Declaration: false for multiple output isn't respected

[matthew-dean]

• Version: 1.4.7
• Rollup Version: 2.59.0
• Operating System and version (if applicable): macOS 11.6
• Node Version (if applicable): 14.18.1
• Does it work with tsc (if applicable): Yes

Reproduction

I have two output bundles for cjs and esm, respectively. For those bundles, I only need to compile / output a declaration file once. However, there doesn't seem to be a way to do this with this plugin: I have this configuration:

    output: [
      {
        file: 'dist/index.cjs.js',
        format: 'cjs'
      },
      {
        file: 'dist/index.esm.js',
        format: 'es'
      }
    ],
    
    // ... 
       ts({
          tsconfig: config => {
            outputDeclaration = !outputDeclaration
            return {...config, declaration: outputDeclaration }
          }
       })

Expected Behavior

Only one declaration .d.ts file is created.

Actual Behavior

If I log the config file, I can see that one tsconfig has declaration: false, and one has declaration: true. However, the plugin acts like both are set to declaration: true. So, two .d.ts files are created.

[wessberg]

Hey there. This is a very common use case, and here are my general recommendations: #146 (comment)

As for what you are describing about the config not being respected, that does indeed sound weird. I'll see if I can reproduce it with a test case and investigate if I can. For now, you can achieve this with my suggestions from the link above.