Better error message when abstract member impl is wrong - fixes dotne…

…t#1203

src/fsharp/FSComp.txt

@@ -21,6 +21,7 @@ commaInsteadOfSemicolonInRecord,"A ';' is used to separate field values in recor
 buildUnexpectedTypeArgs,"The non-generic type '%s' does not expect any type arguments, but here is given %d type argument(s)"
 returnUsedInsteadOfReturnBang,"Consider using 'return!' instead of 'return'."
 yieldUsedInsteadOfYieldBang,"Consider using 'yield!' instead of 'yield'."
+tupleRequiredInAbstractMethod,"\nA tuple type is required for one or more arguments. Consider wrapping the given arguments in additional parentheses or review the definition of the interface."
 203,buildInvalidWarningNumber,"Invalid warning number '%s'"
 204,buildInvalidVersionString,"Invalid version string '%s'"
 205,buildInvalidVersionFile,"Invalid version file '%s'"
@@ -589,8 +590,8 @@ tcExpressionWithIfRequiresParenthesis,"This list or array expression includes an
 765,tcExtraneousFieldsGivenValues,"Extraneous fields have been given values"
 766,tcObjectExpressionsCanOnlyOverrideAbstractOrVirtual,"Only overrides of abstract and virtual members may be specified in object expressions"
 767,tcNoAbstractOrVirtualMemberFound,"The member '%s' does not correspond to any abstract or virtual method available to override or implement"
-768,tcArgumentArityMismatch,"The member '%s' does not accept the correct number of arguments, %d arguments are expected"
-769,tcArgumentArityMismatchOneOverload,"The member '%s' does not accept the correct number of arguments. One overload accepts %d arguments."
+768,tcArgumentArityMismatch,"The member '%s' does not accept the correct number of arguments. %d argument(s) are expected, but %d were given. The required signature is '%s'.%s"
+769,tcArgumentArityMismatchOneOverload,"The member '%s' does not accept the correct number of arguments. One overload accepts %d arguments, but %d were given. The required signature is '%s'.%s"
 770,tcSimpleMethodNameRequired,"A simple method name is required here"
 771,tcPredefinedTypeCannotBeUsedAsSuperType,"The types System.ValueType, System.Enum, System.Delegate, System.MulticastDelegate and System.Array cannot be used as super types in an object expression or class"
 772,tcNewMustBeUsedWithNamedType,"'new' must be used with a named type"

src/fsharp/TypeChecker.fs

@@ -6036,16 +6036,31 @@ and GetNameAndArityOfObjExprBinding _cenv _env b =
         lookPat pat
 
 
-and FreshenObjExprAbstractSlot cenv (_env: TcEnv) implty virtNameAndArityPairs (bind,bindAttribs,bindName,absSlots:(_ * MethInfo) list) = 
-    let (NormalizedBinding (_,_,_,_,_,_,synTyparDecls,_,_,_,mBinding,_)) = bind 
+and FreshenObjExprAbstractSlot cenv (env: TcEnv) implty virtNameAndArityPairs (bind,bindAttribs,bindName,absSlots:(_ * MethInfo) list) = 
+    let (NormalizedBinding (_,_,_,_,_,_,synTyparDecls,_,_,_,mBinding,_)) = bind
     match absSlots with 
     | [] when not (CompileAsEvent cenv.g bindAttribs) -> 
         let absSlotsByName = List.filter (fst >> fst >> (=) bindName) virtNameAndArityPairs
-
+        let getSignature absSlot = (NicePrint.stringOfMethInfo cenv.amap mBinding env.DisplayEnv absSlot).Replace("abstract ","")
+        let getDetails (absSlot:MethInfo) = 
+            if absSlot.GetParamTypes(cenv.amap,mBinding,[]) |> List.exists (fun xs -> xs |> List.exists (isTupleTy cenv.g)) then
+                FSComp.SR.tupleRequiredInAbstractMethod()
+            else ""
+
+        // Compute the argument counts of the member arguments
+        let _,synValInfo = GetNameAndArityOfObjExprBinding cenv env bind
+        let arity = 
+            match SynInfo.AritiesOfArgs synValInfo with            
+            | _::x::_ -> x
+            | _ -> 0
+
         match absSlotsByName with 
-        | []              -> errorR(Error(FSComp.SR.tcNoAbstractOrVirtualMemberFound(bindName),mBinding))
-        | [(_,absSlot:MethInfo)]     -> errorR(Error(FSComp.SR.tcArgumentArityMismatch(bindName, (List.sum absSlot.NumArgs)),mBinding))
-        | (_,absSlot:MethInfo) :: _  -> errorR(Error(FSComp.SR.tcArgumentArityMismatchOneOverload(bindName, (List.sum absSlot.NumArgs)),mBinding))
+        | []              -> 
+            errorR(Error(FSComp.SR.tcNoAbstractOrVirtualMemberFound(bindName),mBinding))
+        | [(_,absSlot:MethInfo)]     ->
+            errorR(Error(FSComp.SR.tcArgumentArityMismatch(bindName, List.sum absSlot.NumArgs, arity, getSignature absSlot, getDetails absSlot),mBinding))
+        | (_,absSlot:MethInfo) :: _  ->
+            errorR(Error(FSComp.SR.tcArgumentArityMismatchOneOverload(bindName, List.sum absSlot.NumArgs, arity, getSignature absSlot, getDetails absSlot),mBinding))
 
         None
 

tests/fsharpqa/Source/Warnings/TupleInAbstractMethod.fs

@@ -0,0 +1,13 @@
+// #Warnings
+//<Expects status="Error" span="(10,16)" id="FS0768">The member 'Function' does not accept the correct number of arguments.</Expects>
+//<Expects>A tuple type is required for one or more arguments</Expects>
+
+type IInterface =
+    abstract Function : (int32 * int32) -> unit
+
+let x = 
+  { new IInterface with
+        member this.Function (i, j) = ()
+  }
+
+exit 0

tests/fsharpqa/Source/Warnings/env.lst

@@ -2,6 +2,7 @@
 	SOURCE=WarnIfMissingElseBranch.fs # WarnIfMissingElseBranch.fs
 	SOURCE=ReturnInsteadOfReturnBang.fs # ReturnInsteadOfReturnBang.fs
 	SOURCE=YieldInsteadOfYieldBang.fs # YieldInsteadOfYieldBang.fs
+	SOURCE=TupleInAbstractMethod.fs # TupleInAbstractMethod.fs
 	SOURCE=CommaInRecCtor.fs # CommaInRecCtor.fs
 	SOURCE=ValidCommaInRecCtor.fs # ValidCommaInRecCtor.fs
 	SOURCE=ElseBranchHasWrongType.fs # ElseBranchHasWrongType.fs