Check for ValueFromPipeline

Author: liamjpeters

Rules/ReviewUnusedParameter.cs

@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Management.Automation.Language;
 using Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic;
+using Microsoft.Windows.PowerShell.ScriptAnalyzer.Extensions;
 #if !CORECLR
 using System.ComponentModel.Composition;
 #endif
@@ -102,6 +103,25 @@ public IEnumerable<DiagnosticRecord> AnalyzeScript(Ast ast, string fileName)
 
                 foreach (ParameterAst parameterAst in parameterAsts)
                 {
+                    // Check if the parameter has the ValueFromPipeline attribute
+                    NamedAttributeArgumentAst valueFromPipeline = (NamedAttributeArgumentAst)parameterAst.Find(
+                        valFromPipelineAst => valFromPipelineAst is NamedAttributeArgumentAst namedAttrib && string.Equals(
+                            namedAttrib.ArgumentName, "ValueFromPipeline",
+                            StringComparison.OrdinalIgnoreCase
+                        ), 
+                        false
+                    );
+                    // If the parameter has the ValueFromPipeline attribute, check for usages of $_ or $PSItem
+                    if (valueFromPipeline?.GetValue() == true)
+                    {
+                        variableCount.TryGetValue("_", out int underscoreVariableCount);
+                        variableCount.TryGetValue("psitem", out int psitemVariableCount);
+                        if (underscoreVariableCount > 0 || psitemVariableCount > 0)
+                        {
+                            continue;
+                        }
+                    }
+
                     // there should be at least two usages of the variable since the parameter declaration counts as one
                     variableCount.TryGetValue(parameterAst.Name.VariablePath.UserPath, out int variableUsageCount);
                     if (variableUsageCount >= 2)

Tests/Rules/ReviewUnusedParameter.tests.ps1

@@ -20,6 +20,18 @@ Describe "ReviewUnusedParameter" {
             $Violations.Count | Should -Be 2
         }
 
+        It "has 1 violation - function with 1 parameter with ValueFromPipeline set to false and `$_ usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline = $false)] $Param1) $_}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 1
+        }
+
+        It "has 1 violation - function with 1 parameter with ValueFromPipeline set to false and `$PSItem usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline = $false)] $Param1) $PSItem}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 1
+        }
+
         It "has 1 violation - scriptblock with 1 unused parameter" {
             $ScriptDefinition = '{ param ($Param1) }'
             $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
@@ -59,6 +71,30 @@ Describe "ReviewUnusedParameter" {
             $Violations.Count | Should -Be 0
         }
 
+        It "has no violation - function with 1 parameter with ValueFromPipeline explictly set to true and `$_ usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline = $true)] $Param1) $_}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 0
+        }
+
+        It "has no violation - function with 1 parameter with ValueFromPipeline explictly set to true and `$PSItem usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline = $true)] $Param1) $PSItem}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 0
+        }
+
+        It "has no violation - function with 1 parameter with ValueFromPipeline implicitly set to true and `$_ usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline)] $Param1) $_}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 0
+        }
+
+        It "has no violation - function with 1 parameter with ValueFromPipeline implicitly set to true and `$PSItem usage" {
+            $ScriptDefinition = 'function BadFunc1 { param ([Parameter(ValueFromPipeline)] $Param1) $PSItem}'
+            $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName
+            $Violations.Count | Should -Be 0
+        }
+
         It "has no violations when using PSBoundParameters" {
             $ScriptDefinition = 'function Bound { param ($Param1) Get-Foo @PSBoundParameters }'
             $Violations = Invoke-ScriptAnalyzer -ScriptDefinition $ScriptDefinition -IncludeRule $RuleName