checker: fix typeof evaluation for generic reference (fix #23951) (fix #23952) (#23958)

vlib/v/checker/assign.v

@@ -965,6 +965,8 @@ fn (mut c Checker) change_flags_if_comptime_expr(mut left ast.Ident, right ast.E
 			if right_ct_var != .no_comptime {
 				left.obj.ct_type_var = right_ct_var
 			}
+		} else if right is ast.StructInit && right.unresolved && right.typ.has_flag(.generic) {
+			left.obj.ct_type_var = .generic_param
 		} else if right is ast.IndexExpr && c.comptime.is_comptime(right) {
 			right_ct_var := c.comptime.get_ct_type_var(right.left)
 			if right_ct_var != .no_comptime {

vlib/v/checker/checker.v

@@ -899,9 +899,7 @@ fn (mut c Checker) fail_if_immutable(mut expr ast.Expr) (string, token.Pos) {
 			mut expr_left := expr.left
 			if mut expr.left is ast.Ident {
 				if mut expr.left.obj is ast.Var {
-					if expr.left.obj.ct_type_var != .generic_param {
+					c.fail_if_immutable(mut expr_left)
-						c.fail_if_immutable(mut expr_left)
-					}
 				}
 			}
 			return '', expr.pos

vlib/v/gen/c/assign.v

@@ -163,7 +163,7 @@ fn (mut g Gen) expr_with_opt(expr ast.Expr, expr_typ ast.Type, ret_typ ast.Type)
 		}
 		g.expr(expr)
 		if expr is ast.ComptimeSelector {
-			return '${expr.left.str()}.${g.comptime.comptime_for_field_value.name}'
+			return g.gen_comptime_selector(expr)
 		} else {
 			return expr.str()
 		}

vlib/v/gen/c/cgen.v

@@ -3728,7 +3728,7 @@ fn (mut g Gen) expr(node_ ast.Expr) {
 				mut is_unwrapped := true
 				if mut node.expr is ast.ComptimeSelector && node.expr.left is ast.Ident {
 					// val.$(field.name)?
-					expr_str = '${node.expr.left.str()}.${g.comptime.comptime_for_field_value.name}'
+					expr_str = g.gen_comptime_selector(node.expr)
 				} else if mut node.expr is ast.Ident && node.expr.ct_expr {
 					// val?
 					expr_str = node.expr.name

vlib/v/gen/c/comptime.v

@@ -39,6 +39,11 @@ fn (mut g Gen) comptime_selector(node ast.ComptimeSelector) {
 	}
 }
 
+fn (mut g Gen) gen_comptime_selector(expr ast.ComptimeSelector) string {
+	arrow_or_dot := if expr.left_type.is_ptr() { '->' } else { '.' }
+	return '${expr.left.str()}${arrow_or_dot}${g.comptime.comptime_for_field_value.name}'
+}
+
 fn (mut g Gen) comptime_call(mut node ast.ComptimeCall) {
 	if node.is_embed {
 		// $embed_file('/path/to/file')

vlib/v/tests/generics/generic_typeof_test.v

@@ -0,0 +1,37 @@
+module main
+
+fn decode_array[T](x []T) string {
+	return 'decode_array: x.typename = ${typeof(x).name}'
+}
+
+fn decode[T]() string {
+	x := T{0}
+	mut s := 'decode: x.typename = ${typeof(x).name}. '
+	s += decode_array(x)
+	return s
+}
+
+fn second[K, V](x map[K]V) string {
+	return 'second: x.typename = ${typeof(x).name}'
+}
+
+fn first[T]() string {
+	x := T{}
+	mut s := 'first: x.typename = ${typeof(x).name}. '
+	s += second(x)
+	return s
+}
+
+fn test_map() {
+	assert first[map[string]string]() == 'first: x.typename = map[string]string. second: x.typename = map[string]string'
+	assert first[map[string]int]() == 'first: x.typename = map[string]int. second: x.typename = map[string]int'
+	assert first[map[string]u8]() == 'first: x.typename = map[string]u8. second: x.typename = map[string]u8'
+	assert first[map[string]rune]() == 'first: x.typename = map[string]rune. second: x.typename = map[string]rune'
+}
+
+fn test_array() {
+	assert decode[[]u8]() == 'decode: x.typename = []u8. decode_array: x.typename = []u8'
+	assert decode[[]u16]() == 'decode: x.typename = []u16. decode_array: x.typename = []u16'
+	assert decode[[]int]() == 'decode: x.typename = []int. decode_array: x.typename = []int'
+	assert decode[[]rune]() == 'decode: x.typename = []rune. decode_array: x.typename = []rune'
+}

vlib/v/tests/options/option_var_test.v

@@ -22,7 +22,7 @@ mut:
 
 struct Decoder {}
 
-fn (d &Decoder) decode[T](typ T) T {
+fn (d &Decoder) decode[T](mut typ T) T {
 	$for field in T.fields {
 		$if field.is_option {
 			if typ.$(field.name) != none {
@@ -36,7 +36,7 @@ fn (d &Decoder) decode[T](typ T) T {
 
 fn test_comptime() {
 	d := Decoder{}
-	result := d.decode(StructType{
+	result := d.decode(mut StructType{
 		a: 'foo'
 		b: 3
 	})