comptime: fix $if var.return_type == 1 { (fix #24391) (#24393)

Author: felipensp

vlib/v/checker/if.v

@@ -182,11 +182,10 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 								} else {
 									.skip
 								}
-							} else if comptime_field_name == c.comptime.comptime_for_method_var {
-								if left.field_name == 'return_type' {
-									skip_state = c.check_compatible_types(c.unwrap_generic(c.comptime.comptime_for_method_ret_type),
-										right as ast.TypeNode)
-								}
+							} else if comptime_field_name == c.comptime.comptime_for_method_var
+								&& left.field_name == 'return_type' {
+								skip_state = c.check_compatible_types(c.unwrap_generic(c.comptime.comptime_for_method_ret_type),
+									right as ast.TypeNode)
 							} else if comptime_field_name in [
 								c.comptime.comptime_for_variant_var,
 								c.comptime.comptime_for_enum_var,
@@ -286,6 +285,14 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 									}
 								}
 							}
+						} else if comptime_field_name == c.comptime.comptime_for_method_var {
+							if left.field_name == 'return_type' {
+								skip_state = if c.unwrap_generic(c.comptime.comptime_for_method_ret_type).idx() == right.val.i64() {
+									ComptimeBranchSkipState.eval
+								} else {
+									ComptimeBranchSkipState.skip
+								}
+							}
 						} else if left.expr is ast.TypeOf {
 							skip_state = if left.expr.typ.nr_muls() == right.val.i64() {
 								ComptimeBranchSkipState.eval

vlib/v/gen/c/comptime.v

@@ -655,6 +655,21 @@ fn (mut g Gen) comptime_if_cond(cond ast.Expr, pkg_exist bool) (bool, bool) {
 									g.write('0')
 								}
 								return is_true, true
+							} else if g.comptime.comptime_for_method_var != ''
+								&& cond.left.expr is ast.Ident
+								&& cond.left.expr.name == g.comptime.comptime_for_method_var
+								&& cond.left.field_name == 'return_type' {
+								is_true := match cond.op {
+									.eq { g.comptime.comptime_for_method_ret_type.idx() == cond.right.val.i64() }
+									.ne { g.comptime.comptime_for_method_ret_type.idx() != cond.right.val.i64() }
+									else { false }
+								}
+								if is_true {
+									g.write('1')
+								} else {
+									g.write('0')
+								}
+								return is_true, true
 							}
 						}
 					}

vlib/v/tests/comptime/comptime_call_void_test.v

@@ -0,0 +1,15 @@
+struct Struct {}
+
+fn (s Struct) func() {}
+
+fn test_main() {
+	$for method in Struct.methods {
+		println('${method.name}: ${method.return_type}')
+		$if method.return_type == 1 {
+			assert true
+		}
+		$if method.return_type == 11 {
+			assert false
+		}
+	}
+}