AvoidAssignmentToAutomaticVariable: Ignore when a Parameter has an Attribute that contains a Variable expression, such as '[ValidateSet($True,$False)]'. (#1988)

Co-authored-by: Christoph Bergmeister <[email protected]>

Author: liamjpeters

Diff for: Rules/AvoidAssignmentToAutomaticVariable.cs

@@ -89,7 +89,12 @@ public IEnumerable<DiagnosticRecord> AnalyzeScript(Ast ast, string fileName)
                 {
                     continue;
                 }
-
+                // also check the parent to exclude variableExpressions that appear within attributes,
+                // such as '[ValidateSet($True,$False)]' where the read-only variables $true,$false appear.
+                if (variableExpressionAst.Parent is AttributeAst)
+                {
+                    continue;
+                }
                 if (_readOnlyAutomaticVariables.Contains(variableName, StringComparer.OrdinalIgnoreCase))
                 {
                     yield return new DiagnosticRecord(DiagnosticRecordHelper.FormatError(Strings.AvoidAssignmentToReadOnlyAutomaticVariableError, variableName),

Diff for: Tests/Rules/AvoidAssignmentToAutomaticVariable.tests.ps1

@@ -94,6 +94,13 @@ Describe "AvoidAssignmentToAutomaticVariables" {
             $warnings.Count | Should -Be 0
         }
 
+        It "Does not flag true or false being used in ValidateSet" {
+            # All other read-only automatic variables cannot be used in ValidateSet
+            # they result in a ParseError. $true and $false are permitted however.
+            [System.Array] $warnings = Invoke-ScriptAnalyzer -ScriptDefinition 'param([ValidateSet($true,$false)]$MyVar)$MyVar' -ExcludeRule PSReviewUnusedParameter
+            $warnings.Count | Should -Be 0
+        }
+
         It "Does not throw a NullReferenceException when using assigning a .Net property to a .Net property (Bug in 1.17.0 - issue 1007)" {
             Invoke-ScriptAnalyzer -ScriptDefinition '[foo]::bar = [baz]::qux' -ErrorAction Stop
         }