`emitDeclarationOnly` in v0.33.0 -- what if I want an empty chunk and only declarations?

[BitPatty]

Troubleshooting

1. Does tsc have the same output? If so, please explain why this is incorrect behavior

No

1. Does your Rollup plugin order match this plugin's compatibility? If not, please elaborate

Yes

1. Can you create a minimal example that reproduces this behavior? Preferably, use this environment for your reproduction

https://stackblitz.com/edit/rpt2-repro-1kadjh?file=package.json

What happens and why it is incorrect

The build crashes if emitDeclarationOnly is set to true in overrides or tsconfig. tsc produces the correct output. Used to work until v0.33.0.

Environment

Versions

  System:
    OS: Linux 5.4 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
    CPU: (4) x64 Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz
    Memory: 5.13 GB / 7.77 GB
    Container: Yes
    Shell: 5.1.4 - /bin/bash
  Binaries:
    Node: 18.4.0 - /usr/local/share/nvm/versions/node/v18.4.0/bin/node
    Yarn: 1.22.19 - /usr/bin/yarn
    npm: 8.18.0 - /usr/local/share/nvm/versions/node/v18.4.0/bin/npm
  npmPackages:
    rollup: 2.78.0 => 2.78.0 
    rollup-plugin-typescript2: 0.33.0 => 0.33.0 
    typescript: 4.7.4 => 4.7.4 

rollup.config.js

:

import typescript from 'rollup-plugin-typescript2';

export default {
  input: './src/index.ts',
  output: {
    file: './dist/index.ts',
    format: 'esm',
    exports: 'named',
  },
  plugins: [
    typescript({
      verbosity: 3,
      clean: true,
    }),
  ],
};

tsconfig.json

:

{
  // https://github.com/agilgur5/tsconfig
  "extends": "@agilgur5/tsconfig/src/tsconfig.library.json",
  // exclude node_modules (the default), dist dir, coverage dir, and example for now
  "exclude": ["node_modules/", "dist/", "coverage/", "example/"],
  // all TS files in the src/ dir
  "include": ["src/**/*"],
  // see https://www.typescriptlang.org/tsconfig to better understand tsconfigs
  "compilerOptions": {
    // output to dist/ dir
    "outDir": "./dist/",
    // match output dir to input dir. e.g. dist/index instead of dist/src/index
    "rootDir": "./src",
    "emitDeclarationOnly": true
  }
}

package.json

:

{
  "name": "rpt2-repro",
  "version": "0.0.0",
  "scripts": {
    "clean": "rm -rf dist/",
    "build": "rollup -c",
    "tsc": "tsc"
  },
  "devDependencies": {
    "@agilgur5/tsconfig": "^0.0.2",
    "rollup": "^2.75.6",
    "rollup-plugin-typescript2": "^0.33.0",
    "typescript": "^4.7.3"
  }
}

plugin output with verbosity 3

:

./src/index.ts → ./dist/index.ts...
rpt2: built-in options overrides: {
    "noEmitHelpers": false,
    "importHelpers": true,
    "noResolve": false,
    "noEmit": false,
    "noEmitOnError": false,
    "inlineSourceMap": false,
    "outDir": "/home/projects/rpt2-repro-1kadjh/node_modules/.cache/rollup-plugin-typescript2/placeholder",
    "moduleResolution": 2,
    "allowNonTsExtensions": true,
    "module": 5
}
rpt2: parsed tsconfig: {
    "options": {
        "strict": true,
        "allowUnusedLabels": false,
        "allowUnreachableCode": false,
        "exactOptionalPropertyTypes": true,
        "noFallthroughCasesInSwitch": true,
        "noImplicitOverride": true,
        "noImplicitReturns": true,
        "noPropertyAccessFromIndexSignature": true,
        "noUncheckedIndexedAccess": true,
        "noUnusedLocals": true,
        "noUnusedParameters": true,
        "importsNotUsedAsValues": 2,
        "checkJs": true,
        "esModuleInterop": true,
        "skipLibCheck": true,
        "forceConsistentCasingInFileNames": true,
        "outDir": "/home/projects/rpt2-repro-1kadjh/node_modules/.cache/rollup-plugin-typescript2/placeholder",
        "sourceMap": true,
        "moduleResolution": 2,
        "resolveJsonModule": true,
        "jsx": 2,
        "noEmit": false,
        "declaration": true,
        "declarationMap": true,
        "rootDir": "/home/projects/rpt2-repro-1kadjh/src",
        "emitDeclarationOnly": true,
        "configFilePath": "/home/projects/rpt2-repro-1kadjh/tsconfig.json",
        "noEmitHelpers": false,
        "importHelpers": true,
        "noResolve": false,
        "noEmitOnError": false,
        "inlineSourceMap": false,
        "allowNonTsExtensions": true,
        "module": 5
    },
    "fileNames": [
        "/home/projects/rpt2-repro-1kadjh/src/index.ts"
    ],
    "typeAcquisition": {
        "enable": false,
        "include": [],
        "exclude": []
    },
    "raw": {
        "extends": "@agilgur5/tsconfig/src/tsconfig.library.json",
        "exclude": [
            "node_modules/",
            "dist/",
            "coverage/",
            "example/"
        ],
        "include": [
            "src/**/*"
        ],
        "compilerOptions": {
            "outDir": "./dist/",
            "rootDir": "./src",
            "emitDeclarationOnly": true
        },
        "compileOnSave": false
    },
    "errors": [],
    "wildcardDirectories": {
        "/home/projects/rpt2-repro-1kadjh/src": 1
    },
    "compileOnSave": false
}
rpt2: typescript version: 4.7.3
rpt2: tslib version: 2.4.0
rpt2: rollup version: 2.75.6
rpt2: rollup-plugin-typescript2 version: 0.33.0
rpt2: plugin options:
{
    "check": true,
    "verbosity": 3,
    "clean": true,
    "cacheRoot": "/home/projects/rpt2-repro-1kadjh/node_modules/.cache/rollup-plugin-typescript2",
    "include": [
        "*.ts+(|x)",
        "**/*.ts+(|x)"
    ],
    "exclude": [
        "*.d.ts",
        "**/*.d.ts"
    ],
    "abortOnError": true,
    "rollupCommonJSResolveHack": false,
    "useTsconfigDeclarationDir": false,
    "tsconfigOverride": {},
    "transformers": [],
    "tsconfigDefaults": {},
    "objectHashIgnoreUnknownHack": false,
    "cwd": "/home/projects/rpt2-repro-1kadjh",
    "typescript": "version 4.7.3"
}
rpt2: rollup config:
{
    "external": [],
    "input": "./src/index.ts",
    "plugins": [
        {
            "name": "rpt2"
        },
        {
            "name": "stdin"
        }
    ],
    "output": [
        {
            "exports": "named",
            "file": "./dist/index.ts",
            "format": "esm",
            "plugins": []
        }
    ]
}
rpt2: tsconfig path: /home/projects/rpt2-repro-1kadjh/tsconfig.json
rpt2: included:
[
    "*.ts+(|x)",
    "**/*.ts+(|x)"
]
rpt2: excluded:
[
    "*.d.ts",
    "**/*.d.ts"
]
rpt2: transpiling '/home/projects/rpt2-repro-1kadjh/src/index.ts'
rpt2: generated declarations for '/home/projects/rpt2-repro-1kadjh/src/index.ts'
rpt2: emitDeclarationOnly enabled, not transforming TS'
[!] (plugin rpt2) Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
src/index.ts (4:29)
2: // run `npm run tsc` in the terminal to type-check this file with tsc
3: 
4: export default function sum(a: number, b: number) {
                                ^
5:   return a + b;
6: }

    at error (/home/projects/rpt2-repro-1kadjh/node_modules/rollup/dist/shared/rollup.js:198:30)
    at Module.error (/home/projects/rpt2-repro-1kadjh/node_modules/rollup/dist/shared/rollup.js:12553:16)
    at Module.tryParse (/home/projects/rpt2-repro-1kadjh/node_modules/rollup/dist/shared/rollup.js:12930:25)
    at Module.setSource (/home/projects/rpt2-repro-1kadjh/node_modules/rollup/dist/shared/rollup.js:12835:24)
    at ModuleLoader.addModuleSource (/home/projects/rpt2-repro-1kadjh/node_modules/rollup/dist/shared/rollup.js:22309:20)

[agilgur5]

This is a new feature in 0.33.0, supporting emitDeclarationOnly. Previously, this tsconfig option was entirely ignored.

Per the log you provided, it states "rpt2: emitDeclarationOnly enabled, not transforming TS". As such, you need another plugin to transform TS to JS when using emitDeclarationOnly.

Per the docs, this feature is meant to be used together with another plugin, such as @rollup/plugin-babel, rollup-plugin-esbuild, rollup-plugin-swc, etc.
With this use-case, you have rpt2 use the TS compiler to type-check and create declarations, while another plugin does the TS -> JS transform.

Per the release notes, this was implemented in #366 to support the highly requested #268.

As such, this is not a bug, but very much intended behavior.

If you want to keep emitDeclarationOnly in your tsconfig for tsc, but still want rpt2 to do TS -> JS transformation, please use tsconfigOverride to reset emitDeclarationOnly to false for rpt2.

[BitPatty]

Per the log you provided, it states "rpt2: emitDeclarationOnly enabled, not transforming TS". As such, you need another plugin to transform TS to JS when using emitDeclarationOnly.

Hope I don't misunderstand: What if I only want to emit declarations and not transpile TS at all?

While it did work before and warn about an empty chunk being generated, it still did emit the declaration as expected. And though tsc itself could be used to build the declaration, the rpt2 simplified the process up until now when using multiple build targets.

[agilgur5]

While it did work before and warn about an empty chunk being generated, it still did emit the declaration as expected.

Oh. I didn't realize that anyone actually wanted an empty chunk. #268 showed that most folks were pretty confused by the resulting empty chunk. But I guess everyone's got their own workflow 😅

And though tsc itself could be used to build the declaration, the rpt2 simplified the process up until now when using multiple build targets.

Any chance you could provide a small example of where rpt2 simplifies the process vs. using tsc for multi-build with only declarations? I think I'm missing a detail here, so an example would be great to wrap my head around.

What if I only want to emit declarations and not transpile TS at all?

So this is still possible in 0.33.0 in a slightly hacky way. As long as your TS files are in your tsconfig include, rpt2 will still emit their declarations, even if they're not directly part of the Rollup bundle (because that's how tsc works as well).

So what you could do is use an empty file for Rollup's output.file EDIT: woops, I meant input, which will result in the same behavior as an empty chunk, and then rpt2 will still emit declarations for anything in your tsconfig include.

Does that satisfy your use-case? It's a bit hacky, but I do think the intent is a little more clear that way (e.g. empty file -> empty chunk). Most people seemed to have been pretty confused by the empty chunk behavior before and that didn't seem intuitive to them.