Previously the value passed to `AstFactory.attachComments()` could be
`undefined` which is counterintuitive, since why attach something that
doesn't exist? Now it expects there to be a defined array. Further it no
longer returns a statement. Both these aspects of the interface were designed
to make the usage simpler but has the result of complicating the implemenation.
The `ExpressionTranslatorVisitor` now has a helper function (`attachComments()`)
to handle `leadingComments` being undefined and also returning the statement.
This keeps the usage in the translator simple, while ensuring that the `AstFactory`
API is not influenced by how it is used.
PR Close#39076
This commit adds the `AstHost` interface, along with implementations for
both Babel and TS.
It also implements the Babel vesion of the `AstFactory` interface, along
with a linker specific implementation of the `ImportGenerator` interface.
These classes will be used by the new "ng-linker" to transform prelinked
library code using a Babel plugin.
PR Close#38866
Pete Bacon Darwin