checker: fix for $if field.unaliased_typ is $Int { (#16982)

vlib/v/checker/if.v

@@ -86,24 +86,29 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 						c.error('invalid `\$if` condition: expected a type', branch.cond.right.pos())
 						return 0
 					}
-					if right is ast.ComptimeType && left is ast.TypeNode {
-						is_comptime_type_is_expr = true
-						checked_type := c.unwrap_generic(left.typ)
-						skip_state = if c.table.is_comptime_type(checked_type, right as ast.ComptimeType) {
-							.eval
-						} else {
-							.skip
-						}
-					} else if right is ast.ComptimeType && left is ast.Ident
-						&& (left as ast.Ident).info is ast.IdentVar {
-						is_comptime_type_is_expr = true
-						if var := left.scope.find_var(left.name) {
-							checked_type := c.unwrap_generic(var.typ)
+					if right is ast.ComptimeType {
+						mut checked_type := ast.void_type
+						if left is ast.TypeNode {
+							is_comptime_type_is_expr = true
+							checked_type = c.unwrap_generic(left.typ)
 							skip_state = if c.table.is_comptime_type(checked_type, right as ast.ComptimeType) {
 								.eval
 							} else {
 								.skip
 							}
+						} else if left is ast.Ident && (left as ast.Ident).info is ast.IdentVar {
+							is_comptime_type_is_expr = true
+							if var := left.scope.find_var(left.name) {
+								checked_type = c.unwrap_generic(var.typ)
+							}
+							skip_state = if c.table.is_comptime_type(checked_type, right as ast.ComptimeType) {
+								.eval
+							} else {
+								.skip
+							}
+						} else if left is ast.SelectorExpr {
+							comptime_field_name = left.expr.str()
+							is_comptime_type_is_expr = true
 						}
 					} else {
 						got_type := c.unwrap_generic((right as ast.TypeNode).typ)

vlib/v/tests/unaliased_typ_checking_test.v

@@ -0,0 +1,44 @@
+type MyArray = []string
+type MyString = string
+type MyFloat = f64
+type MyMap = map[string]string
+
+struct Foo {
+	a string
+	b ?string
+	c MyArray
+	d MyString
+	e MyFloat
+	f MyMap
+}
+
+fn test_main() {
+	mut out := map[string][]string{}
+	$for field in Foo.fields {
+		print('${field.name} is ')
+		$if field.unaliased_typ is $Int {
+			println('numeric')
+			out[field.name] << 'numeric'
+		} $else $if field.unaliased_typ is $Array {
+			println('array')
+			out[field.name] << 'array'
+		} $else $if field.unaliased_typ is $Float {
+			println('float')
+			out[field.name] << 'float'
+		} $else $if field.unaliased_typ is $Map {
+			println('map')
+			out[field.name] << 'map'
+		} $else $if field.unaliased_typ is string || field.unaliased_typ is ?string {
+			println('string opt? ${field.is_option}')
+			out[field.name] << 'string'
+		} $else {
+			assert false
+		}
+	}
+	assert out['a'][0] == 'string'
+	assert out['b'][0] == 'string'
+	assert out['c'][0] == 'array'
+	assert out['d'][0] == 'string'
+	assert out['e'][0] == 'float'
+	assert out['f'][0] == 'map'
+}