Richer Diagnostic Display Meta-Issue

This issue tracks a couple of different useful ideas for making diagnostics "richer" for display purposes. We've wanted some of these for a while, and they're partially inspired by testing tools like Jest and Mocha. We've also seen tools like Rust, Rome, and Flow prove them out to some extent.

Long-term, you could imagine them being interactive with the a richer compiler client.

Printing Messages Across Lines

Types can get unwieldy, and displaying them inline makes it harder to see where things begin/end.

Type

    { x: string, y: number }

is not assignable to

    { x: string, y: string }

Notice no punctuation at the end. Not sure if we can generalize messages that way.

Also not sure how this plays well with

• tools that parse our output.
• diagnostic elaborations

Highlighted Spans in Messages

Imagine being able to highlight individual sections inside of types to indicate where the issue occurs.

                              vvvvvvvvvvv
Type '{ a: string; b: number; c: boolean; }' is not assignable to type '{ a: string; b: number; }'.
                              ^^^^^^^^^^^
  Object literal may only specify known properties, and 'c' does not exist in type '{ a: string; b: number; }'.

Diff Highlighting in Messages

Basically imagine red being the provided color, with green being an expected color.

Type '[string, number, boolean]' is not assignable to type '[string, string, boolean]'.
               ^^^^^^                                                ^^^^^^
               rrrrrr                                                gggggg

Es sind keine Dateien, Tests oder Einstiegspunkte benannt. Prüfe zunächst die drei vorgeschlagenen Bereiche—mehrzeilige Meldungen, hervorgehobene Bereiche und Diff-Hervorhebung—zusammen mit ihren Kompatibilitätsfragen, und ermittle anschließend den relevanten Code für die Diagnoseanzeige und die Tests, bevor du eine abgegrenzte Implementierung vorschlägst. Für den Abschluss sind ein abgestimmtes Design und eine Validierung des ausgewählten Diagnoseverhaltens erforderlich.