Do not trigger UseDeclaredVarsMoreThanAssignment for variables being used via Get-Variable

Rules/UseDeclaredVarsMoreThanAssignments.cs

@@ -1,12 +1,5 @@
-// Copyright (c) Microsoft Corporation.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE.
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
 
 using System;
 using System.Collections.Generic;
@@ -16,6 +9,7 @@
 #endif
 using System.Globalization;
 using Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic;
+using System.Linq;
 
 namespace Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules
 {
@@ -204,6 +198,24 @@ private IEnumerable<DiagnosticRecord> AnalyzeScriptBlockAst(ScriptBlockAst scrip
                 }
             }
 
+            // Detect usages of Get-Variable
+            var getVariableCmdletNamesAndAliases = Helper.Instance.CmdletNameAndAliases("Get-Variable");
+            IEnumerable<Ast> getVariableCommandAsts = scriptBlockAst.FindAll(testAst => testAst is CommandAst commandAst &&
+                getVariableCmdletNamesAndAliases.Contains(commandAst.GetCommandName(), StringComparer.OrdinalIgnoreCase), true);
+            foreach (CommandAst getVariableCommandAst in getVariableCommandAsts)
+            {
+                var commandElements = getVariableCommandAst.CommandElements.ToList();
+                // The following extracts the variable name only in the simplest possibe case 'Get-Variable variableName'
+                if (commandElements.Count == 2 && commandElements[1] is StringConstantExpressionAst constantExpressionAst)
+                {
+                    var variableName = constantExpressionAst.Value;
+                    if (assignments.ContainsKey(variableName))
+                    {
+                        assignments.Remove(variableName);
+                    }
+                }
+            }
+
             foreach (string key in assignments.Keys)
             {
                 yield return new DiagnosticRecord(

Tests/Rules/UseDeclaredVarsMoreThanAssignments.tests.ps1

@@ -73,5 +73,10 @@ function MyFunc2() {
         It "returns no violations" {
             $noViolations.Count | Should -Be 0
         }
+
+        It "Using a variable via 'Get-Variable' does not trigger a warning" {
+            $noViolations = Invoke-ScriptAnalyzer -ScriptDefinition '$a=4; get-variable a' | Where-Object { $_.RuleName -eq $violationName }
+            $noViolations.Count | Should -Be 0
+        }
     }
 }