Add `@(warning=<string>)`

src/check_decl.cpp

@@ -724,6 +724,7 @@ void check_proc_decl(CheckerContext *ctx, Entity *e, DeclInfo *d) {
 
 	e->Procedure.is_export = ac.is_export;
 	e->deprecated_message = ac.deprecated_message;
+	e->warning_message = ac.warning_message;
 	ac.link_name = handle_link_name(ctx, e->token, ac.link_name, ac.link_prefix);
 	if (ac.has_disabled_proc) {
 		if (ac.disabled_proc) {

src/checker.cpp

@@ -1303,6 +1303,10 @@ void add_entity_use(CheckerContext *c, Ast *identifier, Entity *entity) {
 		if (dmsg.len > 0) {
 			warning(identifier, "%.*s is deprecated: %.*s", LIT(entity->token.string), LIT(dmsg));
 		}
+		String wmsg = entity->warning_message;
+		if (wmsg.len > 0) {
+			warning(identifier, "%.*s: %.*s", LIT(entity->token.string), LIT(wmsg));
+		}
 	}
 	entity->flags |= EntityFlag_Used;
 	add_declaration_dependency(c, entity);
@@ -2698,6 +2702,20 @@ DECL_ATTRIBUTE_PROC(proc_decl_attribute) {
 			error(elem, "Expected a string value for '%.*s'", LIT(name));
 		}
 		return true;
+	} else if (name == "warning") {
+		ExactValue ev = check_decl_attribute_value(c, value);
+
+		if (ev.kind == ExactValue_String) {
+			String msg = ev.value_string;
+			if (msg.len == 0) {
+				error(elem, "Warning message cannot be an empty string");
+			} else {
+				ac->warning_message = msg;
+			}
+		} else {
+			error(elem, "Expected a string value for '%.*s'", LIT(name));
+		}
+		return true;
 	} else if (name == "require_results") {
 		if (value != nullptr) {
 			error(elem, "Expected no value for '%.*s'", LIT(name));

src/checker.hpp

@@ -113,6 +113,7 @@ struct AttributeContext {
 	isize   init_expr_list_count;
 	String  thread_local_model;
 	String  deprecated_message;
+	String  warning_message;
 	DeferredProcedure deferred_procedure;
 	u32 optimization_mode; // ProcedureOptimizationMode
 };

src/entity.cpp

@@ -136,6 +136,7 @@ struct Entity {
 
 	u64         order_in_src;
 	String      deprecated_message;
+	String      warning_message;
 
 	// IMPORTANT NOTE(bill): This must be a discriminated union because of patching
 	// later entity kinds