Fixed DeclareAsNullableCodeFixProvider for casts in variable declarat…

…ions

Casting a nullable type to a non-nullable type within a variable declaration no longer ignores the cast type and also no longer changes `var` to `var?`.

Fixes dotnet#1392.

src/CodeFixes/CSharp/CodeFixes/DeclareAsNullableCodeFixProvider.cs

@@ -2,6 +2,7 @@
 
 using System.Collections.Immutable;
 using System.Composition;
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CodeActions;
@@ -30,7 +31,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
  if (!IsEnabled(diagnostic.Id, CodeFixIdentifiers.AddNullableAnnotation, context.Document, root.SyntaxTree))
  return;
 
- if (!TryFindFirstAncestorOrSelf(root, context.Span, out SyntaxNode node, predicate: f => f.IsKind(SyntaxKind.EqualsValueClause, SyntaxKind.DeclarationExpression, SyntaxKind.SimpleAssignmentExpression)))
+ if (!TryFindFirstAncestorOrSelf(root, context.Span, out SyntaxNode node, predicate: f => f.IsKind(SyntaxKind.EqualsValueClause, SyntaxKind.DeclarationExpression, SyntaxKind.SimpleAssignmentExpression, SyntaxKind.CastExpression)))
  return;
 
  if (node is EqualsValueClauseSyntax equalsValueClause)
@@ -67,6 +68,10 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
  }
  }
  }
+ else if (node is CastExpressionSyntax castExpression)
+ {
+ TryRegisterCodeFixForCast(context, diagnostic, castExpression.Type);
+ }
  }
 
  private static void TryRegisterCodeFix(CodeFixContext context, Diagnostic diagnostic, TypeSyntax type)
@@ -85,4 +90,42 @@ private static void TryRegisterCodeFix(CodeFixContext context, Diagnostic diagno
 
  context.RegisterCodeFix(codeAction, diagnostic);
  }
+
+ private static void TryRegisterCodeFixForCast(CodeFixContext context, Diagnostic diagnostic, TypeSyntax type)
+ {
+ if (type.IsKind(SyntaxKind.NullableType))
+ return;
+
+ CodeAction codeAction = CodeAction.Create(
+ "Declare as nullable",
+ async ct =>
+ {
+ NullableTypeSyntax newType = SyntaxFactory.NullableType(type.WithoutTrivia()).WithTriviaFrom(type);
+ Document changedDocument = await context.Document.ReplaceNodeAsync(type, newType, ct).ConfigureAwait(false);
+
+ // This could be in a variable declaration, so grab the new syntax root and find the newly-replaced type node
+ SyntaxNode root = await changedDocument.GetSyntaxRootAsync(ct).ConfigureAwait(false);
+ SyntaxNode insertedNewType = root.FindNode(type.Span);
+
+ // Try finding a surrounding variable declaration whose type we also have to change
+ if (insertedNewType.AncestorsAndSelf().FirstOrDefault(a => a.IsKind(SyntaxKind.EqualsValueClause)) is EqualsValueClauseSyntax equalsValueClause)
+ {
+ ExpressionSyntax expression = equalsValueClause.Value;
+
+ if (equalsValueClause.IsParentKind(SyntaxKind.VariableDeclarator)
+ && equalsValueClause.Parent.Parent is VariableDeclarationSyntax variableDeclaration
+ && variableDeclaration.Variables.Count == 1
+ && !variableDeclaration.Type.IsKind(SyntaxKind.NullableType)
+ && variableDeclaration.Type is not IdentifierNameSyntax { Identifier.Text: "var" })
+ {
+ NullableTypeSyntax newDeclarationType = SyntaxFactory.NullableType(variableDeclaration.Type.WithoutTrivia()).WithTriviaFrom(variableDeclaration.Type);
+ changedDocument = await changedDocument.ReplaceNodeAsync(variableDeclaration.Type, newDeclarationType, ct).ConfigureAwait(false);
+ }
+ }
+ return changedDocument;
+ },
+ GetEquivalenceKey(diagnostic));
+
+ context.RegisterCodeFix(codeAction, diagnostic);
+ }
 }

src/Tests/CodeFixes.Tests/CS8600ConvertingNullLiteralOrPossibleNullValueToNonNullableTypeTests.cs

@@ -42,6 +42,40 @@ void M()
 ", equivalenceKey: EquivalenceKey.Create(DiagnosticId));
  }
 
+ [Fact, Trait(Traits.CodeFix, CompilerDiagnosticIdentifiers.CS8600_ConvertingNullLiteralOrPossibleNullValueToNonNullableType)]
+ public async Task Test_LocalDeclarationWithCast()
+ {
+ await VerifyFixAsync(@"
+using System;
+#nullable enable
+
+public class C
+{
+ private object? Get() => null;
+
+ void M()
+ {
+ var s = (string) Get();
+ string s2 = (string) Get();
+ }
+}
+", @"
+using System;
+#nullable enable
+
+public class C
+{
+ private object? Get() => null;
+
+ void M()
+ {
+ var s = (string?) Get();
+ string? s2 = (string?) Get();
+ }
+}
+", equivalenceKey: EquivalenceKey.Create(DiagnosticId));
+ }
+
  [Fact, Trait(Traits.CodeFix, CompilerDiagnosticIdentifiers.CS8600_ConvertingNullLiteralOrPossibleNullValueToNonNullableType)]
  public async Task Test_DeclarationExpression()
  {