cgen: fix $if typeof[T]().idx, $if typeof[T]().unaliased_typ checking (#23665)

vlib/v/gen/c/cgen.v

@@ -3908,21 +3908,16 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 					}
 					g.type_name(name_type)
 					return
-				} else if node.field_name == 'idx' {
+				} else if node.field_name in ['idx', 'unaliased_typ'] {
+					// `typeof(expr).idx`, // `typeof(expr).unalised_typ`
 					mut name_type := node.name_type
 					if node.expr is ast.TypeOf {
-						name_type = g.type_resolver.typeof_type(node.expr.expr, name_type)
+						name_type = g.type_resolver.typeof_field_type(g.type_resolver.typeof_type(node.expr.expr,
+							name_type), node.field_name)
+						g.write(int(name_type).str())
+					} else {
+						g.write(int(g.unwrap_generic(name_type)).str())
 					}
-					// `typeof(expr).idx`
-					g.write(int(g.unwrap_generic(name_type)).str())
-					return
-				} else if node.field_name == 'unaliased_typ' {
-					mut name_type := node.name_type
-					if node.expr is ast.TypeOf {
-						name_type = g.type_resolver.typeof_type(node.expr.expr, name_type)
-					}
-					// `typeof(expr).unaliased_typ`
-					g.write(int(g.table.unaliased_type(g.unwrap_generic(name_type))).str())
 					return
 				} else if node.field_name == 'indirections' {
 					mut name_type := node.name_type

vlib/v/gen/c/comptime.v

@@ -455,6 +455,10 @@ fn (mut g Gen) get_expr_type(cond ast.Expr) ast.Type {
 			} else if cond.gkind_field == .indirections {
 				return ast.int_type
 			} else {
+				if cond.expr is ast.TypeOf {
+					return g.type_resolver.typeof_field_type(g.type_resolver.typeof_type(cond.expr.expr,
+						cond.name_type), cond.field_name)
+				}
 				name := '${cond.expr}.${cond.field_name}'
 				if name in g.type_resolver.type_map {
 					return g.type_resolver.get_ct_type_or_default(name, ast.void_type)

vlib/v/tests/generics/generic_typeof_idx_test.v

@@ -0,0 +1,37 @@
+type MyInt = int
+type MyString = string
+
+struct Foo {
+	a []int
+	b MyInt
+	c MyString
+}
+
+fn unaliased_typ[T](a T) int {
+	$if typeof[T]().unaliased_typ is $int {
+		return 1
+	} $else $if typeof[T]().unaliased_typ is $string {
+		return 2
+	}
+	return 0
+}
+
+fn idx[T](a [][]T) int {
+	$if typeof[T]().idx is $int {
+		return 1
+	} $else $if typeof[T]().idx is $string {
+		return 2
+	}
+	return 0
+}
+
+fn test_main() {
+	a := Foo{
+		a: [1, 2, 3]
+	}
+	assert idx([a.a]) == 1
+	assert idx([['']]) == 2
+
+	assert unaliased_typ(1) == 1
+	assert unaliased_typ('') == 2
+}

vlib/v/type_resolver/comptime_resolver.v

@@ -82,6 +82,27 @@ pub fn (mut t TypeResolver) typeof_type(node ast.Expr, default_type ast.Type) as
 	return default_type
 }
 
+// typeof_field_type resolves the typeof[T]().<field_name> type
+pub fn (mut t TypeResolver) typeof_field_type(typ ast.Type, field_name string) ast.Type {
+	match field_name {
+		'name' {
+			return ast.string_type
+		}
+		'idx' {
+			return t.resolver.unwrap_generic(typ)
+		}
+		'unaliased_typ' {
+			return t.table.unaliased_type(t.resolver.unwrap_generic(typ))
+		}
+		'indirections' {
+			return ast.int_type
+		}
+		else {
+			return typ
+		}
+	}
+}
+
 // get_ct_type_var gets the comptime type of the variable (.generic_param, .key_var, etc)
 @[inline]
 pub fn (t &ResolverInfo) get_ct_type_var(node ast.Expr) ast.ComptimeVarKind {