…hod of trait `HasAttrs`.

… of by reference)

…reams. Modified tests to point to the new file now.

…eyfried

**syntax-[breaking-change]** cc rust-lang#31645
New `TraitItemKind::Macro` variant

This change adds support for macro expansion inside trait items by adding the new `TraitItemKind::Macro` and associated parsing code.

The AST part of rust-lang#34365

plugin-[breaking-change] cc rust-lang#31645

…excrichton

This PR refactors the 'errors' part of libsyntax into its own crate (librustc_errors).  This is the first part of a few refactorings to simplify error reporting and potentially support more output formats (like a standardized JSON output and possibly an --explain mode that can work with the user's code), though this PR stands on its own and doesn't assume further changes.

As part of separating out the errors crate, I have also refactored the code position portion of codemap into its own crate (libsyntax_pos).  While it's helpful to have the common code positions in a separate crate for the new errors crate, this may also enable further simplifications in the future.

syntax-[breaking-change] cc rust-lang#31645
(Only breaking because ast::TokenTree is now tokenstream::TokenTree.)

This pull request refactors TokenTrees into their own file as src/libsyntax/tokenstream.rs, moving them out of src/libsyntax/ast.rs, in order to prepare for an accompanying TokenStream implementation (per RFC 1566).

Miscellaneous low priority cleanup in `libsyntax`.

Refactor away `ast::Decl`, refactor `ast::Stmt`, and rename `ast::ExprKind::Again` to `ast::ExprKind::Continue`.

…Manishearth

Generalize and abstract `ThinAttributes` to `ThinVec<Attribute>`.

To allow these braced macro invocation, this PR removes the optional expression from `ast::Block` and instead uses a `StmtKind::Expr` at the end of the statement list.

Currently, braced macro invocations in blocks can expand into statements (and items) except when they are last in a block, in which case they can only expand into expressions.

For example,
```rust
macro_rules! make_stmt {
    () => { let x = 0; }
}

fn f() {
    make_stmt! {} //< This is OK...
    let x = 0; //< ... unless this line is commented out.
}
```

Fixes rust-lang#34418.