
 		if (branch_checked_out(full.buf)) {
 			strbuf_release(&full);
+			strbuf_release(&key);
 			continue;
 		}
 		strbuf_release(&full);

@@ -880,18 +883,38 @@ static int prune_merged_branches(int argc, const char **argv, int force,
 		if (upstream &&
 		    string_list_has_string(&protected_default_refs, upstream)) {
 			const char *leaf = strrchr(upstream, '/');
-			if (leaf && !strcmp(leaf + 1, short_name))
+			if (leaf && !strcmp(leaf + 1, short_name)) {
+				strbuf_release(&key);
 				continue;
+			}
 		}
 
 		push_ref = branch ? branch_get_push(branch, NULL) : NULL;
-		if (!push_ref)
+		if (!push_ref) {
+			strbuf_release(&key);
 			continue;
+		}
 		if (refs_ref_exists(get_main_ref_store(the_repository),
-				    push_ref))
+				    push_ref)) {
+			strbuf_release(&key);
+			continue;
+		}
+		if (string_list_has_string(&protected_default_refs, push_ref)) {
+			strbuf_release(&key);
 			continue;
-		if (string_list_has_string(&protected_default_refs, push_ref))
+		}
+
+		strbuf_addf(&key, "branch.%s.prunemerged", short_name);
+		if (!repo_config_get_bool(the_repository, key.buf, &opt_out) &&
+		    !opt_out) {
+			if (!quiet)
+				fprintf(stderr, _("Skipping '%s' "
+						  "(branch.%s.pruneMerged is false)\n"),
+					short_name, short_name);
+			strbuf_release(&key);
 			continue;
+		}
+		strbuf_release(&key);
 
 		strvec_push(&deletable, short_name);
 	}

@@ -1917,4 +1917,44 @@ test_expect_success '--prune-merged spares branches whose push ref is the defaul
 	git -C pm-pushdefault rev-parse --verify refs/heads/topic
 '
 
+test_expect_success '--prune-merged honours branch.<name>.pruneMerged=false' '
+	test_when_finished "rm -rf pm-optout" &&
+	git clone pm-upstream pm-optout &&
+	git -C pm-optout branch one --track origin/one &&
+	git -C pm-optout branch two --track origin/two &&
+	git -C pm-optout config branch.one.pruneMerged false &&
+
+	git -C pm-optout update-ref -d refs/remotes/origin/one &&
+	git -C pm-optout update-ref -d refs/remotes/origin/two &&
+	git -C pm-optout branch --prune-merged origin 2>err &&
+
+	git -C pm-optout rev-parse --verify refs/heads/one &&
+	test_must_fail git -C pm-optout rev-parse --verify refs/heads/two &&
+	test_grep "Skipping .one." err
+'
+
+test_expect_success '--prune-merged --force still honours pruneMerged=false' '
+	test_when_finished "rm -rf pm-optout-force" &&
+	git clone pm-upstream pm-optout-force &&
+	git -C pm-optout-force checkout -b one --track origin/one &&
+	test_commit -C pm-optout-force unpushed &&
+	git -C pm-optout-force checkout - &&
+	git -C pm-optout-force config branch.one.pruneMerged false &&
+
+	git -C pm-optout-force update-ref -d refs/remotes/origin/one &&
+	git -C pm-optout-force branch --force --prune-merged origin &&
+
+	git -C pm-optout-force rev-parse --verify refs/heads/one
+'
+
+test_expect_success 'branch -d still deletes a pruneMerged=false branch' '
+	test_when_finished "rm -rf pm-optout-d" &&
+	git clone pm-upstream pm-optout-d &&
+	git -C pm-optout-d branch one --track origin/one &&
+	git -C pm-optout-d config branch.one.pruneMerged false &&
+
+	git -C pm-optout-d branch -d one &&
+	test_must_fail git -C pm-optout-d rev-parse --verify refs/heads/one
+'
+
 test_done