fetch: add a failing test for prunning with overlapping refspecs

When a remote has multiple fetch refspecs and these overlap in the
target namespace, fetch may prune a remote-tracking branch which still
exists in the remote. The test uses a popular form of this, by putting
pull requests as stored in a popular hosting platform alongside "real"
remote-tracking branches.

The fetch command makes a decision of whether to prune based
on the first matching refspec, which in this case is insufficient, as it
covers the pull request names. This pair of refspecs does work as
expected if the more "specific" refspec is the first in the list.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5510-fetch.sh

@@ -113,6 +113,26 @@ test_expect_success 'fetch --prune with a namespace keeps other namespaces' '
 	git rev-parse origin/master
 '
 
+test_expect_failure 'fetch --prune handles overlapping refspecs' '
+	cd "$D" &&
+	git update-ref refs/pull/42/head master &&
+	git clone . prune-overlapping &&
+	cd prune-overlapping &&
+	git config --add remote.origin.fetch refs/pull/*/head:refs/remotes/origin/pr/* &&
+
+	git fetch --prune origin &&
+	git rev-parse origin/master &&
+	git rev-parse origin/pr/42 &&
+
+	git config --unset-all remote.origin.fetch
+	git config remote.origin.fetch refs/pull/*/head:refs/remotes/origin/pr/* &&
+	git config --add remote.origin.fetch refs/heads/*:refs/remotes/origin/* &&
+
+	git fetch --prune origin &&
+	git rev-parse origin/master &&
+	git rev-parse origin/pr/42
+'
+
 test_expect_success 'fetch --prune --tags does not delete the remote-tracking branches' '
 	cd "$D" &&
 	git clone . prune-tags &&