[MIR] Add Dominators to MIR and Add Graph Algorithms
~~This PR assumes PR #34149 lands.~~
Add generic graph algorithms to rustc_data_structures.
Add dominators and successors to the ~~cache (that currently only holds predecessors).~~ `Mir`.
Remove the return_address intrinsic.
This intrinsic to get the return pointer was introduced in #16248 / #16081 by @pcwalton for Servo.
However, as explained in #34227, it's impossible to ensure it's used correctly, and it broke with `-Zorbit`.
Servo's usage is being replaced in servo/servo#11872, and I expect nobody else to have abused it.
But I've also started a crater run, just in case this is a `[breaking-change]` for anyone else.
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#34418.
syntax-[breaking-change] cc #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).
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 #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.
Renames "lets_do_this" macro more appropriately.
The macro gets used to create a mapping of identifiers to names and their
associated functions. Since it creates a table of language items, let's rename
it in a similar manner to how vec! creates a vec.
Don't ignore errors of syscalls in std::sys::unix::fd
If any of these syscalls fail, it indicates a programmer error that
should not be silently ignored.
