lib,src: refactor assert to load error source from memory

The source code is available from V8 API and assert can avoid reading the source file from the filesystem and parse the file again. PR-URL: #59751 Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
targos · Sep 25, 2025 · Sep 10, 2025 · Sep 8, 2025 · Sep 11, 2025 · Sep 11, 2025
commit b200cd8470a4084c53c91a1b03b6aed29861f31f
diff --git a/lib/internal/assert/utils.js b/lib/internal/assert/utils.js
@@ -1,38 +1,21 @@
 'use strict';
 
 const {
-  ArrayPrototypeShift,
   Error,
   ErrorCaptureStackTrace,
-  FunctionPrototypeBind,
-  RegExpPrototypeSymbolReplace,
-  SafeMap,
   StringPrototypeCharCodeAt,
-  StringPrototypeIncludes,
   StringPrototypeReplace,
-  StringPrototypeSlice,
-  StringPrototypeSplit,
-  StringPrototypeStartsWith,
 } = primordials;
 
-const { Buffer } = require('buffer');
 const {
   isErrorStackTraceLimitWritable,
-  overrideStackTrace,
 } = require('internal/errors');
 const AssertionError = require('internal/assert/assertion_error');
-const { openSync, closeSync, readSync } = require('fs');
-const { EOL } = require('internal/constants');
-const { BuiltinModule } = require('internal/bootstrap/realm');
 const { isError } = require('internal/util');
 
-const errorCache = new SafeMap();
-const { fileURLToPath } = require('internal/url');
-
-let parseExpressionAt;
-let findNodeAround;
-let tokenizer;
-let decoder;
+const {
+  getErrorSourceExpression,
+} = require('internal/errors/error_source');
 
 // Escape control characters but not \n and \t to keep the line breaks and
 // indentation intact.
@@ -50,111 +33,7 @@ const meta = [
 
 const escapeFn = (str) => meta[StringPrototypeCharCodeAt(str, 0)];
 
-function findColumn(fd, column, code) {
-  if (code.length > column + 100) {
-    try {
-      return parseCode(code, column);
-    } catch {
-      // End recursion in case no code could be parsed. The expression should
-      // have been found after 2500 characters, so stop trying.
-      if (code.length - column > 2500) {
-        // eslint-disable-next-line no-throw-literal
-        throw null;
-      }
-    }
-  }
-  // Read up to 2500 bytes more than necessary in columns. That way we address
-  // multi byte characters and read enough data to parse the code.
-  const bytesToRead = column - code.length + 2500;
-  const buffer = Buffer.allocUnsafe(bytesToRead);
-  const bytesRead = readSync(fd, buffer, 0, bytesToRead);
-  code += decoder.write(buffer.slice(0, bytesRead));
-  // EOF: fast path.
-  if (bytesRead < bytesToRead) {
-    return parseCode(code, column);
-  }
-  // Read potentially missing code.
-  return findColumn(fd, column, code);
-}
-
-function getCode(fd, line, column) {
-  let bytesRead = 0;
-  if (line === 0) {
-    // Special handle line number one. This is more efficient and simplifies the
-    // rest of the algorithm. Read more than the regular column number in bytes
-    // to prevent multiple reads in case multi byte characters are used.
-    return findColumn(fd, column, '');
-  }
-  let lines = 0;
-  // Prevent blocking the event loop by limiting the maximum amount of
-  // data that may be read.
-  let maxReads = 32; // bytesPerRead * maxReads = 512 KiB
-  const bytesPerRead = 16384;
-  // Use a single buffer up front that is reused until the call site is found.
-  let buffer = Buffer.allocUnsafe(bytesPerRead);
-  while (maxReads-- !== 0) {
-    // Only allocate a new buffer in case the needed line is found. All data
-    // before that can be discarded.
-    buffer = lines < line ? buffer : Buffer.allocUnsafe(bytesPerRead);
-    bytesRead = readSync(fd, buffer, 0, bytesPerRead);
-    // Read the buffer until the required code line is found.
-    for (let i = 0; i < bytesRead; i++) {
-      if (buffer[i] === 10 && ++lines === line) {
-        // If the end of file is reached, directly parse the code and return.
-        if (bytesRead < bytesPerRead) {
-          return parseCode(buffer.toString('utf8', i + 1, bytesRead), column);
-        }
-        // Check if the read code is sufficient or read more until the whole
-        // expression is read. Make sure multi byte characters are preserved
-        // properly by using the decoder.
-        const code = decoder.write(buffer.slice(i + 1, bytesRead));
-        return findColumn(fd, column, code);
-      }
-    }
-  }
-}
-
-function parseCode(code, offset) {
-  // Lazy load acorn.
-  if (parseExpressionAt === undefined) {
-    const Parser = require('internal/deps/acorn/acorn/dist/acorn').Parser;
-    ({ findNodeAround } = require('internal/deps/acorn/acorn-walk/dist/walk'));
-
-    parseExpressionAt = FunctionPrototypeBind(Parser.parseExpressionAt, Parser);
-    tokenizer = FunctionPrototypeBind(Parser.tokenizer, Parser);
-  }
-  let node;
-  let start;
-  // Parse the read code until the correct expression is found.
-  for (const token of tokenizer(code, { ecmaVersion: 'latest' })) {
-    start = token.start;
-    if (start > offset) {
-      // No matching expression found. This could happen if the assert
-      // expression is bigger than the provided buffer.
-      break;
-    }
-    try {
-      node = parseExpressionAt(code, start, { ecmaVersion: 'latest' });
-      // Find the CallExpression in the tree.
-      node = findNodeAround(node, offset, 'CallExpression');
-      if (node?.node.end >= offset) {
-        return [
-          node.node.start,
-          StringPrototypeReplace(StringPrototypeSlice(code,
-                                                      node.node.start, node.node.end),
-                                 escapeSequencesRegExp, escapeFn),
-        ];
-      }
-    // eslint-disable-next-line no-unused-vars
-    } catch (err) {
-      continue;
-    }
-  }
-  // eslint-disable-next-line no-throw-literal
-  throw null;
-}
-
-function getErrMessage(message, fn) {
+function getErrMessage(fn) {
   const tmpLimit = Error.stackTraceLimit;
   const errorStackTraceLimitIsWritable = isErrorStackTraceLimitWritable();
   // Make sure the limit is set to 1. Otherwise it could fail (<= 0) or it
@@ -166,85 +45,10 @@ function getErrMessage(message, fn) {
   ErrorCaptureStackTrace(err, fn);
   if (errorStackTraceLimitIsWritable) Error.stackTraceLimit = tmpLimit;
 
-  overrideStackTrace.set(err, (_, stack) => stack);
-  const call = err.stack[0];
-
-  let filename = call.getFileName();
-  const line = call.getLineNumber() - 1;
-  let column = call.getColumnNumber() - 1;
-  let identifier;
-
-  if (filename) {
-    identifier = `${filename}${line}${column}`;
-
-    // Skip Node.js modules!
-    if (StringPrototypeStartsWith(filename, 'node:') &&
-        BuiltinModule.exists(StringPrototypeSlice(filename, 5))) {
-      errorCache.set(identifier, undefined);
-      return;
-    }
-  } else {
-    return message;
-  }
-
-  if (errorCache.has(identifier)) {
-    return errorCache.get(identifier);
-  }
-
-  let fd;
-  try {
-    // Set the stack trace limit to zero. This makes sure unexpected token
-    // errors are handled faster.
-    if (errorStackTraceLimitIsWritable) Error.stackTraceLimit = 0;
-
-    if (decoder === undefined) {
-      const { StringDecoder } = require('string_decoder');
-      decoder = new StringDecoder('utf8');
-    }
-
-    // ESM file prop is a file proto. Convert that to path.
-    // This ensure opensync will not throw ENOENT for ESM files.
-    const fileProtoPrefix = 'file://';
-    if (StringPrototypeStartsWith(filename, fileProtoPrefix)) {
-      filename = fileURLToPath(filename);
-    }
-
-    fd = openSync(filename, 'r', 0o666);
-    // Reset column and message.
-    ({ 0: column, 1: message } = getCode(fd, line, column));
-    // Flush unfinished multi byte characters.
-    decoder.end();
-
-    // Always normalize indentation, otherwise the message could look weird.
-    if (StringPrototypeIncludes(message, '\n')) {
-      if (EOL === '\r\n') {
-        message = RegExpPrototypeSymbolReplace(/\r\n/g, message, '\n');
-      }
-      const frames = StringPrototypeSplit(message, '\n');
-      message = ArrayPrototypeShift(frames);
-      for (let i = 0; i < frames.length; i++) {
-        const frame = frames[i];
-        let pos = 0;
-        while (pos < column && (frame[pos] === ' ' || frame[pos] === '\t')) {
-          pos++;
-        }
-        message += `\n  ${StringPrototypeSlice(frame, pos)}`;
-      }
-    }
-    message = `The expression evaluated to a falsy value:\n\n  ${message}\n`;
-    // Make sure to always set the cache! No matter if the message is
-    // undefined or not
-    errorCache.set(identifier, message);
-
-    return message;
-  } catch {
-    // Invalidate cache to prevent trying to read this part again.
-    errorCache.set(identifier, undefined);
-  } finally {
-    // Reset limit.
-    if (errorStackTraceLimitIsWritable) Error.stackTraceLimit = tmpLimit;
-    if (fd !== undefined)
-      closeSync(fd);
+  let source = getErrorSourceExpression(err);
+  if (source) {
+    source = StringPrototypeReplace(source, escapeSequencesRegExp, escapeFn);
+    return `The expression evaluated to a falsy value:\n\n  ${source}\n`;
   }
 }
 
@@ -257,7 +61,7 @@ function innerOk(fn, argLen, value, message) {
       message = 'No value argument passed to `assert.ok()`';
     } else if (message == null) {
       generatedMessage = true;
-      message = getErrMessage(message, fn);
+      message = getErrMessage(fn);
     } else if (isError(message)) {
       throw message;
     }

diff --git a/lib/internal/errors/error_source.js b/lib/internal/errors/error_source.js
@@ -0,0 +1,133 @@
+'use strict';
+
+const {
+  FunctionPrototypeBind,
+  StringPrototypeSlice,
+} = primordials;
+
+const {
+  getErrorSourcePositions,
+} = internalBinding('errors');
+
+/**
+ * Get the source location of an error.
+ *
+ * The `error.stack` must not have been accessed. The resolution is based on the structured
+ * error stack data.
+ * @param {Error|object} error An error object, or an object being invoked with ErrorCaptureStackTrace
+ * @returns {{sourceLine: string, startColumn: number}|undefined}
+ */
+function getErrorSourceLocation(error) {
+  const pos = getErrorSourcePositions(error);
+  const {
+    sourceLine,
+    startColumn,
+  } = pos;
+
+  return { sourceLine, startColumn };
+}
+
+const memberAccessTokens = [ '.', '?.', '[', ']' ];
+const memberNameTokens = [ 'name', 'string', 'num' ];
+let tokenizer;
+/**
+ * Get the first expression in a code string at the startColumn.
+ * @param {string} code source code line
+ * @param {number} startColumn which column the error is constructed
+ * @returns {string}
+ */
+function getFirstExpression(code, startColumn) {
+  // Lazy load acorn.
+  if (tokenizer === undefined) {
+    const Parser = require('internal/deps/acorn/acorn/dist/acorn').Parser;
+    tokenizer = FunctionPrototypeBind(Parser.tokenizer, Parser);
+  }
+
+  let lastToken;
+  let firstMemberAccessNameToken;
+  let terminatingCol;
+  let parenLvl = 0;
+  // Tokenize the line to locate the expression at the startColumn.
+  // The source line may be an incomplete JavaScript source, so do not parse the source line.
+  for (const token of tokenizer(code, { ecmaVersion: 'latest' })) {
+    // Peek before the startColumn.
+    if (token.start < startColumn) {
+      // There is a semicolon. This is a statement before the startColumn, so reset the memo.
+      if (token.type.label === ';') {
+        firstMemberAccessNameToken = null;
+        continue;
+      }
+      // Try to memo the member access expressions before the startColumn, so that the
+      // returned source code contains more info:
+      //   assert.ok(value)
+      //          ^ startColumn
+      // The member expression can also be like
+      //   assert['ok'](value) or assert?.ok(value)
+      //               ^ startColumn      ^ startColumn
+      if (memberAccessTokens.includes(token.type.label) && lastToken?.type.label === 'name') {
+        // First member access name token must be a 'name'.
+        firstMemberAccessNameToken ??= lastToken;
+      } else if (!memberAccessTokens.includes(token.type.label) &&
+        !memberNameTokens.includes(token.type.label)) {
+        // Reset the memo if it is not a simple member access.
+        // For example: assert[(() => 'ok')()](value)
+        //                                    ^ startColumn
+        firstMemberAccessNameToken = null;
+      }
+      lastToken = token;
+      continue;
+    }
+    // Now after the startColumn, this must be an expression.
+    if (token.type.label === '(') {
+      parenLvl++;
+      continue;
+    }
+    if (token.type.label === ')') {
+      parenLvl--;
+      if (parenLvl === 0) {
+        // A matched closing parenthesis found after the startColumn,
+        // terminate here. Include the token.
+        //   (assert.ok(false), assert.ok(true))
+        //           ^ startColumn
+        terminatingCol = token.start + 1;
+        break;
+      }
+      continue;
+    }
+    if (token.type.label === ';') {
+      // A semicolon found after the startColumn, terminate here.
+      //   assert.ok(false); assert.ok(true));
+      //          ^ startColumn
+      terminatingCol = token;
+      break;
+    }
+    // If no semicolon found after the startColumn. The string after the
+    // startColumn must be the expression.
+    //   assert.ok(false)
+    //          ^ startColumn
+  }
+  const start = firstMemberAccessNameToken?.start ?? startColumn;
+  return StringPrototypeSlice(code, start, terminatingCol);
+}
+
+/**
+ * Get the source expression of an error.
+ *
+ * The `error.stack` must not have been accessed, or the source location may be incorrect. The
+ * resolution is based on the structured error stack data.
+ * @param {Error|object} error An error object, or an object being invoked with ErrorCaptureStackTrace
+ * @returns {string|undefined}
+ */
+function getErrorSourceExpression(error) {
+  const loc = getErrorSourceLocation(error);
+  if (loc === undefined) {
+    return;
+  }
+  const { sourceLine, startColumn } = loc;
+  return getFirstExpression(sourceLine, startColumn);
+}
+
+module.exports = {
+  getErrorSourceLocation,
+  getErrorSourceExpression,
+};