Re: [PATCH v2 1/4] setup: add an escape hatch for "no more default hash algorithm" change

>
> Partially revert c8aed5e8 (repository: stop setting SHA1 as the
> default object hash, 2024-05-07), to keep end-user systems still
> broken when we have gap in our test coverage but yet give them an
> escape hatch to set the GIT_TEST_DEFAULT_HASH_IS_SHA1=1 environment
> variable to revert to the previous behaviour.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  repository.c  | 24 ++++++++++++++++++++++++

>  t/test-lib.sh |  4 ++++
>  2 files changed, 28 insertions(+)
>
> diff --git a/repository.c b/repository.c
> index 15c10015b0..6f67966e35 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -26,6 +26,30 @@ void initialize_repository(struct repository *repo)
>         repo->parsed_objects = parsed_object_pool_new();
>         ALLOC_ARRAY(repo->index, 1);
>         index_state_init(repo->index, repo);
> +
> +       /*
> +        * Unfortunately, we need to keep this hack around for the time being:

> +        *
> +        *   - Not setting up the hash algorithm for `the_repository` leads to
> +        *     crashes because `the_hash_algo` is a macro that expands to
> +        *     `the_repository->hash_algo`. So if Git commands try to access
> +        *     `the_hash_algo` without a Git directory we crash.
> +        *
> +        *   - Setting up the hash algorithm to be SHA1 by default breaks other
> +        *     commands when running with SHA256.
> +        *
> +        * This is another point in case why having global state is a bad idea.
> +        * Eventually, we should remove this hack and stop setting the hash
> +        * algorithm in this function altogether. Instead, it should only ever
> +        * be set via our repository setup procedures. But that requires more
> +        * work.
> +        *
> +        * As we discover the code paths that need fixing, we may remove this
> +        * code completely, but we are not there yet.
> +        */
> +       if (repo == the_repository &&
> +           git_env_bool("GIT_TEST_DEFAULT_HASH_IS_SHA1", 0))
> +               repo_set_hash_algo(repo, GIT_HASH_SHA1);
>  }
>
>  static void expand_base_dir(char **out, const char *in,
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 79d3e0e7d9..36d311fb4a 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -542,6 +542,10 @@ export EDITOR
>
>  GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
>  export GIT_DEFAULT_HASH
> +
> +GIT_TEST_DEFAULT_HASH_IS_SHA1=0

> +export GIT_TEST_DEFAULT_HASH_IS_SHA1
> +
>  GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
>  export GIT_DEFAULT_REF_FORMAT
>  GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
> --
> 2.45.0-145-g3e4a232f6e
>
>