Compiler error message improvement: Special casing container objects

Search Terms

array promise container error message compare

Suggestion

Could it be worth having an extra special case message when the only difference is that you haven't included an array indicator instead of listing the property differences e.g.

3.7:

src/index.ts:356:5 - error TS2322: Type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; }[][]' is not assignable to type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; }[]'.
      Type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; }[]' is missing the following properties from type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; }': renderedMessage, id, category, code, start

    356     errors,
            ~~~~~~

      src/index.ts:235:3
        235   errors: {
              ~~~~~~
        The expected type comes from property 'errors' which is declared here on type 'TwoSlashReturn'

To:

src/index.ts:356:5 - error TS2322: Type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; length: number | undefined; }[][]' is not assignable to type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; length: number | undefined; }[]'.

Type '{ renderedMessage: string; id: string; category: 0 | 1 | 2 | 3; code: number; start: number | undefined; length: number | undefined; }[]' is in an array here:

    356     errors,
            ~~~~~~

      src/index.ts:235:3
        235   errors: {
              ~~~~~~
        But not here

and the reverse?

Use Cases

Any case of mismatched types where the difference is that the object on one side of the comparison is the same object but wrapped in an array. Perhaps this could also work for a Promise too?

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Start by reproducing the array-mismatch example and the linked Promise example in the TypeScript playground. The issue names no compiler files or tests, so trace the diagnostic-generation path after establishing the current output; done means the requested container-specific diagnostics are covered without changing runtime behavior.