Prevent disallowed conversions between object and by-ref-like parameter and return types
#665
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object and by-ref-like parameter and return typesobject and by-ref-like parameter and return types
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I think this is good to go. The AppVeyor test run fails only because of #704, and not because of any of the code changes made here. That can be fixed separately. |
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* Most tests fail with a `InvalidProgramException`: "Cannot create boxed ByRef-like values.". * One test fails with a `InvalidOperationException`: "Interceptors failed to set a return value [...]."
* Wherever we are currently converting a by-ref-like argument or return
value to `object`, we substitute `null` (because boxing is disallowed
for by-ref-like types).
* Wherever we convert from `object`, we substitute the default value
for the by-ref-like type (because unboxing likewise doesn't work).
Such conversions happen in 4 places:
1. at the beginning of the interception pipeline, where the original
typed method call arguments are boxed into an `IInvocation`.
2. when proceeding to a target, where the arguments are unboxed from
the same `IInvocation` to typed method call arguments.
3. when returning from a target, its outputs (by-ref parameters and
the return value) must be boxed back into the `IInvocation`.
4. at the end of the interception pipeline, its outputs (again, by-ref
parameters and the return value) must be unboxed from `IInvocation`.
... which might be a bug in the runtime. We need a workaround for that. See also: dotnet/runtime#91532
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DynamicProxy currently does not support intercepting methods that have any by-ref-like (
ref struct) parameter or return types (such asSpan<T>orReadOnlySpan<T>), because by-ref-like types cannot be converted to or fromobject. DynamicProxy however attempts such conversions when it transfers argument and return values into or out ofIInvocationinstances, thus causingInvalidProgramExceptions and, to a lesser degree,NullReferenceExceptions.This PR targets the code locations (hopefully all of them) where such conversions between
objectand by-ref-like types occur, and suppresses those conversions in favor of writing certain default values:nullwhere assignments are made toIInvocation.ArgumentsorIInvocation.ReturnValuedefaultvalue of the by-ref-like type where assignments are made tooutarguments or when values arereturn-ed to callers.This work should be merged before #664, because the code locations that it touches are the same ones where #664 would introduce (optional) user-defined conversions instead of always writing fixed default values.
This is currently still a draft because two things is still missing:
defaultvalues should be written back torefarguments, i. e. those parameters should be left unmodified. They are already initialized and may contain more meaningful values that should perhaps not be overwritten with adefaultvalue.Type.IsByRefLikestill throwNotSupportedException: "Derived classes must provide an implementation" dotnet/runtime#91532#651 will persist even after this, likely because by-ref-like argument values are still lost (reset) when proceeding to targets.