On Tue, Sep 02, 2025 at 10:34:26AM +0200, Karthik Nayak wrote:
> Similar to the previous commit, when using the files-backend on
> case-insensitive filesystems, there is possibility of hitting F/D
> conflicts when creating references within a single transaction, such as:
>
> - 'refs/heads/foo'
> - 'refs/heads/Foo/bar'
Great, I wanted to ask about this scenario.
> Ideally such conflicts are caught in `refs_verify_refnames_available()`
> which is responsible for checking F/D conflicts within a given
> transaction. This utility function is shared across the reference
> backends. As such, it doesn't consider the issues of using a
> case-insensitive, which only affects the files-backend.
>
> While one solution would be to make the function aware of such issues.
> This feels like leaking implementation details of file-backend specific
> issues into the utility function. So opt for the more simpler option, of
> lowercasing all references sent to this function when on a
> case-insensitive filesystem and operating on the files-backend.
>
> To do this, simply use a `struct strbuf` to convert the refname to a
> lower case and append it to the list of refnames to be checked. Since we
> use a `struct strbuf` and the memory is cleared right after, make sure
> that the string list duplicates all provided string.
>
> Without this change, the user would simply be left with a repository
> with '.lock' files which were created in the 'prepare' phase of the
> transaction, as the 'commit' phase would simply abort and not do the
> necessary cleanup.
Oh, that's a clever hack. Does this also work for the case where we have
preexisting refs already that differ only in casing? I guess it should
given that the lookups we perform should yield those refs regardless of
their casing.
In any case, if we don't already have such a test it would be great to
also verify that this works as expected.
> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index 9f58ea4858..466cdfe121 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -869,8 +869,23 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
> * If the ref did not exist and we are creating it, we have to
> * make sure there is no existing packed ref that conflicts
> * with refname. This check is deferred so that we can batch it.
> + *
> + * For case-insensitive filesystems, we should also check for F/D
> + * conflicts between 'foo' and 'Foo/bar'. So let's lowercase
> + * the refname.
> */
> - item = string_list_append(refnames_to_check, refname);
> + if (ignore_case) {
> + struct strbuf lower = STRBUF_INIT;
> +
> + strbuf_addstr(&lower, refname);
> + strbuf_tolower(&lower);
> +
> + item = string_list_append(refnames_to_check, lower.buf);
> + strbuf_release(&lower);
Can we use `string_list_append_nodup()` together with `strbuf_detach()`
here to avoid one memory allocation?
> + } else {
> + item = string_list_append(refnames_to_check, refname);
> + }
> +
> item->util = xmalloc(sizeof(update_idx));
> memcpy(item->util, &update_idx, sizeof(update_idx));
> }
> diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
> index 57f60da81b..84dc68e5f3 100755
> --- a/t/t5510-fetch.sh
> +++ b/t/t5510-fetch.sh
> @@ -53,6 +53,12 @@ test_expect_success "clone and setup child repos" '
> cd case_sensitive &&
> git branch branch1 &&
> git branch bRanch1
> + ) &&
> + git clone --ref-format=reftable . case_sensitive_fd &&
> + (
> + cd case_sensitive_fd &&
> + git branch foo/bar &&
> + git branch Foo
> )
> '
>
Nice idea to use the reftable format here.
> @@ -1546,6 +1552,20 @@ test_expect_success CASE_INSENSITIVE_FS,REFFILES 'existing references in a case
> )
> '
>
> +test_expect_success CASE_INSENSITIVE_FS,REFFILES 'F/D conflict on case insensitive filesystem' '
> + test_when_finished rm -rf case_insensitive &&
> + (
> + git init --bare case_insensitive &&
> + cd case_insensitive &&
> + git remote add origin -- ../case_sensitive_fd &&
> + test_must_fail git fetch -f origin "refs/heads/*:refs/heads/*" 2>err &&
> + test_grep "failed: refname conflict" err &&
> + git rev-parse refs/heads/main >expect &&
> + git rev-parse refs/heads/foo/bar >actual &&
> + test_cmp expect actual
> + )
> +'
Okay, so we again only end up with one of these references, which is the
best we can do.
atrick
