Add test for the fix

src/Compilers/Core/CodeAnalysisTest/Diagnostics/OperationTestAnalyzer.cs

@@ -1709,4 +1709,41 @@ public sealed override void Initialize(AnalysisContext context)
                 OperationKind.PlaceholderExpression);
         }
     }
+    
+
+    public class ForLoopConditionCrashVBTestAnalyzer : DiagnosticAnalyzer
+    {
+        private const string ReliabilityCategory = "Reliability";
+        
+        public static readonly DiagnosticDescriptor ForLoopConditionCrashDescriptor = new DiagnosticDescriptor(
+            "ForLoopConditionCrash",
+            "Ensure ForLoopCondition property doesn't crash",
+            "Ensure ForLoopCondition property doesn't crash",
+            ReliabilityCategory,
+            DiagnosticSeverity.Warning,
+            isEnabledByDefault: true);
+
+        public sealed override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics
+        {
+            get { return ImmutableArray.Create(ForLoopConditionCrashDescriptor); }
+        }
+
+        public sealed override void Initialize(AnalysisContext context)
+        {
+            context.RegisterOperationAction(
+                 (operationContext) =>
+                 {
+                     ILoopStatement loop = (ILoopStatement)operationContext.Operation;
+                     if (loop.LoopKind == LoopKind.For)
+                     {
+                         IForLoopStatement forLoop = (IForLoopStatement)loop;
+                         var forCondition = forLoop.Condition;
+
+                         // Generate a warning to prove we didn't crash
+                         operationContext.ReportDiagnostic(Diagnostic.Create(ForLoopConditionCrashDescriptor, forLoop.Condition.Syntax.GetLocation()));
+                     }
+                 },
+                 OperationKind.LoopStatement);
+        }
+    }
 }
\ No newline at end of file

src/Compilers/VisualBasic/Test/Semantic/Diagnostics/OperationAnalyzerTests.vb

@@ -1654,5 +1654,43 @@ End Class
                 Diagnostic(ConditionalAccessOperationTestAnalyzer.ConditionalAccessOperationDescriptor.Id, "Field1?.M0(Nothing)").WithLocation(32, 9),
                 Diagnostic(ConditionalAccessOperationTestAnalyzer.ConditionalAccessInstanceOperationDescriptor.Id, "Field1?.M0(Nothing)").WithLocation(32, 9))
         End Sub
+
+        <WorkItem(8955, "https://github.com/dotnet/roslyn/issues/8955")>
+        <Fact>
+        Public Sub ForToLoopConditionCrashVisualBasic()
+            Dim source = <compilation>
+                             <file name="c.vb">
+                                 <![CDATA[
+Module M1
+    Class C1(Of t)
+        Shared Widening Operator CType(ByVal p1 As C1(Of t)) As Integer
+            Return 1
+        End Operator
+        Shared Widening Operator CType(ByVal p1 As Integer) As C1(Of t)
+            Return Nothing
+        End Operator
+        Shared Operator -(ByVal p1 As C1(Of t), ByVal p2 As C1(Of t)) As C1(Of Short)
+            Return Nothing
+        End Operator
+        Shared Operator +(ByVal p1 As C1(Of t), ByVal p2 As C1(Of t)) As C1(Of Integer)
+            Return Nothing
+        End Operator
+    End Class
+    Sub foo()
+        For i As C1(Of Integer) = 1 To 10
+        Next
+    End Sub
+End Module
+]]>
+                             </file>
+                         </compilation>
+
+            Dim comp = CompilationUtils.CreateCompilationWithMscorlibAndVBRuntime(source)
+            comp.VerifyDiagnostics(Diagnostic(ERRID.ERR_UnacceptableForLoopOperator2, "For i As C1(Of Integer) = 1 To 10").WithArguments("Public Shared Operator -(p1 As M1.C1(Of Integer), p2 As M1.C1(Of Integer)) As M1.C1(Of Short)", "M1.C1(Of Integer)").WithLocation(17, 9),
+                                   Diagnostic(ERRID.ERR_ForLoopOperatorRequired2, "For i As C1(Of Integer) = 1 To 10").WithArguments("M1.C1(Of Integer)", "<=").WithLocation(17, 9),
+                                   Diagnostic(ERRID.ERR_ForLoopOperatorRequired2, "For i As C1(Of Integer) = 1 To 10").WithArguments("M1.C1(Of Integer)", ">=").WithLocation(17, 9))
+            comp.VerifyAnalyzerDiagnostics({New ForLoopConditionCrashVBTestAnalyzer}, Nothing, Nothing, False,
+                                           Diagnostic(ForLoopConditionCrashVBTestAnalyzer.ForLoopConditionCrashDescriptor.Id, "10").WithLocation(17, 40))
+        End Sub
     End Class
 End Namespace