Nullable annotations part 4 (final) (#2300)

* Nullable annotations part 4 (final)

* PR feedback

- Clean up extra variables introduced as
  nullable versions of existing variables.

* Fix a few annotations

- TryGetMethodStubValue may return null when true
- GetReturnType and GetParameterType may return null in some cases

* More annotations and PR feedback

- Don't resolve a generic typeref that should already be a typedef
- Remove some redundant null checks
- Turn on nullable annotations for ref assembly
- Remove #nullable disable section

* Clean up GetInflatedDeclaringType

- Remove null check
- Replace TryResolve call with an assert
- Add comment and asserts justifying null-forgiving operator

* Replace exception with assert in accessors

* PR feedback

- Add parens to improve readability
- Throw on diagnostic without message
- Remove unnecessary string.empty

* Undo DiagnosticString change

- Some DiagnosticIds intentionally have no fixed format strings because
  we generate different strings in different circumstances.

1 files changed, 10 insertions, 2 deletions

diff --git a/src/linker/Linker.Steps/BaseSubStep.cs b/src/linker/Linker.Steps/BaseSubStep.cs
index 9a3aa250a..4826c7014 100644
--- a/src/linker/Linker.Steps/BaseSubStep.cs
+++ b/src/linker/Linker.Steps/BaseSubStep.cs
@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
+using System.Diagnostics;
 using Mono.Cecil;
 
 namespace Mono.Linker.Steps
@@ -9,13 +11,19 @@ namespace Mono.Linker.Steps
 	{
 		protected AnnotationStore Annotations => Context.Annotations;
 
-		protected LinkContext Context { get; private set; }
+		LinkContext? _context { get; set; }
+		protected LinkContext Context {
+			get {
+				Debug.Assert (_context != null);
+				return _context;
+			}
+		}
 
 		public abstract SubStepTargets Targets { get; }
 
 		public virtual void Initialize (LinkContext context)
 		{
-			Context = context;
+			_context = context;
 		}
 
 		public virtual bool IsActiveFor (AssemblyDefinition assembly) => true;