Merge branch 'mh/reporting-broken-refs-from-for-each-ref'

"git for-each-ref" reported "missing object" for 0{40} when it
encounters a broken ref.  The lack of object whose name is 0{40} is
not the problem; the ref being broken is.

* mh/reporting-broken-refs-from-for-each-ref:
  read_loose_refs(): treat NULL_SHA1 loose references as broken
  read_loose_refs(): simplify function logic
  for-each-ref: report broken references correctly
  t6301: new tests of for-each-ref error handling

builtin/for-each-ref.c

@@ -866,6 +866,11 @@ static int grab_single_ref(const char *refname, const struct object_id *oid,
 		  return 0;
 	}
 
+	if (flag & REF_ISBROKEN) {
+		  warning("ignoring broken ref %s", refname);
+		  return 0;
+	}
+
 	if (*cb->grab_pattern) {
 		const char **pattern;
 		int namelen = strlen(refname);

refs.c

@@ -1373,19 +1373,34 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
 					 create_dir_entry(refs, refname.buf,
 							  refname.len, 1));
 		} else {
+			int read_ok;
+
 			if (*refs->name) {
 				hashclr(sha1);
 				flag = 0;
-				if (resolve_gitlink_ref(refs->name, refname.buf, sha1) < 0) {
-					hashclr(sha1);
-					flag |= REF_ISBROKEN;
-				}
-			} else if (read_ref_full(refname.buf,
-						 RESOLVE_REF_READING,
-						 sha1, &flag)) {
+				read_ok = !resolve_gitlink_ref(refs->name,
+							       refname.buf, sha1);
+			} else {
+				read_ok = !read_ref_full(refname.buf,
+							 RESOLVE_REF_READING,
+							 sha1, &flag);
+			}
+
+			if (!read_ok) {
 				hashclr(sha1);
 				flag |= REF_ISBROKEN;
+			} else if (is_null_sha1(sha1)) {
+				/*
+				 * It is so astronomically unlikely
+				 * that NULL_SHA1 is the SHA-1 of an
+				 * actual object that we consider its
+				 * appearance in a loose reference
+				 * file to be repo corruption
+				 * (probably due to a software bug).
+				 */
+				flag |= REF_ISBROKEN;
 			}
+
 			if (check_refname_format(refname.buf,
 						 REFNAME_ALLOW_ONELEVEL)) {
 				if (!refname_is_safe(refname.buf))

t/t6301-for-each-ref-errors.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+
+test_description='for-each-ref errors for broken refs'
+
+. ./test-lib.sh
+
+ZEROS=$_z40
+MISSING=abababababababababababababababababababab
+
+test_expect_success setup '
+	git commit --allow-empty -m "Initial" &&
+	git tag testtag &&
+	git for-each-ref >full-list &&
+	git for-each-ref --format="%(objectname) %(refname)" >brief-list
+'
+
+test_expect_success 'Broken refs are reported correctly' '
+	r=refs/heads/bogus &&
+	: >.git/$r &&
+	test_when_finished "rm -f .git/$r" &&
+	echo "warning: ignoring broken ref $r" >broken-err &&
+	git for-each-ref >out 2>err &&
+	test_cmp full-list out &&
+	test_cmp broken-err err
+'
+
+test_expect_success 'NULL_SHA1 refs are reported correctly' '
+	r=refs/heads/zeros &&
+	echo $ZEROS >.git/$r &&
+	test_when_finished "rm -f .git/$r" &&
+	echo "warning: ignoring broken ref $r" >zeros-err &&
+	git for-each-ref >out 2>err &&
+	test_cmp full-list out &&
+	test_cmp zeros-err err &&
+	git for-each-ref --format="%(objectname) %(refname)" >brief-out 2>brief-err &&
+	test_cmp brief-list brief-out &&
+	test_cmp zeros-err brief-err
+'
+
+test_expect_success 'Missing objects are reported correctly' '
+	r=refs/heads/missing &&
+	echo $MISSING >.git/$r &&
+	test_when_finished "rm -f .git/$r" &&
+	echo "fatal: missing object $MISSING for $r" >missing-err &&
+	test_must_fail git for-each-ref 2>err &&
+	test_cmp missing-err err &&
+	(
+		cat brief-list &&
+		echo "$MISSING $r"
+	) | sort -k 2 >missing-brief-expected &&
+	git for-each-ref --format="%(objectname) %(refname)" >brief-out 2>brief-err &&
+	test_cmp missing-brief-expected brief-out &&
+	test_must_be_empty brief-err
+'
+
+test_done