Teach read-tree the -n|--dry-run option

The option can be used to check if read-tree with the same set of other
options like "-m" and "-u" would succeed without actually changing either
the index or the working tree.

The relevant tests in the t10?? range were extended to do a read-tree -n
before the real read-tree to make sure neither the index nor any local
files were changed with -n and the same exit code as without -n is
returned. The helper functions added for that purpose reside in the new
t/lib-read-tree.sh file.

The only exception is #13 in t1004 ("unlinking an un-unlink-able
symlink"). As this is an issue of wrong directory permissions it is not
detected with -n.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/t/lib-read-tree.sh b/t/lib-read-tree.sh
new file mode 100644
index 0000000000..abc2c6f57f
--- /dev/null
+++ b/t/lib-read-tree.sh
@@ -0,0 +1,43 @@
+#!/bin/sh
+#
+# Helper functions to check if read-tree would succeed/fail as expected with
+# and without the dry-run option. They also test that the dry-run does not
+# write the index and that together with -u it doesn't touch the work tree.
+#
+read_tree_must_succeed () {
+    git ls-files -s >pre-dry-run &&
+    git read-tree -n "$@" &&
+    git ls-files -s >post-dry-run &&
+    test_cmp pre-dry-run post-dry-run &&
+    git read-tree "$@"
+}
+
+read_tree_must_fail () {
+    git ls-files -s >pre-dry-run &&
+    test_must_fail git read-tree -n "$@" &&
+    git ls-files -s >post-dry-run &&
+    test_cmp pre-dry-run post-dry-run &&
+    test_must_fail git read-tree "$@"
+}
+
+read_tree_u_must_succeed () {
+    git ls-files -s >pre-dry-run &&
+    git diff-files -p >pre-dry-run-wt &&
+    git read-tree -n "$@" &&
+    git ls-files -s >post-dry-run &&
+    git diff-files -p >post-dry-run-wt &&
+    test_cmp pre-dry-run post-dry-run &&
+    test_cmp pre-dry-run-wt post-dry-run-wt &&
+    git read-tree "$@"
+}
+
+read_tree_u_must_fail () {
+    git ls-files -s >pre-dry-run &&
+    git diff-files -p >pre-dry-run-wt &&
+    test_must_fail git read-tree -n "$@" &&
+    git ls-files -s >post-dry-run &&
+    git diff-files -p >post-dry-run-wt &&
+    test_cmp pre-dry-run post-dry-run &&
+    test_cmp pre-dry-run-wt post-dry-run-wt &&
+    test_must_fail git read-tree "$@"
+}