[Outreachy PATCH v7 0/3] store repo specific config values in new `struct repo_config_values`

Hi Git Community, Over the course of my ongoing internship, which focused on moving repo specific global variables in environment.h into local scope, I have attempted to move some variables into the struct repo-settings. However there has been some design concerns as regards the use of `prepare_repo_settings()` with respect to when and where to call the function, and also the change in behaviours when the variable is lazily loaded as discussed in [1] and [2].

After different deliberations, Phillip Wood proposed creating a new config struct [3], adding it to the repository struct and passing the repo struct to `git_default_config()` to store parsed repo specific config values per repo. This ensures the current behaviours will be retained.

In version v6, the fuzz-commit-graph failed due to the test being run multiples times in the same process. This makes us get a BUG due to the repository being reinitialized in the same process. But now resetting the initialization using memset before rerunning the test, the failure is not longer experienced.

1. https://lore.kernel.org/git/43aaec10-2696-44c9-8728-2045b83dc5d3@gmail.com/
2. https://lore.kernel.org/git/a881499d-e236-4f8e-a217-b6bce69e3e3c@gmail.com/
3. https://lore.kernel.org/git/8899016f-eeef-404b-8da6-ff3a90e81cea@gmail.com
4. https://github.com/git/git/actions/runs/21633462506/job/62352191148?pr=2166
5. https://gitlab.com/gitlab-community/gitlab-org/git/-/pipelines/2303203992

Changes in v7:
==============
- Added the code to reset the initialization of the_repository
  in the fuzz-commit-graph test in Patch 1.
- Changed the call to rep_config_values_init() in
  initialze_repository() by passing it the repo config_values_private_
  struct instead of the accessor function in Patch 1.
- Modified the commit message in Patch 1
- Added extra lines between variable declarations and code

Olamide Caleb Bello (3):
  environment: stop storing `core.attributesFile` globally
  environment: stop using core.sparseCheckout globally
  environment: move "branch.autoSetupMerge" into `struct
    repo_config_values`

 attr.c                       |  7 ++++---
 branch.h                     |  2 --
 builtin/backfill.c           |  3 ++-
 builtin/branch.c             |  3 ++-
 builtin/checkout.c           |  3 ++-
 builtin/clone.c              |  4 +++-
 builtin/grep.c               |  2 +-
 builtin/mv.c                 |  3 ++-
 builtin/push.c               |  3 ++-
 builtin/sparse-checkout.c    | 31 ++++++++++++++++++++-----------
 builtin/submodule--helper.c  |  3 ++-
 builtin/worktree.c           |  3 ++-
 dir.c                        |  4 +++-
 environment.c                | 28 ++++++++++++++++++----------
 environment.h                | 17 +++++++++++++++--
 oss-fuzz/fuzz-commit-graph.c |  1 +
 repository.c                 | 14 ++++++++++++++
 repository.h                 |  7 +++++++
 sparse-index.c               |  7 +++++--
 unpack-trees.c               |  3 ++-
 wt-status.c                  |  4 +++-
 21 files changed, 110 insertions(+), 42 deletions(-)

Range diff versus v6:
=====================
1:  7e3082125d ! 1:  48821a3848 environment: stop storing `core.attributesFile` globally
    @@ Commit message

         The `core.attributeFile` config value is parsed in
         git_default_core_config(), loaded eagerly and stored in the global
    -    variable `git_attributes_file`. Storing this value in a global variable
    -    can lead to it being overwritten by another repository when more than one
    -    Git repository run in the same Git process.
    +    variable `git_attributes_file`. Storing this value in a global
    +    variable can lead to it being overwritten by another repository when
    +    more than one Git repository run in the same Git process.

         Create a new struct `repo_config_values` to hold this value and
         other repository dependent values parsed by `git_default_config()`.
         This will ensure the current behaviour remains the same while also
         enabling the libification of Git.

    -    An accessor function 'repo_config_values()' is created and used to access
    -    the new struct member of the repository struct.
    -    This is to ensure that we detect if the struct repository has been
    -    initialized and also prevent double initialization of the repository.
    -
    -    It is important to note that `git_default_config()` is a wrapper to other
    -    `git_default_*_config()` functions such as `git_default_core_config()`.
    -    Therefore to access and modify this global variable,
    -    the change has to be made `git_default_core_config()`.
    +    An accessor function 'repo_config_values()' to ensure that we do not
    +    access an uninitialized repository, or an instance of a different
    +    repository than the current one.

         Suggested-by: Phillip Wood <phillip.wood123@gmail.com>
         Mentored-by: Christian Couder <christian.couder@gmail.com>
    @@ environment.h: extern int assume_unchanged;
      extern int pack_compression_level;
      extern unsigned long pack_size_limit_cfg;

    + ## oss-fuzz/fuzz-commit-graph.c ##
    +@@ oss-fuzz/fuzz-commit-graph.c: int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
    + {
    + 	struct commit_graph *g;
    +
    ++	memset(the_repository, 0, sizeof(*the_repository));
    + 	initialize_repository(the_repository);
    +
    + 	/*
    +
      ## repository.c ##
     @@ repository.c: static void set_default_hash_algo(struct repository *repo)
      	repo_set_hash_algo(repo, algo);
    @@ repository.c: static void set_default_hash_algo(struct repository *repo)

     +struct repo_config_values *repo_config_values(struct repository *repo)
     +{
    ++	if (repo != the_repository)
    ++		BUG("trying to read config from wrong repository instance");
     +	if(!repo->initialized)
     +		BUG("config values from uninitialized repository");
     +	return &repo->config_values_private_;
    @@ repository.c: static void set_default_hash_algo(struct repository *repo)
      	ALLOC_ARRAY(repo->index, 1);
      	index_state_init(repo->index, repo);
      	repo->check_deprecated_config = true;
    -+	repo_config_values_init(repo_config_values(repo));
    ++	repo_config_values_init(&repo->config_values_private_);

      	/*
      	 * When a command runs inside a repository, it learns what
2:  8645b4f595 ! 2:  7d33f1ef0f environment: stop using core.sparseCheckout globally
    @@ builtin/clone.c: static int git_sparse_checkout_init(const char *repo)
      	struct child_process cmd = CHILD_PROCESS_INIT;
      	int result = 0;
     +	struct repo_config_values *cfg = repo_config_values(the_repository);
    ++
      	strvec_pushl(&cmd.args, "-C", repo, "sparse-checkout", "set", NULL);

      	/*
    @@ dir.c: enum pattern_match_result path_matches_pattern_list(
      {
     -	if (!core_apply_sparse_checkout)
     +	struct repo_config_values *cfg = repo_config_values(the_repository);
    ++
     +	if (!cfg->apply_sparse_checkout)
      		return 1;
      	if (istate->sparse_checkout_patterns)
    @@ sparse-index.c: static int index_has_unmerged_entries(struct index_state *istate
      {
     -	if (!core_apply_sparse_checkout || !core_sparse_checkout_cone)
     +	struct repo_config_values *cfg = repo_config_values(the_repository);
    ++
     +	if (!cfg->apply_sparse_checkout || !core_sparse_checkout_cone)
      		return 0;

3:  60451b93a5 = 3:  c3ecfa63b9 environment: move "branch.autoSetupMerge" into `struct repo_config_values`