feat: Print break context

Author: Jan Krems

lib/internal/inspect-repl.js

@@ -20,20 +20,69 @@
  * IN THE SOFTWARE.
  */
 'use strict';
+const Path = require('path');
 const Repl = require('repl');
 const vm = require('vm');
 
+const NATIVES = process.binding('natives');
+
+function getRelativePath(filename) {
+  const dir = `${Path.resolve()}/`;
+
+  // Change path to relative, if possible
+  if (filename.indexOf(dir) === 0) {
+    return filename.slice(dir.length);
+  }
+  return filename;
+}
+
 function toCallback(promise, callback) {
   function forward(...args) {
     process.nextTick(() => callback(...args));
   }
   promise.then(forward.bind(null, null), forward);
 }
 
+// Adds spaces and prefix to number
+// maxN is a maximum number we should have space for
+function leftPad(n, prefix, maxN) {
+  const s = n.toString();
+  const nchars = Math.max(2, String(maxN).length) + 1;
+  const nspaces = nchars - s.length - 1;
+
+  return prefix + ' '.repeat(nspaces) + s;
+}
+
+function markSourceColumn(sourceText, position, repl) {
+  if (!sourceText) return '';
+
+  const head = sourceText.slice(0, position);
+  let tail = sourceText.slice(position);
+
+  // Colourize char if stdout supports colours
+  if (repl.useColors) {
+    tail = tail.replace(/(.+?)([^\w]|$)/, '\u001b[32m$1\u001b[39m$2');
+  }
+
+  // Return source line with coloured char at `position`
+  return [head, tail].join('');
+}
+
 function startRepl(inspector) {
-  let repl; // forward declaration
+  const { Debugger } = inspector;
+
+  let repl; // eslint-disable-line prefer-const
   let lastCommand;
 
+  const knownScripts = {};
+  const watchedExpressions = [];
+  const knownBreakpoints = [];
+
+  // let currentBacktrace;
+  let selectedFrame;
+
+  const print = inspector.print.bind(inspector);
+
   function prepareControlCode(input) {
     if (input === '\n') return lastCommand;
     // exec process.title => exec("process.title");
@@ -61,6 +110,73 @@ function startRepl(inspector) {
     }
   }
 
+  function watchers() {
+    return Promise.resolve(watchedExpressions);
+  }
+
+  // List source code
+  function list(delta = 5) {
+    const { scriptId, lineNumber, columnNumber } = selectedFrame.location;
+    const start = Math.max(1, lineNumber - delta + 1);
+    const end = lineNumber + delta + 1;
+
+    return Debugger.getScriptSource({ scriptId })
+      .then(({ scriptSource }) => {
+        const lines = scriptSource.split('\n');
+        for (let i = start; i <= lines.length && i <= end; ++i) {
+          const isCurrent = i === (lineNumber + 1);
+
+          let lineText = lines[i - 1];
+          if (isCurrent) {
+            lineText = markSourceColumn(lineText, columnNumber, inspector.repl);
+          }
+
+          let isBreakpoint = false;
+          knownBreakpoints.forEach(({ location }) => {
+            if (location && location.scriptId === scriptId && (location.lineNumber + 1) === i) {
+              isBreakpoint = true;
+            }
+          });
+
+          let prefixChar = ' ';
+          if (isCurrent) {
+            prefixChar = '>';
+          } else if (isBreakpoint) {
+            prefixChar = '*';
+          }
+          print(`${leftPad(i, prefixChar, end)} ${lineText}`);
+        }
+      })
+      .then(null, error => {
+        print('You can\'t list source code right now');
+        throw error;
+      });
+  }
+
+  Debugger.on('paused', ({ callFrames, reason /* , hitBreakpoints */ }) => {
+    // Save execution context's data
+    // currentBacktrace = callFrames;
+    selectedFrame = callFrames[0];
+    const { scriptId, lineNumber } = selectedFrame.location;
+
+    const script = knownScripts[scriptId];
+    const scriptUrl = script ? getRelativePath(script.url) : '[unknown]';
+    print(`${reason === 'other' ? 'break' : reason} in ${scriptUrl}:${lineNumber + 1}`);
+
+    inspector.suspendReplWhile(() =>
+      watchers(true)
+        .then(() => list(2)));
+  });
+
+  Debugger.on('scriptParsed', (script) => {
+    const { scriptId, url } = script;
+    if (url) {
+      knownScripts[scriptId] = Object.assign({
+        isNative: url.replace('.js', '') in NATIVES || url === 'bootstrap_node.js',
+      }, script);
+    }
+  });
+
   const replOptions = {
     prompt: 'debug> ',
     input: inspector.stdin,

lib/node-inspect.js

@@ -96,7 +96,7 @@ class NodeInspector {
     this.client = new ProtocolClient(options.port, options.host);
 
     ['Debugger', 'Runtime'].forEach(domain => {
-      this[domain] = createAgentProxy(domain, this);
+      this[domain] = createAgentProxy(domain, this.client);
     });
     this.handleDebugEvent = (fullName, params) => {
       const [domain, name] = fullName.split('.');
@@ -124,6 +124,20 @@ class NodeInspector {
     this.paused = false;
   }
 
+  suspendReplWhile(fn) {
+    this.repl.rli.pause();
+    this.stdin.pause();
+    this.paused = true;
+    return new Promise((resolve) => {
+      resolve(fn());
+    }).then(() => {
+      this.paused = false;
+      this.repl.rli.resume();
+      this.repl.displayPrompt();
+      this.stdin.resume();
+    }).then(null, throwUnexpectedError);
+  }
+
   killChild() {
     this.client.reset();
     if (this.child) {

test/cli/break.test.js

@@ -0,0 +1,24 @@
+'use strict';
+const tap = require('tap');
+
+const startCLI = require('./start-cli');
+
+tap.test('break on first line', (t) => {
+  const cli = startCLI(['examples/empty.js']);
+
+  function onFatal(error) {
+    cli.quit();
+    throw error;
+  }
+
+  return cli.waitFor(/break/)
+    .then(() => cli.waitForPrompt())
+    .then(() => {
+      t.match(cli.output, 'break in examples/empty.js:2',
+        'pauses in the first line of the script');
+      t.match(cli.output, '> 2 });',
+        'shows the source and marks the current line');
+    })
+    .then(() => cli.quit())
+    .then(null, onFatal);
+});