debugger: Add set context line number command

lib/internal/debugger/inspect_repl.js

@@ -81,7 +81,7 @@ out, o                Step out, leaving the current function
 backtrace, bt         Print the current backtrace
 list                  Print the source around the current line where execution
                       is currently paused
-
+setContextLineNumber  Set which lines to check for context
 setBreakpoint, sb     Set a breakpoint
 clearBreakpoint, cb   Clear a breakpoint
 breakpoints           List all known breakpoints
@@ -381,6 +381,7 @@ function createRepl(inspector) {
   let currentBacktrace;
   let selectedFrame;
   let exitDebugRepl;
+  let contextLineNumber = 2;
 
   function resetOnStart() {
     knownScripts = {};
@@ -685,6 +686,19 @@ function createRepl(inspector) {
     });
   }
 
+  function setContextLineNumber(delta = 2) {
+    if (!selectedFrame) {
+      throw new ERR_DEBUGGER_ERROR('Requires execution to be paused');
+    }
+    try {
+      contextLineNumber = delta;
+      print(`The contextLine has been changed to ${delta}.`);
+    } catch (error) {
+      print("You can't setContextLineNumber source code right now");
+      throw error;
+    }
+  }
+
   function handleBreakpointResolved({ breakpointId, location }) {
     const script = knownScripts[location.scriptId];
     const scriptUrl = script && script.url;
@@ -897,7 +911,7 @@ function createRepl(inspector) {
 
     inspector.suspendReplWhile(() =>
       PromisePrototypeThen(
-        SafePromiseAllReturnArrayLike([formatWatchers(true), selectedFrame.list(2)]),
+        SafePromiseAllReturnArrayLike([formatWatchers(true), selectedFrame.list(contextLineNumber)]),
         ({ 0: watcherList, 1: context }) => {
           const breakContext = watcherList ?
             `${watcherList}\n${inspect(context)}` :
@@ -1159,6 +1173,7 @@ function createRepl(inspector) {
       },
 
       list,
+      setContextLineNumber,
     });
     aliasProperties(context, SHORTCUTS);
   }

test/fixtures/debugger/twenty-lines.js

@@ -0,0 +1,20 @@
+let x = 0;
+x = 1;
+x = 2;
+x = 3;
+x = 4;
+x = 5;
+x = 6;
+x = 7;
+x = 8;
+x = 9;
+x = 10;
+x = 11;
+x = 12;
+x = 13;
+x = 14;
+x = 15;
+x = 16;
+x = 17;
+x = 18;
+module.exports = x;

test/sequential/test-debugger-set-context-line-number.mjs

@@ -0,0 +1,44 @@
+import { skipIfInspectorDisabled } from '../common/index.mjs';
+skipIfInspectorDisabled();
+
+import { path } from '../common/fixtures.mjs';
+import startCLI from '../common/debugger.js';
+
+import assert from 'assert';
+
+const script = path('debugger', 'twenty-lines.js');
+const cli = startCLI([script]);
+
+function onFatal(error) {
+  cli.quit();
+  throw error;
+}
+
+function getLastLine(output) {
+  const splitedByLine = output.split(';');
+  return splitedByLine[splitedByLine.length - 2];
+}
+
+// Stepping through breakpoints.
+try {
+  await cli.waitForInitialBreak();
+  await cli.waitForPrompt();
+
+  // Make sure the initial value is 2.
+  await cli.stepCommand('n');
+  assert.ok(getLastLine(cli.output).includes('4 x = 3'));
+
+  await cli.command('setContextLineNumber(5)');
+  await cli.stepCommand('n');
+  assert.ok(getLastLine(cli.output).includes('8 x = 7'));
+
+  await cli.command('setContextLineNumber(3)');
+  await cli.stepCommand('n');
+  assert.ok(getLastLine(cli.output).includes('7 x = 6'));
+  await cli.command('list(3)');
+  assert.ok(getLastLine(cli.output).includes('7 x = 6'));
+
+  await cli.quit();
+} catch (error) {
+  onFatal(error);
+}