Crate root is sufficiently different from `mod` items, at least at syntactic level.
Also remove customization point for "`mod` item or crate root" from AST visitors.
This allows us to avoid synthesizing tokens in `prepend_attr`, since we
have the original tokens available.
We still need to synthesize tokens when expanding `cfg_attr`,
but this is an unavoidable consequence of the syntax of `cfg_attr` -
the user does not supply the `#` and `[]` tokens that a `cfg_attr`
expands to.
Fixes#68690
When we generate the proc macro harness, we now explicitly recorder the
order in which we generate entries. We then use this ordering data to
deserialize the correct proc-macro-data from the crate metadata.
`TokenStream` used to be a complex type, but it is now just a newtype
around a `Lrc<Vec<TreeAndJoint>>`. Currently it uses custom encoding
that discards the `IsJoint` and custom decoding that adds `NonJoint`
back in for every token tree. This requires building intermediate
`Vec<TokenTree>`s.
This commit makes `TokenStream` derive `Rustc{En,De}codable`. This
simplifies the code, and avoids the creation of the intermediate
vectors, saving up to 3% on various benchmarks. It also changes the AST
JSON output in one test.
