environment: stop storing "core.warnAmbiguousRefs" globally

Same as the preceding commits, storing the "core.warnAmbiguousRefs"
value globally is misdesigned as this setting may be set per repository.

Move the logic into the repo-settings subsystem. The usual pattern here
is that users are expected to call `prepare_repo_settings()` before they
access the settings themselves. This seems somewhat fragile though, as
it is easy to miss and leads to somewhat ugly code patterns at the call
sites.

Instead, introduce a new function that encapsulates this logic for us.
This also allows us to change how exactly the lazy initialization works
in the future, e.g. by only partially initializing values as requested
by the caller.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repo-settings.h

@@ -56,16 +56,20 @@ struct repo_settings {
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 
 	int core_multi_pack_index;
+	int warn_ambiguous_refs; /* lazily loaded via accessor */
 };
 #define REPO_SETTINGS_INIT { \
 	.index_version = -1, \
 	.core_untracked_cache = UNTRACKED_CACHE_KEEP, \
 	.fetch_negotiation_algorithm = FETCH_NEGOTIATION_CONSECUTIVE, \
+	.warn_ambiguous_refs = -1, \
 }
 
 void prepare_repo_settings(struct repository *r);
 
 /* Read the value for "core.logAllRefUpdates". */
 enum log_refs_config repo_settings_get_log_all_ref_updates(struct repository *repo);
+/* Read the value for "core.warnAmbiguousRefs". */
+int repo_settings_get_warn_ambiguous_refs(struct repository *repo);
 
 #endif /* REPO_SETTINGS_H */