From 5e73633dbf8a62190611f6eb438a1a2eaaffa919 Mon Sep 17 00:00:00 2001
From: Heiko Voigt <hvoigt@hvoigt.net>
Date: Mon, 14 May 2012 18:24:45 +0200
Subject: [PATCH] teach add_submodule_odb() to look for alternates

Since we allow to link other object databases when loading a submodules
database we should also load possible alternates.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 cache.h                          |  1 +
 sha1_file.c                      |  3 +--
 submodule.c                      |  3 +++
 t/t4041-diff-submodule-option.sh | 34 ++++++++++++++++++++++++++++++++
 4 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/cache.h b/cache.h
index 3a8e1258e7..3a28cb13b3 100644
--- a/cache.h
+++ b/cache.h
@@ -960,6 +960,7 @@ extern struct alternate_object_database {
 	char base[FLEX_ARRAY]; /* more */
 } *alt_odb_list;
 extern void prepare_alt_odb(void);
+extern void read_info_alternates(const char * relative_base, int depth);
 extern void add_to_alternates_file(const char *reference);
 typedef int alt_odb_fn(struct alternate_object_database *, void *);
 extern void foreach_alt_odb(alt_odb_fn, void*);
diff --git a/sha1_file.c b/sha1_file.c
index 4f06a0e450..f615fc7206 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -228,7 +228,6 @@ char *sha1_pack_index_name(const unsigned char *sha1)
 struct alternate_object_database *alt_odb_list;
 static struct alternate_object_database **alt_odb_tail;
 
-static void read_info_alternates(const char * alternates, int depth);
 static int git_open_noatime(const char *name);
 
 /*
@@ -353,7 +352,7 @@ static void link_alt_odb_entries(const char *alt, const char *ep, int sep,
 	}
 }
 
-static void read_info_alternates(const char * relative_base, int depth)
+void read_info_alternates(const char * relative_base, int depth)
 {
 	char *map;
 	size_t mapsz;
diff --git a/submodule.c b/submodule.c
index 9a28060679..b63978a161 100644
--- a/submodule.c
+++ b/submodule.c
@@ -63,6 +63,9 @@ static int add_submodule_odb(const char *path)
 	alt_odb->name[40] = '\0';
 	alt_odb->name[41] = '\0';
 	alt_odb_list = alt_odb;
+
+	/* add possible alternates from the submodule */
+	read_info_alternates(objects_directory.buf, 0);
 	prepare_alt_odb();
 done:
 	strbuf_release(&objects_directory);
diff --git a/t/t4041-diff-submodule-option.sh b/t/t4041-diff-submodule-option.sh
index bf9a7526bd..6c01d0c056 100755
--- a/t/t4041-diff-submodule-option.sh
+++ b/t/t4041-diff-submodule-option.sh
@@ -458,4 +458,38 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'diff --submodule with objects referenced by alternates' '
+	mkdir sub_alt &&
+	(cd sub_alt &&
+		git init &&
+		echo a >a &&
+		git add a &&
+		git commit -m a
+	) &&
+	mkdir super &&
+	(cd super &&
+		git clone -s ../sub_alt sub &&
+		git init &&
+		git add sub &&
+		git commit -m "sub a"
+	) &&
+	(cd sub_alt &&
+		sha1_before=$(git rev-parse --short HEAD)
+		echo b >b &&
+		git add b &&
+		git commit -m b
+		sha1_after=$(git rev-parse --short HEAD)
+		echo "Submodule sub $sha1_before..$sha1_after:
+  > b" >../expected
+	) &&
+	(cd super &&
+		(cd sub &&
+			git fetch &&
+			git checkout origin/master
+		) &&
+		git diff --submodule > ../actual
+	)
+	test_cmp expected actual
+'
+
 test_done