By default, `newtype_index!` types get a default `Encodable`/`Decodable`
impl. You can opt out of this with `custom_encodable`. Opting out is the
opposite to how Rust normally works with autogenerated (derived) impls.
This commit inverts the behaviour, replacing `custom_encodable` with
`encodable` which opts into the default `Encodable`/`Decodable` impl.
Only 23 of the 59 `newtype_index!` occurrences need `encodable`.
Even better, there were eight crates with a dependency on
`rustc_serialize` just from unused default `Encodable`/`Decodable`
impls. This commit removes that dependency from those eight crates.
Remove the `..` from the body, only a few invocations used it and it's
inconsistent with rust syntax.
Use `;` instead of `,` between consts. As the Rust syntax gods inteded.
This removes the `custom` format functionality as its only user was
trivially migrated to using a normal format.
If a new use case for a custom formatting impl pops up, you can add it
back.
Originally, there has been a dedicated pass for renumbering
AST NodeIds to have actual values. This pass had been added by
commit a5ad4c3794.
Then, later, this step was moved to where it resides now,
macro expansion. See commit c86c8d41a2
or PR #36438.
The comment snippet, added by the original commit, has
survived the times without any change, becoming outdated
at removal of the dedicated pass.
Nowadays, grepping for the next_node_id function will show up
multiple places in the compiler that call it, but the main
rewriting that the comment talks about is still done in the
expansion step, inside an innocious looking visit_id function
that's called during macro invocation collection.
