Use shared finder

Cargo.lock

@@ -2343,6 +2343,7 @@ dependencies = [
  "lalrpop",
  "lalrpop-util",
  "memchr",
+ "once_cell",
  "ruff_python_ast",
  "ruff_text_size",
  "rustc-hash",

crates/ruff_python_parser/Cargo.toml

@@ -28,6 +28,7 @@ rustc-hash = { workspace = true }
 static_assertions = { workspace = true }
 unicode-ident = { workspace = true }
 unicode_names2 = { workspace = true }
+once_cell = "1.19.0"
 
 [dev-dependencies]
 insta = { workspace = true }

crates/ruff_python_parser/src/string.rs

@@ -1,6 +1,8 @@
 //! Parsing of string literals, bytes literals, and implicit string concatenation.
 
 use bstr::ByteSlice;
+use memchr::memmem;
+use once_cell::sync::Lazy;
 
 use ruff_python_ast::{self as ast, Expr};
 use ruff_text_size::{Ranged, TextRange, TextSize};
@@ -8,6 +10,8 @@ use ruff_text_size::{Ranged, TextRange, TextSize};
 use crate::lexer::{LexicalError, LexicalErrorType};
 use crate::token::{StringKind, Tok};
 
+const BACKSLASH_FINDER: Lazy<memmem::Finder> = Lazy::new(|| memmem::Finder::new(b"\\"));
+
 pub(crate) enum StringType {
     Str(ast::StringLiteral),
     Bytes(ast::BytesLiteral),
@@ -310,7 +314,7 @@ impl StringParser {
             }));
         }
 
-        let Some(mut escape) = memchr::memchr(b'\\', self.source.as_bytes()) else {
+        let Some(mut escape) = BACKSLASH_FINDER.find(self.source.as_bytes()) else {
             // If the string doesn't contain any escape sequences, return the owned string.
             return Ok(StringType::Bytes(ast::BytesLiteral {
                 value: self.source.into_boxed_bytes(),
@@ -336,7 +340,7 @@ impl StringParser {
                 }
             }
 
-            let Some(next_escape) = memchr::memchr(b'\\', self.source[self.cursor..].as_bytes())
+            let Some(next_escape) = BACKSLASH_FINDER.find(self.source[self.cursor..].as_bytes())
             else {
                 // Add the rest of the string to the value.
                 let rest = &self.source[self.cursor..];
@@ -364,7 +368,7 @@ impl StringParser {
             }));
         }
 
-        let Some(mut escape) = memchr::memchr(b'\\', self.source.as_bytes()) else {
+        let Some(mut escape) = BACKSLASH_FINDER.find(self.source.as_bytes()) else {
             // If the string doesn't contain any escape sequences, return the owned string.
             return Ok(StringType::Str(ast::StringLiteral {
                 value: self.source,
@@ -392,7 +396,7 @@ impl StringParser {
                 }
             }
 
-            let Some(next_escape) = memchr::memchr(b'\\', self.source[self.cursor..].as_bytes())
+            let Some(next_escape) = BACKSLASH_FINDER.find(self.source[self.cursor..].as_bytes())
             else {
                 // Add the rest of the string to the value.
                 let rest = &self.source[self.cursor..];