checker: fix array method error message with generic type

vlib/v/checker/fn.v

@@ -3568,7 +3568,7 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 		if node.args.len != 1 {
 			c.error('`.contains()` expected 1 argument, but got ${node.args.len}', node.pos)
 		} else if !left_sym.has_method('contains') {
-			arg_typ := c.expr(mut node.args[0].expr)
+			arg_typ := c.unwrap_generic(c.expr(mut node.args[0].expr))
 			c.check_expected_call_arg(arg_typ, c.unwrap_generic(elem_typ), node.language,
 				node.args[0]) or {
 				c.error('${err.msg()} in argument 1 to `.contains()`', node.args[0].pos)
@@ -3582,8 +3582,9 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 		if node.args.len != 1 {
 			c.error('`.index()` expected 1 argument, but got ${node.args.len}', node.pos)
 		} else if !left_sym.has_method('index') {
-			arg_typ := c.expr(mut node.args[0].expr)
-			c.check_expected_call_arg(arg_typ, elem_typ, node.language, node.args[0]) or {
+			arg_typ := c.unwrap_generic(c.expr(mut node.args[0].expr))
+			c.check_expected_call_arg(arg_typ, c.unwrap_generic(elem_typ), node.language,
+				node.args[0]) or {
 				c.error('${err.msg()} in argument 1 to `.index()`', node.args[0].pos)
 			}
 		}
@@ -3625,7 +3626,7 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 		if node.args.len != 1 {
 			c.error('`.delete()` expected 1 argument, but got ${node.args.len}', node.pos)
 		} else {
-			arg_typ := c.expr(mut node.args[0].expr)
+			arg_typ := c.unwrap_generic(c.expr(mut node.args[0].expr))
 			c.check_expected_call_arg(arg_typ, ast.int_type, node.language, node.args[0]) or {
 				c.error('${err.msg()} in argument 1 to `.delete()`', node.args[0].pos)
 			}

vlib/v/checker/tests/array_generic_methods_err.out

@@ -0,0 +1,21 @@
+vlib/v/checker/tests/array_generic_methods_err.vv:3:23: error: cannot use `[]string` as `string` in argument 1 to `.contains()`
+    1 | fn generic_fn[T]() {
+    2 |     mut arr := []T{}
+    3 |     println(arr.contains(arr))
+      |                          ~~~
+    4 |     arr.delete(arr)
+    5 |     arr.index(arr)
+vlib/v/checker/tests/array_generic_methods_err.vv:4:13: error: cannot use `[]string` as `int` in argument 1 to `.delete()`
+    2 |     mut arr := []T{}
+    3 |     println(arr.contains(arr))
+    4 |     arr.delete(arr)
+      |                ~~~
+    5 |     arr.index(arr)
+    6 | }
+vlib/v/checker/tests/array_generic_methods_err.vv:5:12: error: cannot use `[]string` as `string` in argument 1 to `.index()`
+    3 |     println(arr.contains(arr))
+    4 |     arr.delete(arr)
+    5 |     arr.index(arr)
+      |               ~~~
+    6 | }
+    7 |

vlib/v/checker/tests/array_generic_methods_err.vv

@@ -0,0 +1,10 @@
+fn generic_fn[T]() {
+	mut arr := []T{}
+	println(arr.contains(arr))
+	arr.delete(arr)
+	arr.index(arr)
+}
+
+fn main() {
+	generic_fn[string]()
+}