macros: fix bug in `stmt` matchers
Today, `stmt` matchers stop too early when parsing expression statements that begin with non-braced macro invocations. For example,
```rust
fn main() {
macro_rules! m { ($s:stmt;) => { $s } }
id!(vec![].push(0););
//^ Before this PR, the `stmt` matcher only consumes "vec![]", so this is an error.
//| After this PR, the `stmt` matcher consumes "vec![].push(0)", so this compiles.
}
```
This change is backwards compatible due to the follow set for `stmt`.
r? @eddyb
Added tokenstream parser procedure
A tiny PR that simply adds a procedure for parsing `TokenStream`s to the parser in `src/libsyntax`. This is to ease using `TokenStream`s with the current (old) procedural macro system.
Simplify librustc_errors
This is part 2 of the error crate refactor, starting with #34403.
In this refactor, I focused on slimming down the error crate to fewer moving parts. As such, I've removed quite a few parts and replaced the with simpler, straight-line code. Specifically, this PR:
* Removes BasicEmitter
* Remove emit from emitter, leaving emit_struct
* Renames emit_struct to emit
* Removes CoreEmitter and focuses on a single Emitter
* Implements the latest changes to error format RFC (#1644)
* Removes (now-unused) code in emitter.rs and snippet.rs
* Moves more tests to the UI tester, removing some duplicate tests in the process
There is probably more that could be done with some additional refactoring, but this felt like it was getting to a good state.
r? @alexcrichton cc: @Manishearth (as there may be breaking changes in stuff I removed/changed)
Better error message for inner attribute following doc comment
Before it was always just "an inner attribute is not permitted in this context", whereas now we add a special case for when an inner attr follows an outer attr. If the outer attr is a doc comment, then the error is "an inner attr is not permitted following a doc comment", and otherwise it's "an inner attr is not permitted following an outer attribute". In all other cases it's still "an inner attribute is not permitted in this context".
Note that the public API and behaviour of `parse_attribute` is unchanged. Also, all new names are very open to bikeshedding -- they're arguably clunky.
Fixes#34516. cc @brson
Simplify the macro hygiene algorithm
This PR removes renaming from the hygiene algorithm and treats differently marked identifiers as unequal.
This change makes the scope of identifiers in `macro_rules!` items empty. That is, identifiers in `macro_rules!` definitions do not inherit any semantics from the `macro_rules!`'s scope.
Since `macro_rules!` macros are items, the scope of their identifiers "should" be the same as that of other items; in particular, the scope should contain only items. Since all items are unhygienic today, this would mean the scope should be empty.
However, the scope of an identifier in a `macro_rules!` statement today is the scope that the identifier would have if it replaced the `macro_rules!` (excluding anything unhygienic, i.e. locals only).
To continue to support this, this PR tracks the scope of each `macro_rules!` and uses it in `resolve` to ensure that an identifier expanded from a `macro_rules!` gets a chance to resolve to the locals in the `macro_rules!`'s scope.
This PR is a pure refactoring. After this PR,
- `syntax::ext::expand` is much simpler.
- We can expand macros in any order without causing problems for hygiene (needed for macro modularization).
- We can deprecate or remove today's `macro_rules!` scope easily.
- Expansion performance improves by 25%, post-expansion memory usage decreases by ~5%.
- Expanding a block is no longer quadratic in the number of `let` statements (fixes#10607).
r? @nrc
```rust
macro_rules! m { () => { let x = 1; x } }
macro_rules! n { () => {
m!() //< This can now expand into statements
}}
fn main() { n!(); }
```
and revert needless fallout fixes.
Fix expansion performance regression
**syntax-[breaking-change] cc #31645**
This fixes#34630 by reverting commit 5bf7970 of PR #33943, which landed in #34424.
By removing the `Rc<_>` wrapping around `Delimited` and `SequenceRepetition` in `TokenTree`, 5bf7970 made cloning `TokenTree`s more expensive. While this had no measurable performance impact on the compiler's crates, it caused an order of magnitude performance regression on some macro-heavy code in the wild. I believe this is due to clones of `TokenTree`s in `macro_parser.rs` and/or `macro_rules.rs`.
r? @nrc
Support `cfg_attr` on `path` attributes
Fixes#25544.
This is technically a [breaking-change]. For example, the following would break:
```rust
mod foo; // Suppose `foo.rs` existed in the appropriate location
```
This is a spiritual succesor to #34268/8531d581, in which we replaced a
number of matches of None to the unit value with `if let` conditionals
where it was judged that this made for clearer/simpler code (as would be
recommended by Manishearth/rust-clippy's `single_match` lint). The same
rationale applies to matches of None to the empty block.
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.
