checker: check generic type indexing error (#10345)

vlib/v/checker/checker.v

@@ -6492,32 +6492,23 @@ fn (mut c Checker) check_index(typ_sym &ast.TypeSymbol, index ast.Expr, index_ty
 
 pub fn (mut c Checker) index_expr(mut node ast.IndexExpr) ast.Type {
 	mut typ := c.expr(node.left)
-	mut typ_sym := c.table.get_final_type_symbol(typ)
+	typ_sym := c.table.get_final_type_symbol(typ)
 	node.left_type = typ
-	for {
+	match typ_sym.kind {
-		match typ_sym.kind {
+		.map {
-			.map {
+			node.is_map = true
-				node.is_map = true
-				break
-			}
-			.array {
-				node.is_array = true
-				break
-			}
-			.array_fixed {
-				node.is_farray = true
-				break
-			}
-			.any {
-				typ = c.unwrap_generic(typ)
-				node.left_type = typ
-				typ_sym = c.table.get_final_type_symbol(typ)
-				continue
-			}
-			else {
-				break
-			}
 		}
+		.array {
+			node.is_array = true
+		}
+		.array_fixed {
+			node.is_farray = true
+		}
+		.any {
+			c.error('generic type `$typ_sym.name` does not support indexing, please use compound type, e.g. `[]$typ_sym.name`',
+				node.pos)
+		}
+		else {}
 	}
 	if typ_sym.kind !in [.array, .array_fixed, .string, .map] && !typ.is_ptr()
 		&& typ !in [ast.byteptr_type, ast.charptr_type] && !typ.has_flag(.variadic) {

vlib/v/checker/tests/generics_type_para_index_err.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/generics_type_para_index_err.vv:2:24: error: generic type `T` does not support indexing, please use compound type, e.g. `[]T`
+    1 | fn show_element<T>(arr &T) string {
+    2 |     return unsafe { '${arr[1]}' }
+      |                           ~~~
+    3 | }
+    4 |

vlib/v/checker/tests/generics_type_para_index_err.vv

@@ -2,9 +2,8 @@ fn show_element<T>(arr &T) string {
 	return unsafe { '${arr[1]}' }
 }
 
-fn test_generic_with_fixed_array_type() {
+fn main() {
 	a := [1, 2, 3]!
 	ret := show_element(a)
 	println(ret)
-	assert ret == '2'
 }