fix bogus "diff --git" header from "diff --no-index"

When "git diff --no-index" is given an absolute pathname, it
would generate a diff header with the absolute path
prepended by the prefix, like:

diff --git a/dev/null b/foo

Not only is this nonsensical, and not only does it violate
the description of diffs given in git-diff(1), but it would
produce broken binary diffs. Unlike text diffs, the binary
diffs don't contain the filenames anywhere else, and so "git
apply" relies on this header to figure out the filename.

This patch just refuses to use an invalid name for anything
visible in the diff.

Now, this fixes the "git diff --no-index --binary a
/dev/null" kind of case (and we'll end up using "a" as the
basename), but some other insane cases are impossible to
handle. If you do

git diff --no-index --binary a /bin/echo

you'll still get a patch like

diff --git a/a b/bin/echo
old mode 100644
new mode 100755
index ...

and "git apply" will refuse to apply it for a couple of
reasons, and the diff is simply bogus.

And that, btw, is no longer a bug, I think. It's impossible
to know whethe the user meant for the patch to be a rename
or not. And as such, refusing to apply it because you don't
know what name you should use is probably _exactly_ the
right thing to do!

Original problem reported by Imre Deak. Test script and problem
description by Jeff King.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/diff.c b/diff.c
index 781fa15ac13ce11f8b77b95665659cfcbcab5836..f91f256c56e5e4be0b3f162695e1d35e63124569 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -1465,6 +1465,10 @@ static void builtin_diff(const char *name_a,
        const char *set = diff_get_color_opt(o, DIFF_METAINFO);
        const char *reset = diff_get_color_opt(o, DIFF_RESET);
 
+       /* Never use a non-valid filename anywhere if at all possible */
+       name_a = DIFF_FILE_VALID(one) ? name_a : name_b;
+       name_b = DIFF_FILE_VALID(two) ? name_b : name_a;
+
        a_one = quote_two(o->a_prefix, name_a + (*name_a == '/'));
        b_two = quote_two(o->b_prefix, name_b + (*name_b == '/'));
        lbl[0] = DIFF_FILE_VALID(one) ? a_one : "/dev/null";

diff --git a/t/t4012-diff-binary.sh b/t/t4012-diff-binary.sh
index 64c372a025bd78afc3d3a2ce13543561f9c97706..eac12712dbcf7a9f59c6c8ae0e5772b19662ab8a 100755 (executable)
--- a/t/t4012-diff-binary.sh
+++ b/t/t4012-diff-binary.sh
@@ -77,4 +77,25 @@ test_expect_success 'apply binary patch' \
         tree1=`git write-tree` &&
         test "$tree1" = "$tree0"'
 
+q_to_nul() {
+       perl -pe 'y/Q/\000/'
+}
+
+nul_to_q() {
+       perl -pe 'y/\000/Q/'
+}
+
+test_expect_success 'diff --no-index with binary creation' '
+       echo Q | q_to_nul >binary &&
+       (:# hide error code from diff, which just indicates differences
+        git diff --binary --no-index /dev/null binary >current ||
+        true
+       ) &&
+       rm binary &&
+       git apply --binary <current &&
+       echo Q >expected &&
+       nul_to_q <binary >actual &&
+       test_cmp expected actual
+'
+
 test_done