[PATCH v2 16/18] fsck: Support demoting errors to warnings

[Johannes Schindelin <johannes.schindelin@gmx.de>]

We already have support in `git receive-pack` to deal with some legacy
repositories which have non-fatal issues.

Let's make `git fsck` itself useful with such repositories, too, by
allowing users to ignore known issues, or at least demote those issues
to mere warnings.

Example: `git -c fsck.ignore=missing-email fsck` would hide problems with
missing emails in author, committer and tagger lines.

In the same spirit that `git receive-pack`'s usage of the fsck machinery
differs from `git fsck`'s – some of the non-fatal warnings in `git fsck`
are fatal with `git receive-pack` when receive.fsckObjects = true, for
example – we strictly separate the fsck.* from the receive.fsck.*
settings.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Documentation/config.txt | 13 +++++++++++++
 builtin/fsck.c           | 15 +++++++++++++++
 t/t1450-fsck.sh          | 11 +++++++++++
 3 files changed, 39 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 7371a5f..0daba8a 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1208,6 +1208,19 @@ filter.<driver>.smudge::
 	object to a worktree file upon checkout.  See
 	linkgit:gitattributes[5] for details.
 
+fsck.*::
+	The `fsck.error`, `fsck.warn` and `fsck.ignore` settings specify
+	comma-separated lists of fsck message IDs which should trigger
+	fsck to error out, to print the message and continue, or to ignore
+	said messages, respectively.
++
+For convenience, fsck prefixes the error/warning with the name of the option,
+e.g.  "missing-email: invalid author/committer line - missing email" means
+that setting `fsck.ignore = missing-email` will hide that issue.
++
+This feature is intended to support working with legacy repositories
+which cannot be repaired without disruptive changes.
+
 gc.aggressiveDepth::
 	The depth parameter used in the delta compression
 	algorithm used by 'git gc --aggressive'.  This defaults
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 99d4538..d5403c4 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -46,6 +46,19 @@ static int show_dangling = 1;
 #define DIRENT_SORT_HINT(de) ((de)->d_ino)
 #endif
 
+static int fsck_config(const char *var, const char *value, void *cb)
+{
+	if (starts_with(var, "fsck.")) {
+		struct strbuf sb = STRBUF_INIT;
+		strbuf_addf(&sb, "%s=%s", var + 5, value);
+		fsck_set_severity(&fsck_obj_options, sb.buf);
+		strbuf_release(&sb);
+		return 0;
+	}
+
+	return git_default_config(var, value, cb);
+}
+
 static void objreport(struct object *obj, const char *severity,
                       const char *err)
 {
@@ -638,6 +651,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		include_reflogs = 0;
 	}
 
+	git_config(fsck_config, NULL);
+
 	fsck_head_link();
 	fsck_object_dir(get_object_directory());
 
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index ea0f216..a79ff9f 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -287,6 +287,17 @@ test_expect_success 'rev-list --verify-objects with bad sha1' '
 	grep -q "error: sha1 mismatch 63ffffffffffffffffffffffffffffffffffffff" out
 '
 
+test_expect_success 'force fsck to ignore double author' '
+	git cat-file commit HEAD >basis &&
+	sed "s/^author .*/&,&/" <basis | tr , \\n >multiple-authors &&
+	new=$(git hash-object -t commit -w --stdin <multiple-authors) &&
+	test_when_finished "remove_object $new" &&
+	git update-ref refs/heads/bogus "$new" &&
+	test_when_finished "git update-ref -d refs/heads/bogus" &&
+	test_must_fail git fsck &&
+	git -c fsck.ignore=multiple-authors fsck
+'
+
 _bz='\0'
 _bz5="$_bz$_bz$_bz$_bz$_bz"
 _bz20="$_bz5$_bz5$_bz5$_bz5"
-- 
2.0.0.rc3.9669.g840d1f9