check_path(): allow symlinked directories to checkout-index --prefix

Merlyn noticed that Documentation/install-doc-quick.sh no longer correctly
removes old installed documents when the target directory has a leading
path that is a symlink.  It turns out that "checkout-index --prefix" was
broken by recent b6986d8 (git-checkout: be careful about untracked
symlinks, 2009-07-29).

I suspect has_symlink_leading_path() could learn the third parameter
(prefix that is allowed to be symlinked directories) to allow us to retire
a similar function has_dirs_only_path().

Another avenue of fixing this I considered was to get rid of base_dir and
base_dir_len from "struct checkout", and instead make "git checkout-index"
when run with --prefix mkdir the leading path and chdir in there.  It
might be the best longer term solution to this issue, as the base_dir
feature is used only by that rather obscure codepath as far as I know.

But at least this patch should fix this breakage.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -469,7 +469,7 @@ extern int index_path(unsigned char *sha1, const char *path, struct stat *st, in
 extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 
 /* "careful lstat()" */
-extern int check_path(const char *path, int len, struct stat *st);
+extern int check_path(const char *path, int len, struct stat *st, int skiplen);
 
 #define REFRESH_REALLY		0x0001	/* ignore_valid */
 #define REFRESH_UNMERGED	0x0002	/* allow unmerged */

entry.c

@@ -177,11 +177,15 @@ static int write_entry(struct cache_entry *ce, char *path, const struct checkout
 
 /*
  * This is like 'lstat()', except it refuses to follow symlinks
- * in the path.
+ * in the path, after skipping "skiplen".
  */
-int check_path(const char *path, int len, struct stat *st)
+int check_path(const char *path, int len, struct stat *st, int skiplen)
 {
-	if (has_symlink_leading_path(path, len)) {
+	const char *slash = path + len;
+
+	while (path < slash && *slash != '/')
+		slash--;
+	if (!has_dirs_only_path(path, slash - path, skiplen)) {
 		errno = ENOENT;
 		return -1;
 	}
@@ -201,7 +205,7 @@ int checkout_entry(struct cache_entry *ce, const struct checkout *state, char *t
 	strcpy(path + len, ce->name);
 	len += ce_namelen(ce);
 
-	if (!check_path(path, len, &st)) {
+	if (!check_path(path, len, &st, state->base_dir_len)) {
 		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID);
 		if (!changed)
 			return 0;

t/t2000-checkout-cache-clash.sh

@@ -48,4 +48,13 @@ test_expect_success \
     'git checkout-index conflicting paths.' \
     'test -f path0 && test -d path1 && test -f path1/file1'
 
+test_expect_success SYMLINKS 'checkout-index -f twice with --prefix' '
+	mkdir -p tar/get &&
+	ln -s tar/get there &&
+	echo first &&
+	git checkout-index -a -f --prefix=there/ &&
+	echo second &&
+	git checkout-index -a -f --prefix=there/
+'
+
 test_done