git-apply: handle a patch that touches the same path more than once better

When working with a lot of people who backport patches all day long, every
once in a while I get a patch that modifies the same file more than once
inside the same patch.  git-apply either fails if the second change relies
on the first change or silently drops the first change if the second change
is independent.

The silent part is the scary scenario for us.  Also this behaviour is
different from the patch-utils.

I have modified git-apply to create a table of the filenames of files it
modifies such that if a later patch chunk modifies a file in the table it
will buffer the previously changed file instead of reading the original file
from disk.

Logic has been put in to handle creations/deletions/renames/copies.  All the
relevant tests of git-apply succeed.

A new test has been added to cover the cases I addressed.

The fix is relatively straight-forward.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/t/t4127-apply-same-fn.sh b/t/t4127-apply-same-fn.sh
new file mode 100755
index 000000000..2a6ed77c6
--- /dev/null
+++ b/t/t4127-apply-same-fn.sh
@@ -0,0 +1,85 @@
+#!/bin/sh
+
+test_description='apply same filename'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	for i in a b c d e f g h i j k l m
+	do
+		echo $i
+	done >same_fn &&
+	cp same_fn other_fn &&
+	git add same_fn other_fn &&
+	git commit -m initial
+'
+test_expect_success 'apply same filename with independent changes' '
+	sed -i -e "s/^d/z/" same_fn &&
+	git diff > patch0 &&
+	git add same_fn &&
+	sed -i -e "s/^i/y/" same_fn &&
+	git diff >> patch0 &&
+	cp same_fn same_fn2 &&
+	git reset --hard &&
+	git-apply patch0 &&
+	diff same_fn same_fn2
+'
+
+test_expect_success 'apply same filename with overlapping changes' '
+	git reset --hard
+	sed -i -e "s/^d/z/" same_fn &&
+	git diff > patch0 &&
+	git add same_fn &&
+	sed -i -e "s/^e/y/" same_fn &&
+	git diff >> patch0 &&
+	cp same_fn same_fn2 &&
+	git reset --hard &&
+	git-apply patch0 &&
+	diff same_fn same_fn2
+'
+
+test_expect_success 'apply same new filename after rename' '
+	git reset --hard
+	git mv same_fn new_fn
+	sed -i -e "s/^d/z/" new_fn &&
+	git add new_fn &&
+	git diff -M --cached > patch1 &&
+	sed -i -e "s/^e/y/" new_fn &&
+	git diff >> patch1 &&
+	cp new_fn new_fn2 &&
+	git reset --hard &&
+	git apply --index patch1 &&
+	diff new_fn new_fn2
+'
+
+test_expect_success 'apply same old filename after rename -- should fail.' '
+	git reset --hard
+	git mv same_fn new_fn
+	sed -i -e "s/^d/z/" new_fn &&
+	git add new_fn &&
+	git diff -M --cached > patch1 &&
+	git mv new_fn same_fn
+	sed -i -e "s/^e/y/" same_fn &&
+	git diff >> patch1 &&
+	git reset --hard &&
+	test_must_fail git apply patch1
+'
+
+test_expect_success 'apply A->B (rename), C->A (rename), A->A -- should pass.' '
+	git reset --hard
+	git mv same_fn new_fn
+	sed -i -e "s/^d/z/" new_fn &&
+	git add new_fn &&
+	git diff -M --cached > patch1 &&
+	git commit -m "a rename" &&
+	git mv other_fn same_fn
+	sed -i -e "s/^e/y/" same_fn &&
+	git add same_fn &&
+	git diff -M --cached >> patch1 &&
+	sed -i -e "s/^g/x/" same_fn &&
+	git diff >> patch1 &&
+	git reset --hard HEAD^ &&
+	git apply patch1
+'
+
+test_done