import/no-duplicates false positives for TypeScript module declarations

[remcohaszing]

The import/no-duplicates rule gives false positives for imports inside TypeScript module declarations.

Practical example:

declare module 'monaco-editor/esm/vs/editor/contrib/documentSymbols/documentSymbols' {
  import { ITextModel, languages } from 'monaco-editor';
}

declare module 'monaco-editor/esm/vs/editor/editor.worker' {
  import { worker } from 'monaco-editor';
}

This is happening, because import/no-duplicates collects all import statements and assumes they are in the program body.

I would expect the import/no-duplicates rule to be applied to each body separately. Currently these are the Program body and the TSModuleBlock body, but who knows what the future holds.

Alternatively the rule could be applied to imports which are direct children Program body only.

This is the same as #2217, but for a different rule. This means I can probably fix this if it gets accepted. :)

[ljharb]

Ideally, the no-duplicates rule runs once for each of:

• the file itself, omitting any declare blocks
• each declare block

This refactoring will be useful if the "module blocks" language proposal advances, as well.