Merge branch 'jc/undecided-is-not-necessarily-sha1-fix'

The base topic started to make it an error for a command to leave
the hash algorithm unspecified, which revealed a few commands that
were not ready for the change.  Give users a knob to revert back to
the "default is sha-1" behaviour as an escape hatch, and start
fixing these breakages.

* jc/undecided-is-not-necessarily-sha1-fix:
  apply: fix uninitialized hash function
  builtin/hash-object: fix uninitialized hash function
  builtin/patch-id: fix uninitialized hash function
  t1517: test commands that are designed to be run outside repository
  setup: add an escape hatch for "no more default hash algorithm" change

3 files changed, 26 insertions, 0 deletions

diff --git a/builtin/apply.c b/builtin/apply.c
index 861a01910c..d623c52f78 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -1,6 +1,7 @@
 #include "builtin.h"
 #include "gettext.h"
 #include "repository.h"
+#include "hash.h"
 #include "apply.h"
 
 static const char * const apply_usage[] = {
@@ -18,6 +19,15 @@ int cmd_apply(int argc, const char **argv, const char *prefix)
 	if (init_apply_state(&state, the_repository, prefix))
 		exit(128);
 
+	/*
+	 * We could to redo the "apply.c" machinery to make this
+	 * arbitrary fallback unnecessary, but it is dubious that it
+	 * is worth the effort.
+	 * cf. https://lore.kernel.org/git/xmqqcypfcmn4.fsf@gitster.g/
+	 */
+	if (!the_hash_algo)
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
+
 	argc = apply_parse_options(argc, argv,
 				   &state, &force_apply, &options,
 				   apply_usage);
diff --git a/builtin/hash-object.c b/builtin/hash-object.c
index 82ca6d2bfd..c767414a0c 100644
--- a/builtin/hash-object.c
+++ b/builtin/hash-object.c
@@ -123,6 +123,9 @@ int cmd_hash_object(int argc, const char **argv, const char *prefix)
 	else
 		prefix = setup_git_directory_gently(&nongit);
 
+	if (nongit && !the_hash_algo)
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
+
 	if (vpath && prefix) {
 		vpath_free = prefix_filename(prefix, vpath);
 		vpath = vpath_free;
diff --git a/builtin/patch-id.c b/builtin/patch-id.c
index 3894d2b970..583099cacf 100644
--- a/builtin/patch-id.c
+++ b/builtin/patch-id.c
@@ -5,6 +5,7 @@
 #include "hash.h"
 #include "hex.h"
 #include "parse-options.h"
+#include "setup.h"
 
 static void flush_current_id(int patchlen, struct object_id *id, struct object_id *result)
 {
@@ -237,6 +238,18 @@ int cmd_patch_id(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, builtin_patch_id_options,
 			     patch_id_usage, 0);
 
+	/*
+	 * We rely on `the_hash_algo` to compute patch IDs. This is dubious as
+	 * it means that the hash algorithm now depends on the object hash of
+	 * the repository, even though git-patch-id(1) clearly defines that
+	 * patch IDs always use SHA1.
+	 *
+	 * NEEDSWORK: This hack should be removed in favor of converting
+	 * the code that computes patch IDs to always use SHA1.
+	 */
+	if (!the_hash_algo)
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
+
 	generate_id_list(opts ? opts > 1 : config.stable,
 			 opts ? opts == 3 : config.verbatim);
 	return 0;