perf(node:util): fast path for extractedSplitNewLines

src/bun.js/node/node_util_binding.zig

@@ -105,3 +105,48 @@ pub fn internalErrorName(globalThis: *JSC.JSGlobalObject, callframe: *JSC.CallFr
     var fmtstring = bun.String.createFormat("Unknown system error {d}", .{err_int}) catch bun.outOfMemory();
     return fmtstring.transferToJS(globalThis);
 }
+
+/// `extractedSplitNewLines` for ASCII/Latin1 strings. Panics if passed a non-string.
+//Returns `undefined` if param is utf8 or utf16 and not fully ascii.
+/// 
+/// ```js
+/// // util.js
+/// const extractedNewLineRe = new RegExp("(?<=\\n)");
+/// extractedSplitNewLines = value => RegExpPrototypeSymbolSplit(extractedNewLineRe, value);
+/// ```
+pub fn extractedSplitNewLinesFastPathStringsOnly(globalThis: *JSC.JSGlobalObject, callframe: *JSC.CallFrame) bun.JSError!JSC.JSValue {
+    var fallback = std.heap.stackFallback(1024, bun.default_allocator);
+    const allocator = fallback.get();
+    bun.assert(callframe.argumentsCount() == 1);
+    const value = callframe.argument(0);
+    bun.assert(value.isString());
+
+    const str = try value.toBunString2(globalThis);
+
+    if (str.is8Bit() or bun.strings.isAllASCII(str.byteSlice())) {
+        var lines: std.ArrayListUnmanaged(bun.String) = .{};
+        defer {
+            for (lines.items) |out| {
+                out.deref();
+            }
+            lines.deinit(allocator);
+        }
+
+        var start: usize = 0;
+        const bytes = str.byteSlice();
+
+        while (std.mem.indexOfScalarPos(u8, bytes, start, '\n')) |delim_start| {
+            const end = delim_start + 1;
+            try lines.append(allocator, bun.String.fromBytes(bytes[start..end])); // include the newline
+            start = end;
+        } 
+
+        if (start < bytes.len) {
+            try lines.append(allocator, bun.String.fromBytes(bytes[start..]));
+        }
+
+        return bun.String.toJSArray(globalThis, lines.items);
+    }
+
+    return JSC.JSValue.jsUndefined();
+}

src/js/internal/util/inspect.js

@@ -141,6 +141,21 @@ const kRejected = Symbol("kRejected"); // state ID 2
 const ALL_PROPERTIES = 0;
 const ONLY_ENUMERABLE = 2;
 
+/**
+ * Fast path for {@link extractedSplitNewLines} for ASCII/Latin1 strings.
+ * @returns `value` split on newlines (newline included at end), or `undefined`
+ * if non-ascii UTF8/UTF16.
+ * 
+ * Passing this a non-string will cause a panic.
+ * 
+ * @type {(value: string) => string[] | undefined}
+ */
+const extractedSplitNewLinesFastPathStringsOnly = $newZigFunction(
+  "node_util_binding.zig",
+  "extractedSplitNewLinesFastPathStringsOnly",
+  1,
+);
+
 const isAsyncFunction = v =>
   typeof v === "function" && StringPrototypeStartsWith(FunctionPrototypeToString(v), "async");
 const isGeneratorFunction = v =>
@@ -397,7 +412,7 @@ let strEscapeSequencesRegExp,
   strEscapeSequencesReplacer,
   strEscapeSequencesRegExpSingle,
   strEscapeSequencesReplacerSingle,
-  extractedSplitNewLines;
+  extractedSplitNewLinesSlow;
 try {
   // Change from regex literals to RegExp constructors to avoid unrecoverable
   // syntax error at load time.
@@ -416,7 +431,7 @@ try {
     "g",
   );
   const extractedNewLineRe = new RegExp("(?<=\\n)");
-  extractedSplitNewLines = value => RegExpPrototypeSymbolSplit(extractedNewLineRe, value);
+  extractedSplitNewLinesSlow = value => RegExpPrototypeSymbolSplit(extractedNewLineRe, value);
   // CI doesn't run in an elderly runtime
 } catch {
   // These are from a previous version of node,
@@ -426,7 +441,7 @@ try {
   strEscapeSequencesReplacer = /[\x00-\x1f\x27\x5c\x7f-\x9f]/g;
   strEscapeSequencesRegExpSingle = /[\x00-\x1f\x5c\x7f-\x9f]/;
   strEscapeSequencesReplacerSingle = /[\x00-\x1f\x5c\x7f-\x9f]/g;
-  extractedSplitNewLines = value => {
+  extractedSplitNewLinesSlow = value => {
     const lines = RegExpPrototypeSymbolSplit(/\n/, value);
     const last = ArrayPrototypePop(lines);
     const nlLines = ArrayPrototypeMap(lines, line => line + "\n");
@@ -437,6 +452,13 @@ try {
   };
 }
 
+const extractedSplitNewLines = value => {
+  if (typeof value === "string") {
+    return extractedSplitNewLinesFastPathStringsOnly(value) || extractedSplitNewLinesSlow(value);
+  }
+  return extractedSplitNewLinesSlow(value);
+}
+
 const keyStrRegExp = /^[a-zA-Z_][a-zA-Z_0-9]*$/;
 const numberRegExp = /^(0|[1-9][0-9]*)$/;