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Bug: The token type of null should be Null instead of Keyword #11027

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JLHwung opened this issue Apr 3, 2025 · 2 comments · Fixed by #11283
Closed
4 tasks done

Bug: The token type of null should be Null instead of Keyword #11027

JLHwung opened this issue Apr 3, 2025 · 2 comments · Fixed by #11283
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accepting prs Go ahead, send a pull request that resolves this issue AST PRs and Issues about the AST structure bug Something isn't working package: typescript-estree Issues related to @typescript-eslint/typescript-estree

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@JLHwung
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JLHwung commented Apr 3, 2025

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

typescript-estree

Playground Link

https://typescript-eslint.io/play/#ts=5.6.2&showAST=es&fileType=.tsx&code=HYVwNmQ&eslintrc=N4KABGBEBOCuA2BTAzpAXGYBfEWg&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=true

Repro Code

null

ESLint Config

module.exports = {
  parser: "@typescript-eslint/parser",
  rules: {
    "@typescript-eslint/<rule-name>": ["error", ...<options>],
  },
};

tsconfig

{
  "compilerOptions": {
    // ...
  }
}

Expected Result

.ast.tokens[0].type should be Null.

Actual Result

.ast.tokens[0].type is Keyword.

Additional Info

No response

Versions

package version
@typescript-eslint/typescript-estree 8.28.0
@JLHwung JLHwung added bug Something isn't working triage Waiting for team members to take a look labels Apr 3, 2025
@JoshuaKGoldberg
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Sorry, I'm still not 100% familiar with these nuances - could you please explain why the token type should be "null" instead of "keyword"? null is a keyword. Other keywords such as instanceof have "keyword" types too:

"a" instanceof "b"

https://typescript-eslint.io/play/#ts=5.6.2&showAST=es&fileType=.tsx&code=EQQ2AIEsDsGcBcTQMYFMD2AzcwBGwg&eslintrc=N4KABGBEBOCuA2BTAzpAXGYBfEWg&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=true

{
  type: "Keyword",
  loc: {end, start},
  range: [4, 14],
  value: "instanceof"
},

@JoshuaKGoldberg JoshuaKGoldberg added awaiting response Issues waiting for a reply from the OP or another party and removed triage Waiting for team members to take a look labels Apr 16, 2025
@JLHwung
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JLHwung commented Apr 16, 2025

could you please explain why the token type should be "null" instead of "keyword"?

Good question. I don't know the design choice behind it. Either a null type or a keyword type look good to me personally. But this is the espree behaviour (AST explorer), here is the espree output for the input source null:

{
  "type": "Program",
  "start": 0,
  "end": 4,
  "range": [
    0,
    4
  ],
  "body": [
    {
      "type": "ExpressionStatement",
      "start": 0,
      "end": 4,
      "range": [
        0,
        4
      ],
      "expression": {
        "type": "Literal",
        "start": 0,
        "end": 4,
        "range": [
          0,
          4
        ],
        "value": null,
        "raw": "null"
      }
    }
  ],
  "sourceType": "module",
  "tokens": [
    {
      "type": "Null",
      "value": "null",
      "start": 0,
      "end": 4,
      "range": [
        0,
        4
      ]
    }
  ]
}

Since espree is the canonical implementation of estree, I think we should just align to it.

@JoshuaKGoldberg JoshuaKGoldberg added triage Waiting for team members to take a look and removed awaiting response Issues waiting for a reply from the OP or another party labels Apr 16, 2025
@bradzacher bradzacher added package: typescript-estree Issues related to @typescript-eslint/typescript-estree AST PRs and Issues about the AST structure accepting prs Go ahead, send a pull request that resolves this issue and removed triage Waiting for team members to take a look labels Apr 17, 2025
@ntdiary ntdiary mentioned this issue Jun 8, 2025
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accepting prs Go ahead, send a pull request that resolves this issue AST PRs and Issues about the AST structure bug Something isn't working package: typescript-estree Issues related to @typescript-eslint/typescript-estree
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fix(typescript-estree): change the token type of null from Keyword to Null ntdiary/typescript-eslint
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@JoshuaKGoldberg @JLHwung @bradzacher