From 99c757ff3ea40d0a4310582f0ec0828f6564e6db Mon Sep 17 00:00:00 2001
From: MartinGC94 <42123497+MartinGC94@users.noreply.github.com>
Date: Tue, 23 Aug 2022 00:17:55 +0200
Subject: [PATCH] Fix positional argument completion (#17796)

---
 .../CommandCompletion/CompletionCompleters.cs | 47 ++++++++++++-------
 .../TabCompletion/TabCompletion.Tests.ps1     | 21 +++++++++
 2 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs b/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
index 1bf0919cf9..59e261e613 100644
--- a/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
+++ b/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
@@ -1586,13 +1586,20 @@ namespace System.Management.Automation
                                               (defaultParameterSetFlag & validParameterSetFlags) != 0;
             MergedCompiledCommandParameter positionalParam = null;
 
+            MergedCompiledCommandParameter bestMatchParam = null;
+            ParameterSetSpecificMetadata bestMatchSet = null;
+
+            // Finds the parameter with the position closest to the specified position
             foreach (MergedCompiledCommandParameter param in parameters)
             {
                 bool isInParameterSet = (param.Parameter.ParameterSetFlags & validParameterSetFlags) != 0 || param.Parameter.IsInAllSets;
                 if (!isInParameterSet)
+                {
                     continue;
+                }
 
                 var parameterSetDataCollection = param.Parameter.GetMatchingParameterSetData(validParameterSetFlags);
+
                 foreach (ParameterSetSpecificMetadata parameterSetData in parameterSetDataCollection)
                 {
                     // in the first pass, we skip the remaining argument ones
@@ -1604,35 +1611,43 @@ namespace System.Management.Automation
                     // Check the position
                     int positionInParameterSet = parameterSetData.Position;
 
-                    if (positionInParameterSet == int.MinValue || positionInParameterSet != position)
+                    if (positionInParameterSet < position)
                     {
-                        // The parameter is not positional, or its position is not what we want
+                        // The parameter is not positional (position == int.MinValue), or its position is lower than what we want.
                         continue;
                     }
 
-                    if (isDefaultParameterSetValid)
+                    if (bestMatchSet is null || bestMatchSet.Position > positionInParameterSet)
                     {
-                        if (parameterSetData.ParameterSetFlag == defaultParameterSetFlag)
+                        bestMatchParam = param;
+                        bestMatchSet = parameterSetData;
+                        if (positionInParameterSet == position)
                         {
-                            ProcessParameter(commandName, commandAst, context, result, param, boundArguments);
-                            isProcessedAsPositional = result.Count > 0;
                             break;
                         }
-                        else
-                        {
-                            positionalParam ??= param;
-                        }
+                    }
+                }
+            }
+
+            if (bestMatchParam is not null)
+            {
+                if (isDefaultParameterSetValid)
+                {
+                    if (bestMatchSet.ParameterSetFlag == defaultParameterSetFlag)
+                    {
+                        ProcessParameter(commandName, commandAst, context, result, bestMatchParam, boundArguments);
+                        isProcessedAsPositional = result.Count > 0;
                     }
                     else
                     {
-                        isProcessedAsPositional = true;
-                        ProcessParameter(commandName, commandAst, context, result, param, boundArguments);
-                        break;
+                        positionalParam ??= bestMatchParam;
                     }
                 }
-
-                if (isProcessedAsPositional)
-                    break;
+                else
+                {
+                    isProcessedAsPositional = true;
+                    ProcessParameter(commandName, commandAst, context, result, bestMatchParam, boundArguments);
+                }
             }
 
             if (!isProcessedAsPositional && positionalParam != null)
diff --git a/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1 b/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1
index 6471b1bf0a..9ab7d735ee 100644
--- a/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1
+++ b/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1
@@ -766,6 +766,27 @@ ConstructorTestClass(int i, bool b)
         $res.CompletionMatches.CompletionText | Should -Contain "-Path"
     }
 
+    it 'Should find the closest positional parameter match' {
+        $TestString = @'
+function Verb-Noun
+{
+    Param
+    (
+        [Parameter(Position = 0)]
+        [string]
+        $Param1,
+        [Parameter(Position = 1)]
+        [System.Management.Automation.ActionPreference]
+        $Param2
+    )
+}
+Verb-Noun -Param1 Hello ^
+'@
+        $CursorIndex = $TestString.IndexOf('^')
+        $res = TabExpansion2 -inputScript $TestString.Remove($CursorIndex, 1) -cursorColumn $CursorIndex
+        $res.CompletionMatches[0].CompletionText | Should -Be "Break"
+    }
+
     Context "Script name completion" {
         BeforeAll {
             Setup -f 'install-powershell.ps1' -Content ""