Add new MissingTryBlock rule

Rules/MissingTryBlock.cs

@@ -0,0 +1,83 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Management.Automation.Language;
+
+#if !CORECLR
+using System.ComponentModel.Composition;
+#endif
+
+namespace Microsoft.Windows.PowerShell.ScriptAnalyzer.BuiltinRules
+{
+#if !CORECLR
+    [Export(typeof(IScriptRule))]
+#endif
+
+    /// <summary>
+    /// Rule that warns when catch or finally blocks are used without a corresponding try block
+    /// </summary>
+    public class MissingTryBlock : IScriptRule
+    {
+        /// <summary>
+        /// Analyzes the PowerShell AST for catch or finally blocks that miss the try block.
+        /// </summary>
+        /// <param name="ast">The PowerShell Abstract Syntax Tree to analyze.</param>
+        /// <param name="fileName">The name of the file being analyzed (for diagnostic reporting).</param>
+        /// <returns>A collection of diagnostic records for each violation.</returns>
+        public IEnumerable<DiagnosticRecord> AnalyzeScript(Ast ast, string fileName)
+        {
+            if (ast == null) throw new ArgumentNullException(Strings.NullAstErrorMessage);
+
+            // Find all FunctionDefinitionAst in the Ast
+            var missingTryAsts = ast.FindAll(testAst =>
+                // Normally should be part of a TryStatementAst
+                testAst is StringConstantExpressionAst stringAst &&
+                // Catch or finally are reserved keywords and should be bare words
+                stringAst.StringConstantType == StringConstantType.BareWord &&
+                (
+                    String.Equals(stringAst.Value, "catch", StringComparison.OrdinalIgnoreCase) ||
+                    String.Equals(stringAst.Value, "finally", StringComparison.OrdinalIgnoreCase)
+                ) &&
+                stringAst.Parent is CommandAst commandAst &&
+                // Only violate if the catch or finally is the first command element
+                commandAst.CommandElements[0] == stringAst,
+                true
+            );
+
+            foreach (StringConstantExpressionAst missingTryAst in missingTryAsts)
+            {
+                yield return new DiagnosticRecord(
+                    string.Format(
+                        CultureInfo.CurrentCulture,
+                        Strings.MissingTryBlockError,
+                        CultureInfo.CurrentCulture.TextInfo.ToTitleCase(missingTryAst.Value)),
+                    missingTryAst.Extent,
+                    GetName(),
+                    DiagnosticSeverity.Warning,
+                    fileName,
+                    missingTryAst.Value
+                );
+            }
+        }
+
+        public string GetCommonName() => Strings.MissingTryBlockCommonName;
+
+        public string GetDescription() => Strings.MissingTryBlockDescription;
+
+        public string GetName() => string.Format(
+                CultureInfo.CurrentCulture,
+                Strings.NameSpaceFormat,
+                GetSourceName(),
+                Strings.MissingTryBlockName);
+
+        public RuleSeverity GetSeverity() => RuleSeverity.Warning;
+
+        public string GetSourceName() => Strings.SourceName;
+
+        public SourceType GetSourceType() => SourceType.Builtin;
+    }
+}

Rules/Strings.resx

@@ -276,6 +276,18 @@
   <data name="MissingModuleManifestFieldCommonName" xml:space="preserve">
     <value>Module Manifest Fields</value>
   </data>
+  <data name="MissingTryBlockName" xml:space="preserve">
+    <value>MissingTryBlock</value>
+  </data>
+  <data name="MissingTryBlockCommonName" xml:space="preserve">
+    <value>Missing Try Block</value>
+  </data>
+  <data name="MissingTryBlockDescription" xml:space="preserve">
+    <value>The catch and finally blocks should be preceded by a try block.</value>
+  </data>
+  <data name="MissingTryBlockError" xml:space="preserve">
+    <value>{0} is missing a try block</value>
+  </data>
   <data name="AvoidUnloadableModuleDescription" xml:space="preserve">
     <value>If a script file is in a PowerShell module folder, then that folder must be loadable.</value>
   </data>

Tests/Rules/MissingTryBlock.tests.ps1

@@ -0,0 +1,133 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+[Diagnostics.CodeAnalysis.SuppressMessage('PSUseDeclaredVarsMoreThanAssignments', '', Justification = 'False positive')]
+param()
+
+BeforeAll {
+    $ruleName = "PSMissingTryBlock"
+}
+
+Describe "MissingTryBlock" {
+    Context "Violates" {
+        It "Catch is missing a try block" {
+            $scriptDefinition = { catch { "An error occurred." } }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations.Count             | Should -Be 1
+            $violations.Severity          | Should -Be Warning
+            $violations.Extent.Text       | Should -Be catch
+            $violations.Message           | Should -Be 'Catch is missing a try block'
+            $violations.RuleSuppressionID | Should -Be catch
+        }
+
+        It "Finally is missing a try block" {
+            $scriptDefinition = { finally { "Finalizing..." } }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations.Count             | Should -Be 1
+            $violations.Severity          | Should -Be Warning
+            $violations.Extent.Text       | Should -Be finally
+            $violations.Message           | Should -Be 'Finally is missing a try block'
+            $violations.RuleSuppressionID | Should -Be finally
+        }
+
+        It "Single line catch and finally is missing a try block" {
+            $scriptDefinition = {
+                catch { "An error occurred." } finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations.Count             | Should -Be 1
+            $violations.Severity          | Should -Be Warning
+            $violations.Extent.Text       | Should -Be catch
+            $violations.Message           | Should -Be 'Catch is missing a try block'
+            $violations.RuleSuppressionID | Should -Be catch
+        }
+
+        It "Multi line catch and finally is missing a try block" {
+            $scriptDefinition = {
+                catch { "An error occurred." }
+                finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations.Count                | Should -Be 2
+            $violations[0].Severity          | Should -Be Warning
+            $violations[0].Extent.Text       | Should -Be catch
+            $violations[0].Message           | Should -Be 'Catch is missing a try block'
+            $violations[0].RuleSuppressionID | Should -Be catch
+            $violations[1].Severity          | Should -Be Warning
+            $violations[1].Extent.Text       | Should -Be finally
+            $violations[1].Message           | Should -Be 'Finally is missing a try block'
+            $violations[1].RuleSuppressionID | Should -Be finally
+        }
+    }
+
+    Context "Compliant" {
+        It "try-catch block" {
+            $scriptDefinition = {
+                try { NonsenseString }
+                catch { "An error occurred." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "try-catch-final statement" {
+            $scriptDefinition = {
+                try { NonsenseString }
+                catch { "An error occurred." }
+                finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "Single line try statement" {
+            $scriptDefinition = {
+                try { NonsenseString } catch { "An error occurred." } finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "Catch as parameter" {
+            $scriptDefinition = { Write-Host Catch }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "Catch as double quoted string" {
+            $scriptDefinition = { "Catch" }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "Catch as single quoted string" {
+            $scriptDefinition = { 'Catch' }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+    }
+
+    Context "Suppressed" {
+        It "Multi line catch and finally is missing a try block" {
+            $scriptDefinition = {
+                [Diagnostics.CodeAnalysis.SuppressMessage('PSMissingTryBlock', '', Justification = 'Test')]
+                param()
+                catch { "An error occurred." }
+                finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations | Should -BeNullOrEmpty
+        }
+
+        It "Multi line catch and finally is missing a try block for catch only" {
+            $scriptDefinition = {
+                [Diagnostics.CodeAnalysis.SuppressMessage('PSMissingTryBlock', 'finally', Justification = 'Test')]
+                param()
+                catch { "An error occurred." }
+                finally { "Finalizing..." }
+            }.ToString()
+            $violations = Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -IncludeRule @($ruleName)
+            $violations.Count | Should -Be 1
+        }
+    }
+}

docs/Rules/MissingTryBlock.md

@@ -0,0 +1,34 @@
+---
+description: Missing Try Block
+ms.date: 04/22/2026
+ms.topic: reference
+title: MissingTryBlock
+---
+# MissingTryBlock
+
+**Severity Level: Warning**
+
+## Description
+
+The `catch` and `finally` blocks should be preceded by a `try` block.
+Otherwise, the `catch` and `finally` blocks will be interpreted as commands, which is likely a mistake and
+will result in a "*The term 'catch' is not recognized as a name of a cmdlet*" error at runtime.
+
+## How
+
+Add a `try` block before the `catch` and `finally` blocks.
+
+## Example
+
+### Wrong
+
+```powershell
+catch { "An error occurred." }
+```
+
+### Correct
+
+```powershell
+try { $a = 1 / $b }
+catch { "Attempted to divide by zero." }
+```

docs/Rules/README.md

@@ -50,6 +50,7 @@ The PSScriptAnalyzer contains the following rule definitions.
 | [DSCUseVerboseMessageInDSCResource](./DSCUseVerboseMessageInDSCResource.md)                       | Error       |        Yes         |                 |
 | [MisleadingBacktick](./MisleadingBacktick.md)                                                     | Warning     |        Yes         |                 |
 | [MissingModuleManifestField](./MissingModuleManifestField.md)                                     | Warning     |        Yes         |                 |
+| [MissingTryBlock](./MissingTryBlock.md)                                                           | Warning     |        Yes         |                 |
 | [PlaceCloseBrace](./PlaceCloseBrace.md)                                                           | Warning     |         No         |       Yes       |
 | [PlaceOpenBrace](./PlaceOpenBrace.md)                                                             | Warning     |         No         |       Yes       |
 | [PossibleIncorrectComparisonWithNull](./PossibleIncorrectComparisonWithNull.md)                   | Warning     |        Yes         |                 |