Merge branch 'ps/weak-sha1-for-tail-sum-fix'

An earlier "csum-file checksum does not have to be computed with
sha1dc" topic had a few code paths that had initialized an
implementation of a hash function to be used by an unmatching hash
by mistake, which have been corrected.

* ps/weak-sha1-for-tail-sum-fix:
  ci: exercise unsafe OpenSSL backend
  builtin/fast-import: fix segfault with unsafe SHA1 backend
  bulk-checkin: fix segfault with unsafe SHA1 backend

builtin/fast-import.c

@@ -1106,7 +1106,7 @@ static void stream_blob(uintmax_t len, struct object_id *oidout, uintmax_t mark)
 		|| (pack_size + PACK_SIZE_THRESHOLD + len) < pack_size)
 		cycle_packfile();
 
-	the_hash_algo->init_fn(&checkpoint.ctx);
+	the_hash_algo->unsafe_init_fn(&checkpoint.ctx);
 	hashfile_checkpoint(pack_file, &checkpoint);
 	offset = checkpoint.offset;
 

bulk-checkin.c

@@ -272,7 +272,7 @@ static int deflate_blob_to_pack(struct bulk_checkin_packfile *state,
 					  OBJ_BLOB, size);
 	the_hash_algo->init_fn(&ctx);
 	the_hash_algo->update_fn(&ctx, obuf, header_len);
-	the_hash_algo->init_fn(&checkpoint.ctx);
+	the_hash_algo->unsafe_init_fn(&checkpoint.ctx);
 
 	/* Note: idx is non-NULL when we are writing */
 	if ((flags & HASH_WRITE_OBJECT) != 0)

ci/run-build-and-tests.sh

@@ -17,6 +17,7 @@ linux-gcc)
 	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 	;;
 linux-TEST-vars)
+	export OPENSSL_SHA1_UNSAFE=YesPlease
 	export GIT_TEST_SPLIT_INDEX=yes
 	export GIT_TEST_MERGE_ALGORITHM=recursive
 	export GIT_TEST_FULL_IN_PACK_ARRAY=true