Visit binary operators in ref safety analysis

src/Compilers/CSharp/Portable/Binder/RefSafetyAnalysis.cs

@@ -258,6 +258,24 @@ private bool ContainsPlaceholderScope(BoundValuePlaceholderBase placeholder)
         public override BoundNode? Visit(BoundNode? node)
         {
 #if DEBUG
+            TrackVisit(node);
+#endif
+            return base.Visit(node);
+        }
+
+#if DEBUG
+        protected override void BeforeVisitingSkippedBoundBinaryOperatorChildren(BoundBinaryOperator node)
+        {
+            TrackVisit(node);
+        }
+
+        protected override void BeforeVisitingSkippedBoundCallChildren(BoundCall node)
+        {
+            TrackVisit(node);
+        }
+
+        private void TrackVisit(BoundNode? node)
+        {
             if (node is BoundValuePlaceholderBase placeholder)
             {
                 Debug.Assert(ContainsPlaceholderScope(placeholder));
@@ -267,14 +285,11 @@ private bool ContainsPlaceholderScope(BoundValuePlaceholderBase placeholder)
                 if (_visited is { } && _visited.Count <= MaxTrackVisited)
                 {
                     bool added = _visited.Add(expr);
-                    Debug.Assert(added);
+                    Debug.Assert(added, $"Expression {expr} `{expr.Syntax}` visited more than once.");
                 }
             }
-#endif
-            return base.Visit(node);
         }
 
-#if DEBUG
         private void AssertVisited(BoundExpression expr)
         {
             if (expr is BoundValuePlaceholderBase placeholder)
@@ -283,7 +298,7 @@ private void AssertVisited(BoundExpression expr)
             }
             else if (_visited is { } && _visited.Count <= MaxTrackVisited)
             {
-                Debug.Assert(_visited.Contains(expr));
+                Debug.Assert(_visited.Contains(expr), $"Expected {expr} `{expr.Syntax}` to be visited.");
             }
         }
 #endif
@@ -659,13 +674,6 @@ protected override void VisitArguments(BoundCall node)
                     _localScopeDepth,
                     _diagnostics);
             }
-
-#if DEBUG
-            if (_visited is { } && _visited.Count <= MaxTrackVisited)
-            {
-                _visited.Add(node);
-            }
-#endif
         }
 
         private void GetInterpolatedStringPlaceholders(

src/Compilers/CSharp/Portable/BoundTree/BoundTreeWalker.cs

@@ -114,13 +114,15 @@ protected BoundTreeWalkerWithStackGuardWithoutRecursionOnTheLeftOfBinaryOperator
 
             var binary = (BoundBinaryOperator)node.Left;
 
+            BeforeVisitingSkippedBoundBinaryOperatorChildren(binary);
             rightOperands.Push(binary.Right);
 
             BoundExpression current = binary.Left;
 
             while (current.Kind == BoundKind.BinaryOperator)
             {
                 binary = (BoundBinaryOperator)current;
+                BeforeVisitingSkippedBoundBinaryOperatorChildren(binary);
                 rightOperands.Push(binary.Right);
                 current = binary.Left;
             }
@@ -136,6 +138,10 @@ protected BoundTreeWalkerWithStackGuardWithoutRecursionOnTheLeftOfBinaryOperator
             return null;
         }
 
+        protected virtual void BeforeVisitingSkippedBoundBinaryOperatorChildren(BoundBinaryOperator node)
+        {
+        }
+
         public sealed override BoundNode? VisitCall(BoundCall node)
         {
             if (node.ReceiverOpt is BoundCall receiver1)
@@ -147,10 +153,13 @@ protected BoundTreeWalkerWithStackGuardWithoutRecursionOnTheLeftOfBinaryOperator
                 node = receiver1;
                 while (node.ReceiverOpt is BoundCall receiver2)
                 {
+                    BeforeVisitingSkippedBoundCallChildren(node);
                     calls.Push(node);
                     node = receiver2;
                 }
 
+                BeforeVisitingSkippedBoundCallChildren(node);
+
                 VisitReceiver(node);
 
                 do
@@ -170,6 +179,10 @@ protected BoundTreeWalkerWithStackGuardWithoutRecursionOnTheLeftOfBinaryOperator
             return null;
         }
 
+        protected virtual void BeforeVisitingSkippedBoundCallChildren(BoundCall node)
+        {
+        }
+
         /// <summary>
         /// Called only for the first (in evaluation order) <see cref="BoundCall"/> in the chain.
         /// </summary>

src/Compilers/CSharp/Test/Semantic/Semantics/RefEscapingTests.cs

@@ -7871,6 +7871,37 @@ ref struct S
                 Diagnostic(ErrorCode.ERR_EscapeVariable, "s").WithArguments("s").WithLocation(47, 16));
         }
 
+        [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/71773")]
+        public void UserDefinedBinaryOperator_RefStruct_Nested()
+        {
+            var source = """
+                class C
+                {
+                    S M()
+                    {
+                        S s;
+                        s = default(S) + 100 + 200;
+                        return s;
+                    }
+                }
+
+                ref struct S
+                {
+                    public static S operator+(S y, in int x) => throw null;
+                }
+                """;
+            CreateCompilation(source).VerifyDiagnostics(
+                // (6,13): error CS8347: Cannot use a result of 'S.operator +(S, in int)' in this context because it may expose variables referenced by parameter 'x' outside of their declaration scope
+                //         s = default(S) + 100 + 200;
+                Diagnostic(ErrorCode.ERR_EscapeCall, "default(S) + 100").WithArguments("S.operator +(S, in int)", "x").WithLocation(6, 13),
+                // (6,13): error CS8347: Cannot use a result of 'S.operator +(S, in int)' in this context because it may expose variables referenced by parameter 'y' outside of their declaration scope
+                //         s = default(S) + 100 + 200;
+                Diagnostic(ErrorCode.ERR_EscapeCall, "default(S) + 100 + 200").WithArguments("S.operator +(S, in int)", "y").WithLocation(6, 13),
+                // (6,26): error CS8156: An expression cannot be used in this context because it may not be passed or returned by reference
+                //         s = default(S) + 100 + 200;
+                Diagnostic(ErrorCode.ERR_RefReturnLvalueExpected, "100").WithLocation(6, 26));
+        }
+
         [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/71773")]
         public void UserDefinedBinaryOperator_RefStruct_Scoped_Left()
         {
@@ -8531,5 +8562,16 @@ static R F2()
                 //         return new R(1) | new R(2);
                 Diagnostic(ErrorCode.ERR_RefReturnLvalueExpected, "1").WithLocation(18, 22));
         }
+
+        [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/72873")]
+        public void Utf8Addition()
+        {
+            var code = """
+                using System;
+                ReadOnlySpan<byte> x = "Hello"u8 + " "u8 + "World!"u8;
+                Console.WriteLine(x.Length);
+                """;
+            CreateCompilation(code, targetFramework: TargetFramework.Net70).VerifyDiagnostics();
+        }
     }
 }