checker: improve error message of fn args mismatch (#15550)

vlib/v/checker/check_types.v

@@ -389,7 +389,12 @@ pub fn (mut c Checker) check_matching_function_symbols(got_type_sym &ast.TypeSym
 		if exp_arg_is_ptr != got_arg_is_ptr {
 			exp_arg_pointedness := if exp_arg_is_ptr { 'a pointer' } else { 'NOT a pointer' }
 			got_arg_pointedness := if got_arg_is_ptr { 'a pointer' } else { 'NOT a pointer' }
-			c.add_error_detail('`$exp_fn.name`\'s expected fn argument: `$exp_arg.name` is $exp_arg_pointedness, but the passed fn argument: `$got_arg.name` is $got_arg_pointedness')
+			if exp_fn.name.len == 0 {
+				c.add_error_detail('expected argument ${i + 1} to be $exp_arg_pointedness, but the passed argument ${
+					i + 1} is $got_arg_pointedness')
+			} else {
+				c.add_error_detail('`$exp_fn.name`\'s expected argument `$exp_arg.name` to be $exp_arg_pointedness, but the passed argument `$got_arg.name` is $got_arg_pointedness')
+			}
 			return false
 		} else if exp_arg_is_ptr && got_arg_is_ptr {
 			continue

vlib/v/checker/tests/array_sort_with_compare_err.out

@@ -12,7 +12,7 @@ vlib/v/checker/tests/array_sort_with_compare_err.vv:4:26: error: cannot use `fn
       |                             ~~~~~~~~~~~~~~~~~
     5 |     println(names)
     6 |
-Details: ``'s expected fn argument: `` is a pointer, but the passed fn argument: `a` is NOT a pointer
+Details: expected argument 1 to be a pointer, but the passed argument 1 is NOT a pointer
 vlib/v/checker/tests/array_sort_with_compare_err.vv:7:26: error: cannot use `int literal` as `fn (voidptr, voidptr) int` in argument 1 to `[]string.sort_with_compare`
     5 |     println(names)
     6 |

vlib/v/checker/tests/fn_args.out

@@ -19,7 +19,7 @@ vlib/v/checker/tests/fn_args.vv:11:6: error: cannot use `fn (&int)` as `fn (int)
       |         ~~~~~~~~~~~~~~
    12 |     fun(fn (ii ...int) {})
    13 | }
-Details: ``'s expected fn argument: `` is NOT a pointer, but the passed fn argument: `i` is a pointer
+Details: expected argument 1 to be NOT a pointer, but the passed argument 1 is a pointer
 vlib/v/checker/tests/fn_args.vv:12:6: error: cannot use `fn (...int)` as `fn (int)` in argument 1 to `fun`
    10 |     arr([5]!)
    11 |     fun(fn (i &int) {})

vlib/v/checker/tests/non_matching_functional_args.out

@@ -5,7 +5,7 @@ vlib/v/checker/tests/non_matching_functional_args.vv:27:6: error: cannot use `fn
       |         ~~~~~~~~~~~~~~~~~~
    28 |         t.rename()
    29 |         println(t.name)
-Details: `main.MyFn`'s expected fn argument: `zzzz` is NOT a pointer, but the passed fn argument: `t` is a pointer
+Details: `main.MyFn`'s expected argument `zzzz` to be NOT a pointer, but the passed argument `t` is a pointer
 vlib/v/checker/tests/non_matching_functional_args.vv:31:6: error: cannot use `fn (mut Table)` as `fn (Table)` in argument 1 to `sum`
    29 |         println(t.name)
    30 |     })
@@ -13,4 +13,4 @@ vlib/v/checker/tests/non_matching_functional_args.vv:31:6: error: cannot use `fn
       |         ~~~
    32 |     sum(yyy)
    33 | }
-Details: `main.MyFn`'s expected fn argument: `zzzz` is NOT a pointer, but the passed fn argument: `mytable` is a pointer
+Details: `main.MyFn`'s expected argument `zzzz` to be NOT a pointer, but the passed argument `mytable` is a pointer

vlib/v/checker/tests/struct_field_type_err.out

@@ -19,7 +19,7 @@ vlib/v/checker/tests/struct_field_type_err.vv:14:3: error: cannot assign to fiel
       |         ~~~~~~~~~~~~~~~~~~~~~~~~
    15 |         f2: fn (v voidptr) {}
    16 |         data: true
-Details: ``'s expected fn argument: `` is a pointer, but the passed fn argument: `v` is NOT a pointer
+Details: expected argument 1 to be a pointer, but the passed argument 1 is NOT a pointer
 vlib/v/checker/tests/struct_field_type_err.vv:15:3: error: cannot assign to field `f2`: expected `fn (...voidptr)`, not `fn (voidptr)`
    13 |         b: 0
    14 |         f1: fn (v ...voidptr) {}
@@ -27,7 +27,7 @@ vlib/v/checker/tests/struct_field_type_err.vv:15:3: error: cannot assign to fiel
       |         ~~~~~~~~~~~~~~~~~~~~~
    16 |         data: true
    17 |     }
-Details: ``'s expected fn argument: `` is NOT a pointer, but the passed fn argument: `v` is a pointer
+Details: expected argument 1 to be NOT a pointer, but the passed argument 1 is a pointer
 vlib/v/checker/tests/struct_field_type_err.vv:16:3: error: cannot assign to field `data`: expected `&Data`, not `bool`
    14 |         f1: fn (v ...voidptr) {}
    15 |         f2: fn (v voidptr) {}