Don't complete parameter name and class member declarations (PowerShell#21182)

Author: MartinGC94

src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs

@@ -5200,6 +5200,12 @@ internal static List<CompletionResult> CompleteVariable(CompletionContext contex
 
             var lastAst = context.RelatedAsts?[^1];
             var variableAst = lastAst as VariableExpressionAst;
+            if (lastAst is PropertyMemberAst ||
+                (lastAst is not null && lastAst.Parent is ParameterAst parameter && parameter.DefaultValue != lastAst))
+            {
+                // User is adding a new parameter or a class member, variable tab completion is not useful.
+                return results;
+            }
             var prefix = variableAst != null && variableAst.Splatted ? "@" : "$";
             bool tokenAtCursorUsedBraces = context.TokenAtCursor is not null && context.TokenAtCursor.Text.StartsWith("${");
 

test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1

@@ -79,6 +79,21 @@ Describe "TabCompletion" -Tags CI {
         $res.CompletionMatches[0].CompletionText | Should -BeExactly '$CurrentItem'
     }
 
+    It 'Should not complete parameter name' {
+        $res = TabExpansion2 -inputScript 'param($P'
+        $res.CompletionMatches.Count | Should -Be 0
+    }
+
+    It 'Should complete variable in default value of a parameter' {
+        $res = TabExpansion2 -inputScript 'param($PS = $P'
+        $res.CompletionMatches.Count | Should -BeGreaterThan 0
+    }
+
+    It 'Should not complete property name in class definition' {
+        $res = TabExpansion2 -inputScript 'class X {$P'
+        $res.CompletionMatches.Count | Should -Be 0
+    }
+
     foreach ($Operator in [System.Management.Automation.CompletionCompleters]::CompleteOperator(""))
     {
         It "Should complete $($Operator.CompletionText)" {