Merge branch 'jc/maint-rerere-in-workdir'

* jc/maint-rerere-in-workdir:
  rerere: make sure it works even in a workdir attached to a young repository

cache.h

@@ -726,6 +726,7 @@ int set_shared_perm(const char *path, int mode);
 #define adjust_shared_perm(path) set_shared_perm((path), 0)
 int safe_create_leading_directories(char *path);
 int safe_create_leading_directories_const(const char *path);
+int mkdir_in_gitdir(const char *path);
 extern char *expand_user_path(const char *path);
 char *enter_repo(char *path, int strict);
 static inline int is_absolute_path(const char *path)

rerere.c

@@ -590,8 +590,7 @@ static int is_rerere_enabled(void)
 	if (rerere_enabled < 0)
 		return rr_cache_exists;
 
-	if (!rr_cache_exists &&
-	    (mkdir(rr_cache, 0777) || adjust_shared_perm(rr_cache)))
+	if (!rr_cache_exists && mkdir_in_gitdir(rr_cache))
 		die("Could not create directory %s", rr_cache);
 	return 1;
 }

sha1_file.c

@@ -68,6 +68,35 @@ static struct cached_object *find_cached_object(const unsigned char *sha1)
 	return NULL;
 }
 
+int mkdir_in_gitdir(const char *path)
+{
+	if (mkdir(path, 0777)) {
+		int saved_errno = errno;
+		struct stat st;
+		struct strbuf sb = STRBUF_INIT;
+
+		if (errno != EEXIST)
+			return -1;
+		/*
+		 * Are we looking at a path in a symlinked worktree
+		 * whose original repository does not yet have it?
+		 * e.g. .git/rr-cache pointing at its original
+		 * repository in which the user hasn't performed any
+		 * conflict resolution yet?
+		 */
+		if (lstat(path, &st) || !S_ISLNK(st.st_mode) ||
+		    strbuf_readlink(&sb, path, st.st_size) ||
+		    !is_absolute_path(sb.buf) ||
+		    mkdir(sb.buf, 0777)) {
+			strbuf_release(&sb);
+			errno = saved_errno;
+			return -1;
+		}
+		strbuf_release(&sb);
+	}
+	return adjust_shared_perm(path);
+}
+
 int safe_create_leading_directories(char *path)
 {
 	char *pos = path + offset_1st_component(path);

t/t1021-rerere-in-workdir.sh

@@ -0,0 +1,55 @@
+#!/bin/sh
+
+test_description='rerere run in a workdir'
+. ./test-lib.sh
+
+test_expect_success SYMLINKS setup '
+	git config rerere.enabled true &&
+	>world &&
+	git add world &&
+	test_tick &&
+	git commit -m initial &&
+
+	echo hello >world &&
+	test_tick &&
+	git commit -a -m hello &&
+
+	git checkout -b side HEAD^ &&
+	echo goodbye >world &&
+	test_tick &&
+	git commit -a -m goodbye &&
+
+	git checkout master
+'
+
+test_expect_success SYMLINKS 'rerere in workdir' '
+	rm -rf .git/rr-cache &&
+	"$SHELL_PATH" "$TEST_DIRECTORY/../contrib/workdir/git-new-workdir" . work &&
+	(
+		cd work &&
+		test_must_fail git merge side &&
+		git rerere status >actual &&
+		echo world >expect &&
+		test_cmp expect actual
+	)
+'
+
+# This fails because we don't resolve relative symlink in mkdir_in_gitdir()
+# For the purpose of helping contrib/workdir/git-new-workdir users, we do not
+# have to support relative symlinks, but it might be nicer to make this work
+# with a relative symbolic link someday.
+test_expect_failure SYMLINKS 'rerere in workdir (relative)' '
+	rm -rf .git/rr-cache &&
+	"$SHELL_PATH" "$TEST_DIRECTORY/../contrib/workdir/git-new-workdir" . krow &&
+	(
+		cd krow &&
+		rm -f .git/rr-cache &&
+		ln -s ../.git/rr-cache .git/rr-cache &&
+		test_must_fail git merge side &&
+		git rerere status >actual &&
+		echo world >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_done