From ab691fd4784bea9301e329aa4683b290028bf317 Mon Sep 17 00:00:00 2001
From: Neal Gafter <neal@gafter.com>
Date: Tue, 10 Apr 2018 12:01:42 -0700
Subject: [PATCH] Fix compiler crash when binding missing property pattern
 member.

---
 .../CSharp/Portable/Binder/Binder_Patterns.cs | 14 +++--
 .../Semantics/PatternMatchingTests2.cs        | 53 +++++++++++++++++++
 2 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs b/src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs
index 2b3a6019634..0c0a549dff4 100644
--- a/src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs
+++ b/src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs
@@ -658,14 +658,16 @@ private BoundPattern BindPropertyPattern(PropertyPatternSyntax node, TypeSymbol
         {
             Symbol symbol = BindPropertyPatternMember(inputType, name, ref hasErrors, diagnostics);
 
-            if (inputType.IsErrorType() || hasErrors)
+            if (inputType.IsErrorType() || hasErrors || symbol == (object)null)
             {
                 memberType = CreateErrorType();
                 return null;
             }
-
-            memberType = symbol.GetTypeOrReturnType();
-            return symbol;
+            else
+            {
+                memberType = symbol.GetTypeOrReturnType();
+                return symbol;
+            }
         }
 
         private Symbol BindPropertyPatternMember(
@@ -726,16 +728,18 @@ private BoundPattern BindPropertyPattern(PropertyPatternSyntax node, TypeSymbol
 
                             default:
                                 Error(diagnostics, ErrorCode.ERR_PropertyLacksGet, memberName, name);
-                                hasErrors = true;
                                 break;
                         }
                     }
+
+                    hasErrors = true;
                     return null;
             }
 
             if (hasErrors || !CheckValueKind(node: memberName.Parent, expr: boundMember, valueKind: BindValueKind.RValue,
                                              checkingReceiver: false, diagnostics: diagnostics))
             {
+                hasErrors = true;
                 return null;
             }
 
diff --git a/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs b/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs
index 5e71ea5e1ea..c0f06540b19 100644
--- a/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs
+++ b/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs
@@ -1254,6 +1254,59 @@ class Cat {}
             var comp = CompileAndVerify(compilation, expectedOutput: @"Fox Cat");
         }
 
+        [Fact]
+        public void PropertyPatternMemberMissing01()
+        {
+            var source =
+@"class Program
+{
+    static void Main(string[] args)
+    {
+        Blah b = null;
+        if (b is Blah { X: int i })
+        {
+        }
+    }
+}
+
+class Blah
+{
+}";
+            var compilation = CreatePatternCompilation(source);
+            compilation.VerifyDiagnostics(
+                // (6,25): error CS0117: 'Blah' does not contain a definition for 'X'
+                //         if (b is Blah { X: int i })
+                Diagnostic(ErrorCode.ERR_NoSuchMember, "X").WithArguments("Blah", "X").WithLocation(6, 25)
+                );
+        }
+
+        [Fact]
+        public void PropertyPatternMemberMissing02()
+        {
+            var source =
+@"class Program
+{
+    static void Main(string[] args)
+    {
+        Blah b = null;
+        if (b is Blah { X: int i })
+        {
+        }
+    }
+}
+
+class Blah
+{
+    public int X { set {} }
+}";
+            var compilation = CreatePatternCompilation(source);
+            compilation.VerifyDiagnostics(
+                // (6,25): error CS0154: The property or indexer 'Blah.X' cannot be used in this context because it lacks the get accessor
+                //         if (b is Blah { X: int i })
+                Diagnostic(ErrorCode.ERR_PropertyLacksGet, "X:").WithArguments("Blah.X").WithLocation(6, 25)
+                );
+        }
+
         // PROTOTYPE(patterns2): Need to have tests that exercise:
         // PROTOTYPE(patterns2): Building the decision tree for the var-pattern
         // PROTOTYPE(patterns2): Definite assignment for the var-pattern
-- 
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