repl: remove internal frames from runtime errors

When a user executes code in the REPLServer which generates an
exception, there is no need to display the REPLServer internal
stack frames.

PR-URL: nodejs/node#15351
Reviewed-By: Prince John Wesley <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>

Refs: nodejs/node#9601

lib/repl.js

@@ -285,14 +285,16 @@ function REPLServer(prompt,
   self._domain.on('error', function debugDomainError(e) {
     debug('domain error');
     const top = replMap.get(self);
-
+    const pstrace = Error.prepareStackTrace;
+    Error.prepareStackTrace = prepareStackTrace(pstrace);
     internalUtil.decorateErrorStack(e);
+    Error.prepareStackTrace = pstrace;
     const isError = internalUtil.isError(e);
     if (e instanceof SyntaxError && e.stack) {
       // remove repl:line-number and stack trace
       e.stack = e.stack
-                 .replace(/^repl:\d+\r?\n/, '')
-                 .replace(/^\s+at\s.*\n?/gm, '');
+        .replace(/^repl:\d+\r?\n/, '')
+        .replace(/^\s+at\s.*\n?/gm, '');
     } else if (isError && self.replMode === exports.REPL_MODE_STRICT) {
       e.stack = e.stack.replace(/(\s+at\s+repl:)(\d+)/,
                                 (_, pre, line) => pre + (line - 1));
@@ -375,6 +377,30 @@ function REPLServer(prompt,
     };
   }
 
+  function filterInternalStackFrames(error, structuredStack) {
+    // search from the bottom of the call stack to
+    // find the first frame with a null function name
+    if (typeof structuredStack !== 'object')
+      return structuredStack;
+    const idx = structuredStack.reverse().findIndex(
+      (frame) => frame.getFunctionName() === null);
+
+    // if found, get rid of it and everything below it
+    structuredStack = structuredStack.splice(idx + 1);
+    return structuredStack;
+  }
+
+  function prepareStackTrace(fn) {
+    return (error, stackFrames) => {
+      const frames = filterInternalStackFrames(error, stackFrames);
+      if (fn) {
+        return fn(error, frames);
+      }
+      frames.push(error);
+      return frames.reverse().join('\n    at ');
+    };
+  }
+
   function _parseREPLKeyword(keyword, rest) {
     var cmd = this.commands[keyword];
     if (cmd) {
@@ -942,8 +968,6 @@ function complete(line, callback) {
       } else {
         const evalExpr = `try { ${expr} } catch (e) {}`;
         this.eval(evalExpr, this.context, 'repl', (e, obj) => {
-          // if (e) console.log(e);
-
           if (obj != null) {
             if (typeof obj === 'object' || typeof obj === 'function') {
               try {

test/fixtures/repl-pretty-stack.js

@@ -0,0 +1,19 @@
+'use strict';
+
+function a() {
+  b();
+}
+
+function b() {
+  c();
+}
+
+function c() {
+  d(function() { throw new Error('Whoops!'); });
+}
+
+function d(f) {
+  f();
+}
+
+a();

test/parallel/test-repl-pretty-custom-stack.js

@@ -0,0 +1,70 @@
+'use strict';
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const repl = require('repl');
+
+
+function run({ command, expected }) {
+  let accum = '';
+
+  const inputStream = new common.ArrayStream();
+  const outputStream = new common.ArrayStream();
+
+  outputStream.write = (data) => accum += data.replace('\r', '');
+
+  const r = repl.start({
+    prompt: '',
+    input: inputStream,
+    output: outputStream,
+    terminal: false,
+    useColors: false
+  });
+
+  r.write(`${command}\n`);
+  assert.strictEqual(accum, expected);
+  r.close();
+}
+
+const origPrepareStackTrace = Error.prepareStackTrace;
+Error.prepareStackTrace = (err, stack) => {
+  if (err instanceof SyntaxError)
+    return err.toString();
+  stack.push(err);
+  return stack.reverse().join('--->\n');
+};
+
+process.on('uncaughtException', (e) => {
+  Error.prepareStackTrace = origPrepareStackTrace;
+  throw e;
+});
+
+process.on('exit', () => (Error.prepareStackTrace = origPrepareStackTrace));
+
+const tests = [
+  {
+    // test .load for a file that throws
+    command: `.load ${fixtures.path('repl-pretty-stack.js')}`,
+    expected: 'Error: Whoops!--->\nrepl:9:24--->\nd (repl:12:3)--->\nc ' +
+              '(repl:9:3)--->\nb (repl:6:3)--->\na (repl:3:3)\n'
+  },
+  {
+    command: 'let x y;',
+    expected: 'let x y;\n      ^\n\nSyntaxError: Unexpected identifier\n'
+  },
+  {
+    command: 'throw new Error(\'Whoops!\')',
+    expected: 'Error: Whoops!\n'
+  },
+  {
+    command: 'foo = bar;',
+    expected: 'ReferenceError: bar is not defined\n'
+  },
+  // test anonymous IIFE
+  {
+    command: '(function() { throw new Error(\'Whoops!\'); })()',
+    expected: 'Error: Whoops!--->\nrepl:1:21\n'
+  }
+];
+
+tests.forEach(run);

test/parallel/test-repl-pretty-stack.js

@@ -0,0 +1,55 @@
+'use strict';
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const repl = require('repl');
+
+
+function run({ command, expected }) {
+  let accum = '';
+
+  const inputStream = new common.ArrayStream();
+  const outputStream = new common.ArrayStream();
+
+  outputStream.write = (data) => accum += data.replace('\r', '');
+
+  const r = repl.start({
+    prompt: '',
+    input: inputStream,
+    output: outputStream,
+    terminal: false,
+    useColors: false
+  });
+
+  r.write(`${command}\n`);
+  assert.strictEqual(accum, expected);
+  r.close();
+}
+
+const tests = [
+  {
+    // test .load for a file that throws
+    command: `.load ${fixtures.path('repl-pretty-stack.js')}`,
+    expected: 'Error: Whoops!\n    at repl:9:24\n    at d (repl:12:3)\n    ' +
+              'at c (repl:9:3)\n    at b (repl:6:3)\n    at a (repl:3:3)\n'
+  },
+  {
+    command: 'let x y;',
+    expected: 'let x y;\n      ^\n\nSyntaxError: Unexpected identifier\n\n'
+  },
+  {
+    command: 'throw new Error(\'Whoops!\')',
+    expected: 'Error: Whoops!\n'
+  },
+  {
+    command: 'foo = bar;',
+    expected: 'ReferenceError: bar is not defined\n'
+  },
+  // test anonymous IIFE
+  {
+    command: '(function() { throw new Error(\'Whoops!\'); })()',
+    expected: 'Error: Whoops!\n    at repl:1:21\n'
+  }
+];
+
+tests.forEach(run);

test/parallel/test-repl.js

@@ -71,7 +71,7 @@ function clean_up() {
 function strict_mode_error_test() {
   send_expect([
     { client: client_unix, send: 'ref = 1',
-      expect: /^ReferenceError:\sref\sis\snot\sdefined\n\s+at\srepl:1:5/ },
+      expect: /^ReferenceError:\sref\sis\snot\sdefined\nnode via Unix socket> $/ },
   ]);
 }