Carry the source file's using directives into the generated file

src/Zomp.SyncMethodGenerator/AsyncToSyncRewriter.cs

@@ -957,6 +957,14 @@ bool RemoveType(TypeSyntax z, int index) =>
         var originalName = @base.Identifier.Text;
         var newName = RemoveAsync(originalName);
 
+        // A method which returned a task returns nothing once it is synchronized, so whatever
+        // its documentation said about the task it returned no longer describes anything. The
+        // documentation of a value which survives is left alone: it is imprecise about the task
+        // it mentions, but dropping it would say less than saying it imprecisely.
+        var returnsNothing = GetReturnType(@base.ReturnType, symbol)
+            is PredefinedTypeSyntax { Keyword.RawKind: (int)SyntaxKind.VoidKeyword }
+            or IdentifierNameSyntax { Identifier.ValueText: "void" };
+
         // Documentation
         var trivia = node.GetLeadingTrivia();
         var newTriviaList = trivia;
@@ -982,6 +990,12 @@ bool RemoveType(TypeSyntax z, int index) =>
                         indicesToRemove.Add(i - 1); // preceding slashes
                         indicesToRemove.Add(i);
                     }
+                    else if (returnsNothing
+                        && xes.StartTag.Name.LocalName.ValueText.Equals("returns", StringComparison.Ordinal))
+                    {
+                        indicesToRemove.Add(i - 1); // preceding slashes
+                        indicesToRemove.Add(i);
+                    }
                 }
 
                 ++i;

src/Zomp.SyncMethodGenerator/MethodToGenerate.cs

@@ -5,6 +5,8 @@
 /// </summary>
 /// <param name="Index">Index of the method in the source file.</param>
 /// <param name="Namespaces">List of namespaces this method is under.</param>
+/// <param name="OuterUsings">Using directives the source file declares outside its namespace.</param>
+/// <param name="InnerUsings">Using directives the source file declares inside its namespace.</param>
 /// <param name="IsNamespaceFileScoped">True if namespace is file scoped.</param>
 /// <param name="IsCSharp14Extension">True if this is C# 14 extension.</param>
 /// <param name="Parents">List of classes/structs/records this method belongs to starting from the outer-most class.</param>
@@ -17,6 +19,8 @@
 internal sealed record MethodToGenerate(
     int Index,
     EquatableArray<string> Namespaces,
+    EquatableArray<string> OuterUsings,
+    EquatableArray<string> InnerUsings,
     bool IsNamespaceFileScoped,
     bool IsCSharp14Extension,
     EquatableArray<MethodParentDeclaration> Parents,

src/Zomp.SyncMethodGenerator/SourceGenerationHelper.cs

@@ -100,6 +100,24 @@ internal static string GenerateExtensionClass(MethodToGenerate methodToGenerate)
             }
         }
 
+        // Directives which were written inside the namespace are emitted inside it, at the
+        // innermost level. One which names a namespace relatively still resolves from there.
+        foreach (var @using in methodToGenerate.InnerUsings)
+        {
+            _ = sbBegin.Append($$"""
+{{new string(' ', 4 * i)}}{{@using}}
+
+""");
+        }
+
+        if (!methodToGenerate.InnerUsings.IsEmpty)
+        {
+            _ = sbBegin.Append("""
+
+
+""");
+        }
+
         // Handle classes
         foreach (var parent in methodToGenerate.Parents)
         {
@@ -136,11 +154,30 @@ internal static string GenerateExtensionClass(MethodToGenerate methodToGenerate)
             ++i;
         }
 
+        var sbOuterUsings = new StringBuilder();
+        foreach (var @using in methodToGenerate.OuterUsings)
+        {
+            if (sbOuterUsings.Length == 0)
+            {
+                // Separates the directives from the header above them.
+                _ = sbOuterUsings.Append("""
+
+
+
+""");
+            }
+
+            _ = sbOuterUsings.Append($$"""
+{{@using}}
+
+""");
+        }
+
         var beforeNamespace = $"""
 // <auto-generated/>{(methodToGenerate.DisableNullable ? string.Empty : """
 
 #nullable enable
-""")}
+""")}{sbOuterUsings}
 """;
 
         return methodToGenerate.IsNamespaceFileScoped ? $$"""

src/Zomp.SyncMethodGenerator/SyncMethodSourceGenerator.cs

@@ -372,6 +372,15 @@ private static string Hash(string value)
         var isNamespaceFileScoped = false;
         var namespaces = ImmutableArray.CreateBuilder<string>();
 
+        // Documentation comments are copied across verbatim, and a cref in one is resolved
+        // against the file it lands in rather than the file it was written in. Without the
+        // using directives which were in scope where it was written, every cref which relied on
+        // one goes unresolved, which a project building with warnings as errors reads as a
+        // build failure. The directives are kept on the side of the namespace they were
+        // declared on, since one declared inside a namespace may name it only relatively.
+        var outerUsings = ImmutableArray.CreateBuilder<string>();
+        var innerUsings = ImmutableArray.CreateBuilder<string>();
+
         if (!hasErrors)
         {
             while (node is not null and not CompilationUnitSyntax)
@@ -380,9 +389,11 @@ private static string Hash(string value)
                 {
                     case NamespaceDeclarationSyntax nds:
                         namespaces.Insert(0, nds.Name.ToString());
+                        InsertUsings(innerUsings, nds.Usings);
                         break;
                     case FileScopedNamespaceDeclarationSyntax file:
                         namespaces.Add(file.Name.ToString());
+                        InsertUsings(innerUsings, file.Usings);
                         isNamespaceFileScoped = true;
                         break;
                     default:
@@ -391,6 +402,11 @@ private static string Hash(string value)
 
                 node = node.Parent;
             }
+
+            if (node is CompilationUnitSyntax compilationUnit)
+            {
+                InsertUsings(outerUsings, compilationUnit.Usings);
+            }
         }
 
 #if ROSLYN_5_0_OR_GREATER
@@ -400,11 +416,26 @@ private static string Hash(string value)
 #endif
         var signature = BuildSignature(sn, namespaces, classes, methodDeclarationSyntax);
 
-        var result = new MethodToGenerate(index, namespaces.ToImmutable(), isNamespaceFileScoped, isCSharp14Extension, classes.ToImmutable(), methodDeclarationSyntax.Identifier.ValueText, content, disableNullable, rewriter.Diagnostics, hasErrors, signature);
+        var result = new MethodToGenerate(index, namespaces.ToImmutable(), outerUsings.ToImmutable(), innerUsings.ToImmutable(), isNamespaceFileScoped, isCSharp14Extension, classes.ToImmutable(), methodDeclarationSyntax.Identifier.ValueText, content, disableNullable, rewriter.Diagnostics, hasErrors, signature);
 
         return result;
     }
 
+    /// <summary>
+    /// Records the directives, innermost first, so that walking outwards from the method builds
+    /// them up in the order they were written.
+    /// </summary>
+    /// <param name="destination">Collected directives.</param>
+    /// <param name="usings">Directives declared at one level.</param>
+    private static void InsertUsings(ImmutableArray<string>.Builder destination, SyntaxList<UsingDirectiveSyntax> usings)
+    {
+        var index = 0;
+        foreach (var @using in usings)
+        {
+            destination.Insert(index++, @using.ToString());
+        }
+    }
+
     /// <summary>
     /// Describes the method which is about to be emitted, precisely enough to tell whether two
     /// of them would declare the same member. The rewritten declaration is used rather than the

tests/Generator.Tests/Snapshots/ExtensionMethodTests.CSharp_14_ExtensionCallingAnotherExtension#Callers.StreamCallers.ext.CopyAndDrainAsync.g.verified.cs

@@ -3,6 +3,8 @@
 #nullable enable
 namespace Callers
 {
+    using Helpers;
+
     public static partial class StreamCallers
     {
         extension(global::System.IO.Stream stream)

tests/Generator.Tests/Snapshots/ExtensionMethodTests.CSharp_14_ExtensionUnwrapsOntoOneLine#Callers.StreamCallers.ext.DrainTwiceAsync.g.verified.cs

@@ -3,6 +3,8 @@
 #nullable enable
 namespace Callers
 {
+    using Helpers;
+
     public static partial class StreamCallers
     {
         extension(global::System.IO.Stream stream)

tests/Generator.Tests/Snapshots/ExtensionMethodTests.EntityFrameworkQueryableExtensions#Zomp.SyncMethodGenerator.IntegrationTests.EntityFrameworkQuery_0f26cde8.QueryableExtensionAsync.g.verified.cs

@@ -1,8 +1,14 @@
 //HintName: Zomp.SyncMethodGenerator.IntegrationTests.EntityFrameworkQuery_0f26cde8.QueryableExtensionAsync.g.cs
 // <auto-generated/>
 #nullable enable
+
+using System.Threading;
+using System.Threading.Tasks;
+
 namespace Zomp.SyncMethodGenerator.IntegrationTests
 {
+    using Microsoft.EntityFrameworkCore;
+
     public partial class EntityFrameworkQueryableExtensions
     {
         public int QueryableExtension(global::Microsoft.EntityFrameworkCore.DbContext dbContext)

tests/Generator.Tests/Snapshots/ExtensionMethodTests.UnwrapGenericExtensionMethod#Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGeneric2ExtensionAsync.g.verified.cs

@@ -1,13 +1,20 @@
-//HintName: Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGeneric2ExtensionAsync.g.cs
-// <auto-generated/>
-#nullable enable
-namespace Zomp.SyncMethodGenerator.IntegrationTests
-{
-    partial class Extensions
-    {
-        public static void HasGeneric2Extension(object o)
-        {
-            var z = global::Extensi.ons123.MyExtensionClass.TryGetValue<global::System.Drawing.Point, global::System.Drawing.PointF>(o, out var _, out var _1);
-        }
-    }
-}
+//HintName: Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGeneric2ExtensionAsync.g.cs
+// <auto-generated/>
+#nullable enable
+
+using System.Drawing;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Zomp.SyncMethodGenerator.IntegrationTests
+{
+    using Extensi.ons123;
+
+    partial class Extensions
+    {
+        public static void HasGeneric2Extension(object o)
+        {
+            var z = global::Extensi.ons123.MyExtensionClass.TryGetValue<global::System.Drawing.Point, global::System.Drawing.PointF>(o, out var _, out var _1);
+        }
+    }
+}

tests/Generator.Tests/Snapshots/ExtensionMethodTests.UnwrapGenericExtensionMethod#Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGenericExtensionAsync.g.verified.cs

@@ -1,13 +1,20 @@
-//HintName: Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGenericExtensionAsync.g.cs
-// <auto-generated/>
-#nullable enable
-namespace Zomp.SyncMethodGenerator.IntegrationTests
-{
-    partial class Extensions
-    {
-        public static void HasGenericExtension(object o)
-        {
-            var z = global::Extensi.ons123.MyExtensionClass.TryGetValue<global::System.Drawing.Point>(o, out var item);
-        }
-    }
-}
+//HintName: Zomp.SyncMethodGenerator.IntegrationTests.Extensions.HasGenericExtensionAsync.g.cs
+// <auto-generated/>
+#nullable enable
+
+using System.Drawing;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Zomp.SyncMethodGenerator.IntegrationTests
+{
+    using Extensi.ons123;
+
+    partial class Extensions
+    {
+        public static void HasGenericExtension(object o)
+        {
+            var z = global::Extensi.ons123.MyExtensionClass.TryGetValue<global::System.Drawing.Point>(o, out var item);
+        }
+    }
+}

tests/Generator.Tests/Snapshots/MemoryTests.NonPredefinedTypes#N1.Class.FillAsync.g.verified.cs

@@ -1,14 +1,18 @@
-//HintName: N1.Class.FillAsync.g.cs
-// <auto-generated/>
-#nullable enable
-namespace N1
-{
-    partial class Class
-    {
-        void Fill(global::System.Span<global::N2.C1.C2.Accelerometer> accelerometers)
-        {
-            global::N2.C1.C2.Accelerometer a = new(1, 2, 3);
-            accelerometers[0] = a;
-        }
-    }
-}
+//HintName: N1.Class.FillAsync.g.cs
+// <auto-generated/>
+#nullable enable
+
+using N2;
+using static N2.C1;
+
+namespace N1
+{
+    partial class Class
+    {
+        void Fill(global::System.Span<global::N2.C1.C2.Accelerometer> accelerometers)
+        {
+            global::N2.C1.C2.Accelerometer a = new(1, 2, 3);
+            accelerometers[0] = a;
+        }
+    }
+}

tests/Generator.Tests/Snapshots/SystemAsyncExtensionsTests.ConfiguredCancelableAsyncEnumerableExtensionUsingStatic#Test.Extensions.GetConfiguredAsyncEnumerator.g.verified.cs

@@ -1,11 +1,14 @@
-//HintName: Test.Extensions.GetConfiguredAsyncEnumerator.g.cs
-// <auto-generated/>
-#nullable enable
-namespace Test;
-internal static partial class Extensions
-{
-    public static System.Collections.Generic.IEnumerator<int> GetConfiguredEnumerator(global::System.Collections.Generic.IEnumerable<int> enumerable)
-    {
-        return enumerable.GetEnumerator();
-    }
-}
+//HintName: Test.Extensions.GetConfiguredAsyncEnumerator.g.cs
+// <auto-generated/>
+#nullable enable
+
+using static System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable<int>;
+
+namespace Test;
+internal static partial class Extensions
+{
+    public static System.Collections.Generic.IEnumerator<int> GetConfiguredEnumerator(global::System.Collections.Generic.IEnumerable<int> enumerable)
+    {
+        return enumerable.GetEnumerator();
+    }
+}

tests/Generator.Tests/Snapshots/TypeTests.EnumPattern#g.verified.cs

@@ -1,2 +1,14 @@
 //HintName: Test.Class.MethodAsync.g.cs
-_ = global::System.Data.ConnectionState.Closed is global::System.Data.ConnectionState.Closed;
+// <auto-generated/>
+#nullable enable
+
+using static System.Data.ConnectionState;
+
+namespace Test;
+partial class Class
+{
+    public void Method()
+    {
+        _ = global::System.Data.ConnectionState.Closed is global::System.Data.ConnectionState.Closed;
+    }
+}

tests/Generator.Tests/Snapshots/UnitTests.DropReturnsDocumentationWhenNothingIsReturned#CountAsync.g.verified.cs

@@ -0,0 +1,11 @@
+//HintName: Test.Class.CountAsync.g.cs
+/// <summary>
+/// Counts the values.
+/// </summary>
+/// <param name="input">Where to read from.</param>
+/// <returns>A <see cref="Task"/> whose result is the number of values.</returns>
+public int Count(global::System.IO.Stream input)
+{
+    input.Flush();
+    return 0;
+}

tests/Generator.Tests/Snapshots/UnitTests.DropReturnsDocumentationWhenNothingIsReturned#ReadAsync.g.verified.cs

@@ -0,0 +1,7 @@
+//HintName: Test.Class.ReadAsync.g.cs
+/// <summary>
+/// Reads a value.
+/// </summary>
+/// <param name="input">Where to read from.</param>
+public void Read(global::System.IO.Stream input)
+    => input.Flush();

tests/Generator.Tests/Snapshots/UnitTests.GenericTypeInDeclarationPattern#M.B.DoSomethingAsync.g.verified.cs

@@ -3,6 +3,8 @@
 #nullable enable
 namespace M
 {
+    using N;
+
     public partial class B
     {
         public void DoSomething(object arg)

tests/Generator.Tests/Snapshots/UnitTests.GenericTypeInTypeOfExpression#M.B.DoSomethingAsync.g.verified.cs

@@ -3,6 +3,8 @@
 #nullable enable
 namespace M
 {
+    using N;
+
     public partial class B
     {
         public void DoSomething()