New Rule: ExcludeFromCodeCoverage attributes should include a justifi…

…cation (#6593)

@Corniel Thank you for the contribution!

README.md

@@ -12,7 +12,7 @@ languages in [SonarQube](http://www.sonarqube.org/), [SonarCloud](https://sonarc
 
 ## Features
 
-* [380+ C# rules](https://rules.sonarsource.com/csharp) and [170+ VB.​NET rules](https://rules.sonarsource.com/vbnet)
+* [390+ C# rules](https://rules.sonarsource.com/csharp) and [170+ VB.​NET rules](https://rules.sonarsource.com/vbnet)
 * Metrics (cognitive complexity, duplications, number of lines etc.)
 * Import of [test coverage reports](https://community.sonarsource.com/t/9871) from Visual Studio Code Coverage, dotCover, OpenCover, Coverlet, Altcover.
 * Import of third party Roslyn Analyzers results

analyzers/rspec/cs/S6513_c#.html

@@ -0,0 +1,53 @@
+<p>The <a
+href="https://learn.microsoft.com/dotnet/api/system.diagnostics.codeanalysis.excludefromcodecoverageattribute">ExcludeFromCodeCoverageAttribute</a> is
+used to exclude portions of code from <a href="https://learn.microsoft.com/dotnet/core/testing/unit-testing-code-coverage">code coverage
+reporting</a>. It is a bad practice to retain code that is not covered by unit tests. In .Net 5, the <code>Justification</code> property was added to
+the <code>ExcludeFromCodeCoverageAttribute</code> as an opportunity to document the rationale for the exclusion. This rule raises an issue when no
+such justification is given.</p>
+<h2>Noncompliant Code Example</h2>
+<pre>
+public struct Coordinates
+{
+    public int X { get; }
+    public int Y { get; }
+
+    [ExcludeFromCodeCoverage] // Noncompliant
+    public override bool Equals(object obj) =&gt; obj is Coordinates coordinates &amp;&amp; X == coordinates.X &amp;&amp; Y == coordinates.Y;
+
+    [ExcludeFromCodeCoverage] // Noncompliant
+    public override int GetHashCode()
+    {
+        var hashCode = 1861411795;
+        hashCode = hashCode * -1521134295 + X.GetHashCode();
+        hashCode = hashCode * -1521134295 + Y.GetHashCode();
+        return hashCode;
+    }
+}
+</pre>
+<h2>Compliant Solution</h2>
+<pre>
+public struct Coordinates
+{
+    public int X { get; }
+    public int Y { get; }
+
+    [ExcludeFromCodeCoverage(Justification = "Code generated by Visual Studio refactoring")] // Compliant
+    public override bool Equals(object obj) =&gt; obj is Coordinates coordinates &amp;&amp; X == coordinates.X &amp;&amp; Y == coordinates.Y;
+
+    [ExcludeFromCodeCoverage(Justification = "Code generated by Visual Studio refactoring")] // Compliant
+    public override int GetHashCode()
+    {
+        var hashCode = 1861411795;
+        hashCode = hashCode * -1521134295 + X.GetHashCode();
+        hashCode = hashCode * -1521134295 + Y.GetHashCode();
+        return hashCode;
+    }
+}
+</pre>
+<h2>See</h2>
+<ul>
+  <li> <a href="https://learn.microsoft.com/dotnet/api/system.diagnostics.codeanalysis.excludefromcodecoverageattribute">API browser</a> -
+  ExcludeFromCodeCoverageAttribute </li>
+  <li> <a href="https://learn.microsoft.com/dotnet/core/testing/unit-testing-code-coverage">DevOps and testing</a> - Code coverage reporting </li>
+</ul>
+

analyzers/rspec/cs/S6513_c#.json

@@ -0,0 +1,17 @@
+{
+  "title": "\"ExcludeFromCodeCoverage\" attributes should include a justification",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [
+    "bad-practice"
+  ],
+  "defaultSeverity": "Minor",
+  "ruleSpecification": "RSPEC-6513",
+  "sqKey": "S6513",
+  "scope": "Main",
+  "quickfix": "unknown"
+}

analyzers/rspec/vbnet/S6513_vb.net.html

@@ -0,0 +1,67 @@
+<p>The <a
+href="https://learn.microsoft.com/dotnet/api/system.diagnostics.codeanalysis.excludefromcodecoverageattribute">ExcludeFromCodeCoverageAttribute</a> is
+used to exclude portions of code from <a href="https://learn.microsoft.com/dotnet/core/testing/unit-testing-code-coverage">code coverage
+reporting</a>. It is a bad practice to retain code that is not covered by unit tests. In .Net 5, the <code>Justification</code> property was added to
+the <code>ExcludeFromCodeCoverageAttribute</code> as an opportunity to document the rationale for the exclusion. This rule raises an issue when no
+such justification is given.</p>
+<h2>Noncompliant Code Example</h2>
+<pre>
+Public Structure Coordinates
+
+    Public ReadOnly Property X As Integer
+    Public ReadOnly Property Y As Integer
+
+    &lt;ExcludeFromCodeCoverage&gt; ' Noncompliant
+    Public Overrides Function Equals(obj As Object) As Boolean
+        If Not (TypeOf obj Is Coordinates) Then
+            Return False
+        End If
+
+        Dim coordinates = DirectCast(obj, Coordinates)
+        Return X = coordinates.X AndAlso
+               Y = coordinates.Y
+    End Function
+
+    &lt;ExcludeFromCodeCoverage&gt; ' Noncompliant
+    Public Overrides Function GetHashCode() As Integer
+        Dim hashCode As Long = 1861411795
+        hashCode = (hashCode * -1521134295 + X.GetHashCode()).GetHashCode()
+        hashCode = (hashCode * -1521134295 + Y.GetHashCode()).GetHashCode()
+        Return hashCode
+    End Function
+End Structure
+</pre>
+<h2>Compliant Solution</h2>
+<pre>
+Public Structure Coordinates
+
+    Public ReadOnly Property X As Integer
+    Public ReadOnly Property Y As Integer
+
+    &lt;ExcludeFromCodeCoverage(Justification:="Code generated by Visual Studio refactoring")&gt; ' Compliant
+    Public Overrides Function Equals(obj As Object) As Boolean
+        If Not (TypeOf obj Is Coordinates) Then
+            Return False
+        End If
+
+        Dim coordinates = DirectCast(obj, Coordinates)
+        Return X = coordinates.X AndAlso
+               Y = coordinates.Y
+    End Function
+
+    &lt;ExcludeFromCodeCoverage(Justification:="Code generated by Visual Studio refactoring")&gt; ' Compliant
+    Public Overrides Function GetHashCode() As Integer
+        Dim hashCode As Long = 1861411795
+        hashCode = (hashCode * -1521134295 + X.GetHashCode()).GetHashCode()
+        hashCode = (hashCode * -1521134295 + Y.GetHashCode()).GetHashCode()
+        Return hashCode
+    End Function
+End Structure
+</pre>
+<h2>See</h2>
+<ul>
+  <li> <a href="https://learn.microsoft.com/dotnet/api/system.diagnostics.codeanalysis.excludefromcodecoverageattribute">API browser</a> -
+  ExcludeFromCodeCoverageAttribute </li>
+  <li> <a href="https://learn.microsoft.com/dotnet/core/testing/unit-testing-code-coverage">DevOps and testing</a> - Code coverage reporting </li>
+</ul>
+

analyzers/rspec/vbnet/S6513_vb.net.json

@@ -0,0 +1,17 @@
+{
+  "title": "\"ExcludeFromCodeCoverage\" attributes should include a justification",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [
+    "bad-practice"
+  ],
+  "defaultSeverity": "Minor",
+  "ruleSpecification": "RSPEC-6513",
+  "sqKey": "S6513",
+  "scope": "Main",
+  "quickfix": "unknown"
+}

analyzers/src/SonarAnalyzer.CSharp/Rules/ExcludeFromCodeCoverageAttributesNeedJustification.cs

@@ -0,0 +1,33 @@
+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2023 SonarSource SA
+ * mailto: contact AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+namespace SonarAnalyzer.Rules.CSharp;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class ExcludeFromCodeCoverageAttributesNeedJustification : ExcludeFromCodeCoverageAttributesNeedJustificationBase<SyntaxKind>
+{
+    protected override ILanguageFacade<SyntaxKind> Language => CSharpFacade.Instance;
+
+    protected override SyntaxNode GetJustificationExpression(SyntaxNode node) =>
+        node is AttributeSyntax { ArgumentList.Arguments: { Count: 1 } arguments }
+            && arguments[0] is { NameEquals.Name.Identifier.ValueText: JustificationPropertyName, Expression: { } expression }
+                ? expression
+                : null;
+}

analyzers/src/SonarAnalyzer.Common/Rules/ExcludeFromCodeCoverageAttributesNeedJustificationBase.cs

@@ -0,0 +1,58 @@
+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2023 SonarSource SA
+ * mailto: contact AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+namespace SonarAnalyzer.Rules;
+
+public abstract class ExcludeFromCodeCoverageAttributesNeedJustificationBase<TSyntaxKind> : SonarDiagnosticAnalyzer<TSyntaxKind>
+    where TSyntaxKind : struct
+{
+    private const string DiagnosticId = "S6513";
+
+    protected const string JustificationPropertyName = "Justification";
+
+    protected override string MessageFormat => "Add a justification.";
+
+    protected abstract SyntaxNode GetJustificationExpression(SyntaxNode node);
+
+    protected ExcludeFromCodeCoverageAttributesNeedJustificationBase() : base(DiagnosticId) { }
+
+    protected sealed override void Initialize(SonarAnalysisContext context) =>
+        context.RegisterNodeAction(
+            Language.GeneratedCodeRecognizer,
+            c =>
+            {
+                if (NoJustification(c.Node, c.SemanticModel)
+                    && c.SemanticModel.GetSymbolInfo(c.Node).Symbol is IMethodSymbol attribute
+                    && attribute.IsInType(KnownType.System_Diagnostics_CodeAnalysis_ExcludeFromCodeCoverageAttribute)
+                    && HasJustificationProperty(attribute.ContainingType))
+                {
+                    c.ReportIssue(Diagnostic.Create(Rule, c.Node.GetLocation()));
+                }
+            },
+            Language.SyntaxKind.Attribute);
+
+    private bool NoJustification(SyntaxNode node, SemanticModel model) =>
+        GetJustificationExpression(node) is not { } justification
+        || string.IsNullOrWhiteSpace(Language.FindConstantValue(model, justification) as string);
+
+    /// <summary>"Justification" was added in .Net 5, while ExcludeFromCodeCoverage in netstandard2.0.</summary>
+    private static bool HasJustificationProperty(INamedTypeSymbol symbol) =>
+        symbol.MemberNames.Contains(JustificationPropertyName);
+}

analyzers/src/SonarAnalyzer.VisualBasic/Rules/ExcludeFromCodeCoverageAttributesNeedJustification.cs

@@ -0,0 +1,34 @@
+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2023 SonarSource SA
+ * mailto: contact AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+namespace SonarAnalyzer.Rules.VisualBasic;
+
+[DiagnosticAnalyzer(LanguageNames.VisualBasic)]
+public sealed class ExcludeFromCodeCoverageAttributesNeedJustification : ExcludeFromCodeCoverageAttributesNeedJustificationBase<SyntaxKind>
+{
+    protected override ILanguageFacade<SyntaxKind> Language => VisualBasicFacade.Instance;
+
+    protected override SyntaxNode GetJustificationExpression(SyntaxNode node) =>
+        node is AttributeSyntax { ArgumentList.Arguments: { Count: 1 } arguments }
+            && arguments[0] is SimpleArgumentSyntax { Expression: { } } argument
+            && Language.NameComparer.Equals(argument.GetName(), JustificationPropertyName)
+                ? argument.Expression
+                : null;
+}

analyzers/tests/SonarAnalyzer.UnitTest/PackagingTests/RuleTypeMappingCS.cs

@@ -6437,7 +6437,7 @@ internal static class RuleTypeMappingCS
         // ["S6510"],
         // ["S6511"],
         // ["S6512"],
-        // ["S6513"],
+        ["S6513"] = "CODE_SMELL",
         // ["S6514"],
         // ["S6515"],
         // ["S6516"],

analyzers/tests/SonarAnalyzer.UnitTest/PackagingTests/RuleTypeMappingVB.cs

@@ -6437,7 +6437,7 @@ internal static class RuleTypeMappingVB
         // ["S6510"],
         // ["S6511"],
         // ["S6512"],
-        // ["S6513"],
+        ["S6513"] = "CODE_SMELL",
         // ["S6514"],
         // ["S6515"],
         // ["S6516"],

analyzers/tests/SonarAnalyzer.UnitTest/Rules/ExcludeFromCodeCoverageAttributesNeedJustificationTest.cs

@@ -0,0 +1,68 @@
+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2022 SonarSource SA
+ * mailto: contact AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+using CS = SonarAnalyzer.Rules.CSharp;
+using VB = SonarAnalyzer.Rules.VisualBasic;
+
+namespace SonarAnalyzer.UnitTest.Rules;
+
+[TestClass]
+public class ExcludeFromCodeCoverageAttributesNeedJustificationTest
+{
+    private readonly VerifierBuilder builderCS = new VerifierBuilder<CS.ExcludeFromCodeCoverageAttributesNeedJustification>();
+    private readonly VerifierBuilder builderVB = new VerifierBuilder<VB.ExcludeFromCodeCoverageAttributesNeedJustification>();
+
+#if NET
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_OnAssembly_CS() =>
+        builderCS.AddSnippet("[assembly:System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage] // Noncompliant").Verify();
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_OnAssembly_VB() =>
+        builderVB.AddSnippet("<Assembly:System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage> ' Noncompliant").Verify();
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_CS() =>
+       builderCS.AddPaths("ExcludeFromCodeCoverageAttributesNeedJustification.cs").Verify();
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_CSharp9() =>
+        builderCS.AddPaths("ExcludeFromCodeCoverageAttributesNeedJustification.CSharp9.cs").WithTopLevelStatements().Verify();
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_CSharp10() =>
+        builderCS.AddPaths("ExcludeFromCodeCoverageAttributesNeedJustification.CSharp10.cs").WithOptions(ParseOptionsHelper.FromCSharp10).Verify();
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_VB() =>
+        builderVB.AddPaths("ExcludeFromCodeCoverageAttributesNeedJustification.vb").Verify();
+
+#endif
+
+#if netframework
+
+    [TestMethod]
+    public void ExcludeFromCodeCoverageAttributesNeedJustification_IgnoredForNet48() =>
+        builderCS.AddPaths("ExcludeFromCodeCoverageAttributesNeedJustification.net48.cs").Verify();
+
+#endif
+
+}