builtin/apply.c: report error on failure to recognize input

When git apply is passed something that is not a patch, it does not produce
an error message or exit with a non-zero status if it was not actually
"applying" the patch i.e. --check or --numstat etc were supplied on the
command line.

Fix this by producing an error when apply fails to find any hunks whatsoever
while parsing the patch.

This will cause some of the output formats (--numstat, --diffstat, etc) to
produce an error when they formerly would have reported zero changes and
exited successfully.  That seems like the correct behavior though.  Failure
to recognize the input as a patch should be an error.

Plus, add a test.

Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -3590,15 +3590,12 @@ static int write_out_one_reject(struct patch *patch)
 	return -1;
 }
 
-static int write_out_results(struct patch *list, int skipped_patch)
+static int write_out_results(struct patch *list)
 {
 	int phase;
 	int errs = 0;
 	struct patch *l;
 
-	if (!list && !skipped_patch)
-		return error("No changes");
-
 	for (phase = 0; phase < 2; phase++) {
 		l = list;
 		while (l) {
@@ -3724,6 +3721,9 @@ static int apply_patch(int fd, const char *filename, int options)
 		offset += nr;
 	}
 
+	if (!list && !skipped_patch)
+		die("unrecognized input");
+
 	if (whitespace_error && (ws_error_action == die_on_ws_error))
 		apply = 0;
 
@@ -3741,7 +3741,7 @@ static int apply_patch(int fd, const char *filename, int options)
 	    !apply_with_reject)
 		exit(1);
 
-	if (apply && write_out_results(list, skipped_patch))
+	if (apply && write_out_results(list))
 		exit(1);
 
 	if (fake_ancestor)

t/t4136-apply-check.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+test_description='git apply should exit non-zero with unrecognized input.'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit 1
+'
+
+test_expect_success 'apply --check exits non-zero with unrecognized input' '
+	test_must_fail git apply --check - <<-\EOF
+	I am not a patch
+	I look nothing like a patch
+	git apply must fail
+	EOF
+'
+
+test_done