Add suggestion for #3961

src/check_type.cpp

@@ -1559,11 +1559,30 @@ gb_internal Type *determine_type_from_polymorphic(CheckerContext *ctx, Type *pol
 		return poly_type;
 	}
 	if (show_error) {
+		ERROR_BLOCK();
 		gbString pts = type_to_string(poly_type);
 		gbString ots = type_to_string(operand.type, true);
 		defer (gb_string_free(pts));
 		defer (gb_string_free(ots));
 		error(operand.expr, "Cannot determine polymorphic type from parameter: '%s' to '%s'", ots, pts);
+
+		Type *pt = poly_type;
+		while (pt && pt->kind == Type_Generic && pt->Generic.specialized) {
+			pt = pt->Generic.specialized;
+		}
+		if (is_type_slice(pt) &&
+		    (is_type_dynamic_array(operand.type) || is_type_array(operand.type))) {
+			Ast *expr = unparen_expr(operand.expr);
+			if (expr->kind == Ast_CompoundLit) {
+				gbString es = type_to_string(base_any_array_type(operand.type));
+				error_line("\tSuggestion: Try using a slice compound literal instead '[]%s{...}'\n", es);
+				gb_string_free(es);
+			} else {
+				gbString os = expr_to_string(operand.expr);
+				error_line("\tSuggestion: Try slicing the value with '%s[:]'\n", os);
+				gb_string_free(os);
+			}
+		}
 	}
 	return t_invalid;
 }

src/types.cpp

@@ -1637,6 +1637,26 @@ gb_internal Type *base_array_type(Type *t) {
 	return t;
 }
 
+
+gb_internal Type *base_any_array_type(Type *t) {
+	Type *bt = base_type(t);
+	if (is_type_array(bt)) {
+		return bt->Array.elem;
+	} else if (is_type_slice(bt)) {
+		return bt->Slice.elem;
+	} else if (is_type_dynamic_array(bt)) {
+		return bt->DynamicArray.elem;
+	} else if (is_type_enumerated_array(bt)) {
+		return bt->EnumeratedArray.elem;
+	} else if (is_type_simd_vector(bt)) {
+		return bt->SimdVector.elem;
+	} else if (is_type_matrix(bt)) {
+		return bt->Matrix.elem;
+	}
+	return t;
+}
+
+
 gb_internal bool is_type_generic(Type *t) {
 	t = base_type(t);
 	return t->kind == Type_Generic;