From 9cdf7e71f9fd3247a15b4a73db37bea5cf358576 Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Fri, 5 Oct 2012 00:18:36 +0200
Subject: [PATCH] Don't show 'method never returns' for iterators containing
 'yield break;'

---
 .../Analysis/ReachabilityAnalysis.cs          |  4 +++
 .../CodeIssues/MethodNeverReturnsIssue.cs     | 34 ++++++-------------
 .../MethodNeverReturnsIssueTests.cs           | 14 ++++++++
 3 files changed, 28 insertions(+), 24 deletions(-)

diff --git a/ICSharpCode.NRefactory.CSharp/Analysis/ReachabilityAnalysis.cs b/ICSharpCode.NRefactory.CSharp/Analysis/ReachabilityAnalysis.cs
index ebb8d419d3..524966d7fb 100644
--- a/ICSharpCode.NRefactory.CSharp/Analysis/ReachabilityAnalysis.cs
+++ b/ICSharpCode.NRefactory.CSharp/Analysis/ReachabilityAnalysis.cs
@@ -78,6 +78,10 @@ namespace ICSharpCode.NRefactory.CSharp.Analysis
 			}
 		}
 		
+		public IEnumerable<Statement> ReachableStatements {
+			get { return reachableStatements; }
+		}
+		
 		public bool IsReachable(Statement statement)
 		{
 			return reachableStatements.Contains(statement);
diff --git a/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/MethodNeverReturnsIssue.cs b/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/MethodNeverReturnsIssue.cs
index 68ae2e8529..44c08d3299 100644
--- a/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/MethodNeverReturnsIssue.cs
+++ b/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/MethodNeverReturnsIssue.cs
@@ -43,8 +43,6 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 
 		class GatherVisitor : GatherVisitorBase
 		{
-			readonly ControlFlowGraphBuilder cfgBuilder = new ControlFlowGraphBuilder ();
-
 			public GatherVisitor(BaseRefactoringContext ctx)
 				: base (ctx)
 			{
@@ -58,30 +56,18 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 				if (methodDeclaration.Body.IsNull)
 					return;
 
-				var cfg = cfgBuilder.BuildControlFlowGraph (methodDeclaration.Body, ctx.Resolver,
-					ctx.CancellationToken);
-				var stack = new Stack<ControlFlowNode> ();
-				var visitedNodes = new HashSet<ControlFlowNode> ();
-				stack.Push (cfg [0]);
-				while (stack.Count > 0) {
-					var node = stack.Pop ();
-
-					// reach method's end
-					if (node.PreviousStatement == methodDeclaration.Body)
-						return;
-					// reach a return statement
-					if (node.NextStatement is ReturnStatement ||
-						node.NextStatement is ThrowStatement)
-						return;
-
-					foreach (var edge in node.Outgoing) {
-						if (visitedNodes.Add(edge.To))
-							stack.Push(edge.To);
+				var reachability = ctx.CreateReachabilityAnalysis(methodDeclaration.Body);
+				bool hasReachableReturn = false;
+				foreach (var statement in reachability.ReachableStatements) {
+					if (statement is ReturnStatement || statement is ThrowStatement || statement is YieldBreakStatement) {
+						hasReachableReturn = true;
+						break;
 					}
 				}
-
-				AddIssue (methodDeclaration.NameToken, 
-					ctx.TranslateString ("Method never reaches its end or a 'return' statement."));
+				if (!hasReachableReturn && !reachability.IsEndpointReachable(methodDeclaration.Body)) {
+					AddIssue (methodDeclaration.NameToken, 
+						ctx.TranslateString ("Method never reaches its end or a 'return' statement."));
+				}
 			}
 		}
 	}
diff --git a/ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/MethodNeverReturnsIssueTests.cs b/ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/MethodNeverReturnsIssueTests.cs
index 2e5e4f5c1f..58b4db6a5d 100644
--- a/ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/MethodNeverReturnsIssueTests.cs
+++ b/ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/MethodNeverReturnsIssueTests.cs
@@ -87,5 +87,19 @@ class TestClass
 }";
 			Test<MethodNeverReturnsIssue> (input, 1);
 		}
+		
+		[Test]
+		public void YieldBreak ()
+		{
+			var input = @"
+class TestClass
+{
+	System.Collections.Generic.IEnumerable<string> TestMethod ()
+	{
+		yield break;
+	}
+}";
+			Test<MethodNeverReturnsIssue> (input, 0);
+		}
 	}
 }