From 5e904f1a4ade49372970bd172d63f9c9fd7b2653 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Mon, 18 Nov 2024 22:19:49 +0000 Subject: [PATCH] fast-import: avoid making replace refs point to themselves If someone replaces a commit with a modified version, then builds on that commit, and then later decides to rewrite history in a format like git fast-export --all | CMD_TO_TWEAK_THE_STREAM | git fast-import and CMD_TO_TWEAK_THE_STREAM undoes the modifications that the replacement did, then at the end you'd get a replace ref that points to itself. For example: $ git show-ref | grep replace fb92ebc654641b310e7d0360d0a5a49316fd7264 refs/replace/fb92ebc654641b310e7d0360d0a5a49316fd7264 Git commands which pay attention to replace refs will die with an error when a self-referencing replace ref is present: $ git log fatal: replace depth too high for object fb92ebc654641b310e7d0360d0a5a49316fd7264 Avoid such problems by deleting replace refs that will simply end up pointing to themselves at the end of our writing. Unless users specify --quiet, warn them when we delete such a replace ref. Two notes about this patch: * We are not ignoring the problematic update of the replace ref (turning it into a no-op), we are replacing the update with a delete. The logic here is that if the repository had a value for the replace ref before fast-import was run, and the replace ref was explicitly named in the fast-import stream, we don't want the replace ref to be left with a pre-fast-import value. * While loops with more than one element (e.g. refs/replace/A points to B, and refs/replace/B points to A) are possible, they seem much less plausible. It is pretty easy to create a sequence of git-filter-repo commands that will trigger a self-referencing replace ref, but I do not know how to trigger a scenario with a cycle length greater than 1. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- builtin/fast-import.c | 16 +++++++++++++++- t/t9300-fast-import.sh | 28 ++++++++++++++++++++++++++++ 2 files changed, 43 insertions(+), 1 deletion(-) diff --git a/builtin/fast-import.c b/builtin/fast-import.c index 1e7ab67f6e..40aea35972 100644 --- a/builtin/fast-import.c +++ b/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; @@ -1604,7 +1605,19 @@ 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), @@ -3390,6 +3403,7 @@ 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")) { diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh index 3b3c371740..27711ff186 100755 --- a/t/t9300-fast-import.sh +++ b/t/t9300-fast-import.sh @@ -3692,6 +3692,34 @@ test_expect_success '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 msgs && + + grep "Dropping.*since it would point to itself" msgs && + git show-ref >refs && + ! grep refs/replace refs + ) +' + ### ### series Y (submodules and hash algorithms) ### -- 2.47.3