bit of refactoring of error message building logic during failed over…

…load resolution

[ConstraintSolver.fsi]

* define OverloadInformation and OverloadResolutionFailure, those replace workflow where `string * ((CalledMeth<_> * exn) list)` values were created at call site mixed with message building and matched later in non obvious fashion in `failOverloading` closure
* adjust UnresolvedOverloading and PossibleOverload exceptions

[ConstraintSolver.fs]

* get rid of `GetPossibleOverloads`, this was used only in `failOverloading` closure, and just being passed the same parameters at call site
* give `failOverloading` a more meaningful signature and consolidate the prefix message building logic there
* fix `failOverloading` call sites

[CompilerOps.fs] adjust pattern matching

Expecting behaviour of this code to be identical as before PR

`

src/fsharp/CompileOps.fs

@@ -188,7 +188,7 @@ let GetRangeOfDiagnostic(err: PhasedDiagnostic) =
       | NameClash(_, _, _, m, _, _, _) 
       | UnresolvedOverloading(_, _, _, m) 
       | UnresolvedConversionOperator (_, _, _, m)
-      | PossibleOverload(_, _, _, m) 
+      | PossibleOverload(_, _, m) 
       | VirtualAugmentationOnNullValuedType m
       | NonVirtualAugmentationOnNullValuedType m
       | NonRigidTypar(_, _, _, _, _, m)
@@ -406,9 +406,9 @@ let warningOn err level specificWarnOn =
 let SplitRelatedDiagnostics(err: PhasedDiagnostic) = 
     let ToPhased e = {Exception=e; Phase = err.Phase}
     let rec SplitRelatedException = function
-      | UnresolvedOverloading(a, overloads, b, c) -> 
+      | UnresolvedOverloading(displayEnv, msg, overloads, m) -> 
            let related = overloads |> List.map ToPhased
-           UnresolvedOverloading(a, [], b, c)|>ToPhased, related
+           UnresolvedOverloading(displayEnv, msg, [], m) |> ToPhased, related
       | ConstraintSolverRelatedInformation(fopt, m2, e) -> 
           let e, related = SplitRelatedException e
           ConstraintSolverRelatedInformation(fopt, m2, e.Exception)|>ToPhased, related
@@ -770,18 +770,18 @@ let OutputPhasedErrorR (os: StringBuilder) (err: PhasedDiagnostic) (canSuggestNa
           os.Append(e.ContextualErrorMessage) |> ignore
 #endif
 
-      | UnresolvedOverloading(_, _, mtext, _) -> 
+      | UnresolvedOverloading(_, mtext, _, _) ->
           os.Append mtext |> ignore
 
       | UnresolvedConversionOperator(denv, fromTy, toTy, _) -> 
           let t1, t2, _tpcs = NicePrint.minimalStringsOfTwoTypes denv fromTy toTy
           os.Append(FSComp.SR.csTypeDoesNotSupportConversion(t1, t2)) |> ignore
 
-      | PossibleOverload(_, minfo, originalError, _) -> 
+      | PossibleOverload(denv, minfo, m) ->
           // print original error that describes reason why this overload was rejected
           let buf = new StringBuilder()
-          OutputExceptionR buf originalError
-
+          OutputExceptionR buf minfo.error
+          let minfo = minfo.OverloadMethodInfo denv m
           os.Append(PossibleOverloadE().Format minfo (buf.ToString())) |> ignore
 
       | FunctionExpected _ ->

src/fsharp/ConstraintSolver.fs

@@ -52,6 +52,7 @@ open FSharp.Compiler.ErrorLogger
 open FSharp.Compiler.Infos
 open FSharp.Compiler.AccessibilityLogic
 open FSharp.Compiler.AttributeChecking
+open FSharp.Compiler.Import
 open FSharp.Compiler.Lib
 open FSharp.Compiler.MethodCalls
 open FSharp.Compiler.PrettyNaming
@@ -181,12 +182,24 @@ type ContextInfo =
     /// The type equation comes from a sequence expression.
     | SequenceExpression of TType
 
-exception ConstraintSolverTupleDiffLengths of displayEnv: DisplayEnv * TType list * TType list * range  * range
-
-exception ConstraintSolverInfiniteTypes of displayEnv: DisplayEnv * contextInfo: ContextInfo * TType * TType * range * range
-
-exception ConstraintSolverTypesNotInEqualityRelation of displayEnv: DisplayEnv * TType * TType * range * range * ContextInfo
-
+/// Captures relevant information for a particular failed overload resolution.
+[<Struct>]
+type OverloadInformation = {
+  methodSlot: CalledMeth<Expr>
+  amap : ImportMap
+  error: exn
+}
+with
+    member OverloadMethodInfo : displayEnv: DisplayEnv -> m: range -> string
+
+/// Cases for overload resolution failure that exists in the implementation of the compiler.
+type OverloadResolutionFailure =
+    | NoOverloadsFound   of methodName: string * candidates: OverloadInformation list
+    | PossibleCandidates of methodName: string * methodNames: string list // methodNames may be different (with operators?), this is refactored from original logic to assemble overload failure message
+
+exception ConstraintSolverTupleDiffLengths              of displayEnv: DisplayEnv * TType list * TType list * range * range
+exception ConstraintSolverInfiniteTypes                 of displayEnv: DisplayEnv * contextInfo: ContextInfo * TType * TType * range * range
+exception ConstraintSolverTypesNotInEqualityRelation    of displayEnv: DisplayEnv * TType * TType * range * range * ContextInfo
 exception ConstraintSolverTypesNotInSubsumptionRelation of displayEnv: DisplayEnv * argT: TType * paramT: TType * range * range
 
 exception ConstraintSolverMissingConstraint of displayEnv: DisplayEnv * Tast.Typar * Tast.TyparConstraint * range  * range 
@@ -200,18 +213,10 @@ exception ErrorFromApplyingDefault of tcGlobals: TcGlobals * displayEnv: Display
 exception ErrorFromAddingTypeEquation of tcGlobals: TcGlobals * displayEnv: DisplayEnv * TType * TType * exn * range
 
 exception ErrorsFromAddingSubsumptionConstraint of tcGlobals: TcGlobals * displayEnv: DisplayEnv * TType * TType * exn * ContextInfo * range
-
-exception ErrorFromAddingConstraint of displayEnv: DisplayEnv * exn * range
-
-exception PossibleOverload of displayEnv: DisplayEnv * string * exn * range
-
-exception UnresolvedOverloading of displayEnv: DisplayEnv * exn list * string * range
-
-exception UnresolvedConversionOperator of displayEnv: DisplayEnv * TType * TType * range
-
-let GetPossibleOverloads  amap m denv (calledMethGroup: (CalledMeth<_> * exn) list) = 
-    calledMethGroup |> List.map (fun (cmeth, e) ->
-        PossibleOverload(denv, NicePrint.stringOfMethInfo amap m denv cmeth.Method, e, m))
+exception ErrorFromAddingConstraint             of displayEnv: DisplayEnv * exn * range
+exception PossibleOverload                      of displayEnv: DisplayEnv * overload: OverloadInformation * range
+exception UnresolvedOverloading                 of displayEnv: DisplayEnv * prefixMessage: string * overloads: PossibleOverload list * range
+exception UnresolvedConversionOperator          of displayEnv: DisplayEnv * TType * TType * range
 
 type TcValF = (ValRef -> ValUseFlag -> TType list -> range -> Expr * TType)
 
@@ -2515,7 +2520,7 @@ and ResolveOverloading
                                    reqdRetTyOpt 
                                    candidate)
 
-            let failOverloading (msg: string) errors = 
+            let failOverloading overloadResolutionFailure = 
                 // Try to extract information to give better error for ambiguous op_Explicit and op_Implicit 
                 let convOpData = 
                     if isOpConversion then 
@@ -2530,11 +2535,26 @@ and ResolveOverloading
                 | Some (fromTy, toTy) -> 
                     UnresolvedConversionOperator (denv, fromTy, toTy, m)
                 | None -> 
-                    // Otherwise collect a list of possible overloads
-                    let overloads = GetPossibleOverloads amap m denv errors
+                    let msg = 
+                        match overloadResolutionFailure with
+                        | NoOverloadsFound (methodName, _) -> FSComp.SR.csNoOverloadsFound methodName
+                        | PossibleCandidates (methodName, methodNames) ->
+                            let msg = FSComp.SR.csMethodIsOverloaded methodName
+                            match methodNames with
+                            | [] -> msg
+                            | names -> sprintf "%s %s" msg (FSComp.SR.csCandidates (String.concat ", " names))                        
+
+                    let overloads =
+                        overloadResolutionFailure
+                        |> function | NoOverloadsFound (_, candidates) -> candidates
+                                    | PossibleCandidates _ -> []
+                        |> List.map (fun overload -> 
+                            PossibleOverload(denv, overload, m)  :?> _ // F# Spec: 8.11 Exception Definitions: The identifier identcan be used to generate values of type exn
+                        )
+
                     // if list of overloads is not empty - append line with "The available overloads are shown below..."
                     let msg = if isNil overloads then msg else sprintf "%s %s" msg (FSComp.SR.csSeeAvailableOverloads ())
-                    UnresolvedOverloading (denv, overloads, msg, m)
+                    UnresolvedOverloading (denv, msg, overloads, m)
 
             match applicable with 
             | [] ->
@@ -2554,9 +2574,9 @@ and ResolveOverloading
                                              reqdRetTyOpt 
                                              calledMeth) with 
                             | OkResult _ -> None
-                            | ErrorResult(_, exn) -> Some (calledMeth, exn))
+                            | ErrorResult(_, exn) -> Some {methodSlot = calledMeth; amap = amap; error = exn })
 
-                None, ErrorD (failOverloading (FSComp.SR.csNoOverloadsFound methodName) errors), NoTrace
+                None, ErrorD (failOverloading (NoOverloadsFound (methodName, errors))), NoTrace
 
             | [(calledMeth, warns, t)] ->
                 Some calledMeth, OkResult (warns, ()), WithTrace t
@@ -2743,12 +2763,8 @@ and ResolveOverloading
                         methods
                         |> List.map (fun cmeth -> NicePrint.stringOfMethInfo amap m denv cmeth.Method)
                         |> List.sort
-                    let msg = FSComp.SR.csMethodIsOverloaded methodName
-                    let msg = 
-                        match methodNames with
-                        | [] -> msg
-                        | names -> sprintf "%s %s" msg (FSComp.SR.csCandidates (String.concat System.Environment.NewLine names)) //   FSComp.SR.csCandidates (String.concat ", " names))
-                    None, ErrorD (failOverloading msg []), NoTrace
+
+                    None, ErrorD (failOverloading (PossibleCandidates(methodName, methodNames))), NoTrace
 
     // If we've got a candidate solution: make the final checks - no undo here! 
     // Allow subsumption on arguments. Include the return type.

src/fsharp/ConstraintSolver.fsi

@@ -90,6 +90,21 @@ type ContextInfo =
     /// The type equation comes from a sequence expression.
     | SequenceExpression of TType
 
+/// Captures relevant information for a particular failed overload resolution.
+[<Struct>]
+type OverloadInformation = {
+  methodSlot: CalledMeth<Expr>
+  amap : ImportMap
+  error: exn
+}
+with
+    member OverloadMethodInfo : displayEnv: DisplayEnv -> m: range -> string
+
+/// Cases for overload resolution failure that exists in the implementation of the compiler.
+type OverloadResolutionFailure =
+    | NoOverloadsFound   of methodName: string * candidates: OverloadInformation list
+    | PossibleCandidates of methodName: string * methodNames: string list // methodNames may be different (with operators?), this is refactored from original logic to assemble overload failure message
+
 exception ConstraintSolverTupleDiffLengths              of displayEnv: DisplayEnv * TType list * TType list * range * range
 exception ConstraintSolverInfiniteTypes                 of displayEnv: DisplayEnv * contextInfo: ContextInfo * TType * TType * range * range
 exception ConstraintSolverTypesNotInEqualityRelation    of displayEnv: DisplayEnv * TType * TType * range * range * ContextInfo
@@ -103,8 +118,8 @@ exception ErrorFromAddingTypeEquation           of tcGlobals: TcGlobals * displa
 exception ErrorsFromAddingSubsumptionConstraint of tcGlobals: TcGlobals * displayEnv: DisplayEnv * TType * TType * exn * ContextInfo * range
 exception ErrorFromAddingConstraint             of displayEnv: DisplayEnv * exn * range
 exception UnresolvedConversionOperator          of displayEnv: DisplayEnv * TType * TType * range
-exception PossibleOverload                      of displayEnv: DisplayEnv * string * exn * range
-exception UnresolvedOverloading                 of displayEnv: DisplayEnv * exn list * string * range
+exception PossibleOverload                      of displayEnv: DisplayEnv * overload: OverloadInformation * range
+exception UnresolvedOverloading                 of displayEnv: DisplayEnv * prefixMessage: string * overloads: PossibleOverload list * range
 exception NonRigidTypar                         of displayEnv: DisplayEnv * string option * range * TType * TType * range
 
 /// A function that denotes captured tcVal, Used in constraint solver and elsewhere to get appropriate expressions for a ValRef.