[PATCH v3 3/5] read-cache & fetch-negotiator: check "enum" values in switch()

Change tweak_untracked_cache() in "read-cache.c" to use a switch() to
have the compiler assert that we checked all possible values in the
"enum untracked_cache_setting" type, and likewise remove the "default"
case in fetch_negotiator_init() in favor of checking for
"FETCH_NEGOTIATION_UNSET" and "FETCH_NEGOTIATION_NONE".

As will be discussed in a subsequent we'll only ever have either of
these set to FETCH_NEGOTIATION_NONE, FETCH_NEGOTIATION_UNSET and
UNTRACKED_CACHE_UNSET within the prepare_repo_settings() function
itself. In preparation for fixing that code let's add a BUG() here to
mark this as unreachable code.

See ad0fb659993 (repo-settings: parse core.untrackedCache, 2019-08-13)
for when the "unset" and "keep" handling for core.untrackedCache was
consolidated, and aaf633c2ad1 (repo-settings: create
feature.experimental setting, 2019-08-13) for the addition of the
"default" pattern in "fetch-negotiator.c".

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 fetch-negotiator.c |  4 +++-
 read-cache.c       | 15 ++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/fetch-negotiator.c b/fetch-negotiator.c
index 57ed5784e14..237f92b8696 100644
--- a/fetch-negotiator.c
+++ b/fetch-negotiator.c

@@ -19,8 +19,10 @@ void fetch_negotiator_init(struct repository *r,
 		return;
 
 	case FETCH_NEGOTIATION_DEFAULT:
-	default:
 		default_negotiator_init(negotiator);
 		return;
+	case FETCH_NEGOTIATION_NONE:
+	case FETCH_NEGOTIATION_UNSET:
+		BUG("FETCH_NEGOTIATION_UNSET only in prepare_repo_settings()");
 	}
 }

diff --git a/read-cache.c b/read-cache.c
index 9048ef9e905..6918dc3d8b2 100644
--- a/read-cache.c
+++ b/read-cache.c

@@ -1944,13 +1944,18 @@ static void tweak_untracked_cache(struct index_state *istate)
 
 	prepare_repo_settings(r);
 
-	if (r->settings.core_untracked_cache  == UNTRACKED_CACHE_REMOVE) {
+	switch (r->settings.core_untracked_cache) {
+	case UNTRACKED_CACHE_REMOVE:
 		remove_untracked_cache(istate);
-		return;
-	}
-
-	if (r->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE)
+		break;
+	case UNTRACKED_CACHE_WRITE:
 		add_untracked_cache(istate);
+		break;
+	case UNTRACKED_CACHE_KEEP:
+		break;
+	case UNTRACKED_CACHE_UNSET:
+		BUG("UNTRACKED_CACHE_UNSET only in prepare_repo_settings()");
+	}
 }
 
 static void tweak_split_index(struct index_state *istate)

-- 
2.33.0.1092.g44c994ea1be