macros: Make metavariables hygienic
This PR makes metavariables hygienic. For example, consider:
```rust
macro_rules! foo {
($x:tt) => { // Suppose that this token tree argument is always a metavariable.
macro_rules! bar { ($x:expr, $y:expr) => { ($x, $y) } }
}
}
fn main() {
foo!($z); // This currently compiles.
foo!($y); // This is an error today but compiles after this PR.
}
```
Today, the `macro_rules! bar { ... }` definition is only valid when the metavariable passed to `foo` is not `$y` (since it unhygienically conflicts with the `$y` in the definition of `bar`) or `$x` (c.f. #35450).
After this PR, the definition of `bar` is always valid (and `bar!(a, b)` always expands to `(a, b)` as expected).
This can break code that was allowed in #34925 (landed two weeks ago). For example,
```rust
macro_rules! outer {
($t:tt) => {
macro_rules! inner { ($i:item) => { $t } }
}
}
outer!($i); // This `$i` should not interact with the `$i` in the definition of `inner!`.
inner!(fn main() {}); // After this PR, this is an error ("unknown macro variable `i`").
```
Due to the severe limitations on nested `macro_rules!` before #34925, this is not a breaking change for stable/beta.
Fixes#35450.
r? @nrc
Better attribute and metaitem encapsulation throughout the compiler
This PR refactors most (hopefully all?) of the `MetaItem` interactions outside of `libsyntax` (and a few inside) to interact with MetaItems through the provided traits instead of directly creating / destruct / matching against them. This is a necessary first step to eventually converting `MetaItem`s to internally use `TokenStream` representations (which will make `MetaItem` interactions much nicer for macro writers once the new macro system is in place).
r? @nrc
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
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
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.
Forbid type parameters and global paths in macro invocations
Fixes#28558.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m { () => { () } }
fn main() {
m::<T>!(); // Type parameters are no longer allowed in macro invocations
::m!(); // Global paths are no longer allowed in macro invocations
}
```
Any breakage can be fixed by removing the type parameters or the leading `::` (respectively).
r? @eddyb
Batch up libsyntax breaking changes
Batch of the following syntax-[breaking-change] changes:
- #34213: Add a variant `Macro` to `TraitItemKind`
- #34368: Merge the variant `QPath` of `PatKind` into the variant `PatKind::Path`
- #34385: Move `syntax::ast::TokenTree` into a new module `syntax::tokenstream`
- #33943:
- Remove the type parameter from `visit::Visitor`
- Remove `attr::WithAttrs` -- use `attr::HasAttrs` instead.
- Change `fold_tt`/`fold_tts` to take token trees by value and avoid wrapping token trees in `Rc`.
- Remove the field `ctxt` of `ast::Mac_`
- Remove inherent method `attrs()` of types -- use the method `attrs` of `HasAttrs` instead.
- #34316:
- Remove `ast::Decl`/`ast::DeclKind` and add variants `Local` and `Item` to `StmtKind`.
- Move the node id for statements from the `StmtKind` variants to a field of `Stmt` (making `Stmt` a struct instead of an alias for `Spanned<StmtKind>`)
- Rename `ast::ExprKind::Again` to `Continue`.
- #34339: Generalize and abstract `ThinAttributes` to `ThinVec<Attribute>`
- Use `.into()` in convert between `Vec<Attribute>` and `ThinVec<Attribute>`
- Use autoderef instead of `.as_attr_slice()`
- #34436: Remove the optional expression from `ast::Block` and instead use a `StmtKind::Expr` at the end of the statement list.
- #34403: Move errors into a separate crate (unlikely to cause breakage)
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.
bors