From 81d1d918740e9ba3cb2eb063b6f28c3139ca9cfa Mon Sep 17 00:00:00 2001
From: Will Smith <lol.tihan@gmail.com>
Date: Fri, 25 Sep 2020 22:17:37 -0700
Subject: [PATCH] Able to remap DecisionTreeTest.Error (#10187)

---
 src/fsharp/TypedTreeOps.fs                    |  2 +-
 .../FSharp.Compiler.ComponentTests.fsproj     |  1 +
 .../Language/RegressionTests.fs               | 21 +++++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 tests/FSharp.Compiler.ComponentTests/Language/RegressionTests.fs

diff --git a/src/fsharp/TypedTreeOps.fs b/src/fsharp/TypedTreeOps.fs
index 2736d6f3e12..0e511a19646 100644
--- a/src/fsharp/TypedTreeOps.fs
+++ b/src/fsharp/TypedTreeOps.fs
@@ -5348,7 +5348,7 @@ and remapDecisionTree g compgen tmenv x =
                     | DecisionTreeTest.IsInst (srcty, tgty) -> DecisionTreeTest.IsInst (remapType tmenv srcty, remapType tmenv tgty) 
                     | DecisionTreeTest.IsNull -> DecisionTreeTest.IsNull 
                     | DecisionTreeTest.ActivePatternCase _ -> failwith "DecisionTreeTest.ActivePatternCase should only be used during pattern match compilation"
-                    | DecisionTreeTest.Error _ -> failwith "DecisionTreeTest.Error should only be used during pattern match compilation"
+                    | DecisionTreeTest.Error(m) -> DecisionTreeTest.Error(m)
                   TCase(test', remapDecisionTree g compgen tmenv y)) csl, 
                 Option.map (remapDecisionTree g compgen tmenv) dflt, 
                 m)
diff --git a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
index 27f4cb4c6dd..74d960c1c92 100644
--- a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
+++ b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
@@ -40,6 +40,7 @@
     <Compile Include="ErrorMessages\WarnExpressionTests.fs" />
     <Compile Include="ErrorMessages\WrongSyntaxInForLoop.fs" />
     <Compile Include="ErrorMessages\ConfusingTypeName.fs" />
+    <Compile Include="Language\RegressionTests.fs" />
     <Compile Include="Language\XmlComments.fs" />
     <Compile Include="Language\CompilerDirectiveTests.fs" />
     <Compile Include="Language\CodeQuotationTests.fs" />
diff --git a/tests/FSharp.Compiler.ComponentTests/Language/RegressionTests.fs b/tests/FSharp.Compiler.ComponentTests/Language/RegressionTests.fs
new file mode 100644
index 00000000000..4e878fddae5
--- /dev/null
+++ b/tests/FSharp.Compiler.ComponentTests/Language/RegressionTests.fs
@@ -0,0 +1,21 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace FSharp.Compiler.ComponentTests.Language
+
+open Xunit
+open FSharp.Test.Utilities.Compiler
+
+module RegressionTests =
+
+    [<Fact>]
+    let ``No internal errors should be raised``() =
+        FSharp """
+namespace FSharpBug
+
+type TestItemSeq = 
+    static member Test1 item = item
+    static member Test2 item = match item with Typo2 x -> x
+        """
+        |> compile
+        |> withErrorCodes [39]
+        |> ignore