Depickling assertion followed by nullref internal errors in units-of-measure case

[latkin]

Came across this while poking around this SO question. Have reduced code to more minimal example.

Use the F# 3.1 compiler to create a library from the following:

// test.fs
namespace Test

type Vector2<[<Measure>]'T> =
    { X : float<'T>
      Y : float<'T> }

    static member (*) (v:Vector2<'a>, f:float<'b>) : Vector2<'a * 'b> =
        { X = v.X * f; Y = v.Y * f }

Then try to consume the Vector2 type from a console app like so, with F# 4.0 compiler:

// program.fs
open Test
open Microsoft.FSharp.Data.UnitSystems.SI.UnitSymbols

{ X = 1.<m>; Y = 1.<m>} |> printfn "%A"

> [3.1] fsc.exe -a test.fs
> [4.0] fsc.exe -r:test.dll program.fs

Assuming debug build of 4.0 compiler you will get the following assert then a series of nullrefs (below).

• Using 3.1 compiler for both steps results in same errors
• Using 4.0 compiler for both steps results in successful compile

So it seems like this was a bad pickling behavior in 3.1 that is now corrected, but when consuming bad format we are not handling it gracefully.

---------------------------
Assertion Failed: Abort=Quit, Retry=Debug, Ignore=Continue
---------------------------
*** unpickle: osgn 10 in table itypars with IL scope test, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null had no matching declaration (was not fixed up)
Please report this warning. (Note for compiler developers: to get information about which item this index relates to, enable the conditional in Pickle.p_osgn_ref to refer to the given index number and recompile an identical copy of the source for the DLL containing the data being unpickled.  A message will then be printed indicating the name of the item.
   at Microsoft.FSharp.Compiler.Pickle.check[a,b](ILScopeRef ilscope, NodeInTable`2 inMap)
   at Microsoft.FSharp.Compiler.Pickle.unpickleObjWithDanglingCcus[T](String file, ILScopeRef viewedScope, ILModuleDef ilModule, FSharpFunc`2 u, Byte[] phase2bytes)
   at Microsoft.FSharp.Compiler.Build.GetSignatureData(String file, ILScopeRef ilScopeRef, ILModuleDef ilModule, FSharpFunc`2 byteReader)
   at Microsoft.FSharp.Compiler.Build.ccuRawDataAndInfos@4013.Invoke(Tuple`2 tupledArg)
   at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x)
   at Microsoft.FSharp.Collections.ListModule.Map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 list)
   at Microsoft.FSharp.Compiler.Build.TcImports.PrepareToImportReferencedFSharpDll(FSharpList`1 tpApprovals, range m, String filename, FSharpOption`1 displayPSTypeProviderSecurityDialogBlockingUI, ImportedBinary dllinfo)
   <snip>

-------

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.FSharp.Compiler.Tast.Typar.get_Solution()
   at Microsoft.FSharp.Compiler.Tast.Typar.get_IsSolved()
   at Microsoft.FSharp.Compiler.Tast.stripUnitEqnsAux(Boolean canShortcut, MeasureExpr unt)
   at Microsoft.FSharp.Compiler.Tastops.stripUnitEqnsFromMeasureAux(Boolean canShortcut, MeasureExpr unt)
   at Microsoft.FSharp.Compiler.Tastops.stripUnitEqnsFromMeasure(MeasureExpr m)
   at Microsoft.FSharp.Compiler.Tastops.gather@434-2.Invoke(FSharpList`1 acc, MeasureExpr unt)
   at Microsoft.FSharp.Compiler.Tastops.gather@434-2.Invoke(FSharpList`1 acc, MeasureExpr unt)
   at Microsoft.FSharp.Compiler.Tastops.gather@434-2.Invoke(FSharpList`1 acc, MeasureExpr unt)
   at Microsoft.FSharp.Compiler.Tastops.isDimensionless(TcGlobals g, TType tyarg)
   at Microsoft.FSharp.Primitives.Basics.List.forall[T](FSharpFunc`2 predicate, FSharpList`1 xs1)
   at Microsoft.FSharp.Collections.ListModule.ForAll[T](FSharpFunc`2 predicate, FSharpList`1 list)
   at Microsoft.FSharp.Compiler.Tastops.stripTyEqnsA(TcGlobals g, Boolean canShortcut, TType ty)
   at Microsoft.FSharp.Compiler.Tastops.stripTyEqns(TcGlobals g, TType ty)
   at Microsoft.FSharp.Compiler.Tastops.stripTyEqnsAndErase(Boolean eraseFuncAndTuple, TcGlobals g, TType ty)
   at Microsoft.FSharp.Compiler.Tastops.stripTyEqnsWrtErasure(Erasure erasureFlag, TcGlobals g, TType ty)
   at Microsoft.FSharp.Compiler.Tastops.typeAEquivAux(Erasure erasureFlag, TcGlobals g, TypeEquivEnv aenv, TType ty1, TType ty2)
   at Microsoft.FSharp.Collections.ListModule.forall2aux[a,b](FSharpFunc`3 f, FSharpList`1 list1, FSharpList`1 list2)
   at Microsoft.FSharp.Collections.ListModule.ForAll2[T1,T2](FSharpFunc`2 predicate, FSharpList`1 list1, FSharpList`1 list2)
   at Microsoft.FSharp.Collections.ListModule.forall2aux[a,b](FSharpFunc`3 f, FSharpList`1 list1, FSharpList`1 list2)
   at Microsoft.FSharp.Collections.ListModule.ForAll2[T1,T2](FSharpFunc`2 predicate, FSharpList`1 list1, FSharpList`1 list2)
   at Microsoft.FSharp.Collections.ListModule.TryFind[T](FSharpFunc`2 predicate, FSharpList`1 list)
   at Microsoft.FSharp.Compiler.Tast.ValRef.get_Deref()
   at Microsoft.FSharp.Compiler.Tast.ValRef.get_IsIncrClassConstructor()
   at Microsoft.FSharp.Compiler.TypeChecker.TcRecordConstruction@5830.Invoke(ValRef v)
   <snip>

[dsyme]

I'm not entirely sure there's going to be a nice fix for this, do you think it's a must fix for F# 4.0?

[latkin]

Can we at least issue a proper error instead of nullrefing? "Corrupt F# metadata encountered" or something like that?

[dsyme]

Yes, to do that take the this code out of #if DEBUG and surface the error as a reported exception. I don't think there is any file location with which to associate the error though, so it won't be seen in the IDE, and you'll have to use Range.range0 I think