Use related error spans for "implement abstract class" errors

[mjbvz]

From microsoft/vscode#78048

TypeScript Version: 3.6.0-dev.20190810

Search Terms:

• abstract class
• related error spans
• diagnostics

Problem
For the TypeScript:

abstract class A {
	abstract b(): void;
	abstract c(): void;
}

class B extends A { }

The typescript server currently generates two errors on B, one for b not being implemented and one for c not being implemented.

Having two errors causes VS Code to show a fix all... quick fix even though the single implement abstract class quick fix will resolve both errors. See microsoft/vscode#78048

Proposal
Instead of generating two errors in this case, generate a single, generic diagnostic that states something like: B does not implement all abstract members of A and on that diagnostic return related spans that state specifically which members are not implemented (b and c).

Related Issues:

• Related error spans for derived members in interfaces/classes #25033

/cc @DanielRosenwasser

[crc442]

@DanielRosenwasser can I take a crack at it?

[DanielRosenwasser]

Go for it! Start at the checker to consolidate the error messages, and then work within src/services/codefixes.

[karthikkp]

@crc442 Still working on this?

[FlyingPumba]

Hi everyone, I just submitted a PR for this issue.

[DanielRosenwasser]

Thanks @FlyingPumba!