environment: stop storing `core.attributesFile` globally

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.

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()' s created 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>
Mentored-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Olamide Caleb Bello <belkid98@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

attr.c

@@ -881,10 +881,11 @@ const char *git_attr_system_file(void)
 
 const char *git_attr_global_file(void)
 {
-	if (!git_attributes_file)
-		git_attributes_file = xdg_config_home("attributes");
+	struct repo_config_values *cfg = repo_config_values(the_repository);
+	if (!cfg->attributes_file)
+		cfg->attributes_file = xdg_config_home("attributes");
 
-	return git_attributes_file;
+	return cfg->attributes_file;
 }
 
 int git_attr_system_is_enabled(void)

environment.c

@@ -53,7 +53,6 @@ char *git_commit_encoding;
 char *git_log_output_encoding;
 char *apply_default_whitespace;
 char *apply_default_ignorewhitespace;
-char *git_attributes_file;
 int zlib_compression_level = Z_BEST_SPEED;
 int pack_compression_level = Z_DEFAULT_COMPRESSION;
 int fsync_object_files = -1;
@@ -327,6 +326,8 @@ next_name:
 static int git_default_core_config(const char *var, const char *value,
 				   const struct config_context *ctx, void *cb)
 {
+	struct repo_config_values *cfg = repo_config_values(the_repository);
+
 	/* This needs a better name */
 	if (!strcmp(var, "core.filemode")) {
 		trust_executable_bit = git_config_bool(var, value);
@@ -364,8 +365,8 @@ static int git_default_core_config(const char *var, const char *value,
 	}
 
 	if (!strcmp(var, "core.attributesfile")) {
-		FREE_AND_NULL(git_attributes_file);
-		return git_config_pathname(&git_attributes_file, var, value);
+		FREE_AND_NULL(cfg->attributes_file);
+		return git_config_pathname(&cfg->attributes_file, var, value);
 	}
 
 	if (!strcmp(var, "core.bare")) {
@@ -756,3 +757,8 @@ int git_default_config(const char *var, const char *value,
 	/* Add other config variables here and to Documentation/config.adoc. */
 	return 0;
 }
+
+void repo_config_values_init(struct repo_config_values *cfg)
+{
+	cfg->attributes_file = NULL;
+}

environment.h

@@ -84,6 +84,14 @@ extern const char * const local_repo_env[];
 
 struct strvec;
 
+struct repository;
+struct repo_config_values {
+	/* section "core" config values */
+	char *attributes_file;
+};
+
+struct repo_config_values *repo_config_values(struct repository *repo);
+
 /*
  * Wrapper of getenv() that returns a strdup value. This value is kept
  * in argv to be freed later.
@@ -107,6 +115,8 @@ const char *strip_namespace(const char *namespaced_ref);
 int git_default_config(const char *, const char *,
 		       const struct config_context *, void *);
 
+void repo_config_values_init(struct repo_config_values *cfg);
+
 /*
  * TODO: All the below state either explicitly or implicitly relies on
  * `the_repository`. We should eventually get rid of these and make the
@@ -152,7 +162,6 @@ extern int assume_unchanged;
 extern int warn_on_object_refname_ambiguity;
 extern char *apply_default_whitespace;
 extern char *apply_default_ignorewhitespace;
-extern char *git_attributes_file;
 extern int zlib_compression_level;
 extern int pack_compression_level;
 extern unsigned long pack_size_limit_cfg;

oss-fuzz/fuzz-commit-graph.c

@@ -10,6 +10,7 @@ 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

@@ -50,13 +50,27 @@ static void set_default_hash_algo(struct repository *repo)
 	repo_set_hash_algo(repo, algo);
 }
 
+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_;
+}
+
 void initialize_repository(struct repository *repo)
 {
+	if (repo->initialized)
+		BUG("repository initialized already");
+	repo->initialized = true;
+
 	repo->remote_state = remote_state_new();
 	repo->parsed_objects = parsed_object_pool_new(repo);
 	ALLOC_ARRAY(repo->index, 1);
 	index_state_init(repo->index, repo);
 	repo->check_deprecated_config = true;
+	repo_config_values_init(&repo->config_values_private_);
 
 	/*
 	 * When a command runs inside a repository, it learns what

repository.h

@@ -3,6 +3,7 @@
 
 #include "strmap.h"
 #include "repo-settings.h"
+#include "environment.h"
 
 struct config_set;
 struct git_hash_algo;
@@ -148,6 +149,9 @@ struct repository {
 	/* Repository's compatibility hash algorithm. */
 	const struct git_hash_algo *compat_hash_algo;
 
+	/* Repository's config values parsed by git_default_config() */
+	struct repo_config_values config_values_private_;
+
 	/* Repository's reference storage format, as serialized on disk. */
 	enum ref_storage_format ref_storage_format;
 
@@ -171,6 +175,9 @@ struct repository {
 
 	/* Should repo_config() check for deprecated settings */
 	bool check_deprecated_config;
+
+	/* Has this repository instance been initialized? */
+	bool initialized;
 };
 
 #ifdef USE_THE_REPOSITORY_VARIABLE