checker: check errors of cast to byte (#12961)

vlib/v/checker/checker.v

@@ -3487,10 +3487,6 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 			c.error('cannot convert type `$from_type_sym.name` to `$to_type_sym.name` (alias to `$to_type_sym_final.name`)',
 				node.pos)
 		}
-	} else if to_type_sym.kind == .byte && from_type_sym.kind == .alias
-		&& from_type_sym_final.kind != .byte && !from_type.is_ptr() {
-		type_name := c.table.type_to_str(from_type)
-		c.error('cannot cast type `$type_name` to `byte`', node.pos)
 	} else if to_type_sym.kind == .struct_ && !to_type.is_ptr()
 		&& !(to_type_sym.info as ast.Struct).is_typedef {
 		// For now we ignore C typedef because of `C.Window(C.None)` in vlib/clipboard
@@ -3523,10 +3519,13 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		if (to_type.is_ptr() || to_type_sym.kind !in [.sum_type, .interface_]) && !c.is_builtin_mod {
 			from_type_name := c.table.type_to_str(from_type)
 			type_name := c.table.type_to_str(to_type)
-			snexpr := node.expr.str()
+			c.error('cannot cast struct `$from_type_name` to `$type_name`', node.pos)
-			c.error('cannot cast struct `$from_type_name` to `$type_name`, use `${snexpr}.str()` instead.',
-				node.pos)
 		}
+	} else if to_type_sym.kind == .byte && !from_type_sym_final.is_number()
+		&& !from_type_sym_final.is_pointer() && !from_type.is_ptr()
+		&& from_type_sym_final.kind !in [.char, .enum_, .bool] {
+		type_name := c.table.type_to_str(from_type)
+		c.error('cannot cast type `$type_name` to `byte`', node.pos)
 	} else if from_type.has_flag(.optional) || from_type.has_flag(.variadic) {
 		// variadic case can happen when arrays are converted into variadic
 		msg := if from_type.has_flag(.optional) { 'an optional' } else { 'a variadic' }

vlib/v/checker/tests/cast_alias_to_byte_err.out

@@ -1,7 +0,0 @@
-vlib/v/checker/tests/cast_alias_to_byte_err.vv:5:7: error: cannot cast type `Foo` to `byte`
-    3 | fn main() {
-    4 |     a := Foo('hello')
-    5 |     b := byte(a)
-      |          ~~~~~~~
-    6 |     println(b)
-    7 | }

vlib/v/checker/tests/cast_alias_to_byte_err.vv

@@ -1,7 +0,0 @@
-type Foo = string
-
-fn main() {
-	a := Foo('hello')
-	b := byte(a)
-	println(b)
-}

vlib/v/checker/tests/cast_string_err.out

@@ -12,7 +12,7 @@ vlib/v/checker/tests/cast_string_err.vv:18:9: error: cannot cast sumtype `Sumtyp
       |            ~~~~~~~~~~
    19 |     println(sst)
    20 |     //
-vlib/v/checker/tests/cast_string_err.vv:22:10: error: cannot cast struct `Abc` to `string`, use `abc.str()` instead.
+vlib/v/checker/tests/cast_string_err.vv:22:10: error: cannot cast struct `Abc` to `string`
    20 |     //
    21 |     abc := Abc{}
    22 |     sabc := string(abc)

vlib/v/checker/tests/cast_to_byte_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/cast_to_byte_err.vv:10:7: error: cannot cast type `string` to `byte`
+    8 | fn main() {
+    9 |     // should be errors:
+   10 |     _ := byte('hello')
+      |          ~~~~~~~~~~~~~
+   11 |     _ := byte(SAlias('hello'))
+   12 |
+vlib/v/checker/tests/cast_to_byte_err.vv:11:7: error: cannot cast type `SAlias` to `byte`
+    9 |     // should be errors:
+   10 |     _ := byte('hello')
+   11 |     _ := byte(SAlias('hello'))
+      |          ~~~~~~~~~~~~~~~~~~~~~
+   12 |
+   13 |     // should be allowed:

vlib/v/checker/tests/cast_to_byte_err.vv

@@ -0,0 +1,23 @@
+type SAlias = string
+
+type CAlias = char
+type IAlias = int
+type UAlias = u32
+type FAlias = f32
+
+fn main() {
+	// should be errors:
+	_ := byte('hello')
+	_ := byte(SAlias('hello'))
+
+	// should be allowed:
+	_ := byte(char(1))
+	_ := byte(int(1))
+	_ := byte(u32(1))
+	_ := byte(f32(1.0))
+
+	_ := byte(CAlias(1))
+	_ := byte(IAlias(1))
+	_ := byte(UAlias(1))
+	_ := byte(FAlias(1))
+}

vlib/v/checker/tests/struct_type_cast_err.out

@@ -1,60 +1,60 @@
-vlib/v/checker/tests/struct_type_cast_err.vv:5:10: error: cannot cast struct `Foo` to `string`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:5:10: error: cannot cast struct `Foo` to `string`
     3 | fn main() {
     4 |     foo := Foo{}
     5 |     _ := string(foo)
       |          ~~~~~~~~~~~
     6 |     _ := int(foo)
     7 |     _ := u64(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:6:10: error: cannot cast struct `Foo` to `int`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:6:10: error: cannot cast struct `Foo` to `int`
     4 |     foo := Foo{}
     5 |     _ := string(foo)
     6 |     _ := int(foo)
       |          ~~~~~~~~
     7 |     _ := u64(foo)
     8 |     _ := u32(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:7:10: error: cannot cast struct `Foo` to `u64`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:7:10: error: cannot cast struct `Foo` to `u64`
     5 |     _ := string(foo)
     6 |     _ := int(foo)
     7 |     _ := u64(foo)
       |          ~~~~~~~~
     8 |     _ := u32(foo)
     9 |     _ := rune(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:8:10: error: cannot cast struct `Foo` to `u32`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:8:10: error: cannot cast struct `Foo` to `u32`
     6 |     _ := int(foo)
     7 |     _ := u64(foo)
     8 |     _ := u32(foo)
       |          ~~~~~~~~
     9 |     _ := rune(foo)
    10 |     _ := byte(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:9:10: error: cannot cast struct `Foo` to `rune`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:9:10: error: cannot cast struct `Foo` to `rune`
     7 |     _ := u64(foo)
     8 |     _ := u32(foo)
     9 |     _ := rune(foo)
       |          ~~~~~~~~~
    10 |     _ := byte(foo)
    11 |     _ := i8(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:10:10: error: cannot cast struct `Foo` to `byte`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:10:10: error: cannot cast struct `Foo` to `byte`
     8 |     _ := u32(foo)
     9 |     _ := rune(foo)
    10 |     _ := byte(foo)
       |          ~~~~~~~~~
    11 |     _ := i8(foo)
    12 |     _ := i64(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:11:10: error: cannot cast struct `Foo` to `i8`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:11:10: error: cannot cast struct `Foo` to `i8`
     9 |     _ := rune(foo)
    10 |     _ := byte(foo)
    11 |     _ := i8(foo)
       |          ~~~~~~~
    12 |     _ := i64(foo)
    13 |     _ := int(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:12:10: error: cannot cast struct `Foo` to `i64`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:12:10: error: cannot cast struct `Foo` to `i64`
    10 |     _ := byte(foo)
    11 |     _ := i8(foo)
    12 |     _ := i64(foo)
       |          ~~~~~~~~
    13 |     _ := int(foo)
    14 |     _ = &I1(foo)
-vlib/v/checker/tests/struct_type_cast_err.vv:13:10: error: cannot cast struct `Foo` to `int`, use `foo.str()` instead.
+vlib/v/checker/tests/struct_type_cast_err.vv:13:10: error: cannot cast struct `Foo` to `int`
    11 |     _ := i8(foo)
    12 |     _ := i64(foo)
    13 |     _ := int(foo)