oid: don't assume thread local state was initialized

git_oid_tostr_s could fail if thread-local state initialization fails.
In that case, it will now return `NULL`.  Callers should check for
`NULL` and propagate the failure.

include/git2/oid.h

@@ -225,7 +225,7 @@ GIT_EXTERN(int) git_oid_pathfmt(char *out, const git_oid *id);
  * concurrent calls of the function.
  *
  * @param oid The oid structure to format
- * @return the c-string
+ * @return the c-string or NULL on failure
  */
 GIT_EXTERN(char *) git_oid_tostr_s(const git_oid *oid);
 

src/libgit2/indexer.c

@@ -519,7 +519,13 @@ static int store_object(git_indexer *idx)
 	pentry->offset = entry_start;
 
 	if (git_oidmap_exists(idx->pack->idx_cache, &pentry->id)) {
-		git_error_set(GIT_ERROR_INDEXER, "duplicate object %s found in pack", git_oid_tostr_s(&pentry->id));
+		const char *idstr = git_oid_tostr_s(&pentry->id);
+
+		if (!idstr)
+			git_error_set(GIT_ERROR_INDEXER, "failed to parse object id");
+		else
+			git_error_set(GIT_ERROR_INDEXER, "duplicate object %s found in pack", idstr);
+
 		git__free(pentry);
 		goto on_error;
 	}

src/libgit2/odb.c

@@ -1494,11 +1494,16 @@ static int read_prefix_1(git_odb_object **out, git_odb *db,
 
 			if (found && git_oid__cmp(&full_oid, &found_full_oid)) {
 				git_str buf = GIT_STR_INIT;
+				const char *idstr;
 
-				git_str_printf(&buf, "multiple matches for prefix: %s",
-					git_oid_tostr_s(&full_oid));
-				git_str_printf(&buf, " %s",
-					git_oid_tostr_s(&found_full_oid));
+				if ((idstr = git_oid_tostr_s(&full_oid)) == NULL) {
+					git_str_puts(&buf, "failed to parse object id");
+				} else {
+					git_str_printf(&buf, "multiple matches for prefix: %s", idstr);
+
+					if ((idstr = git_oid_tostr_s(&found_full_oid)) != NULL)
+						git_str_printf(&buf, " %s", idstr);
+				}
 
 				error = git_odb__error_ambiguous(buf.ptr);
 				git_str_dispose(&buf);

src/libgit2/oid.c

@@ -155,7 +155,13 @@ int git_oid_pathfmt(char *str, const git_oid *oid)
 
 char *git_oid_tostr_s(const git_oid *oid)
 {
-	char *str = GIT_THREADSTATE->oid_fmt;
+	git_threadstate *threadstate = GIT_THREADSTATE;
+	char *str;
+
+	if (!threadstate)
+		return NULL;
+
+	str = threadstate->oid_fmt;
 	git_oid_nfmt(str, git_oid_hexsize(git_oid_type(oid)) + 1, oid);
 	return str;
 }

src/libgit2/repository.c

@@ -3422,12 +3422,18 @@ cleanup:
 
 static int checkout_message(git_str *out, git_reference *old, const char *new)
 {
+	const char *idstr;
+
 	git_str_puts(out, "checkout: moving from ");
 
-	if (git_reference_type(old) == GIT_REFERENCE_SYMBOLIC)
+	if (git_reference_type(old) == GIT_REFERENCE_SYMBOLIC) {
 		git_str_puts(out, git_reference__shorthand(git_reference_symbolic_target(old)));
-	else
-		git_str_puts(out, git_oid_tostr_s(git_reference_target(old)));
+	} else {
+		if ((idstr = git_oid_tostr_s(git_reference_target(old))) == NULL)
+			return -1;
+
+		git_str_puts(out, idstr);
+	}
 
 	git_str_puts(out, " to ");
 
@@ -3463,8 +3469,11 @@ static int detach(git_repository *repo, const git_oid *id, const char *new)
 	if ((error = git_object_peel(&peeled, object, GIT_OBJECT_COMMIT)) < 0)
 		goto cleanup;
 
-	if (new == NULL)
-		new = git_oid_tostr_s(git_object_id(peeled));
+	if (new == NULL &&
+	    (new = git_oid_tostr_s(git_object_id(peeled))) == NULL) {
+		error = -1;
+		goto cleanup;
+	}
 
 	if ((error = checkout_message(&log_message, current, new)) < 0)
 		goto cleanup;
@@ -3552,6 +3561,7 @@ int git_repository_detach_head(git_repository *repo)
 	git_reference *old_head = NULL,	*new_head = NULL, *current = NULL;
 	git_object *object = NULL;
 	git_str log_message = GIT_STR_INIT;
+	const char *idstr;
 	int error;
 
 	GIT_ASSERT_ARG(repo);
@@ -3565,7 +3575,12 @@ int git_repository_detach_head(git_repository *repo)
 	if ((error = git_object_lookup(&object, repo, git_reference_target(old_head), GIT_OBJECT_COMMIT)) < 0)
 		goto cleanup;
 
-	if ((error = checkout_message(&log_message, current, git_oid_tostr_s(git_object_id(object)))) < 0)
+	if ((idstr = git_oid_tostr_s(git_object_id(object))) == NULL) {
+		error = -1;
+		goto cleanup;
+	}
+
+	if ((error = checkout_message(&log_message, current, idstr)) < 0)
 		goto cleanup;
 
 	error = git_reference_create(&new_head, repo, GIT_HEAD_FILE, git_reference_target(old_head),