2b91cbe2d4
Remove `TokenStreamBuilder` `TokenStreamBuilder` is used to combine multiple token streams. It can be removed, leaving the code a little simpler and a little faster. r? `@Aaron1011`
The rustc_ast crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), along with some definitions for tokens and token streams, data structures/traits for mutating ASTs, and shared definitions for other AST-related parts of the compiler (like the lexer and macro-expansion).
For more information about how these things work in rustc, see the rustc dev guide: