diff: do not short-cut CHECK_SIZE_ONLY check in diff_populate_filespec()

Callers of diff_populate_filespec() can choose to ask only for the
size of the blob without grabbing the blob data, and the function,
after running lstat() when the filespec points at a working tree
file, returns by copying the value in size field of the stat
structure into the size field of the filespec when this is the case.

However, this short-cut cannot be taken if the contents from the
path needs to go through convert_to_git(), whose resulting real blob
data may be different from what is in the working tree file.

As "git diff --quiet" compares the .size fields of filespec
structures to skip content comparison, this bug manifests as a
false "there are differences" for a file that needs eol conversion,
for example.

Reported-by: Mike Crowe <mac@mcrowe.com>
Helped-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/t/t4035-diff-quiet.sh b/t/t4035-diff-quiet.sh
index 461f4bb58..2f1737fce 100755
--- a/t/t4035-diff-quiet.sh
+++ b/t/t4035-diff-quiet.sh
@@ -152,4 +152,13 @@ test_expect_success 'git diff --quiet ignores stat-change only entries' '
 	test_expect_code 1 git diff --quiet
 '
 
+test_expect_success 'git diff --quiet on a path that need conversion' '
+	echo "crlf.txt text=auto" >.gitattributes &&
+	printf "Hello\r\nWorld\r\n" >crlf.txt &&
+	git add .gitattributes crlf.txt &&
+
+	printf "Hello\r\nWorld\n" >crlf.txt &&
+	git diff --quiet crlf.txt
+'
+
 test_done