From 5386b6fe50543d5d8c57c77037ccf3ed2e4e1b13 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Sun, 28 Aug 2022 00:58:49 +0200
Subject: [PATCH] Improve error message #543

---
 src/compiler/sema_expr.c                | 9 +++++++++
 test/test_suite/errors/missing_bang.c3  | 7 +++++++
 test/test_suite2/errors/missing_bang.c3 | 7 +++++++
 3 files changed, 23 insertions(+)
 create mode 100644 test/test_suite/errors/missing_bang.c3
 create mode 100644 test/test_suite2/errors/missing_bang.c3

diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index 46000b232..eff0935ed 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -8082,6 +8082,15 @@ bool sema_analyse_expr_rhs(SemaContext *context, Type *to, Expr *expr, bool allo
 		assert(allow_failable);
 	}
 	if (!sema_analyse_inferred_expr(context, to, expr)) return false;
+	if (to && allow_failable && to->canonical != expr->type->canonical && expr->type->canonical->type_kind == TYPE_FAULTTYPE)
+	{
+		Type *canonical = type_flatten_distinct(to);
+		if (canonical != type_anyerr && canonical->type_kind != TYPE_FAULTTYPE && expr->expr_kind == EXPR_CONST)
+		{
+			sema_error_at_after(expr->span, "You need to add a trailing '!' here to make this an optional.");
+			return false;
+		}
+	}
 	if (to && !cast_implicit(expr, to)) return false;
 	if (!allow_failable && IS_OPTIONAL(expr))
 	{
diff --git a/test/test_suite/errors/missing_bang.c3 b/test/test_suite/errors/missing_bang.c3
new file mode 100644
index 000000000..93d41fa64
--- /dev/null
+++ b/test/test_suite/errors/missing_bang.c3
@@ -0,0 +1,7 @@
+
+fault Bob { FOO }
+
+fn int! test()
+{
+	return Bob.FOO; // #error: You need to add a trailing
+}
\ No newline at end of file
diff --git a/test/test_suite2/errors/missing_bang.c3 b/test/test_suite2/errors/missing_bang.c3
new file mode 100644
index 000000000..93d41fa64
--- /dev/null
+++ b/test/test_suite2/errors/missing_bang.c3
@@ -0,0 +1,7 @@
+
+fault Bob { FOO }
+
+fn int! test()
+{
+	return Bob.FOO; // #error: You need to add a trailing
+}
\ No newline at end of file