mailmap: default mailmap.blob in bare repositories

The motivation for mailmap.blob is to let users of bare
repositories use the mailmap feature, as they would not have
a checkout containing the .mailmap file. We can make it even
easier for them by just looking in HEAD:.mailmap by default.

We can't know for sure that this is where they would keep a
mailmap, of course, but it is the best guess (and it matches
the non-bare behavior, which reads from HEAD:.mailmap in the
working tree). If it's missing, git will silently ignore the
setting.

We do not do the same magic in the non-bare case, because:

  1. In the common case, HEAD:.mailmap will be the same as
     the .mailmap in the working tree, which is a no-op.

  2. In the uncommon case, the user has modified .mailmap
     but not yet committed it, and would expect the working
     tree version to take precedence.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1519,9 +1519,11 @@ mailmap.file::
 
 mailmap.blob::
 	Like `mailmap.file`, but consider the value as a reference to a
-	blob in the repository (e.g., `HEAD:.mailmap`). If both
-	`mailmap.file` and `mailmap.blob` are given, both are parsed,
-	with entries from `mailmap.file` taking precedence.
+	blob in the repository. If both `mailmap.file` and
+	`mailmap.blob` are given, both are parsed, with entries from
+	`mailmap.file` taking precedence. In a bare repository, this
+	defaults to `HEAD:.mailmap`. In a non-bare repository, it
+	defaults to empty.
 
 man.viewer::
 	Specify the programs that may be used to display help in the

mailmap.c

@@ -233,7 +233,12 @@ static int read_mailmap_blob(struct string_list *map,
 int read_mailmap(struct string_list *map, char **repo_abbrev)
 {
 	int err = 0;
+
 	map->strdup_strings = 1;
+
+	if (!git_mailmap_blob && is_bare_repository())
+		git_mailmap_blob = "HEAD:.mailmap";
+
 	err |= read_mailmap_file(map, ".mailmap", repo_abbrev);
 	err |= read_mailmap_blob(map, git_mailmap_blob, repo_abbrev);
 	err |= read_mailmap_file(map, git_mailmap_file, repo_abbrev);

t/t4203-mailmap.sh

@@ -218,6 +218,31 @@ test_expect_success 'mailmap.blob can be missing' '
 	test_cmp expect actual
 '
 
+test_expect_success 'mailmap.blob defaults to off in non-bare repo' '
+	git init non-bare &&
+	(
+		cd non-bare &&
+		test_commit one .mailmap "Fake Name <author@example.com>" &&
+		echo "     1	Fake Name" >expect &&
+		git shortlog -ns HEAD >actual &&
+		test_cmp expect actual &&
+		rm .mailmap &&
+		echo "     1	A U Thor" >expect &&
+		git shortlog -ns HEAD >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'mailmap.blob defaults to HEAD:.mailmap in bare repo' '
+	git clone --bare non-bare bare &&
+	(
+		cd bare &&
+		echo "     1	Fake Name" >expect &&
+		git shortlog -ns HEAD >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'cleanup after mailmap.blob tests' '
 	rm -f .mailmap
 '