mailmap: support reading mailmap from blobs

In a bare repository, there isn't a simple way to respect an
in-tree mailmap without extracting it to a temporary file.
This patch provides a config variable, similar to
mailmap.file, which reads the mailmap from a blob in the
repository.

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

Documentation/config.txt

@@ -1517,6 +1517,12 @@ mailmap.file::
 	subdirectory, or somewhere outside of the repository itself.
 	See linkgit:git-shortlog[1] and linkgit:git-blame[1].
 
+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.
+
 man.viewer::
 	Specify the programs that may be used to display help in the
 	'man' format. See linkgit:git-help[1].

cache.h

@@ -1155,6 +1155,7 @@ extern int author_ident_sufficiently_given(void);
 extern const char *git_commit_encoding;
 extern const char *git_log_output_encoding;
 extern const char *git_mailmap_file;
+extern const char *git_mailmap_blob;
 
 /* IO helper functions */
 extern void maybe_flush_or_die(FILE *, const char *);

config.c

@@ -839,6 +839,8 @@ static int git_default_mailmap_config(const char *var, const char *value)
 {
 	if (!strcmp(var, "mailmap.file"))
 		return git_config_string(&git_mailmap_file, var, value);
+	if (!strcmp(var, "mailmap.blob"))
+		return git_config_string(&git_mailmap_blob, var, value);
 
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;

mailmap.c

@@ -10,6 +10,7 @@ static inline void debug_mm(const char *format, ...) {}
 #endif
 
 const char *git_mailmap_file;
+const char *git_mailmap_blob;
 
 struct mailmap_info {
 	char *name;
@@ -177,12 +178,56 @@ static int read_mailmap_file(struct string_list *map, const char *filename,
 	return 0;
 }
 
+static void read_mailmap_buf(struct string_list *map,
+			     const char *buf, unsigned long len,
+			     char **repo_abbrev)
+{
+	while (len) {
+		const char *end = strchrnul(buf, '\n');
+		unsigned long linelen = end - buf + 1;
+		char *line = xmemdupz(buf, linelen);
+
+		read_mailmap_line(map, line, repo_abbrev);
+
+		free(line);
+		buf += linelen;
+		len -= linelen;
+	}
+}
+
+static int read_mailmap_blob(struct string_list *map,
+			     const char *name,
+			     char **repo_abbrev)
+{
+	unsigned char sha1[20];
+	char *buf;
+	unsigned long size;
+	enum object_type type;
+
+	if (!name)
+		return 1;
+	if (get_sha1(name, sha1) < 0)
+		return 1;
+
+	buf = read_sha1_file(sha1, &type, &size);
+	if (!buf)
+		return 1;
+	if (type != OBJ_BLOB)
+		return 1;
+
+	read_mailmap_buf(map, buf, size, repo_abbrev);
+
+	free(buf);
+	return 0;
+}
+
 int read_mailmap(struct string_list *map, char **repo_abbrev)
 {
 	map->strdup_strings = 1;
-	/* each failure returns 1, so >1 means both calls failed */
+	/* each failure returns 1, so >2 means all calls failed */
 	return read_mailmap_file(map, ".mailmap", repo_abbrev) +
-	       read_mailmap_file(map, git_mailmap_file, repo_abbrev) > 1;
+	       read_mailmap_blob(map, git_mailmap_blob, repo_abbrev) +
+	       read_mailmap_file(map, git_mailmap_file, repo_abbrev) > 2;
 }
 
 void clear_mailmap(struct string_list *map)

t/t4203-mailmap.sh

@@ -149,6 +149,79 @@ test_expect_success 'No mailmap files, but configured' '
 	test_cmp expect actual
 '
 
+test_expect_success 'setup mailmap blob tests' '
+	git checkout -b map &&
+	test_when_finished "git checkout master" &&
+	cat >just-bugs <<-\EOF &&
+	Blob Guy <bugs@company.xx>
+	EOF
+	cat >both <<-\EOF &&
+	Blob Guy <author@example.com>
+	Blob Guy <bugs@company.xx>
+	EOF
+	git add just-bugs both &&
+	git commit -m "my mailmaps" &&
+	echo "Repo Guy <author@example.com>" >.mailmap &&
+	echo "Internal Guy <author@example.com>" >internal.map
+'
+
+test_expect_success 'mailmap.blob set' '
+	cat >expect <<-\EOF &&
+	Blob Guy (1):
+	      second
+
+	Repo Guy (1):
+	      initial
+
+	EOF
+	git -c mailmap.blob=map:just-bugs shortlog HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'mailmap.blob overrides .mailmap' '
+	cat >expect <<-\EOF &&
+	Blob Guy (2):
+	      initial
+	      second
+
+	EOF
+	git -c mailmap.blob=map:both shortlog HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'mailmap.file overrides mailmap.blob' '
+	cat >expect <<-\EOF &&
+	Blob Guy (1):
+	      second
+
+	Internal Guy (1):
+	      initial
+
+	EOF
+	git \
+	  -c mailmap.blob=map:both \
+	  -c mailmap.file=internal.map \
+	  shortlog HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'mailmap.blob can be missing' '
+	cat >expect <<-\EOF &&
+	Repo Guy (1):
+	      initial
+
+	nick1 (1):
+	      second
+
+	EOF
+	git -c mailmap.blob=map:nonexistent shortlog HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'cleanup after mailmap.blob tests' '
+	rm -f .mailmap
+'
+
 # Extended mailmap configurations should give us the following output for shortlog
 cat >expect <<\EOF
 A U Thor <author@example.com> (1):