perf(oxfmt): Use simdutf8 based read_to_string

apps/oxfmt/Cargo.toml

@@ -38,6 +38,7 @@ cow-utils = { workspace = true }
 ignore = { workspace = true, features = ["simd-accel"] }
 miette = { workspace = true }
 rayon = { workspace = true }
+simdutf8 = { workspace = true }
 tracing-subscriber = { workspace = true, features = [] } # Omit the `regex` feature
 
 # NAPI dependencies (conditional on napi feature)

apps/oxfmt/src/service.rs

@@ -1,4 +1,4 @@
-use std::{fs, path::Path, sync::mpsc, time::Instant};
+use std::{fs, io, path::Path, sync::mpsc, time::Instant};
 
 use cow_utils::CowUtils;
 use rayon::prelude::*;
@@ -77,7 +77,7 @@ impl FormatService {
         let source_type = enable_jsx_source_type(entry.source_type);
 
         let allocator = self.allocator_pool.get();
-        let source_text = fs::read_to_string(path).expect("Failed to read file");
+        let source_text = read_to_string(path).expect("Failed to read file");
 
         let ret = Parser::new(&allocator, &source_text, source_type)
             .with_options(get_parse_options())
@@ -148,3 +148,17 @@ impl FormatService {
         }
     }
 }
+
+fn read_to_string(path: &Path) -> io::Result<String> {
+    // `simdutf8` is faster than `std::str::from_utf8` which `fs::read_to_string` uses internally
+    let bytes = fs::read(path)?;
+    if simdutf8::basic::from_utf8(&bytes).is_err() {
+        // Same error as `fs::read_to_string` produces (using `io::ErrorKind::InvalidData`)
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "stream did not contain valid UTF-8",
+        ));
+    }
+    // SAFETY: `simdutf8` has ensured it's a valid UTF-8 string
+    Ok(unsafe { String::from_utf8_unchecked(bytes) })
+}