Client: Cache global state assemblies by name

1. Open Workbooks
2. Create a XF iOS workbook
3. Create a non-XF iOS workbook

The second workbook, for whatever reason, doesn't set a PEImage for the
global state assembly, so the client tries to resolve it from a different
location, leading to an exception.

Cache to avoid this. Will be nice when this reflection loading can go away.

Agents/Xamarin.Interactive/CodeAnalysis/EvaluationContextInitializeRequest.cs

@@ -38,6 +38,9 @@ protected override Task<TargetCompilationConfiguration> HandleAsync (Agent agent
                 var globalStateType = evaluationContext.GlobalState.GetType ();
                 response.GlobalStateTypeName = globalStateType.FullName;
 
+                // TODO: Why is globalStateType.Assembly.Location null when you
+                //       create a non-XF workbook after creating an XF workbook?
+
                 // HACK: This is a temporary fix to get iOS agent/app assemblies sent to the
                 //       Windows client when using the remote sim.
                 var peImage = IncludePeImage && File.Exists (globalStateType.Assembly.Location)

Clients/Xamarin.Interactive.Client/Compilation/CompilationWorkspaceFactory.cs

@@ -17,6 +17,7 @@
 using Xamarin.Interactive.Core;
 using Xamarin.Interactive.Logging;
 using Xamarin.Interactive.Reflection;
+using Xamarin.Interactive.Representations.Reflection;
 
 using static Xamarin.Interactive.Compilation.InteractiveDependencyResolver;
 
@@ -145,6 +146,8 @@ static InteractiveDependencyResolver CreateDependencyResolver (
 
         static Assembly netStandardAssembly;
         static Assembly xiAssembly;
+        static Dictionary<RepresentedAssemblyName, Assembly> globalStateAssembliesByName =
+            new Dictionary<RepresentedAssemblyName, Assembly> ();
 
         static Type ResolveHostObjectType (
             InteractiveDependencyResolver dependencyResolver,
@@ -184,9 +187,16 @@ static Type ResolveHostObjectType (
                 Assembly globalStateAssembly;
                 if (globalStateAssemblyDef.Name.Name == "Xamarin.Interactive")
                     globalStateAssembly = xiAssembly;
-                else
-                    globalStateAssembly = Assembly.ReflectionOnlyLoadFrom (
-                        globalStateAssemblyCachePath ?? globalStateAssemblyDef.Content.Location);
+                else {
+                    // Cache assemblies in case subsequent agents lead us to try to load from a different location later.
+                    // For example, if you create an XF workbook, we'll resolve from the remote assembly cache. If you
+                    // then create a non-XF workbook, we'll resolve locally because PEImage doesn't get set for some reason.
+                    if (!globalStateAssembliesByName.TryGetValue (configuration.GlobalStateAssembly.Name, out globalStateAssembly)) {
+                        globalStateAssembly = Assembly.ReflectionOnlyLoadFrom (
+                            globalStateAssemblyCachePath ?? globalStateAssemblyDef.Content.Location);
+                        globalStateAssembliesByName [configuration.GlobalStateAssembly.Name] = globalStateAssembly;
+                    }
+                }
 
                 return globalStateAssembly.GetType (configuration.GlobalStateTypeName);
             }