checker,cgen: allow method.name checking in comptime (#16931)

vlib/v/checker/comptime.v

@@ -561,7 +561,9 @@ fn (mut c Checker) comptime_if_branch(cond ast.Expr, pos token.Pos) ComptimeBran
 					}
 				}
 				.eq, .ne {
-					if cond.left is ast.SelectorExpr && cond.right is ast.IntegerLiteral {
+					if cond.left is ast.SelectorExpr
+						&& cond.right in [ast.IntegerLiteral, ast.StringLiteral] {
+						return .unknown
 						// $if method.args.len == 1
 					} else if cond.left is ast.SelectorExpr
 						&& c.check_comptime_is_field_selector_bool(cond.left as ast.SelectorExpr) {

vlib/v/gen/c/cgen.v

@@ -193,6 +193,7 @@ mut:
 	// nr_vars_to_free       int
 	// doing_autofree_tmp    bool
 	comptime_for_method              string // $for method in T.methods {}
+	comptime_for_method_var          string // $for method in T.methods {}; the variable name
 	comptime_for_field_var           string // $for field in T.fields {}; the variable name
 	comptime_for_field_value         ast.StructField // value of the field variable
 	comptime_for_field_type          ast.Type        // type of the field variable inferred from `$if field.typ is T {}`

vlib/v/gen/c/comptime.v

@@ -496,6 +496,20 @@ fn (mut g Gen) comptime_if_cond(cond ast.Expr, pkg_exist bool) (bool, bool) {
 				}
 				.eq, .ne {
 					// TODO Implement `$if method.args.len == 1`
+					if cond.left is ast.SelectorExpr && g.comptime_for_method.len > 0
+						&& cond.right is ast.StringLiteral {
+						selector := cond.left as ast.SelectorExpr
+						if selector.expr is ast.Ident
+							&& (selector.expr as ast.Ident).name == g.comptime_for_method_var && selector.field_name == 'name' {
+							is_equal := g.comptime_for_method == cond.right.val
+							if is_equal {
+								g.write('1')
+							} else {
+								g.write('0')
+							}
+							return is_equal, true
+						}
+					}
 					if cond.left is ast.SelectorExpr || cond.right is ast.SelectorExpr {
 						l, d1 := g.comptime_if_cond(cond.left, pkg_exist)
 						g.write(' ${cond.op} ')
@@ -594,20 +608,22 @@ fn (mut g Gen) comptime_if_cond(cond ast.Expr, pkg_exist bool) (bool, bool) {
 struct CurrentComptimeValues {
 	inside_comptime_for_field bool
 	comptime_for_method       string
+	comptime_for_method_var   string
 	comptime_for_field_var    string
 	comptime_for_field_value  ast.StructField
 	comptime_for_field_type   ast.Type
 	comptime_var_type_map     map[string]ast.Type
 }
 
 fn (mut g Gen) push_existing_comptime_values() {
-	g.comptime_values_stack << CurrentComptimeValues{g.inside_comptime_for_field, g.comptime_for_method, g.comptime_for_field_var, g.comptime_for_field_value, g.comptime_for_field_type, g.comptime_var_type_map.clone()}
+	g.comptime_values_stack << CurrentComptimeValues{g.inside_comptime_for_field, g.comptime_for_method, g.comptime_for_method_var, g.comptime_for_field_var, g.comptime_for_field_value, g.comptime_for_field_type, g.comptime_var_type_map.clone()}
 }
 
 fn (mut g Gen) pop_existing_comptime_values() {
 	old := g.comptime_values_stack.pop()
 	g.inside_comptime_for_field = old.inside_comptime_for_field
 	g.comptime_for_method = old.comptime_for_method
+	g.comptime_for_method_var = old.comptime_for_method_var
 	g.comptime_for_field_var = old.comptime_for_field_var
 	g.comptime_for_field_value = old.comptime_for_field_value
 	g.comptime_for_field_type = old.comptime_for_field_type
@@ -647,6 +663,7 @@ fn (mut g Gen) comptime_for(node ast.ComptimeFor) {
 				}
 			}
 			g.comptime_for_method = method.name
+			g.comptime_for_method_var = node.val_var
 			g.writeln('/* method ${i} */ {')
 			g.writeln('\t${node.val_var}.name = _SLIT("${method.name}");')
 			if method.attrs.len == 0 {

vlib/v/tests/comptime_method_call_with_check_test.v

@@ -0,0 +1,26 @@
+struct TestStruct {}
+
+fn (t TestStruct) one_arg(a string) string {
+	println(a)
+	return a
+}
+
+fn (t TestStruct) two_args(a string, b int) string {
+	println('${a}:${b}')
+	return a
+}
+
+fn test_main() {
+	t := TestStruct{}
+	mut out := ''
+	$for method in TestStruct.methods {
+		$if method.name == 'one_arg' {
+			res := t.$method(method.name)
+			out += res
+		} $else $if method.name == 'two_args' {
+			res := t.$method(method.name, 42)
+			out += res
+		}
+	}
+	assert out == 'one_argtwo_args'
+}