dx: be more explicit with emitSkipped error

[agilgur5]

Summary

Provide a bit more details when erroring on emitSkipped and link to my TS issue since this is unfortunately undocumented

• See my upstream issue: Document when emitSkipped is true in Compiler API microsoft/TypeScript#49790
• Related to Vague failed to transpile error -- noEmitOnError: true breaks rpt2 #254, failed to transpile tslib.es6.js after update to v0.30.0 #264, test: add initial integration test suite #371 (comment)

Details

• a few issues have reported that "failed to transpile" is a vague / confusing error
  • and emitSkipped actually doesn't mean that it failed to transpile, as, in current versions of TS, it's not due to syntactic or semantic errors (c.f. Struggling to get an emit failure with 1.5 microsoft/TypeScript#2290 (comment), which is linked in my upstream issue)
• so explicitly say "Emit skipped" instead, which is slightly less vague, in that it can actually be used as a search term
  • and provide a link to my TS issue that lists some reasons why emitSkipped occurs, since this is unfortunately otherwise undocumented by TS
    • in the future, hopefully that issue will be resolved and we'll be able to give better or more specific error messages, but for now this is probably the best we can do due to its undocumented nature, unfortunately

[agilgur5]

Hmm... so with latest rpt2 0.33.0 on #254 I was still getting emitSkipped despite all the fixes. I added some logging and saw something interesting:

❯ npx rollup -c

src/runtime/navigation/index.ts, src/runtime/stores/index.ts → assets/runtime...
{
  outputFiles: [],
  emitSkipped: true,
  diagnostics: [
    {
      file: [SourceFileObject],
      start: 617,
      length: 5,
      messageText: "Property 'route' of exported interface has or is using private name 'Route'.",
      category: 1,
      code: 4033,
      reportsUnnecessary: undefined,
      reportsDeprecated: undefined
    }
  ],
  exportedModulesFromDeclarationEmit: undefined
}
/rpt2-issue-254/packages/kit/src/runtime/navigation/index.ts
[]
[!] (plugin rpt2) Error: Emit skipped for '/rpt2-issue-254/packages/kit/src/runtime/navigation/index.ts'. See https://github.com/microsoft/TypeScript/issues/49790 for potential reasons why this may occur
src/runtime/navigation/index.ts

    at error (/rpt2-issue-254/node_modules/.pnpm/rollup@2.32.0/node_modules/rollup/dist/shared/rollup.js:5251:30)
    at throwPluginError (/rpt2-issue-254/node_modules/.pnpm/rollup@2.32.0/node_modules/rollup/dist/shared/rollup.js:17912:12)
    at Object.error (/rpt2-issue-254/node_modules/.pnpm/rollup@2.32.0/node_modules/rollup/dist/shared/rollup.js:18519:24)
    at Object.error (/rpt2-issue-254/node_modules/.pnpm/rollup@2.32.0/node_modules/rollup/dist/shared/rollup.js:18081:38)
    at /rpt2-issue-254/node_modules/.pnpm/rollup-plugin-typescript2@0.33.0_g55licvlyixydf5tadtvtnn3hq/node_modules/rollup-plugin-typescript2/src/index.ts:232:12
    at TsCache.getCached (/rpt2-issue-254/node_modules/.pnpm/rollup-plugin-typescript2@0.33.0_g55licvlyixydf5tadtvtnn3hq/node_modules/rollup-plugin-typescript2/src/tscache.ts:274:25)
    at TsCache.getCompiled (/rpt2-issue-254/node_modules/.pnpm/rollup-plugin-typescript2@0.33.0_g55licvlyixydf5tadtvtnn3hq/node_modules/rollup-plugin-typescript2/src/tscache.ts:213:15)
    at Object.transform (/rpt2-issue-254/node_modules/.pnpm/rollup-plugin-typescript2@0.33.0_g55licvlyixydf5tadtvtnn3hq/node_modules/rollup-plugin-typescript2/src/index.ts:222:16)
    at /rpt2-issue-254/node_modules/.pnpm/rollup@2.32.0/node_modules/rollup/dist/shared/rollup.js:18718:25

In this case, there are diagnostics with the output. But typecheckFile doesn't output anything.

That's because the type error is in types.ts instead of index.ts (per the issue).
But index.ts gets a different diagnostic error because of that type error apparently, and it appears to be neither a syntactic nor a semantic error, oddly enough... 🤔 It also doesn't show up in tsc's output.

This might be a TS bug upstream? I'm really not sure... 😕