[RFC PATCH] dir: add discoverable local-only .gitlocalignore

Documentation/config/core.adoc

@@ -493,6 +493,15 @@ core.excludesFile::
 	If `$XDG_CONFIG_HOME` is either not set or empty, `$HOME/.config/git/ignore`
 	is used instead. See linkgit:gitignore[5].
 
+core.gitLocalIgnore::
+	If set to `true`, Git additionally reads ignore patterns from
+	a file named `.gitlocalignore` at the root of the working tree.
+	This file is meant for machine-local, uncommitted ignore rules:
+	it is ignored by Git itself (self-excluding) and is never tracked.
+	Its patterns are applied with lower precedence than
+	`.git/info/exclude` but higher than `core.excludesFile`.
+	Defaults to `false`. See linkgit:gitignore[5].
+
 core.askPass::
 	Some commands (e.g. svn and http interfaces) that interactively
 	ask for a password can be told to use an external program given

Documentation/gitignore.adoc

@@ -7,7 +7,7 @@ gitignore - Specifies intentionally untracked files to ignore
 
 SYNOPSIS
 --------
-$XDG_CONFIG_HOME/git/ignore, $GIT_COMMON_DIR/info/exclude, .gitignore
+$XDG_CONFIG_HOME/git/ignore, $GIT_COMMON_DIR/info/exclude, .gitignore, .gitlocalignore
 
 DESCRIPTION
 -----------
@@ -34,10 +34,17 @@ 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 `$GIT_COMMON_DIR/info/exclude`.
+  * Patterns read from `$GIT_COMMON_DIR/info/exclude`.
 
- * Patterns read from the file specified by the configuration
-   variable `core.excludesFile`.
+  * Patterns read from a `.gitlocalignore` file at the root of the
+    working tree, but only when the `core.gitLocalIgnore` configuration
+    variable is enabled (it is `false` by default). This file is intended
+    for machine-local, uncommitted ignore rules: Git ignores the file
+    itself (self-excluding) and never tracks it. Its precedence is below
+    `$GIT_COMMON_DIR/info/exclude` but above `core.excludesFile`.
+
+  * Patterns read from the file specified by the configuration
+    variable `core.excludesFile`.
 
 Which file to place a pattern in depends on how the pattern is meant to
 be used.
@@ -57,7 +64,15 @@ be used.
    the user's editor of choice) generally go into a file specified by
    `core.excludesFile` in the user's `~/.gitconfig`. Its default value is
    $XDG_CONFIG_HOME/git/ignore. If $XDG_CONFIG_HOME is either not set or
-   empty, $HOME/.config/git/ignore is used instead.
+    empty, $HOME/.config/git/ignore is used instead.
+
+  * Patterns which apply only to your local machine and which you do
+    not want to share or commit (e.g., paths that exist only in your
+    checkout) can go into a `.gitlocalignore` file at the root of the
+    working tree, once `core.gitLocalIgnore` is enabled. Unlike the
+    other files above, `.gitlocalignore` is ignored by Git itself and
+    will never be tracked or pushed.
+
 
 The underlying Git plumbing tools, such as
 'git ls-files' and 'git read-tree', read

dir.c

@@ -3490,6 +3490,35 @@ void setup_standard_excludes(struct dir_struct *dir)
 		add_patterns_from_file_1(dir, excludes_file,
 					 dir->untracked ? &dir->internal.ss_excludes_file : NULL);
 
+	/*
+	 * .gitlocalignore: a discoverable, local-only ignore file at the
+	 * worktree root, gated on core.gitLocalIgnore (off by default, to
+	 * avoid surprising repositories that already contain a file with
+	 * this name). Read here, between core.excludesFile and
+	 * info/exclude, so its precedence ranks below info/exclude but
+	 * above core.excludesFile.
+	 */
+	if (startup_info->have_repository) {
+		int git_local_ignore = 0;
+		if (repo_config_get_bool(the_repository, "core.gitLocalIgnore",
+				&git_local_ignore) >= 0 && git_local_ignore) {
+			const char *wt = the_repository->worktree;
+			if (wt) {
+				char *gl_path = mkpathdup("%s/.gitlocalignore", wt);
+				if (!access_or_warn(gl_path, R_OK, 0))
+					add_patterns_from_file_1(dir, gl_path, NULL);
+				{
+					struct pattern_list *self =
+						add_pattern_list(dir, EXC_CMDL,
+								 ".gitlocalignore");
+						add_pattern(".gitlocalignore", "", 0,
+							   self, -1);
+					}
+				dir->internal.unmanaged_exclude_files++;
+			}
+		}
+	}
+
 	/* per repository user preference */
 	if (startup_info->have_repository) {
 		const char *path = git_path_info_exclude();

t/meson.build

@@ -84,6 +84,7 @@ integration_tests = [
   't0008-ignores.sh',
   't0009-git-dir-validation.sh',
   't0010-racy-git.sh',
+  't0011-gitlocalignore.sh',
   't0012-help.sh',
   't0013-sha1dc.sh',
   't0014-alias.sh',

t/t0011-gitlocalignore.sh

@@ -0,0 +1,73 @@
+#!/bin/sh
+
+test_description='.gitlocalignore support (core.gitLocalIgnore)'
+
+TEST_PASSES_SANITIZE_LEAK=true
+. ./test-lib.sh
+
+# off by default: .gitlocalignore is not consulted at all
+test_expect_success 'off by default: .gitlocalignore is ignored' '
+	echo content >a.txt &&
+	printf "a.txt\n" >.gitlocalignore &&
+	test_must_fail git check-ignore a.txt
+'
+
+test_expect_success 'core.gitLocalIgnore enables .gitlocalignore' '
+	test_config core.gitLocalIgnore true &&
+	echo content >b.txt &&
+	printf "b.txt\n" >.gitlocalignore &&
+	git check-ignore b.txt
+'
+
+test_expect_success '.gitlocalignore is self-excluding' '
+	test_config core.gitLocalIgnore true &&
+	printf "b.txt\n" >.gitlocalignore &&
+	git check-ignore .gitlocalignore
+'
+
+test_expect_success 'info/exclude outranks .gitlocalignore' '
+	test_config core.gitLocalIgnore true &&
+	mkdir -p .git/info &&
+	echo "c.txt" >.git/info/exclude &&
+	echo content >c.txt &&
+	printf "c.txt\n" >.gitlocalignore &&
+	git check-ignore -v c.txt >out &&
+	grep "info/exclude" out
+'
+
+test_expect_success '.gitlocalignore outranks core.excludesFile' '
+	test_config core.gitLocalIgnore true &&
+	echo content >d.txt &&
+	printf "d.txt\n" >.gitlocalignore &&
+	echo "d.txt" >.git/excludes-extra &&
+	test_config core.excludesFile "$(pwd)/.git/excludes-extra" &&
+	git check-ignore -v d.txt >out &&
+	grep "\.gitlocalignore" out
+'
+
+test_expect_success 'nested .gitlocalignore contents are not read' '
+	test_config core.gitLocalIgnore true &&
+	rm -f .gitlocalignore &&
+	mkdir -p sub &&
+	echo content >sub/e.txt &&
+	printf "e.txt\n" >sub/.gitlocalignore &&
+	test_must_fail git check-ignore sub/e.txt
+'
+
+test_expect_success 'ignored files stay out of git status' '
+	test_config core.gitLocalIgnore true &&
+	echo content >f.txt &&
+	printf "f.txt\n" >.gitlocalignore &&
+	git status --porcelain >out &&
+	! grep f.txt out
+'
+
+test_expect_success 'git add refuses .gitlocalignore unless forced' '
+	test_config core.gitLocalIgnore true &&
+	printf "f.txt\n" >.gitlocalignore &&
+	test_must_fail git add .gitlocalignore &&
+	git add -f .gitlocalignore &&
+	git ls-files --error-unmatch .gitlocalignore
+'
+
+test_done