Bug: `JSDocNonNullableType` has extra nested `typeAnnotation` with invalid position #11064

leaysgur · 2025-04-14T05:01:51Z

Before You File a Bug Report Please Confirm You Have Done The Following...

I have tried restarting my IDE and the issue persists.
I have updated to the latest version of the packages.
I have searched for related issues and found none that matched my issue.
I have read the FAQ and my problem is not listed.

Relevant Package

parser

Playground Link

https://typescript-eslint.io/play/#ts=5.4.3&showAST=es&fileType=.tsx&code=GYVwdgxgLglg9mABMAjACgIYC5EbATwEocNEYBnRcqAJxjAHMBCAbwChFEaBTKEGpLRDcA3GwC%2BbIA&eslintrc=N4KABGBEBOCuA2BTAzpAXGYBfEWg&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

function f1(a: any): a is string!{
  return true;
}

ESLint Config

tsconfig

Expected Result

{
  "type": "Program",
  "start": 0,
  "end": 51,
  "body": [
    {
      "type": "FunctionDeclaration",
      "start": 0,
      "end": 51,
      "id": {
        "type": "Identifier",
        "start": 9,
        "end": 11,
        "name": "f1",
        "decorators": [],
        "optional": false,
        "typeAnnotation": null
      },
      "expression": false,
      "generator": false,
      "async": false,
      "params": [
        {
          "type": "Identifier",
          "start": 12,
          "end": 18,
          "name": "a",
          "decorators": [],
          "optional": false,
          "typeAnnotation": {
            "type": "TSTypeAnnotation",
            "start": 13,
            "end": 18,
            "typeAnnotation": {
              "type": "TSAnyKeyword",
              "start": 15,
              "end": 18
            }
          }
        }
      ],
      "body": {
        "type": "BlockStatement",
        "start": 33,
        "end": 51,
        "body": [
          {
            "type": "ReturnStatement",
            "start": 37,
            "end": 49,
            "argument": {
              "type": "Literal",
              "start": 44,
              "end": 48,
              "value": true,
              "raw": "true"
            }
          }
        ]
      },
      "declare": false,
      "typeParameters": null,
      "returnType": {
        "type": "TSTypeAnnotation",
        "start": 19,
        "end": 33,
        "typeAnnotation": {
          "type": "TSTypePredicate",
          "start": 21,
          "end": 33,
          "parameterName": {
            "type": "Identifier",
            "start": 21,
            "end": 22,
            "name": "a",
            "decorators": [],
            "optional": false,
            "typeAnnotation": null
          },
          "asserts": false,
          "typeAnnotation": { // ============================== 👀
            "type": "TSTypeAnnotation",
            "start": 26,
            "end": 33,
            "typeAnnotation": {
              "type": "TSJSDocNonNullableType",
              "start": 26,
              "end": 33,
              "typeAnnotation": {
                "type": "TSStringKeyword",
                "start": 26,
                "end": 32
              },
              "postfix": true
            } // ============================================= 👀
          }
        }
      }
    }
  ],
  "sourceType": "module"
}

Actual Result

{
  "type": "Program",
  "start": 0,
  "end": 51,
  "body": [
    {
      "type": "FunctionDeclaration",
      "start": 0,
      "end": 51,
      "async": false,
      "body": {
        "type": "BlockStatement",
        "start": 33,
        "end": 51,
        "body": [
          {
            "type": "ReturnStatement",
            "start": 37,
            "end": 49,
            "argument": {
              "type": "Literal",
              "start": 44,
              "end": 48,
              "raw": "true",
              "value": true
            }
          }
        ]
      },
      "declare": false,
      "expression": false,
      "generator": false,
      "id": {
        "type": "Identifier",
        "start": 9,
        "end": 11,
        "decorators": [],
        "name": "f1",
        "optional": false,
        "typeAnnotation": null
      },
      "params": [
        {
          "type": "Identifier",
          "start": 12,
          "end": 18,
          "decorators": [],
          "name": "a",
          "optional": false,
          "typeAnnotation": {
            "type": "TSTypeAnnotation",
            "start": 13,
            "end": 18,
            "typeAnnotation": {
              "type": "TSAnyKeyword",
              "start": 15,
              "end": 18
            }
          }
        }
      ],
      "returnType": {
        "type": "TSTypeAnnotation",
        "start": 19,
        "end": 33,
        "typeAnnotation": {
          "type": "TSTypePredicate",
          "start": 21,
          "end": 33,
          "asserts": false,
          "parameterName": {
            "type": "Identifier",
            "start": 21,
            "end": 22,
            "decorators": [],
            "name": "a",
            "optional": false,
            "typeAnnotation": null
          },
          "typeAnnotation": { // ============================== 👀
            "type": "TSTypeAnnotation",
            "start": 26,
            "end": 33,
            "typeAnnotation": {
              "type": "TSJSDocNonNullableType",
              "start": 26,
              "end": 33,
              "typeAnnotation": {
                "type": "TSTypeAnnotation",
                "start": 24, // ❗️
                "end": 32,
                "typeAnnotation": {
                  "type": "TSStringKeyword",
                  "start": 26,
                  "end": 32
                }
              },
              "id": 0,
              "original": null,
              "emitNode": null,
              "postfix": true
            }
          }
        } // ================================================== 👀
      },
      "typeParameters": null
    }
  ],
  "sourceType": "module"
}

Additional Info

I'm not sure if extra typeAnnotation nesting is intended or not, but at least its starting position should be fixed?

Versions

package	version
`@typescript-eslint/parser`	`8.29.1`

The text was updated successfully, but these errors were encountered:

kirkwaiblinger · 2025-04-14T05:06:17Z

Hi @leaysgur! I think this is just a consequence of the string! being illegal syntax.... In your playground link I get

'!' at the end of a type is not valid TypeScript syntax. Did you mean to write 'string'?(17019)

Do you have an example of syntactically valid TS with unexpected AST?

leaysgur · 2025-04-14T05:15:43Z

Thank you for triage! ✋🏻

Do you have an example of syntactically valid TS with unexpected AST?

No, I don't have it. This code is from a TypeScript test case.

https://github.com/microsoft/TypeScript/blob/main/tests/cases/compiler/parseInvalidNonNullableTypes.ts

If noCheck: true, the TS itself does not seem to show any errors, how is such a case handled as TS-ESLint? 👀

https://www.typescriptlang.org/play/?noCheck=true#code/GYVwdgxgLglg9mABMAjACgIYC5EbATwEocNEYBnRcqAJxjAHMBCAbwChFEaBTKEGpLRDcA3GwC+QA

bradzacher · 2025-04-14T13:18:26Z

We're built on top of TS and TS is a forgiving parser.
It will recover from invalid syntax as best it can and produce an AST so that that AST can be used to power IDE features. This is why you can still have autocomplete and hover types even if you've got syntax errors!

Because of this behaviour TS doesn't generally emit many true, crashing syntax errors. Most of its "syntax" errors are instead emitted as what it defines as "semantic" errors. This has tripped some users up in the past -- but just because they're not crashing syntax errors doesn't mean they're not syntax errors -- TS just emits them as semantic errors so that downstream tools can recover and continue working if they desire (eg the mentioned IDE usecase).

We have some errors in place to try and catch bad syntax so we don't produce an invalid AST. We could add a bunch more errors around the place -- but because it's forgiving parser that auto-recovers -- the cases are realistically going to be limitless and it's going to be difficult to check every possible case without tanking performance.

In general our philosophy is "if you have TS errors in your code then expect undefined behaviour from our rules". This applies to any form of TS error be it type error or "semantic syntax error" (which your case is the latter).

leaysgur added bug Something isn't working triage Waiting for team members to take a look labels Apr 14, 2025

leaysgur mentioned this issue Apr 14, 2025

Align JS-side AST with standard for TypeScript oxc-project/oxc#9705

Open

bradzacher closed this as not planned Won't fix, can't repro, duplicate, stale Apr 14, 2025

bradzacher added working as intended Issues that are closed as they are working as intended wontfix This will not be worked on and removed triage Waiting for team members to take a look labels Apr 14, 2025

bradzacher mentioned this issue Apr 15, 2025

Bug: Duplicate extends clause for interface should be reported #11077

Open

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github-actions bot added the locked due to age Please open a new issue if you'd like to say more. See https://typescript-eslint.io/contributing. label Apr 22, 2025

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Bug: `JSDocNonNullableType` has extra nested `typeAnnotation` with invalid position #11064

Bug: `JSDocNonNullableType` has extra nested `typeAnnotation` with invalid position #11064

leaysgur commented Apr 14, 2025

kirkwaiblinger commented Apr 14, 2025

leaysgur commented Apr 14, 2025

bradzacher commented Apr 14, 2025 •

edited

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Bug: JSDocNonNullableType has extra nested typeAnnotation with invalid position #11064

Bug: JSDocNonNullableType has extra nested typeAnnotation with invalid position #11064

Comments

leaysgur commented Apr 14, 2025

Before You File a Bug Report Please Confirm You Have Done The Following...

Relevant Package

Playground Link

Repro Code

ESLint Config

tsconfig

Expected Result

Actual Result

Additional Info

Versions

kirkwaiblinger commented Apr 14, 2025

leaysgur commented Apr 14, 2025

bradzacher commented Apr 14, 2025 • edited Loading

Bug: `JSDocNonNullableType` has extra nested `typeAnnotation` with invalid position #11064

Bug: `JSDocNonNullableType` has extra nested `typeAnnotation` with invalid position #11064

bradzacher commented Apr 14, 2025 •

edited

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