Disallow attributes on type extensions (#7481)

* add test for feature

* add error logic to typechecker

* update strings

* address comments

* update tests

Author: nelson-wu

src/fsharp/FSComp.txt

@@ -1461,6 +1461,7 @@ notAFunctionButMaybeDeclaration,"This value is not a function and cannot be appl
 3243,parsInvalidAnonRecdExpr,"Invalid anonymous record expression"
 3244,parsInvalidAnonRecdType,"Invalid anonymous record type"
 3245,tcCopyAndUpdateNeedsRecordType,"The input to a copy-and-update expression that creates an anonymous record must be either an anonymous record or a record"
+3246,tcAugmentationsCannotHaveAttributes,"Attributes cannot be applied to type extensions."
 3300,chkInvalidFunctionParameterType,"The parameter '%s' has an invalid type '%s'. This is not permitted by the rules of Common IL."
 3301,chkInvalidFunctionReturnType,"The function or method has an invalid return type '%s'. This is not permitted by the rules of Common IL."
 useSdkRefs,"Use reference assemblies for .NET framework references when available (Enabled by default)."

src/fsharp/TypeChecker.fs

@@ -16429,6 +16429,11 @@ module TcDeclarations =
                 if not (isNil members) && tcref.IsTypeAbbrev then 
                     errorR(Error(FSComp.SR.tcTypeAbbreviationsCannotHaveAugmentations(), tyDeclRange))
 
+                let (ComponentInfo (attributes, _, _, _, _, _, _, _)) = synTyconInfo
+                if not (List.isEmpty attributes) && (declKind = ExtrinsicExtensionBinding || declKind = IntrinsicExtensionBinding) then
+                    let attributeRange = (List.head attributes).Range
+                    error(Error(FSComp.SR.tcAugmentationsCannotHaveAttributes(), attributeRange))
+
                 MutRecDefnsPhase2DataForTycon(tyconOpt, innerParent, declKind, tcref, baseValOpt, safeInitInfo, declaredTyconTypars, members, tyDeclRange, newslotsOK, fixupFinalAttrs))
 
         // By now we've established the full contents of type definitions apart from their