Fix bug in 'this' optimization for classes

src/Compilers/CSharp/Portable/Lowering/LambdaRewriter/LambdaRewriter.Analysis.cs

@@ -246,9 +246,13 @@ private void InlineThisOnlyEnvironments()
                 }
                 else
                 {
-                    // Class-based 'this' closures can move member functions
-                    // to the top-level type and environments which capture
-                    // the 'this' environment can capture 'this' directly
+                    // Class-based 'this' closures can move member functions to
+                    // the top-level type and environments which capture the 'this'
+                    // environment can capture 'this' directly.
+                    // Note: the top-level type is treated as the initial containing
+                    // environment, so by removing the 'this' environment, all
+                    // nested environments which captured a pointer to the 'this'
+                    // environment will now capture 'this'
                     RemoveEnv();
                     VisitClosures(ScopeTree, (scope, closure) =>
                     {
@@ -257,35 +261,6 @@ private void InlineThisOnlyEnvironments()
                             closure.ContainingEnvironmentOpt = null;
                         }
                     });
-
-                    // Find all environments in the scope below that could
-                    // capture the parent. If there are any, add 'this' to
-                    // the list of captured variables and remove the parent
-                    // link
-                    VisitFirstLevelScopes(ScopeTree);
-                    void VisitFirstLevelScopes(Scope scope)
-                    {
-                        var classEnvs = scope.DeclaredEnvironments.Where(e => !e.IsStruct);
-                        if (classEnvs.IsEmpty())
-                        {
-                            // Keep looking for nested environments
-                            foreach (var nested in scope.NestedScopes)
-                            {
-                                VisitFirstLevelScopes(nested);
-                            }
-                        }
-                        else
-                        {
-                            foreach (var declEnv in classEnvs)
-                            {
-                                if (declEnv.CapturesParent)
-                                {
-                                    declEnv.CapturedVariables.Insert(0, thisParam);
-                                    declEnv.CapturesParent = false;
-                                }
-                            }
-                        }
-                    }
                 }
 
                 void RemoveEnv()

src/Compilers/CSharp/Portable/Lowering/LambdaRewriter/LambdaRewriter.cs

@@ -187,8 +187,7 @@ public MappedLocalFunction(SynthesizedLambdaMethod symbol, ClosureKind closureKi
             _assignLocals = assignLocals;
             _currentTypeParameters = method.TypeParameters;
             _currentLambdaBodyTypeMap = TypeMap.Empty;
-            _innermostFramePointer = null;
-            _currentFrameThis = thisParameterOpt;
+            _innermostFramePointer = _currentFrameThis = thisParameterOpt;
             _framePointers[thisType] = thisParameterOpt;
             _seenBaseCall = method.MethodKind != MethodKind.Constructor; // only used for ctors
             _synthesizedFieldNameIdDispenser = 1;

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenLocalFunctionTests.cs

@@ -30,6 +30,72 @@ public static IMethodSymbol FindLocalFunction(this CompilationVerifier verifier,
     [CompilerTrait(CompilerFeature.LocalFunctions)]
     public class CodeGenLocalFunctionTests : CSharpTestBase
     {
+        [Fact]
+        public void CaptureThisInDifferentScopes()
+        {
+            CompileAndVerify(@"
+using System;
+class C
+{
+    int _x;
+    void M()
+    {
+        {
+            int y = 0;
+            Func<int> f1 = () => _x + y;
+        }
+        {
+            int y = 0;
+            Func<int> f2 = () => _x + y;
+        }
+    }
+}");
+        }
+
+        [Fact]
+        public void CaptureThisInDifferentScopes2()
+        {
+            CompileAndVerify(@"
+using System;
+class C
+{
+    int _x;
+    void M()
+    {
+        {
+            int y = 0;
+            int L1() => _x + y;
+        }
+        {
+            int y = 0;
+            int L2() => _x + y;
+        }
+    }
+}");
+        }
+
+        [Fact]
+        public void CaptureFramePointerInDifferentScopes()
+        {
+            CompileAndVerify(@"
+using System;
+class C
+{
+    void M(int x)
+    {
+        Func<int> f1 = () => x;
+        {
+            int z = 0;
+            Func<int> f2 = () => x + z;
+        }
+        {
+            int z = 0;
+            Func<int> f3 = () => x + z;
+        }
+    }
+}");
+        }
+
         [Fact]
         public void EnvironmentChainContainsStructEnvironment()
         {