diff-index.c: "git diff" has no need to read blob from the standard input

Only "diff --no-index -" does.  Bolting the logic into the low-level
function diff_populate_filespec() was a layering violation from day
one.  Move populate_from_stdin() function out of the generic diff.c
to its only user, diff-index.c.

Also make sure "-" from the command line stays a special token "read
from the standard input", even if we later decide to sanitize the
result from prefix_filename() function in a few obvious ways,
e.g. removing unnecessary "./" prefix, duplicated slashes "//" in
the middle, etc.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-no-index.c

@@ -32,6 +32,13 @@ static int read_directory(const char *path, struct string_list *list)
 	return 0;
 }
 
+/*
+ * This should be "(standard input)" or something, but it will
+ * probably expose many more breakages in the way no-index code
+ * is bolted onto the diff callchain.
+ */
+static const char file_from_standard_input[] = "-";
+
 static int get_mode(const char *path, int *mode)
 {
 	struct stat st;
@@ -42,7 +49,7 @@ static int get_mode(const char *path, int *mode)
 	else if (!strcasecmp(path, "nul"))
 		*mode = 0;
 #endif
-	else if (!strcmp(path, "-"))
+	else if (path == file_from_standard_input)
 		*mode = create_ce_mode(0666);
 	else if (lstat(path, &st))
 		return error("Could not access '%s'", path);
@@ -51,6 +58,36 @@ static int get_mode(const char *path, int *mode)
 	return 0;
 }
 
+static int populate_from_stdin(struct diff_filespec *s)
+{
+	struct strbuf buf = STRBUF_INIT;
+	size_t size = 0;
+
+	if (strbuf_read(&buf, 0, 0) < 0)
+		return error("error while reading from stdin %s",
+				     strerror(errno));
+
+	s->should_munmap = 0;
+	s->data = strbuf_detach(&buf, &size);
+	s->size = size;
+	s->should_free = 1;
+	s->is_stdin = 1;
+	return 0;
+}
+
+static struct diff_filespec *noindex_filespec(const char *name, int mode)
+{
+	struct diff_filespec *s;
+
+	if (!name)
+		name = "/dev/null";
+	s = alloc_filespec(name);
+	fill_filespec(s, null_sha1, mode);
+	if (name == file_from_standard_input)
+		populate_from_stdin(s);
+	return s;
+}
+
 static int queue_diff(struct diff_options *o,
 		const char *name1, const char *name2)
 {
@@ -135,15 +172,8 @@ static int queue_diff(struct diff_options *o,
 			tmp_c = name1; name1 = name2; name2 = tmp_c;
 		}
 
-		if (!name1)
+		d1 = noindex_filespec(name1, mode1);
-			name1 = "/dev/null";
+		d2 = noindex_filespec(name2, mode2);
-		if (!name2)
-			name2 = "/dev/null";
-		d1 = alloc_filespec(name1);
-		d2 = alloc_filespec(name2);
-		fill_filespec(d1, null_sha1, mode1);
-		fill_filespec(d2, null_sha1, mode2);
-
 		diff_queue(&diff_queued_diff, d1, d2);
 		return 0;
 	}
@@ -238,7 +268,7 @@ void diff_no_index(struct rev_info *revs,
 			 * stdin should be spelled as "-"; if you have
 			 * path that is "-", spell it as "./-".
 			 */
-			p = p;
+			p = file_from_standard_input;
 		else if (prefixlen)
 			p = xstrdup(prefix_filename(prefix, prefixlen, p));
 		paths[i] = p;

diff.c

@@ -2426,22 +2426,6 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int
 	return 0;
 }
 
-static int populate_from_stdin(struct diff_filespec *s)
-{
-	struct strbuf buf = STRBUF_INIT;
-	size_t size = 0;
-
-	if (strbuf_read(&buf, 0, 0) < 0)
-		return error("error while reading from stdin %s",
-				     strerror(errno));
-
-	s->should_munmap = 0;
-	s->data = strbuf_detach(&buf, &size);
-	s->size = size;
-	s->should_free = 1;
-	return 0;
-}
-
 static int diff_populate_gitlink(struct diff_filespec *s, int size_only)
 {
 	int len;
@@ -2491,9 +2475,6 @@ int diff_populate_filespec(struct diff_filespec *s, int size_only)
 		struct stat st;
 		int fd;
 
-		if (!strcmp(s->path, "-"))
-			return populate_from_stdin(s);
-
 		if (lstat(s->path, &st) < 0) {
 			if (errno == ENOENT) {
 			err_empty:
@@ -2855,7 +2836,7 @@ static void diff_fill_sha1_info(struct diff_filespec *one)
 	if (DIFF_FILE_VALID(one)) {
 		if (!one->sha1_valid) {
 			struct stat st;
-			if (!strcmp(one->path, "-")) {
+			if (one->is_stdin) {
 				hashcpy(one->sha1, null_sha1);
 				return;
 			}

diffcore.h

@@ -43,6 +43,7 @@ struct diff_filespec {
 	unsigned should_free : 1; /* data should be free()'ed */
 	unsigned should_munmap : 1; /* data should be munmap()'ed */
 	unsigned dirty_submodule : 2;  /* For submodules: its work tree is dirty */
+	unsigned is_stdin : 1;
 #define DIRTY_SUBMODULE_UNTRACKED 1
 #define DIRTY_SUBMODULE_MODIFIED  2
 

t/t7501-commit.sh

@@ -458,4 +458,16 @@ test_expect_success 'amend can copy notes' '
 
 '
 
+test_expect_success 'commit a file whose name is a dash' '
+	git reset --hard &&
+	for i in 1 2 3 4 5
+	do
+		echo $i
+	done >./- &&
+	git add ./- &&
+	test_tick &&
+	git commit -m "add dash" >output </dev/null &&
+	test_i18ngrep " changed, 5 insertions" output
+'
+
 test_done