Add artifical stack frame to represent context

When stepping into certain contexts like a param block's default value
expression, the engine does not provide a call stack frame to represent
it. In this scenario we want to create an artifical call stack frame to
represent the context we've stepped into.

Author: SeeminglyScience

src/PowerShellEditorServices/Services/DebugAdapter/DebugService.cs

@@ -994,10 +994,45 @@ await _remoteFileManager.FetchRemoteFileAsync(
                     // Augment the top stack frame with details from the stop event
                     if (invocationTypeScriptPositionProperty.GetValue(e.InvocationInfo) is IScriptExtent scriptExtent)
                     {
-                        stackFrameDetails[0].StartLineNumber = scriptExtent.StartLineNumber;
-                        stackFrameDetails[0].EndLineNumber = scriptExtent.EndLineNumber;
-                        stackFrameDetails[0].StartColumnNumber = scriptExtent.StartColumnNumber;
-                        stackFrameDetails[0].EndColumnNumber = scriptExtent.EndColumnNumber;
+                        StackFrameDetails targetFrame = stackFrameDetails[0];
+
+                        // Certain context changes (like stepping into the default value expression
+                        // of a parameter) do not create a call stack frame. In order to represent
+                        // this context change we create a fake call stack frame.
+                        if (!string.IsNullOrEmpty(scriptExtent.File)
+                            && !PathUtils.IsPathEqual(scriptExtent.File, targetFrame.ScriptPath))
+                        {
+                            await debugInfoHandle.WaitAsync().ConfigureAwait(false);
+                            try
+                            {
+                                targetFrame = new StackFrameDetails
+                                {
+                                    ScriptPath = scriptExtent.File,
+                                    // Just use the last frame's variables since we don't have a
+                                    // good way to get real values.
+                                    AutoVariables = targetFrame.AutoVariables,
+                                    CommandVariables = targetFrame.CommandVariables,
+                                    // Ideally we'd get a real value here but since there's no real
+                                    // call stack frame for this, we'd need to replicate a lot of
+                                    // engine code.
+                                    FunctionName = "<ScriptBlock>",
+                                };
+
+                                StackFrameDetails[] newFrames = new StackFrameDetails[stackFrameDetails.Length + 1];
+                                newFrames[0] = targetFrame;
+                                stackFrameDetails.CopyTo(newFrames, 1);
+                                stackFrameDetails = newFrames;
+                            }
+                            finally
+                            {
+                                debugInfoHandle.Release();
+                            }
+                        }
+
+                        targetFrame.StartLineNumber = scriptExtent.StartLineNumber;
+                        targetFrame.EndLineNumber = scriptExtent.EndLineNumber;
+                        targetFrame.StartColumnNumber = scriptExtent.StartColumnNumber;
+                        targetFrame.EndColumnNumber = scriptExtent.EndColumnNumber;
                     }
                 }
 

src/PowerShellEditorServices/Services/DebugAdapter/Debugging/StackFrameDetails.cs

@@ -31,7 +31,7 @@ internal class StackFrameDetails
         /// <summary>
         /// Gets the name of the function where the stack frame occurred.
         /// </summary>
-        public string FunctionName { get; private set; }
+        public string FunctionName { get; internal init; }
 
         /// <summary>
         /// Gets the start line number of the script where the stack frame occurred.
@@ -62,12 +62,12 @@ internal class StackFrameDetails
         /// <summary>
         /// Gets or sets the VariableContainerDetails that contains the auto variables.
         /// </summary>
-        public VariableContainerDetails AutoVariables { get; private set; }
+        public VariableContainerDetails AutoVariables { get; internal init; }
 
         /// <summary>
         /// Gets or sets the VariableContainerDetails that contains the call stack frame variables.
         /// </summary>
-        public VariableContainerDetails CommandVariables { get; private set; }
+        public VariableContainerDetails CommandVariables { get; internal init; }
 
         #endregion
 

src/PowerShellEditorServices/Utility/PathUtils.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System;
 using System.IO;
 using System.Management.Automation;
 using System.Runtime.InteropServices;
@@ -29,13 +30,34 @@ internal static class PathUtils
         /// </summary>
         internal static readonly char AlternatePathSeparator = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? '/' : '\\';
 
+        internal static readonly StringComparison PathComparison = RuntimeInformation.IsOSPlatform(OSPlatform.Linux)
+            ? StringComparison.Ordinal
+            : StringComparison.OrdinalIgnoreCase;
+
         /// <summary>
         /// Converts all alternate path separators to the current platform's main path separators.
         /// </summary>
         /// <param name="path">The path to normalize.</param>
         /// <returns>The normalized path.</returns>
         public static string NormalizePathSeparators(string path) => string.IsNullOrWhiteSpace(path) ? path : path.Replace(AlternatePathSeparator, DefaultPathSeparator);
 
+        internal static bool IsPathEqual(string left, string right)
+        {
+            if (string.IsNullOrEmpty(left))
+            {
+                return string.IsNullOrEmpty(right);
+            }
+
+            if (string.IsNullOrEmpty(right))
+            {
+                return false;
+            }
+
+            left = Path.GetFullPath(left).TrimEnd(DefaultPathSeparator);
+            right = Path.GetFullPath(right).TrimEnd(DefaultPathSeparator);
+            return left.Equals(right, PathComparison);
+        }
+
         /// <summary>
         /// Return the given path with all PowerShell globbing characters escaped,
         /// plus optionally the whitespace.