The first array type in a generic method doesn't work

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Steps to reproduce

When I try to flatten a two-dimensional array by Enumerable.SelectMany method with generic type arguments, the first type argument int[] may not be treated correctly.

[Linq.Enumerable]::SelectMany[int[], int](
  [int[][]] @((,2), (,4), (,6), (,8)),
  [Func[[int[]], int[]]] { param ($x); $x }
) | ConvertTo-Json -Compress

Expected behavior

[2,4,6,8]

Actual behavior

Unable to find type [int,int].

Error details

Exception             :
    Type        : System.Management.Automation.RuntimeException
    ErrorRecord :
        Exception             :
            Type    : System.Management.Automation.ParentContainsErrorRecordException
            Message : Unable to find type [int,int].
            HResult : -2146233087
        TargetObject          : int,int
        CategoryInfo          : InvalidOperation: (int,int:TypeName) [], ParentContainsErrorRecordException
        FullyQualifiedErrorId : TypeNotFound
        InvocationInfo        :
            ScriptLineNumber : 2
            OffsetInLine     : 31
            HistoryId        : -1
            Line             : [Linq.Enumerable]::SelectMany[int[], int](

            PositionMessage  : At line:2 char:31
                               + [Linq.Enumerable]::SelectMany[int[], int](
                               +                               ~~~~~
            CommandOrigin    : Internal
        ScriptStackTrace      : at <ScriptBlock>, <No file>: line 2
    TargetSite  :
        Name          : ResolveTypeName
        DeclaringType : System.Management.Automation.TypeOps, System.Management.Automation, Version=7.3.0.500, Culture=
neutral, PublicKeyToken=31bf3856ad364e35
        MemberType    : Method
        Module        : System.Management.Automation.dll
    Message     : Unable to find type [int,int].
    Data        : System.Collections.ListDictionaryInternal
    Source      : System.Management.Automation
    HResult     : -2146233087
    StackTrace  :
   at System.Management.Automation.TypeOps.ResolveTypeName(ITypeName typeName, IScriptExtent errorPos)
   at System.Management.Automation.TypeOps.ResolveTypeName(ITypeName typeName, IScriptExtent errorPos)
   at System.Management.Automation.Adapter.ResolveGenericTypeParameters(Object[] genericTypeParameters)
   at System.Management.Automation.Adapter.FindBestMethodImpl(MethodInformation[] methods, PSMethodInvocationConstraint
s invocationConstraints, Boolean allowCastingToByRefLikeType, Object[] arguments, String& errorId, String& errorMsg, Bo
olean& expandParamsOnBest)
   at System.Management.Automation.Adapter.FindBestMethod(MethodInformation[] methods, PSMethodInvocationConstraints in
vocationConstraints, Boolean allowCastingToByRefLikeType, Object[] arguments, String& errorId, String& errorMsg, Boolea
n& expandParamsOnBest, Boolean& callNonVirtually)
   at System.Management.Automation.Language.PSInvokeMemberBinder.InvokeDotNetMethod(CallInfo callInfo, String name, PSM
ethodInvocationConstraints psMethodInvocationConstraints, MethodInvocationType methodInvocationType, DynamicMetaObject
target, DynamicMetaObject[] args, BindingRestrictions restrictions, MethodInformation[] mi, Type errorExceptionType)
   at System.Management.Automation.Language.PSInvokeMemberBinder.FallbackInvokeMember(DynamicMetaObject target, Dynamic
MetaObject[] args, DynamicMetaObject errorSuggestion)
   at System.Dynamic.DynamicMetaObjectBinder.Bind(Object[] args, ReadOnlyCollection`1 parameters, LabelTarget returnLab
el)
   at System.Runtime.CompilerServices.CallSiteBinder.BindCore[T](CallSite`1 site, Object[] args)
   at System.Dynamic.UpdateDelegates.UpdateAndExecute3[T0,T1,T2,TRet](CallSite site, T0 arg0, T1 arg1, T2 arg2)
   at System.Management.Automation.Interpreter.DynamicInstruction`4.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
TargetObject          : int,int
CategoryInfo          : InvalidOperation: (int,int:TypeName) [], RuntimeException
FullyQualifiedErrorId : TypeNotFound
InvocationInfo        :
    ScriptLineNumber : 2
    OffsetInLine     : 31
    HistoryId        : -1
    Line             : [Linq.Enumerable]::SelectMany[int[], int](

    PositionMessage  : At line:2 char:31
                       + [Linq.Enumerable]::SelectMany[int[], int](
                       +                               ~~~~~
    CommandOrigin    : Internal
ScriptStackTrace      : at <ScriptBlock>, <No file>: line 2

Environment data

Name                           Value
----                           -----
PSVersion                      7.3.0
PSEdition                      Core
GitCommitId                    7.3.0
OS                             Microsoft Windows 10.0.22621
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[CarloToso]

It should work like this:

[Linq.Enumerable]::SelectMany(
  [int[][]] @((,2), (,4), (,6), (,8)),
  [Func[[int[]], int[]]] { param ($x); $x }
) | ConvertTo-Json -Compress

Great reference for Linq in Powershell:
https://www.red-gate.com/simple-talk/sysadmin/powershell/high-performance-powershell-linq/

[mklement0]

It looks like the list of the generic-method type arguments isn't recognized as such and instead (mis)interpreted as a type literal, and the problem seemingly only occurs when the first type in such a list is an array type ([]) (as you state).

A simpler repro (note that the call doesn't make sense, but the error message reveals wether type arguments where formally parsed as such):

# !! -> "InvalidOperation: Unable to find type [int,int]."
[char]::ToUpper[int[], int]()
# !!  Using the list as a (broken) type literal yields the same error.
[int[], int]

# (Formally) OK; -> "Could not find a suitable generic method overload for ..."
[char]::ToUpper[int, int[]]()

[SeeminglyScience]

I believe this is an existing problem with generic types that has just been made more common. I don't think I ever filed an issue, but I've hit this quite a few times with delegate types:

# Also throws
[Func[int[], int]]

Fortunately the work around is really easy for generic types, just surround the inner type in more square brackets:

[Func[[int[]], int]]

Unfortunately, this doesn't work with generic method args:

# Throws differently because we don't seem to be checking for brackets around generic args
[Linq.Enumerable]::SelectMany[[int[]], int](
  [int[][]] @((,2), (,4), (,6), (,8)),
  [Func[[int[]], int[]]] { param ($x); $x }
) | ConvertTo-Json -Compress

[SeeminglyScience]

/cc @daxian-dbw @vexx32 FYI

[vexx32]

The latter you mention (double-bracketing) I think was at least semi-intentional, since $a.[[int[]]] is potentially valid array-access syntax (passing a type token as an array lookup). In fact I think @daxian-dbw did a patch after the initial PR to ensure weird stuff like that worked.

The initial issue here seems to be... hm. Not a parsing error directly perhaps, but definitely something strange.

This code path parser-wise at least is very messy due to the overloaded meaning for [] being used for both type tokens and for array indexing. Not simple to tease out :/

[MartinGC94]

I believe this is an existing problem with generic types that has just been made more common. I don't think I ever filed an issue, but I've hit this quite a few times with delegate types:

Rob has reported it here: #9639

[SeeminglyScience]

I even already gave it a thumb! Good catch, thanks @MartinGC94!

[ghost]

🎉This issue was addressed in #19205, which has now been successfully released as v7.4.0-preview.4.:tada:

Handy links:

• Release Notes