fix: PH2141 false positive for regions containing copyright comments (#961)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: bcollamore <57269455+bcollamore@users.noreply.github.com>

Author: Copilot

Documentation/Diagnostics/PH2141.md

@@ -12,11 +12,11 @@
 
 ## Introduction
 
-Avoid writing regions with no code inside.
+Avoid writing regions with no code inside. Regions that contain only comments are considered empty, unless the comments contain copyright information.
 
 ## How to solve
 
-Remove the empty region.
+Remove the empty region. If the region contains copyright information, it is not considered empty and no action is needed.
 
 ## Example
 
@@ -26,6 +26,10 @@ class BadExample
 {
     #region Put some stuff here later
     #endregion
+
+    #region Just a comment
+    // This is just a regular comment
+    #endregion
 }
 
 ```
@@ -42,10 +46,16 @@ class GoodExample
     }
 
     #endregion
+
+    #region Copyright Information
+    // © 2025 Koninklijke Philips N.V. All rights reserved.
+    #endregion
 }
 
 ```
 
+Note: Regions containing copyright information (with copyright symbols or "Copyright" keyword and a year) are not considered empty.
+
 ## Configuration
 
 This analyzer does not offer any special configuration. The general ways of [suppressing](https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/suppress-warnings) diagnostics apply.

Philips.CodeAnalysis.MaintainabilityAnalyzers/Readability/AvoidEmptyRegionsAnalyzer.cs

@@ -1,7 +1,10 @@
 // © 2025 Koninklijke Philips N.V. See License.md in the project root for license information.
 
+using System;
 using System.Collections.Immutable;
 using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -22,6 +25,9 @@ public class AvoidEmptyRegionsAnalyzer : DiagnosticAnalyzerBase
 		private static readonly DiagnosticDescriptor AvoidEmpty = new(DiagnosticId.AvoidEmptyRegions.ToId(), AvoidEmptyRegionTitle,
 			AvoidEmptyRegionMessageFormat, AvoidEmptyRegionCategory, DiagnosticSeverity.Error, isEnabledByDefault: true, description: AvoidEmptyRegionDescription);
 
+		private static readonly Regex CopyrightRegex = new(@"©|\uFFFD|Copyright", RegexOptions.Singleline | RegexOptions.Compiled | RegexOptions.IgnoreCase, TimeSpan.FromSeconds(1));
+		private static readonly Regex YearRegex = new(@"\d\d\d\d", RegexOptions.Singleline | RegexOptions.Compiled, TimeSpan.FromSeconds(1));
+
 		public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(AvoidEmpty);
 
 		protected override void InitializeCompilation(CompilationStartAnalysisContext context)
@@ -87,20 +93,66 @@ private static bool IsRegionEmpty(RegionDirectiveTriviaSyntax regionStart, EndRe
 			var regionStartLine = regionStart.GetLocation().GetLineSpan().StartLinePosition.Line;
 			var regionEndLine = regionEnd.GetLocation().GetLineSpan().StartLinePosition.Line;
 
+			var hasCommentContent = false;
+
 			// Check each line between the region start and end
 			for (var lineNumber = regionStartLine + 1; lineNumber < regionEndLine; lineNumber++)
 			{
 				TextLine line = sourceText.Lines[lineNumber];
 				var lineText = line.ToString().Trim();
 
-				// If we find any non-empty, non-comment line, the region is not empty
-				if (!string.IsNullOrEmpty(lineText) && !lineText.StartsWith("//"))
+				// Skip empty lines
+				if (string.IsNullOrEmpty(lineText))
+				{
+					continue;
+				}
+
+				// If we find any non-comment line, the region is definitely not empty
+				if (!lineText.StartsWith("//"))
 				{
 					return false;
 				}
+
+				// Track that we have comment content
+				hasCommentContent = true;
+			}
+
+			// If we have no content at all (only whitespace), the region is empty
+			if (!hasCommentContent)
+			{
+				return true;
 			}
 
-			return true; // Region contains only whitespace and/or comments
+			// We have only comments - check if they contain copyright information
+			return !ContainsCopyrightInformation(regionStart, regionEnd, sourceText);
+		}
+
+		private static bool ContainsCopyrightInformation(RegionDirectiveTriviaSyntax regionStart, EndRegionDirectiveTriviaSyntax regionEnd, SourceText sourceText)
+		{
+			var regionStartLine = regionStart.GetLocation().GetLineSpan().StartLinePosition.Line;
+			var regionEndLine = regionEnd.GetLocation().GetLineSpan().StartLinePosition.Line;
+
+			var commentTextBuilder = new StringBuilder();
+
+			// Collect all comment text in the region
+			for (var lineNumber = regionStartLine + 1; lineNumber < regionEndLine; lineNumber++)
+			{
+				TextLine line = sourceText.Lines[lineNumber];
+				var lineText = line.ToString().Trim();
+
+				if (!string.IsNullOrEmpty(lineText) && lineText.StartsWith("//"))
+				{
+					_ = commentTextBuilder.Append(lineText).Append(' ');
+				}
+			}
+
+			var allCommentText = commentTextBuilder.ToString();
+
+			// Check if the comments contain copyright information
+			var hasCopyright = CopyrightRegex.IsMatch(allCommentText);
+			var hasYear = YearRegex.IsMatch(allCommentText);
+
+			return hasCopyright && hasYear;
 		}
 	}
 }

Philips.CodeAnalysis.Test/Maintainability/Readability/AvoidEmptyRegionsAnalyzerTest.cs

@@ -231,6 +231,62 @@ public class ObjectList {{ }}
 			await VerifySuccessfulCompilation(givenText).ConfigureAwait(false);
 		}
 
+		[TestMethod]
+		[TestCategory(TestDefinitions.UnitTests)]
+		public async Task RegionWithCopyrightShouldNotTriggerDiagnostic()
+		{
+			const string input = @"public class Foo
+{
+  #region Header
+  // © 2019 Koninklijke Philips N.V.  All rights reserved.
+  // Reproduction or transmission in whole or in part, in any form or by any means, 
+  // electronic, mechanical or otherwise, is prohibited without the prior  written consent of 
+  // the owner.
+  #endregion
+}";
+			await VerifySuccessfulCompilation(input).ConfigureAwait(false);
+		}
+
+		[TestMethod]
+		[TestCategory(TestDefinitions.UnitTests)]
+		public async Task RegionWithOnlyCopyrightCommentShouldNotTriggerDiagnostic()
+		{
+			const string input = @"public class Foo
+{
+  #region Copyright
+  // © 2025 Koninklijke Philips N.V.
+  #endregion
+}";
+			await VerifySuccessfulCompilation(input).ConfigureAwait(false);
+		}
+
+		[TestMethod]
+		[TestCategory(TestDefinitions.UnitTests)]
+		public async Task RegionWithRegularCommentsShouldTriggerDiagnostic()
+		{
+			const string input = @"public class Foo
+{
+  #region TODO
+  // This is just a regular comment
+  // Nothing special here
+  #endregion
+}";
+			await VerifyDiagnostic(input, DiagnosticId.AvoidEmptyRegions).ConfigureAwait(false);
+		}
+
+		[TestMethod]
+		[TestCategory(TestDefinitions.UnitTests)]
+		public async Task RegionWithCopyrightKeywordShouldNotTriggerDiagnostic()
+		{
+			const string input = @"public class Foo
+{
+  #region License
+  // Copyright 2023 Koninklijke Philips N.V.
+  #endregion
+}";
+			await VerifySuccessfulCompilation(input).ConfigureAwait(false);
+		}
+
 		protected override CodeFixProvider GetCodeFixProvider()
 		{
 			return new EnforceRegionsRemoveEmptyRegionCodeFixProvider();