assert: fix single assert first line

lib/assert.js

@@ -35,6 +35,10 @@ const { NativeModule } = require('internal/bootstrap/loaders');
 
 let isDeepEqual;
 let isDeepStrictEqual;
+let parseExpressionAt;
+let findNodeAround;
+let columnOffset = 0;
+let decoder;
 
 function lazyLoadComparison() {
   const comparison = require('internal/util/comparisons');
@@ -114,52 +118,141 @@ function fail(actual, expected, message, operator, stackStartFn) {
 assert.fail = fail;
 
 // The AssertionError is defined in internal/error.
-// new assert.AssertionError({ message: message,
-//                             actual: actual,
-//                             expected: expected });
 assert.AssertionError = AssertionError;
 
-function getBuffer(fd, assertLine) {
+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 = 64; // bytesPerRead * maxReads = 512 kb
-  let bytesRead = 0;
-  let startBuffer = 0; // Start reading from that char on
   const bytesPerRead = 8192;
-  const buffers = [];
-  do {
-    const buffer = Buffer.allocUnsafe(bytesPerRead);
+  // 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 (var i = 0; i < bytesRead; i++) {
-      if (buffer[i] === 10) {
-        lines++;
-        if (lines === assertLine) {
-          startBuffer = i + 1;
-        // Read up to 15 more lines to make sure all code gets matched
-        } else if (lines === assertLine + 16) {
-          buffers.push(buffer.slice(startBuffer, i));
-          return buffers;
+      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);
       }
     }
-    if (lines >= assertLine) {
-      buffers.push(buffer.slice(startBuffer, bytesRead));
-      // Reset the startBuffer in case we need more than one chunk
-      startBuffer = 0;
+  }
+}
+
+function parseCode(code, offset) {
+  // Lazy load acorn.
+  if (parseExpressionAt === undefined) {
+    ({ parseExpressionAt } = require('internal/deps/acorn/dist/acorn'));
+    ({ findNodeAround } = require('internal/deps/acorn/dist/walk'));
+  }
+  let node;
+  let start = 0;
+  // Parse the read code until the correct expression is found.
+  do {
+    try {
+      node = parseExpressionAt(code, start);
+      start = node.end + 1 || start;
+      // Find the CallExpression in the tree.
+      node = findNodeAround(node, offset, 'CallExpression');
+    } catch (err) {
+      // Unexpected token error and the like.
+      start += err.raisedAt || 1;
+      if (start > offset) {
+        // No matching expression found. This could happen if the assert
+        // expression is bigger than the provided buffer.
+        // eslint-disable-next-line no-throw-literal
+        throw null;
+      }
     }
-  } while (--maxReads !== 0 && bytesRead !== 0);
-  return buffers;
+  } while (node === undefined || node.node.end < offset);
+
+  return [
+    node.node.start,
+    code.slice(node.node.start, node.node.end)
+        .replace(escapeSequencesRegExp, escapeFn)
+  ];
 }
 
-function getErrMessage(call) {
+function getErrMessage(message, fn) {
+  const tmpLimit = Error.stackTraceLimit;
+  // Make sure the limit is set to 1. Otherwise it could fail (<= 0) or it
+  // does to much work.
+  Error.stackTraceLimit = 1;
+  // We only need the stack trace. To minimize the overhead use an object
+  // instead of an error.
+  const err = {};
+  Error.captureStackTrace(err, fn);
+  Error.stackTraceLimit = tmpLimit;
+
+  const tmpPrepare = Error.prepareStackTrace;
+  Error.prepareStackTrace = (_, stack) => stack;
+  const call = err.stack[0];
+  Error.prepareStackTrace = tmpPrepare;
+
   const filename = call.getFileName();
+
   if (!filename) {
-    return;
+    return message;
   }
 
   const line = call.getLineNumber() - 1;
-  const column = call.getColumnNumber() - 1;
+  let column = call.getColumnNumber() - 1;
+
+  // Line number one reports the wrong column due to being wrapped in a
+  // function. Remove that offset to get the actual call.
+  if (line === 0) {
+    if (columnOffset === 0) {
+      const { wrapper } = require('internal/modules/cjs/loader');
+      columnOffset = wrapper[0].length;
+    }
+    column -= columnOffset;
+  }
+
   const identifier = `${filename}${line}${column}`;
 
   if (errorCache.has(identifier)) {
@@ -172,57 +265,49 @@ function getErrMessage(call) {
     return;
   }
 
-  let fd, message;
+  let fd;
   try {
+    // Set the stack trace limit to zero. This makes sure unexpected token
+    // errors are handled faster.
+    Error.stackTraceLimit = 0;
+
+    if (decoder === undefined) {
+      const { StringDecoder } = require('string_decoder');
+      decoder = new StringDecoder('utf8');
+    }
+
     fd = openSync(filename, 'r', 0o666);
-    const buffers = getBuffer(fd, line);
-    const code = Buffer.concat(buffers).toString('utf8');
-    // Lazy load acorn.
-    const { parseExpressionAt } = require('internal/deps/acorn/dist/acorn');
-    const nodes = parseExpressionAt(code, column);
-    // Node type should be "CallExpression" and some times
-    // "SequenceExpression".
-    const node = nodes.type === 'CallExpression' ? nodes : nodes.expressions[0];
-    const name = node.callee.name;
-    // Calling `ok` with .apply or .call is uncommon but we use a simple
-    // safeguard nevertheless.
-    if (name !== 'apply' && name !== 'call') {
-    // Only use `assert` and `assert.ok` to reference the "real API" and
-    // not user defined function names.
-      const ok = name === 'ok' ? '.ok' : '';
-      const args = node.arguments;
-      message = code
-        .slice(args[0].start, args[args.length - 1].end)
-        .replace(escapeSequencesRegExp, escapeFn);
+    // Reset column and message.
+    [column, message] = getCode(fd, line, column);
+    // Flush unfinished multi byte characters.
+    decoder.end();
+    // Always normalize indentation, otherwise the message could look weird.
+    if (message.indexOf('\n') !== -1) {
       if (EOL === '\r\n') {
         message = message.replace(/\r\n/g, '\n');
       }
-      // Always normalize indentation, otherwise the message could look weird.
-      if (message.indexOf('\n') !== -1) {
-        const tmp = message.split('\n');
-        message = tmp[0];
-        for (var i = 1; i < tmp.length; i++) {
-          let pos = 0;
-          while (pos < column &&
-              (tmp[i][pos] === ' ' || tmp[i][pos] === '\t')) {
-            pos++;
-          }
-          message += `\n  ${tmp[i].slice(pos)}`;
+      const frames = message.split('\n');
+      message = frames.shift();
+      for (const frame of frames) {
+        let pos = 0;
+        while (pos < column && (frame[pos] === ' ' || frame[pos] === '\t')) {
+          pos++;
         }
+        message += `\n  ${frame.slice(pos)}`;
       }
-      message = 'The expression evaluated to a falsy value:' +
-        `\n\n  assert${ok}(${message})\n`;
     }
+    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 (e) {
   // Invalidate cache to prevent trying to read this part again.
     errorCache.set(identifier, undefined);
   } finally {
+    // Reset limit.
+    Error.stackTraceLimit = tmpLimit;
     if (fd !== undefined)
       closeSync(fd);
   }
@@ -236,25 +321,8 @@ function innerOk(fn, argLen, value, message) {
       generatedMessage = true;
       message = 'No value argument passed to `assert.ok()`';
     } else if (message == null) {
-      // Use the call as error message if possible.
-      // This does not work with e.g. the repl.
-      // eslint-disable-next-line no-restricted-syntax
-      const err = new Error();
-      // Make sure the limit is set to 1. Otherwise it could fail (<= 0) or it
-      // does to much work.
-      const tmpLimit = Error.stackTraceLimit;
-      Error.stackTraceLimit = 1;
-      Error.captureStackTrace(err, fn);
-      Error.stackTraceLimit = tmpLimit;
-
-      const tmpPrepare = Error.prepareStackTrace;
-      Error.prepareStackTrace = (_, stack) => stack;
-      const call = err.stack[0];
-      Error.prepareStackTrace = tmpPrepare;
-
-      // Make sure it would be "null" in case that is used.
-      message = getErrMessage(call) || message;
       generatedMessage = true;
+      message = getErrMessage(message, fn);
     } else if (message instanceof Error) {
       throw message;
     }

test/fixtures/assert-first-line.js

@@ -0,0 +1,2 @@
+'use strict'; const ässört = require('assert'); ässört(true); ässört.ok(''); ässört(null);
+// aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(false);