Merge pull request #17059 from CyrusNajmabadi/typeParameterResolution

Fix crash when trying to resolve a generic method that doesn't exist in the later compilation.
Fixes #17056

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.MethodSymbolKey.cs

@@ -144,8 +144,13 @@ public static SymbolKeyResolution Resolve(SymbolKeyReader reader)
                 {
                     // We didn't find any candidates.  We still need to stream through this
                     // method signature so the reader is in a proper position.
+
+                    // Push an null-method to our stack so that any method-type-parameters
+                    // can at least be read (if not resolved) properly.
+                    reader.PushMethod(methodOpt: null);
                     var parameterTypeResolutions = reader.ReadSymbolKeyArray();
                     var returnType = GetFirstSymbol<ITypeSymbol>(reader.ReadSymbolKey());
+                    reader.PopMethod(methodOpt: null);
                 }
 
                 return CreateSymbolInfo(result);

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyReader.cs

@@ -360,13 +360,13 @@ public override void Dispose()
                 return true;
             }
 
-            public void PushMethod(IMethodSymbol method)
-                => _methodSymbolStack.Add(method);
+            public void PushMethod(IMethodSymbol methodOpt)
+                => _methodSymbolStack.Add(methodOpt);
 
-            public void PopMethod(IMethodSymbol method)
+            public void PopMethod(IMethodSymbol methodOpt)
             {
                 Contract.ThrowIfTrue(_methodSymbolStack.Count == 0);
-                Contract.ThrowIfFalse(method.Equals(_methodSymbolStack.Last()));
+                Contract.ThrowIfFalse(Equals(methodOpt, _methodSymbolStack.Last()));
                 _methodSymbolStack.RemoveAt(_methodSymbolStack.Count - 1);
             }
 

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.TypeParameterOrdinalSymbolKey.cs

@@ -20,8 +20,11 @@ public static SymbolKeyResolution Resolve(SymbolKeyReader reader)
             {
                 var methodIndex = reader.ReadInteger();
                 var ordinal = reader.ReadInteger();
-                var typeParameter = reader.ResolveMethod(methodIndex).TypeParameters[ordinal];
-                return new SymbolKeyResolution(typeParameter);
+                var method = reader.ResolveMethod(methodIndex);
+                var typeParameter = method?.TypeParameters[ordinal];
+                return typeParameter == null
+                    ? default(SymbolKeyResolution)
+                    : new SymbolKeyResolution(typeParameter);
             }
         }
     }

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.Shared.Utilities;
@@ -105,7 +106,9 @@ public static IEqualityComparer<SymbolKey> GetComparer(bool ignoreCase, bool ign
         {
             using (var reader = SymbolKeyReader.GetReader(symbolKey, compilation, ignoreAssemblyKey, cancellationToken))
             {
-                return reader.ReadFirstSymbolKey();
+                var result = reader.ReadFirstSymbolKey();
+                Debug.Assert(reader.Position == symbolKey.Length);
+                return result;
             }
         }
 

src/Workspaces/CoreTest/SymbolKeyTests.cs

@@ -579,6 +579,33 @@ void foo()
             Assert.NotNull(SymbolKey.Create(xSymbol));
         }
 
+        [Fact]
+        public void TestGenericMethodTypeParameterMissing1()
+        {
+            var source1 = @"
+public class C
+{
+    void M<T>(T t) { }
+}
+";
+
+            var source2 = @"
+public class C
+{
+}
+";
+
+            var compilation1 = GetCompilation(source1, LanguageNames.CSharp);
+            var compilation2 = GetCompilation(source2, LanguageNames.CSharp);
+
+            var methods = GetDeclaredSymbols(compilation1).OfType<IMethodSymbol>();
+            foreach (var method in methods)
+            {
+                var key = SymbolKey.Create(method);
+                key.Resolve(compilation2);
+            }
+        }
+
         [Fact, WorkItem(377839, "https://devdiv.visualstudio.com/DevDiv/_workitems?id=377839")]
         public void TestConstructedMethodInsideLocalFunctionWithTypeParameters()
         {