config: match both symlink & realpath versions in IncludeIf.gitdir:*

Change the conditional inclusion mechanism to support
e.g. gitdir:~/git_tree/repo where ~/git_tree is a symlink to
/mnt/stuff/repo.

This worked in the initial version of this facility[1], but regressed
later in the series while solving a related bug[2].

Now gitdir: will match against the symlinked
path (e.g. gitdir:~/git_tree/repo) in addition to the current
/mnt/stuff/repo path.

Since this is already in a release version note in the documentation
that this behavior changed, so users who expect their configuration to
work on both v2.13.0 and some future version of git with this fix
aren't utterly confused.

1. commit 3efd0bedc6 ("config: add conditional include", 2017-03-01)
2. commit 86f9515708 ("config: resolve symlinks in conditional
   include's patterns", 2017-04-05)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -140,6 +140,16 @@ A few more notes on matching via `gitdir` and `gitdir/i`:
 
  * Symlinks in `$GIT_DIR` are not resolved before matching.
 
+ * Both the symlink & realpath versions of paths will be matched
+   outside of `$GIT_DIR`. E.g. if ~/git is a symlink to
+   /mnt/storage/git, both `gitdir:~/git` and `gitdir:/mnt/storage/git`
+   will match.
++
+This was not the case in the initial release of this feature in
+v2.13.0, which only matched the realpath version. Configuration that
+wants to be compatible with the initial release of this feature needs
+to either specify only the realpath version, or both versions.
+
  * Note that "../" is not special and will match literally, which is
    unlikely what you want.
 

config.c

@@ -214,6 +214,7 @@ static int include_by_gitdir(const struct config_options *opts,
 	struct strbuf pattern = STRBUF_INIT;
 	int ret = 0, prefix;
 	const char *git_dir;
+	int already_tried_absolute = 0;
 
 	if (opts->git_dir)
 		git_dir = opts->git_dir;
@@ -226,6 +227,7 @@ static int include_by_gitdir(const struct config_options *opts,
 	strbuf_add(&pattern, cond, cond_len);
 	prefix = prepare_include_condition_pattern(&pattern);
 
+again:
 	if (prefix < 0)
 		goto done;
 
@@ -245,6 +247,20 @@ static int include_by_gitdir(const struct config_options *opts,
 	ret = !wildmatch(pattern.buf + prefix, text.buf + prefix,
 			 icase ? WM_CASEFOLD : 0, NULL);
 
+	if (!ret && !already_tried_absolute) {
+		/*
+		 * We've tried e.g. matching gitdir:~/work, but if
+		 * ~/work is a symlink to /mnt/storage/work
+		 * strbuf_realpath() will expand it, so the rule won't
+		 * match. Let's match against a
+		 * strbuf_add_absolute_path() version of the path,
+		 * which'll do the right thing
+		 */
+		strbuf_reset(&text);
+		strbuf_add_absolute_path(&text, git_dir);
+		already_tried_absolute = 1;
+		goto again;
+	}
 done:
 	strbuf_release(&pattern);
 	strbuf_release(&text);

t/t1305-config-include.sh

@@ -273,6 +273,29 @@ test_expect_success SYMLINKS 'conditional include, relative path with symlinks'
 	)
 '
 
+test_expect_success SYMLINKS 'conditional include, gitdir matching symlink' '
+	ln -s foo bar &&
+	(
+		cd bar &&
+		echo "[includeIf \"gitdir:bar/\"]path=bar7" >>.git/config &&
+		echo "[test]seven=7" >.git/bar7 &&
+		echo 7 >expect &&
+		git config test.seven >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success SYMLINKS 'conditional include, gitdir matching symlink, icase' '
+	(
+		cd bar &&
+		echo "[includeIf \"gitdir/i:BAR/\"]path=bar8" >>.git/config &&
+		echo "[test]eight=8" >.git/bar8 &&
+		echo 8 >expect &&
+		git config test.eight >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig