Unit type return results in InvalidProgramException about foq HOT 3 OPEN

@drivehappy Thank you for your very detailed problem report and steps to reproduce this problem. I took a closer look at the problem myself and was able to isolate it @ptrelford. It is caused by loading a return variable of type void and issuing multiple Ret statements (both problems are directly related). The given code causes the following statements to be emitted (for foo):

...

// Part1
OpCodes.Ldarg_0
OpCodes.Ldfld, returnValuesField
OpCodes.Ldc_I4, returnValuesIndex
OpCodes.Ldelem_Ref
OpCodes.Unbox_Any, returnType
OpCodes.Ret

// Part2
OpCodes.Ret

The first instruction stream (Part1) is generated by iterating over all overloads https://github.com/fsprojects/Foq/blob/master/Foq/Foq.fs#L573. Then, a valid overload is detected to generate code https://github.com/fsprojects/Foq/blob/master/Foq/Foq.fs#L576, which in turn triggers code generation for a ReturnValue(value, returnType) (https://github.com/fsprojects/Foq/blob/master/Foq/Foq.fs#L223). I think this piece of code contains the "actual issue", as it does not differentiate between a void return and the return of a single value. However, I could be wrong, as the surrounding of this code could compensate for this problem in most cases (except this one).

Additionally, we pass the check https://github.com/fsprojects/Foq/blob/master/Foq/Foq.fs#L580 if the function has a unit or void return (which I believe is correct). Depending on how we solve this problem in the first place, this could already avoid issuing duplicate return statements.

I can also prepare a PR if we decide on a possible way to fix this 😃

from foq.

@drivehappy, any thoughts about @m4rs-mt's approach?

from foq.

@m4rs-mt

I can also prepare a PR if we decide on a possible way to fix this 😃

If you have a solution please raise a PR (preferably with a test that asserts it fixes this issue). I'm more than happy to review and merge.

from foq.