Collection of issues with byref analysis

[dsyme]

There are a number of holes in checking the use of byref values. I'm collecting these into one issue since if we fix any one of them we may as well go through and address them all.

Addressed:

• Compiler allows invalid uses of byref in interface methods Compiler allows invalid uses of byref in interface methods #127 (Related to No error on function with a invalid byref type parameter #5459)
• Tupling causes problems in argument poitions The generic type 'System.Tuple`2' was used with an invalid instantiation (likely byref issue) #3362 (Doesn't fail in Release, but dies in Debug)
• Base calls and byrefs: Base calls with byref arguments are not analyzed correctly #130
• Inlined tupled arguments and byrefs: Inlined Tuple'd arguments with byref<> cause Debug builds to crash at runtime #820 and F# System.TypeLoadException : The generic type 'System.Tuple`2' was used with an invalid instantiation in assembly #558
• Struct field returns Bug in byref-return checking: passing local struct address should not be permitted #1401
• Some uses of currying and byrefs: Currying and byref are not friends #819

I'll close the individual bug entries and reactivate if we don't fix them all in one go.

[kbattocchi]

Would it make sense to tackle (parts of) this planned User Voice item at the same time, since it will also affect the safety rules by loosening them in some cases?

[kbattocchi]

Regarding my last comment, byref locals and returns have now been merged into the Roslyn tree - see here.

[cartermp]

@dsyme / @TIHan is it worth going through this list again to see what/if should be improved given the recent work?

[TIHan]

This is worth going through.

[TIHan]

I've updated the checklist.

These still have issues:

• Compiler allows invalid uses of byref in interface methods Compiler allows invalid uses of byref in interface methods #127 (Related to No error on function with a invalid byref type parameter #5459)
• Tupling causes problems in argument poitions The generic type 'System.Tuple`2' was used with an invalid instantiation (likely byref issue) #3362 (Doesn't fail in Release, but dies in Debug)

[TIHan]

The tupling one is a bit more concerning. We need to always error if we can't guarantee the compiler will not make a tuple, which we do in some situations. For example, this will not compile:

type Test() =

    static member Cool(r: inref<int>, x: int) = ()

type Test2() =

    static member Dooby((r: inref<int>, x: int) as y) =
        Test.Cool y

[TIHan]

We have resolved these in 15.9 now.