No description
4c110014f1
This PR improves the internal DX when working with `u8` classification
into a smaller enum. This is done by implementing a `ClassifyBytes` proc
derive macro. The benefit of this is that the DX is much better and
everything you will see here is done at compile time.
Before:
```rs
#[derive(Debug, Clone, Copy, PartialEq)]
enum Class {
ValidStart,
ValidInside,
OpenBracket,
OpenParen,
Slash,
Other,
}
const CLASS_TABLE: [Class; 256] = {
let mut table = [Class::Other; 256];
macro_rules! set {
($class:expr, $($byte:expr),+ $(,)?) => {
$(table[$byte as usize] = $class;)+
};
}
macro_rules! set_range {
($class:expr, $start:literal ..= $end:literal) => {
let mut i = $start;
while i <= $end {
table[i as usize] = $class;
i += 1;
}
};
}
set_range!(Class::ValidStart, b'a'..=b'z');
set_range!(Class::ValidStart, b'A'..=b'Z');
set_range!(Class::ValidStart, b'0'..=b'9');
set!(Class::OpenBracket, b'[');
set!(Class::OpenParen, b'(');
set!(Class::Slash, b'/');
set!(Class::ValidInside, b'-', b'_', b'.');
table
};
```
After:
```rs
#[derive(Debug, Clone, Copy, PartialEq, ClassifyBytes)]
enum Class {
#[bytes_range(b'a'..=b'z', b'A'..=b'Z', b'0'..=b'9')]
ValidStart,
#[bytes(b'-', b'_', b'.')]
ValidInside,
#[bytes(b'[')]
OpenBracket,
#[bytes(b'(')]
OpenParen,
#[bytes(b'/')]
Slash,
#[fallback]
Other,
}
```
Before we were generating a `CLASS_TABLE` that we could access directly,
but now it will be part of the `Class`. This means that the usage has to
change:
```diff
- CLASS_TABLE[cursor.curr as usize]
+ Class::TABLE[cursor.curr as usize]
```
This is slightly worse UX, and this is where another change comes in. We
implemented the `From<u8> for #enum_name` trait inside of the
`ClassifyBytes` derive macro. This allows us to use `.into()` on any
`u8` as long as we are comparing it to a `Class` instance. In our
scenario:
```diff
- Class::TABLE[cursor.curr as usize]
+ cursor.curr.into()
```
Usage wise, this looks something like this:
```diff
while cursor.pos < len {
- match Class::TABLE[cursor.curr as usize] {
+ match cursor.curr.into() {
- Class::Escape => match Class::Table[cursor.next as usize] {
+ Class::Escape => match cursor.next.into() {
// An escaped whitespace character is not allowed
Class::Whitespace => return MachineState::Idle,
// An escaped character, skip ahead to the next character
_ => cursor.advance(),
},
// End of the string
Class::Quote if cursor.curr == end_char => return self.done(start_pos, cursor),
// Any kind of whitespace is not allowed
Class::Whitespace => return MachineState::Idle,
// Everything else is valid
_ => {}
};
cursor.advance()
}
MachineState::Idle
}
}
```
If you manually look at the `Class::TABLE` in your editor for example,
you can see that it is properly generated at compile time.
Given this input:
```rs
#[derive(Clone, Copy, ClassifyBytes)]
enum Class {
#[bytes_range(b'a'..=b'z')]
AlphaLower,
#[bytes_range(b'A'..=b'Z')]
AlphaUpper,
#[bytes(b'@')]
At,
#[bytes(b':')]
Colon,
#[bytes(b'-')]
Dash,
#[bytes(b'.')]
Dot,
#[bytes(b'\0')]
End,
#[bytes(b'!')]
Exclamation,
#[bytes_range(b'0'..=b'9')]
Number,
#[bytes(b'[')]
OpenBracket,
#[bytes(b']')]
CloseBracket,
#[bytes(b'(')]
OpenParen,
#[bytes(b'%')]
Percent,
#[bytes(b'"', b'\'', b'`')]
Quote,
#[bytes(b'/')]
Slash,
#[bytes(b'_')]
Underscore,
#[bytes(b' ', b'\t', b'\n', b'\r', b'\x0C')]
Whitespace,
#[fallback]
Other,
}
```
This is the result:
<img width="1244" alt="image"
src="https://github.com/user-attachments/assets/6ffd6ad3-0b2f-4381-a24c-593e4c72080e"
/>
|
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