[PATCH] dir: use per-worktree repository ignore patterns upon request

["D. Ben Knoble" <ben.knoble+github@gmail.com>]

Today we have $GIT_DIR/info/exclude for the main worktree, but $(git
rev-parse --git-dir)/info/exclude for secondary worktrees does not
actually contribute to ignore specs; instead, secondary worktrees also
use $GIT_COMMON_DIR/info/exclude.

Some users may prefer each worktree use its own ignore file; some may
prefer both; some may prefer the current behavior.

Add, test, and document extensions.worktreeIgnore that controls which
set of ignore files to use for worktrees.

Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com>
---

Notes (benknoble/commits):
    Discussed briefly at https://lore.kernel.org/git/CALnO6CCXmA+ATT7CuyWkU6P8qmLCCpMi5Ppr1c78s0heznpVyw@mail.gmail.com/T

    This is based on next (4f69b47b94 (Merge branch 'ps/test-set-e-clean' into
    next, 2026-04-23)) but cleanly applies to master (94f057755b (Git 2.54,
    2026-04-19)) and seen (50541634cb (Merge branch
    'js/parseopt-subcommand-autocorrection' into seen, 2026-04-23)).

 Documentation/config/extensions.adoc |  7 ++++
 Documentation/git-worktree.adoc      |  3 ++
 Documentation/gitignore.adoc         |  6 ++--
 dir.c                                | 48 +++++++++++++++++++++++---
 t/meson.build                        |  1 +
 t/t2408-worktree-ignore.sh           | 50 ++++++++++++++++++++++++++++
 6 files changed, 109 insertions(+), 6 deletions(-)
 create mode 100755 t/t2408-worktree-ignore.sh

diff --git a/Documentation/config/extensions.adoc b/Documentation/config/extensions.adoc
index be6678bb5b..5bfb06a54b 100644
--- a/Documentation/config/extensions.adoc
+++ b/Documentation/config/extensions.adoc
@@ -148,3 +148,10 @@ details.
 +
 For historical reasons, this extension is respected regardless of the
 `core.repositoryFormatVersion` setting.
+
+worktreeIgnore:::
+	If enabled, then worktrees will load per-repository ignore files from
+	`$GIT_DIR/info/exclude` (that is,
+	`$GIT_COMMON_DIR/worktrees/<id>/info/exclude`). If set to `merge`, then
+	both `$GIT_COMMON_DIR/info/exclude` and `$GIT_DIR/info/exclude` are
+	used.
diff --git a/Documentation/git-worktree.adoc b/Documentation/git-worktree.adoc
index fbf8426cd9..611c1e06b0 100644
--- a/Documentation/git-worktree.adoc
+++ b/Documentation/git-worktree.adoc
@@ -412,6 +412,9 @@ linkgit:gitrepository-layout[5] for details.
 When `extensions.worktreeConfig` is enabled, the config file
 `.git/worktrees/<id>/config.worktree` is read after `.git/config` is.
 
+See `extensions.worktreeIgnore` in linkgit:git-config[1] to control how
+per-repository ignore files are found in worktrees.
+
 LIST OUTPUT FORMAT
 ------------------
 The `worktree list` command has two output formats. The default format shows the
diff --git a/Documentation/gitignore.adoc b/Documentation/gitignore.adoc
index a3d24e5c34..d6976a44e4 100644
--- a/Documentation/gitignore.adoc
+++ b/Documentation/gitignore.adoc
@@ -7,7 +7,7 @@ gitignore - Specifies intentionally untracked files to ignore
 
 SYNOPSIS
 --------
-$XDG_CONFIG_HOME/git/ignore, $GIT_DIR/info/exclude, .gitignore
+$XDG_CONFIG_HOME/git/ignore, $GIT_COMMON_DIR/info/exclude, .gitignore
 
 DESCRIPTION
 -----------
@@ -34,7 +34,9 @@ precedence, the last matching pattern decides the outcome):
    includes such `.gitignore` files in its repository, containing patterns for
    files generated as part of the project build.
 
- * Patterns read from `$GIT_DIR/info/exclude`.
+ * Patterns read from `$GIT_COMMON_DIR/info/exclude`. (See
+   `extensions.worktreeIgnore` in linkgit:git-config[1] to change how this
+   applies to worktrees.)
 
  * Patterns read from the file specified by the configuration
    variable `core.excludesFile`.
diff --git a/dir.c b/dir.c
index fcb8f6dd2a..9592eb0062 100644
--- a/dir.c
+++ b/dir.c
@@ -36,6 +36,7 @@
 #include "trace2.h"
 #include "tree.h"
 #include "hex.h"
+#include "worktree.h"
 
  /*
   * The maximum size of a pattern/exclude file. If the file exceeds this size
@@ -3478,6 +3479,23 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 }
 
 static GIT_PATH_FUNC(git_path_info_exclude, "info/exclude")
+static const char *git_worktree_info_exclude(void)
+{
+	static const char *ret;
+	if (!ret)
+	{
+		const struct worktree *wt = get_worktree_from_repository(the_repository);
+		ret = worktree_git_path(wt, "info/exclude");
+	}
+	return ret;
+}
+
+static void standard_exclude_from_info(const char *path, struct dir_struct *dir)
+{
+	struct oid_stat *oid_stat = dir->untracked ? &dir->internal.ss_info_exclude : NULL;
+	if (!access_or_warn(path, R_OK, 0))
+		add_patterns_from_file_1(dir, path, oid_stat);
+}
 
 void setup_standard_excludes(struct dir_struct *dir)
 {
@@ -3492,10 +3510,32 @@ void setup_standard_excludes(struct dir_struct *dir)
 
 	/* per repository user preference */
 	if (startup_info->have_repository) {
-		const char *path = git_path_info_exclude();
-		if (!access_or_warn(path, R_OK, 0))
-			add_patterns_from_file_1(dir, path,
-						 dir->untracked ? &dir->internal.ss_info_exclude : NULL);
+		/* extensions.worktreeIgnore determines which includes we add */
+		const char *wt_ignore;
+		int do_wt_ignore;
+		if (repo_config_get_value(the_repository,
+					  "extensions.worktreeIgnore",
+					  &wt_ignore)) {
+			/* unset: use main/.git/info/exclude */
+			standard_exclude_from_info(git_path_info_exclude(), dir);
+			return;
+		}
+		do_wt_ignore = git_parse_maybe_bool(wt_ignore);
+		if (!do_wt_ignore) {
+			/* false: as above */
+			standard_exclude_from_info(git_path_info_exclude(), dir);
+		} else if (do_wt_ignore > 0 || !strcmp(wt_ignore, "worktree")) {
+			/* true/worktree: use worktree/.git‡/info/exclude
+			 * ‡: resolving .git */
+			standard_exclude_from_info(git_worktree_info_exclude(), dir);
+		} else if (!strcmp(wt_ignore, "merge")) {
+			/* merge both! worktree last */
+			standard_exclude_from_info(git_path_info_exclude(), dir);
+			standard_exclude_from_info(git_worktree_info_exclude(), dir);
+		} else {
+			die(_("invalid value for '%s': '%s'"),
+			      "extensions.worktreeIgnore", wt_ignore);
+		}
 	}
 }
 
diff --git a/t/meson.build b/t/meson.build
index 7528e5cda5..30624b59e8 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -307,6 +307,7 @@ integration_tests = [
   't2405-worktree-submodule.sh',
   't2406-worktree-repair.sh',
   't2407-worktree-heads.sh',
+  't2408-worktree-ignore.sh',
   't2500-untracked-overwriting.sh',
   't2501-cwd-empty.sh',
   't3000-ls-files-others.sh',
diff --git a/t/t2408-worktree-ignore.sh b/t/t2408-worktree-ignore.sh
new file mode 100755
index 0000000000..67644ddd8d
--- /dev/null
+++ b/t/t2408-worktree-ignore.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+test_description='extensions.worktreeIgnore'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit init &&
+	git worktree add wt &&
+	echo main >.git/info/exclude &&
+	echo contents >main &&
+	echo contents >wt/main &&
+	wt_exclude="$(git -C wt rev-parse --git-dir)"/info/exclude &&
+	mkdir -p "$(dirname "$wt_exclude")" &&
+	echo worktree >"$wt_exclude" &&
+	echo contents >worktree &&
+	echo contents >wt/worktree
+'
+
+test_ignore_main() {
+	git check-ignore main &&
+	git -C wt check-ignore main
+}
+
+test_expect_success 'ignores main items by default' '
+	test_ignore_main
+'
+
+test_expect_success 'ignores main items with extensions.worktreeIgnore=no' '
+	test_config extensions.worktreeIgnore no &&
+	test_ignore_main
+'
+
+test_expect_success 'ignores worktree items with extensions.worktreeIgnore=worktree' '
+	test_config extensions.worktreeIgnore worktree &&
+	git check-ignore main &&
+	! git check-ignore worktree &&
+	! git -C wt check-ignore main &&
+	git -C wt check-ignore worktree
+'
+
+test_expect_success 'ignores all items with extensions.worktreeIgnore=merge' '
+	test_config extensions.worktreeIgnore merge &&
+	git check-ignore main &&
+	! git check-ignore worktree &&
+	git -C wt check-ignore main &&
+	git -C wt check-ignore worktree
+'
+
+test_done

base-commit: 4f69b47b940100b02630f745a52f9d9850f122b2
-- 
2.54.0.rc2.544.gc7ae2d5bb8.dirty