Extend tsserver interface to allow refactoring failure reporting

Search Terms

refactoring report failure fail

Suggestion

I would like a way to report refactoring failures similar to rename fail report ("You cannot rename this element").
This change improves transparency.

Edit: This might imply changes in VS Code language server extension as well. I'm not familiar with it though.

Use Cases

This would be useful to allow refactorings to initially show the refactoring, but when invoking it, an error message should be shown, instead of just not showing the refactoring. This would be confusing to the user.

Examples

Let's say we want to inline a variable, that is not initialized. This should not be possible. But it is still useful to show the refactoring initially, since the user may be confused why the option doesn't show up.
Then, if the user wants to invoke the refactoring, they get the error message "Cannot inline uninitialized variable."

let notInitialized; // should not allow inlining, but tell user why

foo(notInitialized);

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. new expression-level syntax)

Start by tracing the tsserver interface used for refactorings and compare it with the existing rename failure reporting. Check how the VS Code language server extension consumes these responses. Done means a failed refactoring returns a reason that the client can display instead of silently hiding the failure.