"Content mapper file extension '.const.json' is a built-in extension and cannot be registered by a content mapper." error is misleading #64917

🔎 Search Terms

is a built-in extension and cannot be registered by a content mapper

🕗 Version & Regression Information

7.1-beta

⏯ Playground Link

No response

💻 Code

{
    "compilerOptions": {
        "resolveJsonModule": true
    },
    "contentMappers": [{ "package": "json-const-content-mapper", "extensions": [".const.json"] }]
}

🙁 Actual behavior

> tsc --runExternalCode
error TS18066: Content mapper file extension '.const.json' is a built-in extension and cannot be registered by a content mapper.

this error message implies that .const.json specifically is a built-in extension, when in reality it's just .json.

🙂 Expected behavior

my preferred solution is that patterns like .const.json should be supported, to support content mappers like const-json-content-mapper

alternatively, the error message should be updated to clarify that .const.json isn't allowed because it conflicts with .json

Additional information about the issue

relevant issue: #32063