content-mapper generates inconsistent declaration extensions, making management of package.json#exports hard / verbose

🔎 Search Terms

• content-mapper
• extensions custom declarations

🕗 Version & Regression Information

Using:

"typescript": "7.1.0-dev.20260821.1"

⏯ Playground Link

n/a

💻 Code

Here is the repo with the code: https://github.com/NullVoxPopuli/ember-content-mapper/tree/main/examples/cli-library-v2

As you can see, we have 3 different declaration extensions

• .d.ts
• .d.gjs.ts
• .d.gts.ts

Which makes the package.json exports mapping hard, because for each file type (which can change as refactoring occurs), I'd have to specify different types globs depending on which public entrypoint maps to which file.

It seems no resolving tool (node, rollup, etc) supports arrays of globs for package.json#exports like tsconfig.json#compilerOptions.paths does

🙁 Actual behavior

Too many declaration extension types

🙂 Expected behavior

I'm compliling to JS (not with tsc), so I don't think the emitted imports, nor the declarations, should have any extension other than .d.ts (with the in-declaration imports being extensionless, ofc)

Additional information about the issue

Somewhat related, but I've battled this quite a bit using TS < 7, and have hacked around it via https://github.com/NullVoxPopuli/fix-bad-declaration-output and https://github.com/embroider-build/embroider/blob/5449eb2944cd13548794ceff97df1d86a8c5d53d/packages/addon-dev/src/rollup-declarations.ts#L127

as far as I know, this is an issue in other ecosystems, like MDX
(and any ecosystem that has a custom syntax, and compiles to JS for library publishing)

Potentially related issues:

• https://github.com/microsoft/TypeScript/issues/61037

Docs I know about:

• https://www.typescriptlang.org/tsconfig/#allowImportingTsExtensions
• https://www.typescriptlang.org/tsconfig/#allowArbitraryExtensions (I think ? (idk actually) this option might be the problem, because it assumes the file isn't transformed for publish)

The full expanded tsconfig

{
    "compilerOptions": {
        "allowJs": true,
        "allowImportingTsExtensions": true,
        "emitDeclarationOnly": true,
        "declaration": true,
        "declarationDir": "./declarations",
        "declarationMap": true,
        "experimentalDecorators": true,
        "module": "esnext",
        "moduleResolution": "bundler",
        "noEmit": false,
        "noUncheckedIndexedAccess": true,
        "noEmitOnError": false,
        "rootDir": "./src",
        "skipLibCheck": true,
        "strict": true,
        "target": "es2024",
        "types": [],
        "verbatimModuleSyntax": true,
        "allowSyntheticDefaultImports": true,
        "isolatedModules": true,
        "preserveConstEnums": true
    },
    "files": [
        "./src/index.ts",
        "./src/template-registry.ts",
        "./src/utils/format.ts"
    ],
    "include": [
        "./src/**/*"
    ],
    "exclude": [
        "<repo>/examples/ember-library-v2/declarations"
    ]
}

I've also tried with adding:
allowArbitraryExtensions: true and rewriteRelativeImportExtensions: true