New Rule T0036: Do not activate a nullable context (#9171)

analyzers/src/SonarAnalyzer.CSharp.Styling/Rules/AvoidNullable.cs

@@ -0,0 +1,37 @@
+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2024 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.Styling;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class AvoidNullable : StylingAnalyzer
+{
+    public AvoidNullable() : base("T0036", "Do not use nullable context.") { }
+
+    protected override void Initialize(SonarAnalysisContext context) =>
+        context.RegisterNodeAction(c =>
+            {
+                if (((NullableDirectiveTriviaSyntax)c.Node).SettingToken.IsKind(SyntaxKind.EnableKeyword))
+                {
+                    c.ReportIssue(Rule, c.Node);
+                }
+            },
+            SyntaxKind.NullableDirectiveTrivia);
+}

analyzers/tests/SonarAnalyzer.CSharp.Styling.Test/Rules/AvoidNullableTest.cs

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+/*
+ * SonarAnalyzer for .NET
+ * Copyright (C) 2015-2024 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.CSharp.Styling.Test.Rules;
+
+[TestClass]
+public class AvoidNullableTest
+{
+    [TestMethod]
+    public void AvoidNullable() =>
+        StylingVerifierBuilder.Create<AvoidNullable>().AddPaths("AvoidNullable.cs").Verify();
+}

analyzers/tests/SonarAnalyzer.CSharp.Styling.Test/TestCases/AvoidNullable.cs

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+
+// This is not expected to raise when the whole project is configured with nullable context.
+
+// Noncompliant@+1 {{Do not use nullable context.}}
+  #nullable enable
+//^^^^^^^^^^^^^^^^
+
+#nullable disable // Compliant
+
+#nullable restore // Compliant