Smudge the files fed to external diff and textconv

When preparing temporary files for an external diff or textconv, it is
easier on the external tools, especially when they are implemented using
platform tools, if they are fed the input after convert_to_working_tree().

This fixes msysGit issue 177.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -1948,24 +1948,31 @@ void diff_free_filespec_data(struct diff_filespec *s)
 	s->cnt_data = NULL;
 }
 
-static void prep_temp_blob(struct diff_tempfile *temp,
+static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
 			   void *blob,
 			   unsigned long size,
 			   const unsigned char *sha1,
 			   int mode)
 {
 	int fd;
+	struct strbuf buf = STRBUF_INIT;
 
 	fd = git_mkstemp(temp->tmp_path, PATH_MAX, ".diff_XXXXXX");
 	if (fd < 0)
 		die("unable to create temp-file: %s", strerror(errno));
+	if (convert_to_working_tree(path,
+			(const char *)blob, (size_t)size, &buf)) {
+		blob = buf.buf;
+		size = buf.len;
+	}
 	if (write_in_full(fd, blob, size) != size)
 		die("unable to write temp-file");
 	close(fd);
 	temp->name = temp->tmp_path;
 	strcpy(temp->hex, sha1_to_hex(sha1));
 	temp->hex[40] = 0;
 	sprintf(temp->mode, "%06o", mode);
+	strbuf_release(&buf);
 }
 
 static struct diff_tempfile *prepare_temp_file(const char *name,
@@ -2006,7 +2013,7 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
 				die("readlink(%s)", name);
 			if (ret == sizeof(buf))
 				die("symlink too long: %s", name);
-			prep_temp_blob(temp, buf, ret,
+			prep_temp_blob(name, temp, buf, ret,
 				       (one->sha1_valid ?
 					one->sha1 : null_sha1),
 				       (one->sha1_valid ?
@@ -2032,7 +2039,7 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
 	else {
 		if (diff_populate_filespec(one, 0))
 			die("cannot read data blob for %s", one->path);
-		prep_temp_blob(temp, one->data, one->size,
+		prep_temp_blob(name, temp, one->data, one->size,
 			       one->sha1, one->mode);
 	}
 	return temp;

t/t4020-diff-external.sh

@@ -136,4 +136,20 @@ test_expect_success 'GIT_EXTERNAL_DIFF with more than one changed files' '
 	GIT_EXTERNAL_DIFF=echo git diff
 '
 
+echo "#!$SHELL_PATH" >fake-diff.sh
+cat >> fake-diff.sh <<\EOF
+cat $2 >> crlfed.txt
+EOF
+chmod a+x fake-diff.sh
+
+keep_only_cr () {
+	tr -dc '\015'
+}
+
+test_expect_success 'external diff with autocrlf = true' '
+	git config core.autocrlf true &&
+	GIT_EXTERNAL_DIFF=./fake-diff.sh git diff &&
+	test $(wc -l < crlfed.txt) = $(cat crlfed.txt | keep_only_cr | wc -c)
+'
+
 test_done