[PATCH v1 1/1] git diff --quiet exits with 1 on clean tree with CRLF conversions

[tboegi@web.de]

From: Junio C Hamano <gitster@pobox.com>

git diff --quiet may take a short-cut to see if a file is changed
in the working tree:
Whenever the file size differs from what is recorded in the index,
the file is assumed to be changed and git diff --quiet returns
exit with code 1

This shortcut must be suppressed whenever the line endings are converted
or a filter is in use.
The attributes say "* text=auto" and a file has
"Hello\nWorld\n" in the index with a length of 12.
The file in the working tree has "Hello\r\nWorld\r\n" with a length of 14.
(Or even "Hello\r\nWorld\n").
In this case "git add" will not do any changes to the index, and
"git diff -quiet" should exit 0.

Add calls to would_convert_to_git() before blindly saying that a different
size means different content.

Reported-By: Mike Crowe <mac@mcrowe.com>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
---
This is what I can come up with, collecting all the loose ends.
I'm not sure if Mike wan't to have the Reported-By with a
Signed-off-by ?
The other question is, if the commit message summarizes the discussion
well enough ?

diff.c                    | 18 ++++++++++++++----
 t/t0028-diff-converted.sh | 27 +++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)
 create mode 100755 t/t0028-diff-converted.sh

diff --git a/diff.c b/diff.c
index 051761b..c264758 100644
--- a/diff.c
+++ b/diff.c
@@ -4921,9 +4921,10 @@ static int diff_filespec_check_stat_unmatch(struct diff_filepair *p)
 	 *    differences.
 	 *
 	 * 2. At this point, the file is known to be modified,
-	 *    with the same mode and size, and the object
-	 *    name of one side is unknown.  Need to inspect
-	 *    the identical contents.
+	 *    with the same mode and size, the object
+	 *    name of one side is unknown, or size comparison
+	 *    cannot be depended upon.  Need to inspect the
+	 *    contents.
 	 */
 	if (!DIFF_FILE_VALID(p->one) || /* (1) */
 	    !DIFF_FILE_VALID(p->two) ||
@@ -4931,7 +4932,16 @@ static int diff_filespec_check_stat_unmatch(struct diff_filepair *p)
 	    (p->one->mode != p->two->mode) ||
 	    diff_populate_filespec(p->one, CHECK_SIZE_ONLY) ||
 	    diff_populate_filespec(p->two, CHECK_SIZE_ONLY) ||
-	    (p->one->size != p->two->size) ||
+
+	    /*
+	     * only if eol and other conversions are not involved,
+	     * we can say that two contents of different sizes
+	     * cannot be the same without checking their contents.
+	     */
+	    (!would_convert_to_git(p->one->path) &&
+	     !would_convert_to_git(p->two->path) &&
+	     (p->one->size != p->two->size)) ||
+
 	    !diff_filespec_is_identical(p->one, p->two)) /* (2) */
 		p->skip_stat_unmatch_result = 1;
 	return p->skip_stat_unmatch_result;
diff --git a/t/t0028-diff-converted.sh b/t/t0028-diff-converted.sh
new file mode 100755
index 0000000..3d5ab95
--- /dev/null
+++ b/t/t0028-diff-converted.sh
@@ -0,0 +1,27 @@
+#!/bin/sh
+#
+# Copyright (c) 2017 Mike Crowe
+#
+# These tests ensure that files changing line endings in the presence
+# of .gitattributes to indicate that line endings should be ignored
+# don't cause 'git diff' or 'git diff --quiet' to think that they have
+# been changed.
+
+test_description='git diff with files that require CRLF conversion'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo "* text=auto" >.gitattributes &&
+	printf "Hello\r\nWorld\r\n" >crlf.txt &&
+	git add .gitattributes crlf.txt &&
+	git commit -m "initial"
+'
+
+test_expect_success 'quiet diff works on file with line-ending change that has no effect on repository' '
+	printf "Hello\r\nWorld\n" >crlf.txt &&
+	git status &&
+	git diff --quiet
+'
+
+test_done
-- 
2.10.0