Expressions can be typed as open generic types

[JonHanna]

The likes of Expression.Default(typeof(List<>)), Expression.Constant(null, typeof(Dictionary<,>)) and some other expressions (though often other rules will get in the way) are allowed.

Since these represent a value of an open generic type, they aren't really meaningful.

They can have a value of null which can be used as long as it is converted to object and both compilation types accept Expression.Lambda<Func‎<object>>(Expression.Default(typeof(List<>))) as an expression that can be compiled into a delegate that returns null.

While they can be pressed into service, it seems more appropriate to prohibit them.

Factory methods that have at least one overload that takes Type arguments directly. Will check these off when they're either found to already prohibit such types, or fixed to do so (PRs just adding tests of already-correct behaviour marked immediately, PRs fixing behaviour upon acceptance):

• Block (entailed in check that type is reference-assignable from type of last child expression).
• Break
• Call Test confirming Expression.Call fails with open generic type. corefx#17333
• Catch
• Condition
• Constant
• Continue
• Convert
• ConvertChecked
• Default
• Dynamic (Entailed in check that arguments match delegate method).
• Field Prohibit open generics in Expression.Property and Expression.Field corefx#16231
• GetActionType (Exception: Has practical use here)
• GetDelegateType (Exception: Has practical use here)
• GetFuncType (Exception: Has practical use here)
• Goto
• Label Throw on byref or pointer types in LabelTarget corefx#16140
• Lambda Prohibit open generic delegate types for LambdaExpression corefx#16233
• MakeCatchBlock
• MakeDynamic (Entailed in check that arguments match delegate method).
• MakeGoto
• MakeTry (entailed by check that type is void or that body and catch types are reference-assignable)
• MakeUnary Waiting on Throw on byref or pointer types in linq Throw expressions. corefx#16141
• New
• NewArrayBounds
• NewArrayInit
• Parameter (byref types allowed)
• Property Prohibit open generics in Expression.Property and Expression.Field corefx#16231
• Rethrow Throw on byref or pointer types in linq Throw expressions. corefx#16141
• Return
• Switch (Entailed by check that type is void or default and case types are reference-assignable)
• Throw Throw on byref or pointer types in linq Throw expressions. corefx#16141
• TryGetActionType (Exception: Has practical use here)
• TryGetFuncType (Exception: Has practical use here)
• TypeAs
• TypeEqual Test and optimise TypeEqual and TypeIs behaviour for pointer types. corefx#16150 (pointer types allowed; always results in false)
• TypeIs Test and optimise TypeEqual and TypeIs behaviour for pointer types. corefx#16150 (pointer types allowed; always results in false)
• Unbox Test byref, pointer & generic types can't be used with Expression.Unbox corefx#16186
• Variable

Also the following have overrides that take MemberInfo, which could be generic and/or be related to an open generic type. Most will block this with restrictions they place on those MemberInfo arguments relating to other types, but they need to be checked.

• Add Add test of binary expression validation against generic methods. corefx#16142
• AddAsign Add test of binary expression validation against generic methods. corefx#16142
• AddAsignChecked Add test of binary expression validation against generic methods. corefx#16142
• AddChecked Add test of binary expression validation against generic methods. corefx#16142
• And Add test of binary expression validation against generic methods. corefx#16142
• AndAlso Add test of binary expression validation against generic methods. corefx#16142
• AndAssign Add test of binary expression validation against generic methods. corefx#16142
• Bind Prohibit Expression.Bind with members of open generic types. corefx#18610
• Call
• Convert Add test of unary expression validation against generic methods. corefx#16437
• ConvertChecked Add test of unary expression validation against generic methods. corefx#16437
• Decrement Add test of unary expression validation against generic methods. corefx#16437
• Divide Add test of binary expression validation against generic methods. corefx#16142
• DivideAssign Add test of binary expression validation against generic methods. corefx#16142
• ElementInit
• Equal Add test of binary expression validation against generic methods. corefx#16142
• ExclusiveOr Add test of binary expression validation against generic methods. corefx#16142
• ExclusiveOrAssign Add test of binary expression validation against generic methods. corefx#16142
• Field Prohibit open generics in Expression.Property and Expression.Field corefx#16231
• GreaterThan Add test of binary expression validation against generic methods. corefx#16142
• GreaterThanOrEqual Add test of binary expression validation against generic methods. corefx#16142
• Increment Add test of unary expression validation against generic methods. corefx#16437
• IsFalse Add test of unary expression validation against generic methods. corefx#16437
• IsTrue Add test of unary expression validation against generic methods. corefx#16437
• LeftShift Add test of binary expression validation against generic methods. corefx#16142
• LeftShiftAssign Add test of binary expression validation against generic methods. corefx#16142
• LessThan Add test of binary expression validation against generic methods. corefx#16142
• LessThanOrEqual Add test of binary expression validation against generic methods. corefx#16142
• ListBind Prohibit Expression.ListBind with members of open generic types. corefx#18011
• ListInit Add tests of ListInit validation against generic methods. corefx#16624
• MakeBinary Add test of binary expression validation against generic methods. corefx#16142
• MakeIndex
• MakeMemberAccess
• MakeUnary Add test of unary expression validation against generic methods. corefx#16437
• MemberBind (Covered by validation added in Prohibit Expression.ListBind with members of open generic types. corefx#18011 but also entailed by need of type to match).
• Modulo Add test of binary expression validation against generic methods. corefx#16142
• ModuloAssign Add test of binary expression validation against generic methods. corefx#16142
• Multiply Add test of binary expression validation against generic methods. corefx#16142
• MultiplyAssign Add test of binary expression validation against generic methods. corefx#16142
• MultiplyAssignChecked Add test of binary expression validation against generic methods. corefx#16142
• MultiplyChecked Add test of binary expression validation against generic methods. corefx#16142
• Negate Add test of unary expression validation against generic methods. corefx#16437
• NegateChecked Add test of unary expression validation against generic methods. corefx#16437
• New
• Not Add test of unary expression validation against generic methods. corefx#16437
• NotEqual Add test of binary expression validation against generic methods. corefx#16142
• OnesComplement Add test of unary expression validation against generic methods. corefx#16437
• Or Add test of binary expression validation against generic methods. corefx#16142
• OrAssign Add test of binary expression validation against generic methods. corefx#16142
• OrElse Add test of binary expression validation against generic methods. corefx#16142
• PostDecrementAssign Add test of unary expression validation against generic methods. corefx#16437
• PostIncrementAssign Add test of unary expression validation against generic methods. corefx#16437
• Power Add test of binary expression validation against generic methods. corefx#16142
• PowerAssign Add test of binary expression validation against generic methods. corefx#16142
• PreDecrementAssign Add test of unary expression validation against generic methods. corefx#16437
• PreIncrementAssign Add test of unary expression validation against generic methods. corefx#16437
• Property Prohibit open generics in Expression.Property and Expression.Field corefx#16231
• RightShift Add test of binary expression validation against generic methods. corefx#16142
• RightShiftAssign Add test of binary expression validation against generic methods. corefx#16142
• Subtract Add test of binary expression validation against generic methods. corefx#16142
• SubtractAssign Add test of binary expression validation against generic methods. corefx#16142
• SubtractAssignChecked Add test of binary expression validation against generic methods. corefx#16142
• SubtractChecked Add test of binary expression validation against generic methods. corefx#16142
• Switch Prohibit open generic comparison methods in SwitchExpression corefx#16344
• UnaryPlus Add test of unary expression validation against generic methods. corefx#16437

[JonHanna]

Several of them can also be typed as byref and/or pointer types.

[hughbe]

Should the following be prohibited or allowed (they are currently allowed):

Expression.Variable(typeof(GenericClass<>);
Expression.Parameter(typeof(GenericClass<>);

I'm fairly sure the Variable one is a bug (the C# compiler doesn't allow it), but I'm uncertain about Parameter.

[svick]

@hughbe Since Variable() and Parameter() are almost interchangeable, I think they should behave the same here.

And as far as open generic types go, I don't see any reason to allow them.

[hughbe]

@svick perf, I'll make a PR once dotnet/corefx#11701 is merged

[JonHanna]

I've just found that TypeAs can be typed as pointer and ref types, so there's at least one case that is still affected by this.

[hughbe]

Oh whoops I'm not sure I meant to close this issue. Feel free to reopen if u want

[JonHanna]

I can't due to isaacs/github#583

[JonHanna]

I had been working systematically on this, before I wasn't able to contribute much for a while last summer. Need to track what, if anything remains in this, issue. Shall update the opening comment with a task list.

[JonHanna]

Marking MakeIndex and MakeMemberAccess as okay as they make quite simple calls into methods already covered.