readonly and declare invalid property for MethodDefinition.

[sosukesuzuki]

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have read the FAQ and my problem is not listed.

Repro

// the code you're trying to parse
class Foo {
  readonly bar() {}
  declare baz() {}
}

// the code you're using to do the parse of the aforementioned code
import { parse } from '@typescript-eslint/typescript-estree';

const code = `
class Foo {
  readonly bar() {}
  declare baz() {}
}
`;
const ast = parse(code);

Expected Result

Expect that MethodDefinition nodes have readonly and declare property.

AST

{
  "type": "ClassDeclaration",
  "id": {
    "type": "Identifier",
    "name": "Foo"
  },
  "body": {
    "type": "ClassBody",
    "body": [
      {
        "type": "MethodDefinition",
        "key": {
          "type": "Identifier",
          "name": "bar"
        },
        "value": {
          "type": "FunctionExpression",
          "id": null,
          "generator": false,
          "expression": false,
          "async": false,
          "body": {
            "type": "BlockStatement",
            "body": []
          },
          "params": []
        },
        "computed": false,
        "static": false,
        "kind": "method",
+        "readonly": true
      },
      {
        "type": "MethodDefinition",
        "key": {
          "type": "Identifier",
          "name": "baz"
        },
        "value": {
          "type": "FunctionExpression",
          "id": null,
          "generator": false,
          "expression": false,
          "async": false,
          "body": {
            "type": "BlockStatement",
            "body": []
          },
          "params": []
        },
        "computed": false,
        "static": false,
        "kind": "method",
+       "declare": true
      }
    ]
  },
  "superClass": null
}

Actual Result

AST

{
  "type": "ClassDeclaration",
  "id": {
    "type": "Identifier",
    "name": "Foo"
  },
  "body": {
    "type": "ClassBody",
    "body": [
      {
        "type": "MethodDefinition",
        "key": {
          "type": "Identifier",
          "name": "bar"
        },
        "value": {
          "type": "FunctionExpression",
          "id": null,
          "generator": false,
          "expression": false,
          "async": false,
          "body": {
            "type": "BlockStatement",
            "body": []
          },
          "params": []
        },
        "computed": false,
        "static": false,
        "kind": "method"
      },
      {
        "type": "MethodDefinition",
        "key": {
          "type": "Identifier",
          "name": "baz"
        },
        "value": {
          "type": "FunctionExpression",
          "id": null,
          "generator": false,
          "expression": false,
          "async": false,
          "body": {
            "type": "BlockStatement",
            "body": []
          },
          "params": []
        },
        "computed": false,
        "static": false,
        "kind": "method"
      }
    ]
  },
  "superClass": null
}

Additional Info

prettier/prettier#9760

I know the above code is invalid as TypeScript program (TS Playground). But I think code formatters should correctly treat those cases. What do you think about?

If the request is accepted, I can work on this.

Versions

package	version
@typescript-eslint/typescript-estree	master
TypeScript	4.1.2
node	v14.8.0

[bradzacher]

Whilst the parser treats them as valid (because we throw no errors currently #1852) they shouldn't be included in the AST.

I think this falls into the same category as decorators on things that aren't classes - we don't error for them, we don't emit AST for them, and consumers can use the underlying TS AST to look for them if they want.

With the next major we'll start properly handling syntax errors, so this won't be an issue.

[sosukesuzuki]

I got it. Certainly, it seems unreasonable for typescript-estree to address this problem.