Merge branch 'en/fast-import-avoid-self-replace'

"git fast-import" can be tricked into a replace ref that maps an
object to itself, which is a useless thing to do.

* en/fast-import-avoid-self-replace:
  fast-import: avoid making replace refs point to themselves

Author: gitster

builtin/fast-import.c

@@ -179,6 +179,7 @@ static unsigned long branch_load_count;
 static int failure;
 static FILE *pack_edges;
 static unsigned int show_stats = 1;
+static unsigned int quiet;
 static int global_argc;
 static const char **global_argv;
 static const char *global_prefix;
@@ -1602,7 +1603,19 @@ static int update_branch(struct branch *b)
 	struct ref_transaction *transaction;
 	struct object_id old_oid;
 	struct strbuf err = STRBUF_INIT;
-
+	static const char *replace_prefix = "refs/replace/";
+
+	if (starts_with(b->name, replace_prefix) &&
+	    !strcmp(b->name + strlen(replace_prefix),
+		    oid_to_hex(&b->oid))) {
+		if (!quiet)
+			warning("Dropping %s since it would point to "
+				"itself (i.e. to %s)",
+				b->name, oid_to_hex(&b->oid));
+		refs_delete_ref(get_main_ref_store(the_repository),
+				NULL, b->name, NULL, 0);
+		return 0;
+	}
 	if (is_null_oid(&b->oid)) {
 		if (b->delete)
 			refs_delete_ref(get_main_ref_store(the_repository),
@@ -3388,6 +3401,7 @@ static int parse_one_option(const char *option)
 		option_export_pack_edges(option);
 	} else if (!strcmp(option, "quiet")) {
 		show_stats = 0;
+		quiet = 1;
 	} else if (!strcmp(option, "stats")) {
 		show_stats = 1;
 	} else if (!strcmp(option, "allow-unsafe-features")) {

t/t9300-fast-import.sh

@@ -3692,6 +3692,34 @@ test_expect_success ICONV 'X: handling encoding' '
 	git log -1 --format=%B encoding | grep $(printf "\317\200")
 '
 
+test_expect_success 'X: replace ref that becomes useless is removed' '
+	git init -qb main testrepo &&
+	cd testrepo &&
+	(
+		test_commit test &&
+
+		test_commit msg somename content &&
+
+		git mv somename othername &&
+		NEW_TREE=$(git write-tree) &&
+		MSG="$(git log -1 --format=%B HEAD)" &&
+		NEW_COMMIT=$(git commit-tree -p HEAD^1 -m "$MSG" $NEW_TREE) &&
+		git replace main $NEW_COMMIT &&
+
+		echo more >>othername &&
+		git add othername &&
+		git commit -qm more &&
+
+		git fast-export --all >tmp &&
+		sed -e s/othername/somename/ tmp >tmp2 &&
+		git fast-import --force <tmp2 2>msgs &&
+
+		grep "Dropping.*since it would point to itself" msgs &&
+		git show-ref >refs &&
+		! grep refs/replace refs
+	)
+'
+
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