f852568fa6
I.e. change the return type from `TokenStream` to `Vec<TokenTree>`. Most of the callsites require a `TokenStream`, but the recursive call used to create `target_tokens` requires a `Vec<TokenTree>`. It's easy to convert a `Vec<TokenTree>` to a `TokenStream` (just call `TokenStream::new`) but it's harder to convert a `TokenStream` to a `Vec<TokenTree>` (either iterate/clone/collect, or use `Lrc::into_inner` if appropriate). So this commit changes the return value to simplify that `target_tokens` call site.
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: