Lambda with an anonymous parameter type gets mixed parameter typing (CS0748)

[sailro]

Summary

When one lambda parameter has an anonymous type, ILSpy correctly omits that parameter's
unnameable type but leaves sibling parameter types explicit. C# requires lambda parameter
types to be either all explicit or all implicit, so the output fails with CS0748.

Input code

Compiled in Release targeting .NET 10.0:

using System;

public static class C
{
    private static TValue GetOrCreate<TKey, TValue>(
        TKey key,
        Func<TKey, int, TValue> factory) => factory(key, 1);

    public static int Read()
    {
        var key = new { Value = 1 };
        return GetOrCreate(key, (item, context) => item.Value + context);
    }
}

Erroneous output

public static int Read()
{
    return GetOrCreate(new
    {
        Value = 1
    }, (item, int context) => item.Value + context);
}

Recompiling this output fails:

error CS0748: Inconsistent lambda parameter usage; parameter types must be all explicit or all implicit

Expected output

Because the anonymous type cannot be named, every parameter should remain implicit:

(item, context) => item.Value + context

Details

• Product in use: ICSharpCode.Decompiler
• Version in use: master 7554c1b0 (11.0.0.9223)
• The repro was verified in an isolated compile, decompile, recompile round trip.
• ExpressionBuilder.MakeParameters removes the type only from parameters whose type contains an anonymous type, leaving the remaining parameter declarations explicitly typed.
• I am happy to contribute a fix.