From 141b84fb72776acf122273958760c01e93e8a01a Mon Sep 17 00:00:00 2001
From: Fredric Silberberg <frsilb@microsoft.com>
Date: Tue, 23 Oct 2018 17:59:24 -0700
Subject: [PATCH] Correctly return cached blocks in the IncrementalBinder for
 things that use BindEmbeddedBlock.

---
 .../Portable/Binder/Binder_Statements.cs      |  2 +-
 .../Compilation/MemberSemanticModel.cs        |  5 +++
 .../IOperation/IOperation/IOperationTests.cs  | 33 +++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs b/src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs
index e02d59058df..85fd5b6c379 100644
--- a/src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs
+++ b/src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs
@@ -1588,7 +1588,7 @@ protected virtual LocalFunctionSymbol LookupLocalFunction(SyntaxToken nameToken)
         /// </summary>
         internal virtual uint LocalScopeDepth => Next.LocalScopeDepth;
 
-        internal BoundBlock BindEmbeddedBlock(BlockSyntax node, DiagnosticBag diagnostics)
+        internal virtual BoundBlock BindEmbeddedBlock(BlockSyntax node, DiagnosticBag diagnostics)
         {
             return BindBlock(node, diagnostics);
         }
diff --git a/src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs b/src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs
index 4164dfe5ffe..9cdbe61e7b2 100644
--- a/src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs
+++ b/src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs
@@ -2085,6 +2085,11 @@ public override BoundStatement BindStatement(StatementSyntax node, DiagnosticBag
                 return (BoundStatement)boundNode;
             }
 
+            internal override BoundBlock BindEmbeddedBlock(BlockSyntax node, DiagnosticBag diagnostics)
+            {
+                return (BoundBlock)TryGetBoundNodeFromMap(node) ?? base.BindEmbeddedBlock(node, diagnostics);
+            }
+
             private BoundNode TryGetBoundNodeFromMap(CSharpSyntaxNode node)
             {
                 ImmutableArray<BoundNode> boundNodes = _semanticModel.GuardedGetBoundNodesFromMap(node);
diff --git a/src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests.cs b/src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests.cs
index 0636f4886af..e25fd8c2d48 100644
--- a/src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests.cs
+++ b/src/Compilers/CSharp/Test/IOperation/IOperation/IOperationTests.cs
@@ -493,6 +493,39 @@ void M(int x)
 ");
         }
 
+        [Fact, WorkItem(26649, "https://github.com/dotnet/roslyn/issues/26649")]
+        public void IncrementalBindingReusesBlock()
+        {
+            var source = @"
+class C
+{
+    void M()
+    {
+        try
+        {
+        }
+        catch (Exception e)
+        {
+            throw new Exception();
+        }
+    }
+}";
+
+            var compilation = CreateCompilation(source);
+            var syntaxTree = compilation.SyntaxTrees[0];
+            var semanticModel = compilation.GetSemanticModel(syntaxTree);
+
+            // We want to get the IOperation for the { throw new Exception(); } first, and then for the containing catch block, to
+            // force the semantic model to bind the inner first. It should reuse that inner block when binding the outer catch.
+
+            var catchBlock = syntaxTree.GetRoot().DescendantNodes().OfType<CatchClauseSyntax>().Single();
+            var exceptionBlock = catchBlock.Block;
+
+            var blockOperation = semanticModel.GetOperation(exceptionBlock);
+            var catchOperation = (ICatchClauseOperation)semanticModel.GetOperation(catchBlock);
+            Assert.Same(blockOperation, catchOperation.Handler);
+        }
+
         private static void VerifyRootAndModelForOperationAncestors(
             IOperation operation,
             SemanticModel model,
-- 
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