Maximum call stack size exceeded when I add in a validation function?

[durianwaffle]

I wrote my own validator, and registered it in my-module,ts file like registerValidationChecks(My);
But after I added the checks, I found that parsing autocompletion, and tooltip failed. There is a rangeError: Maximum call stack size exceeded in MyAstReflection.computeIsSubtype src/language/generated/ast.ts:812:29.

src/language/generated/ast.ts:812:29
    810|             }
    811|             case NamedElement: {
    812|                 return this.isSubtype(StElement, supertype) || this.isSubtype(VariableDeclaration, supertype);
       |                             ^
    813|             }
    814|             case Statement: {

My code about the validator is as below:

import type { ValidationAcceptor, ValidationChecks } from 'langium';
import type { AssignmentStatement, MyAstType } from './generated/ast.js';
import { VariableReference } from './generated/ast.js';
import type { MyServices } from './structured-text-module.js';

/**
 * Register custom validation checks.
 */
export function registerValidationChecks(services: MyServices ) {
    const registry = services.validation.ValidationRegistry;
    const validator = services.validation.StructuredTextValidator;
    const checks: ValidationChecks<MyAstType > = {
        AssignmentStatement: validator.checkAssignmentType
    };
    registry.register(checks, validator);
}

/**
 * Implementation of custom validations.
 */
export class MyValidator {
    checkAssignmentType(assignemntStatement: AssignmentStatement, accept: ValidationAcceptor): void {
        if (assignemntStatement.left) {
            const left = assignemntStatement.left as VariableReference;
            const leftType = left.$type;
            const rightType = 'BitVariable';
            console.log('Left op of assignment', leftType);
            if (leftType.toLocaleUpperCase() !== rightType) {
                accept('error', `Can’t assign ${leftType} type to variable with type ${rightType} assignment.`, { node: assignemntStatement, property: 'left' });
            }
        }
    }
}

[msujew]

Hey @durianwaffle,

Can you share a reproducible example? It's hard to tell what's wrong from the snippet you provided.

[durianwaffle]

Hi @msujew sorry for that!
I updated the link. Now you can see it.

https://github.com/durianwaffle/validation-dsl/blob/main/examples/maxiumcallstacksizeexceed/README.md

[msujew]

You've produced a cyclical inheritance chain that hasn't been discovered by our type system validation system.

Effectively, you've written your types like this:

type VariableDeclaration = NamedElement;
type NamedElement = VariableDeclaration;

To fix this, you need to remove the returns NamedElement from all the parser rules.

[durianwaffle]

NamedElement is there to make membercalls.
In the LOX sample: "VariableDeclaration returns NamedElement"
But there is no "maximum call stack size" issue in LOX sample.
Why is it?

[msujew]

No idea why it works in Lox, it's likely a very specific set of circumstances. It's not supposed to work like this. You either write:

type NamedElement = VariableDeclaration | ...;

or

VariableDeclaration returns NamedElement: ...;

but not both.

[durianwaffle]

Hi @msujew, a follow up question.
After I deleted the other returns NamedElement, the validator works.
But I will see Coud not resolve reference to NamedElement when I access struct within a struct.
Do you know how I can troubleshot for this issue?

[msujew]

@durianwaffle Looks like a scoping issue. You should look into your scoping/type system code to ensure everything works as expected there.

[durianwaffle]

Okay thank you @msujew ! It helps a lot!