[PATCH v3 6/6] Revert "repository: pre-initialize hash algo pointer"

[Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>]

This reverts commit e26f7f19b6c7485f04234946a59ab8f4fd21d6d1. The root
problem, git clone not setting up the_hash_algo, has been fixed in the
previous patch.

Since this is a dangerous move and could potentially break stuff after
release (and leads to workaround like the reverted commit), the
workaround technically remains, but is hidden behind a new environment
variable GIT_HASH_FIXUP. This should let the users continue to use git
while we fix the problem. This variable can be deleted after one or two
releases.

test-dump-split-index.c needs to call setup_git_directory() after this
to configure hash algorithm before parsing the index file. It's not the
best way (i.e. check index file version) but it's a test tool, this is
good enough.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
 common-main.c                    | 10 ++++++++++
 repository.c                     |  2 +-
 repository.h                     |  5 +++++
 t/helper/test-dump-split-index.c |  2 ++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/common-main.c b/common-main.c
index 6a689007e7..fbfa98c3b8 100644
--- a/common-main.c
+++ b/common-main.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "exec_cmd.h"
 #include "attr.h"
+#include "repository.h"
 
 /*
  * Many parts of Git have subprograms communicate via pipe, expect the
@@ -40,5 +41,14 @@ int main(int argc, const char **argv)
 
 	restore_sigpipe_to_default();
 
+	/*
+	 * Temporary recovery measure while hashing code is being
+	 * refactored. This variable should be gone after everybody
+	 * has used the_hash_algo in one or two releases and nobody
+	 * complains anything.
+	 */
+	if (getenv("GIT_HASH_FIXUP"))
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
+
 	return cmd_main(argc, argv);
 }
diff --git a/repository.c b/repository.c
index 4ffbe9bc94..0d715f4fdb 100644
--- a/repository.c
+++ b/repository.c
@@ -5,7 +5,7 @@
 
 /* The main repository */
 static struct repository the_repo = {
-	NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, &the_index, &hash_algos[GIT_HASH_SHA1], 0, 0
+	NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, &the_index, NULL, 0, 0
 };
 struct repository *the_repository = &the_repo;
 
diff --git a/repository.h b/repository.h
index 02c695bc74..40bd49611f 100644
--- a/repository.h
+++ b/repository.h
@@ -110,6 +110,11 @@ extern int repo_read_index(struct repository *repo);
 static inline const struct git_hash_algo *repo_get_hash_algo(
 	const struct repository *repo)
 {
+	if (!repo->hash_algo)
+		die("BUG: hash_algo is not initialized!\n%s",
+		    _("You can work around this by setting environment"
+		      " variable GIT_HASH_FIXUP=1.\n"
+		      "Please report this to git@xxxxxxxxxxxxxxx"));
 	return repo->hash_algo;
 }
 
diff --git a/t/helper/test-dump-split-index.c b/t/helper/test-dump-split-index.c
index e44430b699..b759fe3fc1 100644
--- a/t/helper/test-dump-split-index.c
+++ b/t/helper/test-dump-split-index.c
@@ -12,6 +12,8 @@ int cmd_main(int ac, const char **av)
 	struct split_index *si;
 	int i;
 
+	setup_git_directory();
+
 	do_read_index(&the_index, av[1], 1);
 	printf("own %s\n", sha1_to_hex(the_index.sha1));
 	si = the_index.split_index;
-- 
2.16.1.435.g8f24da2e1a