Try to fix the #+lazy entities

src/check_decl.cpp

@@ -2137,10 +2137,16 @@ gb_internal void check_entity_decl(CheckerContext *ctx, Entity *e, DeclInfo *d,
 	if (e->state == EntityState_Resolved)  {
 		return;
 	}
-	GlobalEntityTimingFrame timing_frame = global_entity_timing_begin(e);
-	if (e->flags & EntityFlag_Lazy) {
+	bool is_lazy = (e->flags & EntityFlag_Lazy) != 0;
+	if (is_lazy) {
 		mutex_lock(&ctx->info->lazy_mutex);
+		if (e->state == EntityState_Resolved) {
+			// NOTE: another thread checked it whilst this one waited
+			mutex_unlock(&ctx->info->lazy_mutex);
+			return;
+		}
 	}
+	GlobalEntityTimingFrame timing_frame = global_entity_timing_begin(e);
 
 	String name = e->token.string;
 
@@ -2225,12 +2231,22 @@ gb_internal void check_entity_decl(CheckerContext *ctx, Entity *e, DeclInfo *d,
 end:;
 	global_entity_timing_end(timing_frame, e);
 	// NOTE(bill): Add it to the list of checked entities
-	if (e->flags & EntityFlag_Lazy) {
+	if (is_lazy) {
 		array_add(&ctx->info->entities, e);
 		mutex_unlock(&ctx->info->lazy_mutex);
 	}
 }
 
+// A lazy entity is only ever in progress on the thread holding `lazy_mutex`, so taking it (it is
+// recursive) waits out another thread and is a no-op on the thread that is checking it
+gb_internal void wait_for_lazy_entity(CheckerContext *ctx, Entity *e) {
+	if ((e->flags & EntityFlag_Lazy) == 0 || e->state == EntityState_Resolved) {
+		return;
+	}
+	mutex_lock(&ctx->info->lazy_mutex);
+	mutex_unlock(&ctx->info->lazy_mutex);
+}
+
 
 gb_internal void add_deps_from_child_to_parent(DeclInfo *decl) {
 	if (decl && decl->parent) {