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refactor(lexer): harden safety of transmute #11013

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Merged
graphite-app merged 1 commit into from
May 14, 2025
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refactor(lexer): harden safety of transmute #11013

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9 changes: 6 additions & 3 deletions crates/oxc_parser/src/lexer/token.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
//! Token

use std::mem;

use oxc_span::Span;

use super::kind::Kind;
Expand Down Expand Up @@ -55,9 +57,10 @@ impl Token {

#[inline]
pub fn kind(&self) -> Kind {
// SAFETY: This conversion is safe because `Kind` is `#[repr(u8)]`,
// and we ensure the value stored is a valid `Kind` variant
unsafe { std::mem::transmute(((self.0 >> KIND_SHIFT) & KIND_MASK) as u8) }
// SAFETY: `Kind` is `#[repr(u8)]`. Only `Token::set_kind` alters these bits,
// and it sets them to the `u8` value of an existing `Kind`.
// So transmuting these bits back to `Kind` must produce a valid `Kind`.
unsafe { mem::transmute::<u8, Kind>(((self.0 >> KIND_SHIFT) & KIND_MASK) as u8) }
}

#[inline]
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