Stand in CancellationToken.None for a removed token

src/Zomp.SyncMethodGenerator/AsyncToSyncRewriter.cs

@@ -284,9 +284,24 @@ _ when GetReplacement(symbol) is { } name => @base.WithIdentifier(Identifier(Glo
 
     /// <inheritdoc/>
     public override SyntaxNode? VisitIdentifierName(IdentifierNameSyntax node)
-        => renamedLocalFunctions.TryGetValue(node.Identifier.ValueText, out var newName)
-            ? node.WithIdentifier(Identifier(newName))
-            : base.VisitIdentifierName(node);
+    {
+        if (renamedLocalFunctions.TryGetValue(node.Identifier.ValueText, out var newName))
+        {
+            return node.WithIdentifier(Identifier(newName));
+        }
+
+        // A statement or an argument which mentions a removed CancellationToken is dropped whole,
+        // but an expression such as a catch filter has to keep its shape. CancellationToken.None
+        // stands in for the parameter: it is never cancelled, which is what the synchronized
+        // method does.
+        if (GetSymbol(node) is IParameterSymbol { Type: INamedTypeSymbol { IsCancellationToken: true } } parameter
+            && removedParameters.Contains(parameter))
+        {
+            return IdentifierName(Global("System.Threading.CancellationToken.None")).WithTriviaFrom(node);
+        }
+
+        return base.VisitIdentifierName(node);
+    }
 
     public override SyntaxNode? VisitLocalFunctionStatement(LocalFunctionStatementSyntax node)
     {

tests/Generator.Tests/IsCancellationRequestedTests.cs

@@ -129,4 +129,47 @@ public Task WhileNotCancelledReplacedBySyncOnly() => """
 }
 #endif
 """.Verify(sourceType: SourceType.MethodBody);
+
+    [Fact]
+    public Task CatchFilterChecksCancellation() => """
+try
+{
+    await Task.Delay(1, ct);
+}
+catch (OperationCanceledException) when (ct.IsCancellationRequested)
+{
+    throw;
+}
+catch (Exception)
+{
+}
+""".Verify(sourceType: SourceType.MethodBody);
+
+    [Fact]
+    public Task CatchFilterChecksCancellationAndMore() => """
+try
+{
+    await Task.Delay(1, ct);
+}
+catch (OperationCanceledException) when (ct.IsCancellationRequested || Environment.TickCount > 0)
+{
+    throw;
+}
+""".Verify(sourceType: SourceType.MethodBody);
+
+    [Fact]
+    public Task CatchFilterKeepsPreservedToken() => """
+[CreateSyncVersion(PreserveCancellationToken = true)]
+public async Task MethodAsync(CancellationToken ct)
+{
+    try
+    {
+        await Task.Delay(1, ct);
+    }
+    catch (OperationCanceledException) when (ct.IsCancellationRequested)
+    {
+        throw;
+    }
+}
+""".Verify();
 }

tests/Generator.Tests/Snapshots/IsCancellationRequestedTests.CatchFilterChecksCancellation#g.verified.cs

@@ -0,0 +1,12 @@
+//HintName: Test.Class.MethodAsync.g.cs
+try
+{
+    global::System.Threading.Thread.Sleep(1);
+}
+catch (global::System.OperationCanceledException) when (global::System.Threading.CancellationToken.None.IsCancellationRequested)
+{
+    throw;
+}
+catch (global::System.Exception)
+{
+}

tests/Generator.Tests/Snapshots/IsCancellationRequestedTests.CatchFilterChecksCancellationAndMore#g.verified.cs

@@ -0,0 +1,9 @@
+//HintName: Test.Class.MethodAsync.g.cs
+try
+{
+    global::System.Threading.Thread.Sleep(1);
+}
+catch (global::System.OperationCanceledException) when (global::System.Threading.CancellationToken.None.IsCancellationRequested || global::System.Environment.TickCount > 0)
+{
+    throw;
+}

tests/Generator.Tests/Snapshots/IsCancellationRequestedTests.CatchFilterKeepsPreservedToken#g.verified.cs

@@ -0,0 +1,12 @@
+//HintName: Test.Class.MethodAsync.g.cs
+public void Method(global::System.Threading.CancellationToken ct)
+{
+    try
+    {
+        global::System.Threading.Thread.Sleep(1);
+    }
+    catch (global::System.OperationCanceledException) when (ct.IsCancellationRequested)
+    {
+        throw;
+    }
+}