feat: backtrace/bt

Author: Jan Krems

examples/backtrace.js

@@ -0,0 +1,31 @@
+'use strict';
+const { exports: moduleScoped } = module;
+
+function topFn(a, b = false) {
+  const l1 = a;
+  let t = typeof l1;
+  var v = t.length;
+  debugger;
+  return b || t || v || moduleScoped;
+}
+
+class Ctor {
+  constructor(options) {
+    this.options = options;
+  }
+
+  m() {
+    const mLocal = this.options;
+    topFn(this);
+    return mLocal;
+  }
+}
+
+(function () {
+  const theOptions = { x: 42 };
+  const arr = [theOptions];
+  arr.forEach(options => {
+    const obj = new Ctor(options);
+    return obj.m();
+  });
+}());

lib/internal/inspect-repl.js

@@ -31,7 +31,7 @@ const SHORTCUTS = {
   next: 'n',
   step: 's',
   out: 'o',
-  // backtrace: 'bt',
+  backtrace: 'bt',
   setBreakpoint: 'sb',
   // clearBreakpoint: 'cb',
   // pause_: 'pause',
@@ -116,7 +116,7 @@ function createRepl(inspector) {
   const watchedExpressions = [];
   const knownBreakpoints = [];
 
-  // let currentBacktrace;
+  let currentBacktrace;
   let selectedFrame;
 
   const print = inspector.print.bind(inspector);
@@ -148,6 +148,16 @@ function createRepl(inspector) {
     }
   }
 
+  function printBacktrace() {
+    currentBacktrace.forEach((callFrame, idx) => {
+      const { location: { scriptId, lineNumber, columnNumber }, functionName } = callFrame;
+      const script = knownScripts[scriptId];
+      const relativeUrl = (script && getRelativePath(script && script.url)) || '<unknown>';
+      const name = functionName || '(anonymous)';
+      print(`#${idx} ${name} ${relativeUrl}:${lineNumber + 1}:${columnNumber}`);
+    });
+  }
+
   function watchers() {
     return Promise.resolve(watchedExpressions);
   }
@@ -297,7 +307,7 @@ function createRepl(inspector) {
 
   Debugger.on('paused', ({ callFrames, reason /* , hitBreakpoints */ }) => {
     // Save execution context's data
-    // currentBacktrace = callFrames;
+    currentBacktrace = callFrames;
     selectedFrame = callFrames[0];
     const { scriptId, lineNumber } = selectedFrame.location;
 
@@ -343,6 +353,10 @@ function createRepl(inspector) {
         return Debugger.pause();
       },
 
+      get backtrace() {
+        return printBacktrace();
+      },
+
       setBreakpoint,
       list,
     });

test/cli/backtrace.test.js

@@ -0,0 +1,27 @@
+'use strict';
+const tap = require('tap');
+
+const startCLI = require('./start-cli');
+
+tap.test('display and navigate backtrace', (t) => {
+  const cli = startCLI(['examples/backtrace.js']);
+
+  function onFatal(error) {
+    cli.quit();
+    throw error;
+  }
+
+  return cli.waitFor(/break/)
+    .then(() => cli.waitForPrompt())
+    .then(() => cli.stepCommand('c'))
+    .then(() => cli.command('bt'))
+    .then(() => {
+      t.match(cli.output, '#0 topFn examples/backtrace.js:8:2');
+    })
+    .then(() => cli.command('backtrace'))
+    .then(() => {
+      t.match(cli.output, '#0 topFn examples/backtrace.js:8:2');
+    })
+    .then(() => cli.quit())
+    .then(null, onFatal);
+});

test/cli/start-cli.js

@@ -19,7 +19,7 @@ function startCLI(args) {
 
   function getOutput() {
     return outputBuffer.join('').toString()
-      .replace(/^[^\n]*[\b]/mg, '\n');
+      .replace(/^[^\n]*?[\b]/mg, '');
   }
 
   child.stdout.setEncoding('utf8');
@@ -80,6 +80,10 @@ function startCLI(args) {
       return getOutput();
     },
 
+    get rawOutput() {
+      return outputBuffer.join('').toString();
+    },
+
     parseSourceLines() {
       return getOutput().split('\n')
         .map((line) => line.match(/(?:\*|>)?\s*(\d+)/))