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feature list
while we could make this change (it's all unstable after all), there are crates.io crates that use the feature and that the compiler depends upon. We can instead roll out this feature while still supporting the old way.
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This commit changes `syntax::fold::Folder` from a functional style
(where most methods take a `T` and produce a new `T`) to a more
imperative style (where most methods take and modify a `&mut T`), and
renames it `syntax::mut_visit::MutVisitor`.
The first benefit is speed. The functional style does not require any
reallocations, due to the use of `P::map` and
`MoveMap::move_{,flat_}map`. However, every field in the AST must be
overwritten; even those fields that are unchanged are overwritten with
the same value. This causes a lot of unnecessary memory writes. The
imperative style reduces instruction counts by 1--3% across a wide range
of workloads, particularly incremental workloads.
The second benefit is conciseness; the imperative style is usually more
concise. E.g. compare the old functional style:
```
fn fold_abc(&mut self, abc: ABC) {
ABC {
a: fold_a(abc.a),
b: fold_b(abc.b),
c: abc.c,
}
}
```
with the imperative style:
```
fn visit_abc(&mut self, ABC { a, b, c: _ }: &mut ABC) {
visit_a(a);
visit_b(b);
}
```
(The reductions get larger in more complex examples.)
Overall, the patch removes over 200 lines of code -- even though the new
code has more comments -- and a lot of the remaining lines have fewer
characters.
Some notes:
- The old style used methods called `fold_*`. The new style mostly uses
methods called `visit_*`, but there are a few methods that map a `T`
to something other than a `T`, which are called `flat_map_*` (`T` maps
to multiple `T`s) or `filter_map_*` (`T` maps to 0 or 1 `T`s).
- `move_map.rs`/`MoveMap`/`move_map`/`move_flat_map` are renamed
`map_in_place.rs`/`MapInPlace`/`map_in_place`/`flat_map_in_place` to
reflect their slightly changed signatures.
- Although this commit renames the `fold` module as `mut_visit`, it
keeps it in the `fold.rs` file, so as not to confuse git. The next
commit will rename the file.
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Make `TokenStream` less recursive.
`TokenStream` is currently recursive in *two* ways:
- the `TokenTree` variant contains a `ThinTokenStream`, which can
contain a `TokenStream`;
- the `TokenStream` variant contains a `Vec<TokenStream>`.
The latter is not necessary and causes significant complexity. This
commit replaces it with the simpler `Vec<(TokenTree, IsJoint)>`.
This reduces complexity significantly. In particular, `StreamCursor` is
eliminated, and `Cursor` becomes much simpler, consisting now of just a
`TokenStream` and an index.
The commit also removes the `Extend` impl for `TokenStream`, because it
is only used in tests. (The commit also removes those tests.)
Overall, the commit reduces the number of lines of code by almost 200.
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This avoids 770,000 allocations when compiling the `html5ever`
benchmark, reducing instruction counts by up to 2%.
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`TokenStream` is currently recursive in *two* ways:
- the `TokenTree` variant contains a `ThinTokenStream`, which can
contain a `TokenStream`;
- the `TokenStream` variant contains a `Vec<TokenStream>`.
The latter is not necessary and causes significant complexity. This
commit replaces it with the simpler `Vec<(TokenTree, IsJoint)>`.
This reduces complexity significantly. In particular, `StreamCursor` is
eliminated, and `Cursor` becomes much simpler, consisting now of just a
`TokenStream` and an index.
The commit also removes the `Extend` impl for `TokenStream`, because it
is only used in tests. (The commit also removes those tests.)
Overall, the commit reduces the number of lines of code by almost 200.
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Found with `git grep -P '\b([a-z]+)\s+\1\b'`
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`TokenStream::new` is a better name for the former, and the latter is
now just equivalent to `TokenStream::Stream`.
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Because it's an extra type layer that doesn't really help; in a couple
of places it actively gets in the way, and overall removing it makes the
code nicer. It does, however, move `tokenstream::TokenTree` further away
from the `TokenTree` in `quote.rs`.
More importantly, this change reduces the size of `TokenStream` from 48
bytes to 40 bytes on x86-64, which is enough to slightly reduce
instruction counts on numerous benchmarks, the best by 1.5%.
Note that `open_tt` and `close_tt` have gone from being methods on
`Delimited` to associated methods of `TokenTree`.
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libsyntax_pos: A few tweaks
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`Edition` is not a public API, we want users to break when a new edition is added
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Point at end of macro arm when encountering EOF
Fix #52866.
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Fix #52866
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Fix typos.
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This avoids some allocations.
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Custom diagnostic when trying to doc comment argument
When writing
```
pub fn f(
/// Comment
id: u8,
) {}
```
Produce a targeted diagnostic
```
error: documentation comments cannot be applied to method arguments
--> $DIR/fn-arg-doc-comment.rs:2:5
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LL | /// Comment
| ^^^^^^^^^^^ doc comments are not allowed here
```
Fix #54801.
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This avoids some allocations.
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`create_matches` creates a `Vec<Rc<Vec<NamedMatch>>>`. Even though all the
inner `Vec`s are empty, each one is created separately.
This commit changes `create_matches` so it instead creates one empty inner
`Vec`, and shares it.
The commit also changes `MatcherPos::matches` to a boxed slice, because its
length doesn't change.
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Suggest to remove prefix `b` in cfg attribute lint string
Closes #54926
r? @estebank
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Remove redundant clone (2)
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List allowed tokens after macro fragments
Fix #34069.
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Point at macro definition when no rules expect token
Fix #35150.
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Macro diagnostics tweaks
Fix #30128, fix #10951 by adding an appropriate span to the diagnostic.
Fix #26288 by suggesting adding semicolon to macro call.
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Accept `Option<Box<$t:ty>>` in macro argument
Given the following code, compile successfuly:
```
macro_rules! test {
(
fn fun() -> Option<Box<$t:ty>>;
) => {
fn fun(x: $t) -> Option<Box<$t>>
{ Some(Box::new(x)) }
}
}
test! {
fn fun() -> Option<Box<i32>>;
}
```
Fix #25274.
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