[PATCH] pathspec: give better message for submodule related pathspec error

[Stefan Beller <sbeller@google.com>]

Every once in a while someone complains to the mailing list to have
run into this weird assertion[1].

The usual response from the mailing list is link to old discussions[2],
and acknowledging the problem stating it is known.

For now just improve the user visible error message.

[1] https://www.google.com/search?q=item-%3Enowildcard_len
[2] http://git.661346.n2.nabble.com/assert-failed-in-submodule-edge-case-td7628687.html
    https://www.spinics.net/lists/git/msg249473.html

Signed-off-by: Stefan Beller <sbeller@google.com>
---

 * a more defensive check and message
 * with tests!
 
 pathspec.c                       | 19 +++++++++++++++++--
 t/t6134-pathspec-in-submodule.sh | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 2 deletions(-)
 create mode 100755 t/t6134-pathspec-in-submodule.sh

diff --git a/pathspec.c b/pathspec.c
index 22ca74a126..b446d79615 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -313,8 +313,23 @@ static unsigned prefix_pathspec(struct pathspec_item *item,
 	}
 
 	/* sanity checks, pathspec matchers assume these are sane */
-	assert(item->nowildcard_len <= item->len &&
-	       item->prefix         <= item->len);
+	if (item->nowildcard_len > item->len ||
+	    item->prefix         > item->len) {
+		/* Historically this always was a submodule issue */
+		for (i = 0; i < active_nr; i++) {
+			struct cache_entry *ce = active_cache[i];
+			int ce_len = ce_namelen(ce);
+			int len = ce_len < item->len ? ce_len : item->len;
+			if (!S_ISGITLINK(ce->ce_mode))
+				continue;
+			if (!memcmp(ce->name, item->match, len))
+				die (_("Pathspec '%s' is in submodule '%.*s'"),
+					item->original, ce_len, ce->name);
+		}
+		/* The error is a new unknown bug */
+		die ("BUG: item->nowildcard_len > item->len || item->prefix > item->len)");
+	}
+
 	return magic;
 }
 
diff --git a/t/t6134-pathspec-in-submodule.sh b/t/t6134-pathspec-in-submodule.sh
new file mode 100755
index 0000000000..e62dbb7327
--- /dev/null
+++ b/t/t6134-pathspec-in-submodule.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+test_description='test case exclude pathspec'
+
+. ./test-lib.sh
+
+test_expect_success 'setup a submodule' '
+	test_commit 1 &&
+	git submodule add ./ sub &&
+	git commit -a -m "add submodule" &&
+	git submodule deinit --all
+'
+
+cat <<EOF >expect
+fatal: Pathspec 'sub/a' is in submodule 'sub'
+EOF
+
+test_expect_success 'error message for path inside submodule' '
+	echo a >sub/a &&
+	test_must_fail git add sub/a 2>actual &&
+	test_cmp expect actual
+'
+
+cat <<EOF >expect
+fatal: Pathspec '.' is in submodule 'sub'
+EOF
+
+test_expect_success 'error message for path inside submodule from within submodule' '
+	test_must_fail git -C sub add . 2>actual &&
+	test_cmp expect actual
+'
+
+test_done
-- 
2.11.0.259.ga95e92af08.dirty