Added additional checking to C# Codegen.Tests to validate return types

Author: rekhoff

crates/bindings-csharp/Codegen.Tests/Tests.cs

@@ -4,6 +4,7 @@ namespace SpacetimeDB.Codegen.Tests;
 using System.Runtime.CompilerServices;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.MSBuild;
 using Microsoft.CodeAnalysis.Text;
 
@@ -15,8 +16,19 @@ public static class GeneratorSnapshotTests
 
     record struct StepOutput(string Key, IncrementalStepRunReason Reason, object Value);
 
-    class Fixture(string projectDir, CSharpCompilation sampleCompilation)
+    class Fixture
     {
+        private readonly string projectDir;
+        private readonly CSharpCompilation sampleCompilation;
+
+        public Fixture(string projectDir, CSharpCompilation sampleCompilation)
+        {
+            this.projectDir = projectDir;
+            this.sampleCompilation = sampleCompilation;
+        }
+
+        public CSharpCompilation SampleCompilation => sampleCompilation;
+
         public static async Task<Fixture> Compile(string name)
         {
             var projectDir = Path.Combine(GetProjectDir(), "fixtures", name);
@@ -63,6 +75,14 @@ IIncrementalGenerator generator
             return genResult.GeneratedTrees;
         }
 
+        public GeneratorDriverRunResult RunGeneratorAndGetResult(
+            IIncrementalGenerator generator
+        )
+        {
+            var driver = CreateDriver(generator, sampleCompilation.LanguageVersion);
+            return driver.RunGenerators(sampleCompilation).GetRunResult();
+        }
+
         public async Task<CSharpCompilation> RunAndCheckGenerators(
             params IIncrementalGenerator[] generators
         ) =>
@@ -257,4 +277,38 @@ public static async Task TestDiagnostics()
         AssertRuntimeDoesNotDefineLocal(compilationAfterGen);
         AssertGeneratedCodeDoesNotUseInternalBound(compilationAfterGen);
     }
+
+    [Fact]
+    public static async Task ViewInvalidReturnHighlightsReturnType()
+    {
+        var fixture = await Fixture.Compile("diag");
+
+        var runResult = fixture.RunGeneratorAndGetResult(new SpacetimeDB.Codegen.Module());
+
+        var method = fixture.SampleCompilation.SyntaxTrees
+            .Select(tree => new { Tree = tree, Root = tree.GetRoot() })
+            .SelectMany(entry => entry.Root.DescendantNodes()
+                .OfType<MethodDeclarationSyntax>()
+                .Select(method => new { entry.Tree, entry.Root, Method = method }))
+            .Single(entry => entry.Method.Identifier.Text == "ViewDefIEnumerableReturnFromIter");
+
+        var returnTypeSpan = method.Method.ReturnType.Span;
+        var diagnostics = runResult.Results.SelectMany(result => result.Diagnostics)
+            .Where(d => d.Id == "STDB0024")
+            .ToList();
+        var diagnostic = diagnostics.FirstOrDefault(d =>
+            d.GetMessage().Contains("ViewDefIEnumerableReturnFromIter")
+            && d.Location.SourceTree == method.Tree
+        );
+
+        Assert.NotNull(diagnostic);
+
+        Assert.Equal(returnTypeSpan, diagnostic!.Location.SourceSpan);
+
+        var returnTypeText = method.Root.ToFullString().Substring(
+            returnTypeSpan.Start,
+            returnTypeSpan.Length
+        );
+        Assert.Contains("IEnumerable", returnTypeText);
+    }
 }

crates/bindings-csharp/Codegen.Tests/fixtures/diag/Lib.cs

@@ -554,20 +554,34 @@ public static List<Player> ViewDefWrongContext(ReducerContext ctx)
     }
 
     // TODO: Investigate why void return breaks the FFI generation
-    // // Invalid: Void return type is not Vec<T> or Option<T>
+    // // Invalid: Void return type is not List<T> or T?
     // [SpacetimeDB.View(Accessor = "view_def_no_return", Public = true)]
     // public static void ViewDefNoReturn(ViewContext ctx)
     // {
     //     return;
     // }
 
-    // Invalid: Wrong return type is not Vec<T> or Option<T>
+    // Invalid: Wrong return type is not List<T> or T?
     [SpacetimeDB.View(Accessor = "view_def_wrong_return", Public = true)]
     public static Player ViewDefWrongReturn(ViewContext ctx)
     {
         return new Player { Identity = new() };
     }
 
+    // Invalid: IEnumerable<T> return type (from Iter()) is not List<T> or T?
+    [SpacetimeDB.View(Accessor = "view_def_ienumerable_return_from_iter", Public = true)]
+    public static IEnumerable<Player> ViewDefIEnumerableReturnFromIter(ViewContext ctx)
+    {
+        return ctx.Db.Player.Iter();
+    }
+
+    // Invalid: IEnumerable<T> return type (from Filter()) is not List<T> or T?
+    [SpacetimeDB.View(Accessor = "view_def_ienumerable_return_from_filter", Public = true)]
+    public static IEnumerable<Player> ViewDefIEnumerableReturnFromFilter(ViewContext ctx)
+    {
+        return ctx.Db.Player.Identity.Filter(ctx.Sender);
+    }
+
     // Invalid: Returns type that is not a SpacetimeType
     [SpacetimeDB.View(Accessor = "view_def_returns_not_a_spacetime_type", Public = true)]
     public static NotSpacetimeType? ViewDefReturnsNotASpacetimeType(AnonymousViewContext ctx)

crates/bindings-csharp/Codegen.Tests/fixtures/diag/snapshots/ExtraCompilationErrors.verified.txt

@@ -114,6 +114,29 @@ SpacetimeDB.Internal.Module.RegisterClientVisibilityFilter(global::Module.MY_FOU
       ]
     }
   },
+  {/*
+    {
+        return ctx.Db.Player.Iter();
+                             ^^^^
+    }
+*/
+    Message: 'PlayerReadOnly' does not contain a definition for 'Iter' and no accessible extension method 'Iter' accepting a first argument of type 'PlayerReadOnly' could be found (are you missing a using directive or an assembly reference?),
+    Severity: Error,
+    Descriptor: {
+      Id: CS1061,
+      Title: ,
+      HelpLink: https://msdn.microsoft.com/query/roslyn.query?appId=roslyn&k=k(CS1061),
+      MessageFormat: '{0}' does not contain a definition for '{1}' and no accessible extension method '{1}' accepting a first argument of type '{0}' could be found (are you missing a using directive or an assembly reference?),
+      Category: Compiler,
+      DefaultSeverity: Error,
+      IsEnabledByDefault: true,
+      CustomTags: [
+        Compiler,
+        Telemetry,
+        NotConfigurable
+      ]
+    }
+  },
   {/*
     {
         ctx.Db.Player.Iter();
@@ -137,6 +160,29 @@ SpacetimeDB.Internal.Module.RegisterClientVisibilityFilter(global::Module.MY_FOU
       ]
     }
   },
+  {/*
+    {
+        return ctx.Db.Player.Identity.Filter(ctx.Sender);
+                                      ^^^^^^
+    }
+*/
+    Message: 'ReadOnlyUniqueIndex<PlayerReadOnly, Player, Identity, Identity.BSATN>.Filter(Identity)' is inaccessible due to its protection level,
+    Severity: Error,
+    Descriptor: {
+      Id: CS0122,
+      Title: ,
+      HelpLink: https://msdn.microsoft.com/query/roslyn.query?appId=roslyn&k=k(CS0122),
+      MessageFormat: '{0}' is inaccessible due to its protection level,
+      Category: Compiler,
+      DefaultSeverity: Error,
+      IsEnabledByDefault: true,
+      CustomTags: [
+        Compiler,
+        Telemetry,
+        NotConfigurable
+      ]
+    }
+  },
   {/*
     // Valid Filter, but [ClientVisibilityFilter] is disabled
     [SpacetimeDB.ClientVisibilityFilter]