Ron Buckton

ready to merge

@typescript-bot perf test @typescript-bot run dt @typescript-bot test top400 @typescript-bot test tsserver top100 @typescript-bot user test this @typescript-bot user test tsserver

The other option here would be to not widen `null` or `undefined` in cases like `promise.catch(() => null)`, such that the result is `T | null`.

> The other option here would be to not widen `null` or `undefined` in cases like `promise.catch(() => null)`, such that the result is `T | null`. While this seems...

@weswigham, @andrewbranch: can you take a look?

> The linked issue and PR description mention the`.then`/`.catch` case but there doesn't seem to be a test for it; is that intentional? The fix applies regardless as to whether...

Unfortunately, I would not classify this as "low-hanging fruit". I'm very wary about adding a `beforeDeclaration` transformer given that the current declaration transformer expects to receive the original parse tree,...

> may be making many assumptions about the provenance of nodes in the tree. For example, *src/compiler/transformers/declarations.ts* contains *at least* 38 references to `.parent`, but a transformed source tree does...

> I understand your concern, but how is `beforeDeclarations` much different to normal `before` transformers? > With your argumentation `before` transformers should be removed because devs might create transformers producing...

> Are there already some good tests for `before` transformers which try to break the built-in transformers I could look at? We have a number of tests in src\testRunner\unittests\transform.ts and...