debugger: add a command to set which lines to check for context

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);
   }