Use a MaxBuffer for Suggestions

src/fsharp/CompileOps.fs

@@ -827,7 +827,7 @@ let OutputPhasedErrorR (os: StringBuilder) (err: PhasedDiagnostic) (suggestNames
           os.Append(k (DecompileOpName id.idText)) |> ignore
           if suggestNames then
               let filtered = ErrorResolutionHints.FilterPredictions suggestionsF id.idText 
-              if List.isEmpty filtered |> not then
+              if Array.isEmpty filtered |> not then
                   os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
 
 
@@ -1368,7 +1368,7 @@ let OutputPhasedErrorR (os: StringBuilder) (err: PhasedDiagnostic) (suggestNames
           os.Append(DecompileOpName s) |> ignore
           if suggestNames then
               let filtered = ErrorResolutionHints.FilterPredictions suggestionF idText
-              if List.isEmpty filtered |> not then
+              if Array.isEmpty filtered |> not then
                   os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
 
       | NumberedError ((_, s), _) -> os.Append s |> ignore

src/fsharp/ConstraintSolver.fs

@@ -2195,8 +2195,7 @@ and ReportNoCandidatesError (csenv: ConstraintSolverEnv) (nUnnamedCallerArgs, nN
             if minfo.IsConstructor then
                 let predictFields() =
                     minfo.DeclaringTyconRef.AllInstanceFieldsAsList
-                    |> List.map (fun p -> p.Name.Replace("@", ""))
-                    |> System.Collections.Generic.HashSet
+                    |> Seq.map (fun p -> p.Name.Replace("@", ""))
 
                 ErrorWithSuggestions((msgNum, FSComp.SR.csCtorHasNoArgumentOrReturnProperty(methodName, id.idText, msgText)), id.idRange, id.idText, predictFields)
             else

src/fsharp/ErrorLogger.fs

@@ -46,9 +46,9 @@ let rec findOriginalException err =
     | WrappedError(err, _)  -> findOriginalException err
     | _ -> err
 
-type Suggestions = unit -> Collections.Generic.HashSet<string>
+type Suggestions = unit -> seq<string>
 
-let NoSuggestions : Suggestions = fun () -> Collections.Generic.HashSet()
+let NoSuggestions : Suggestions = fun () -> Seq.empty
 
 /// Thrown when we stop processing the F# Interactive entry or #load.
 exception StopProcessingExn of exn option with

src/fsharp/ErrorResolutionHints.fs

@@ -11,6 +11,39 @@ let minThresholdForSuggestions = 0.7
 let highConfidenceThreshold = 0.85
 let minStringLengthForThreshold = 3
 
+type MaxBuffer<'K,'V when 'K : comparison and 'V : equality>(max:int) = 
+    let data = Array.zeroCreate<System.Collections.Generic.KeyValuePair<'K,'V voption>>(max)
+    let rec backup i j =
+        if i < j  then
+            data.[i] <- data.[i + 1]
+            backup (i + 1) j
+
+    let rec find i k v =
+        let kvpr : byref<_> = &data.[i] //only want key (not KVP)
+        let kr = kvpr.Key
+        if k < kr then 
+            if i = 0 then 
+                false
+            else 
+                backup 0 (i-1)
+                data.[i-1] <- System.Collections.Generic.KeyValuePair<_,_>(k, ValueSome v)
+                true
+        else
+            if i = max - 1 then // end of the line, replace at head
+                backup 0 i
+                data.[i] <- System.Collections.Generic.KeyValuePair<_,_>(k, ValueSome v)
+                true
+            else 
+                find (i + 1) k v
+    member __.Insert (k,v) = find 0 k v
+    member __.Values() : 'V [] =
+        let hashSet = System.Collections.Generic.HashSet<'V>()
+        for kv in data do
+            match kv.Value with 
+            | ValueSome x -> hashSet.Add x |> ignore
+            | _ -> ()
+        hashSet |> Seq.toArray
+
 /// We report a candidate if its edit distance is <= the threshold.
 /// The threshold is set to about a quarter of the number of characters.
 let IsInEditDistanceProximity idText suggestion =
@@ -42,41 +75,40 @@ let FilterPredictions (suggestionF:ErrorLogger.Suggestions) (idText:string) =
             let name = name.[2..name.Length - 3]
             name |> Seq.forall (fun c -> c <> ' ')
 
-    if allSuggestions.Contains idText then [] else // some other parsing error occurred
     let dotIdText = "." + idText
-    allSuggestions
-    |> Seq.choose (fun suggestion ->
-        // Because beginning a name with _ is used both to indicate an unused
-        // value as well as to formally squelch the associated compiler
-        // error/warning (FS1182), we remove such names from the suggestions,
-        // both to prevent accidental usages as well as to encourage good taste
-        if IsOperatorName suggestion || suggestion.StartsWithOrdinal("_") then None else
-        let suggestion:string = demangle suggestion
-        let suggestedText = suggestion.ToUpperInvariant()
-        let similarity = EditDistance.JaroWinklerDistance uppercaseText suggestedText
-        if similarity >= highConfidenceThreshold || suggestion.EndsWithOrdinal(dotIdText) then
-            Some(similarity, suggestion)
-        elif similarity < minThresholdForSuggestions && suggestedText.Length > minStringLengthForThreshold then
-            None
-        elif IsInEditDistanceProximity uppercaseText suggestedText then
-            Some(similarity, suggestion)
+    let mutable parsingError = false
+    let buffer = MaxBuffer(maxSuggestions)
+    for suggestion in allSuggestions do
+        if parsingError || suggestion = idText then 
+            parsingError <- true // some other parsing error occurred
         else
-            None)
-    |> Seq.sortByDescending fst
-    |> Seq.mapi (fun i x -> i, x) 
-    |> Seq.takeWhile (fun (i, _) -> i < maxSuggestions) 
-    |> Seq.map snd 
-    |> Seq.toList
+            // Because beginning a name with _ is used both to indicate an unused
+            // value as well as to formally squelch the associated compiler
+            // error/warning (FS1182), we remove such names from the suggestions,
+            // both to prevent accidental usages as well as to encourage good taste
+            if IsOperatorName suggestion || suggestion.StartsWithOrdinal("_") then 
+                ()
+            else
+                let suggestion:string = demangle suggestion
+                let suggestedText = suggestion.ToUpperInvariant()
+                let similarity = EditDistance.JaroWinklerDistance uppercaseText suggestedText
+                if similarity >= highConfidenceThreshold || suggestion.EndsWithOrdinal(dotIdText) then
+                    buffer.Insert(similarity, suggestion) |> ignore
+                elif similarity < minThresholdForSuggestions && suggestedText.Length > minStringLengthForThreshold then
+                    ()
+                elif IsInEditDistanceProximity uppercaseText suggestedText then
+                    buffer.Insert(similarity, suggestion) |> ignore
+
+    if parsingError then [||] else buffer.Values()
 
 /// Formats the given predictions according to the error style.
-let FormatPredictions normalizeF (predictions: (float * string) list) =
-    match predictions with
-    | [] -> System.String.Empty
-    | _ ->
+let FormatPredictions normalizeF (predictions: #seq<string>) =
+    if Seq.isEmpty predictions then
+        System.String.Empty
+    else
         let suggestions =
             predictions
-            |> List.map (snd >> normalizeF) 
-            |> List.map (sprintf "%s   %s" System.Environment.NewLine)
+            |> Seq.map (fun p -> sprintf "%s   %s" System.Environment.NewLine (normalizeF p))
             |> String.concat ""
 
         " " + FSComp.SR.undefinedNameSuggestionsIntro() + suggestions

src/fsharp/NameResolution.fs

@@ -899,9 +899,7 @@ let AddResults res1 res2 =
     | Result x, Exception _ -> Result x
     // If we have error messages for the same symbol, then we can merge suggestions.
     | Exception (UndefinedName(n1, f, id1, suggestions1)), Exception (UndefinedName(n2, _, id2, suggestions2)) when n1 = n2 && id1.idText = id2.idText && Range.equals id1.idRange id2.idRange ->
-        let suggestions = HashSet(suggestions1())
-        suggestions.UnionWith(suggestions2())
-        Exception(UndefinedName(n1, f, id1, fun () -> suggestions))
+        Exception(UndefinedName(n1, f, id1, fun () -> Seq.append (suggestions1()) (suggestions2())))
     // This prefers error messages coming from deeper failing long identifier paths
     | Exception (UndefinedName(n1, _, _, _) as e1), Exception (UndefinedName(n2, _, _, _) as e2) ->
         if n1 < n2 then Exception e2 else Exception e1
@@ -1845,7 +1843,6 @@ let rec ResolveLongIndentAsModuleOrNamespace sink atMostOne amap m first fullyQu
                 |> Seq.collect (fun kv -> kv.Value)
                 |> Seq.filter (fun modref -> IsEntityAccessible amap m ad modref)
                 |> Seq.collect (fun e -> [e.DisplayName; e.DemangledModuleOrNamespaceName])
-                |> HashSet
 
             UndefinedName(0, FSComp.SR.undefinedNameNamespaceOrModule, id, suggestModulesAndNamespaces))
 
@@ -1858,7 +1855,6 @@ let rec ResolveLongIndentAsModuleOrNamespace sink atMostOne amap m first fullyQu
                     mty.ModulesAndNamespacesByDemangledName
                     |> Seq.filter (fun kv -> IsEntityAccessible amap m ad (modref.NestedTyconRef kv.Value))
                     |> Seq.collect (fun e -> [e.Value.DisplayName; e.Value.DemangledModuleOrNamespaceName])
-                    |> HashSet
 
                 let error = raze (UndefinedName(depth, FSComp.SR.undefinedNameNamespace, id, suggestNames))
                 moduleNotFoundErrorCache <- Some(id.idRange, error)
@@ -2260,13 +2256,13 @@ let rec ResolveLongIdentInTypePrim (ncenv: NameResolver) nenv lookupKind (resInf
                         [||]
                 | _ -> [||]
 
-            [ yield! suggestions1
+            seq {
+              yield! suggestions1
               yield! suggestions2
               yield! suggestions3
               yield! suggestions4
               yield! suggestions5
-              yield! suggestions6 ]
-            |> HashSet
+              yield! suggestions6 }
 
         raze (UndefinedName (depth, FSComp.SR.undefinedNameFieldConstructorOrMember, id, suggestMembers))
 
@@ -2411,12 +2407,12 @@ let rec ResolveExprLongIdentInModuleOrNamespace (ncenv: NameResolver) nenv (type
                     |> Seq.filter (fun e -> IsTyconReprAccessible ncenv.amap m ad (modref.NestedTyconRef e.Value))
                     |> Seq.map (fun e -> e.Value.DisplayName)
 
-                [ yield! types
+                seq{
+                  yield! types
                   yield! submodules
                   yield! unions
                   yield! vals
-                  yield! exns ]
-                |> HashSet
+                  yield! exns }
 
             raze (UndefinedName(depth, FSComp.SR.undefinedNameValueConstructorNamespaceOrType, id, suggestPossibleTypesAndNames))
         | results -> AtMostOneResult id.idRange results
@@ -2534,11 +2530,11 @@ let rec ResolveExprLongIdentPrim sink (ncenv: NameResolver) first fullyQualified
                                                     None)
                                         |> Seq.map (fun t -> t.DisplayName + "." + id.idText)
 
-                                    [ yield! suggestedNames
+                                    seq {
+                                      yield! suggestedNames
                                       yield! suggestedTypes
                                       yield! suggestedModulesAndNamespaces
-                                      yield! unions ]
-                                    |> HashSet
+                                      yield! unions }
 
                                 raze (UndefinedName(0, FSComp.SR.undefinedNameValueOfConstructor, id, suggestNamesAndTypes))
                         ForceRaise failingCase
@@ -2620,14 +2616,11 @@ let rec ResolveExprLongIdentPrim sink (ncenv: NameResolver) first fullyQualified
                                 yield!
                                     nenv.eUnqualifiedItems
                                     |> Seq.map (fun e -> e.Value.DisplayName)
-                          } |> HashSet
+                          }
 
                       match innerSearch with
                       | Exception (UndefinedName(0, _, id1, suggestionsF)) when Range.equals id.idRange id1.idRange ->
-                            let mergeSuggestions() =
-                                let res = suggestEverythingInScope()
-                                res.UnionWith(suggestionsF())
-                                res
+                            let mergeSuggestions() = Seq.append (suggestionsF()) (suggestEverythingInScope())
 
                             let failingCase = raze (UndefinedName(0, FSComp.SR.undefinedNameValueNamespaceTypeOrModule, id, mergeSuggestions))
                             ForceRaise failingCase
@@ -2720,9 +2713,9 @@ let rec ResolvePatternLongIdentInModuleOrNamespace (ncenv: NameResolver) nenv nu
                 |> Seq.filter (fun e -> IsEntityAccessible ncenv.amap m ad e.Value)
                 |> Seq.map (fun e -> e.Value.DisplayName)
 
-            [ yield! submodules
-              yield! suggestedTypes ]
-            |> HashSet
+            seq {
+              yield! submodules
+              yield! suggestedTypes }
 
         raze (UndefinedName(depth, FSComp.SR.undefinedNameConstructorModuleOrNamespace, id, suggestPossibleTypes))
     | results -> AtMostOneResult id.idRange results
@@ -2831,7 +2824,6 @@ let rec ResolveTypeLongIdentInTyconRefPrim (ncenv: NameResolver) (typeNameResInf
             let suggestTypes() =
                 tcref.ModuleOrNamespaceType.TypesByDemangledNameAndArity id.idRange
                 |> Seq.map (fun e -> e.Value.DisplayName)
-                |> HashSet
 
             raze (UndefinedName(depth, FSComp.SR.undefinedNameType, id, suggestTypes))
     | id2 :: rest2 ->
@@ -2852,7 +2844,6 @@ let rec ResolveTypeLongIdentInTyconRefPrim (ncenv: NameResolver) (typeNameResInf
                 let suggestTypes() =
                     tcref.ModuleOrNamespaceType.TypesByDemangledNameAndArity id.idRange
                     |> Seq.map (fun e -> e.Value.DisplayName)
-                    |> HashSet
 
                 raze (UndefinedName(depth, FSComp.SR.undefinedNameType, id, suggestTypes))
 
@@ -2877,7 +2868,6 @@ let SuggestTypeLongIdentInModuleOrNamespace depth (modref: ModuleOrNamespaceRef)
         modref.ModuleOrNamespaceType.AllEntities
         |> Seq.filter (fun e -> IsEntityAccessible amap m ad (modref.NestedTyconRef e))
         |> Seq.collect (fun e -> [e.DisplayName; e.DemangledModuleOrNamespaceName])
-        |> HashSet
 
     let errorTextF s = FSComp.SR.undefinedNameTypeIn(s, fullDisplayTextOfModRef modref)
     UndefinedName(depth, errorTextF, id, suggestPossibleTypes)
@@ -2905,7 +2895,6 @@ let rec private ResolveTypeLongIdentInModuleOrNamespace sink nenv (ncenv: NameRe
                     modref.ModuleOrNamespaceType.ModulesAndNamespacesByDemangledName
                     |> Seq.filter (fun kv -> IsEntityAccessible ncenv.amap m ad (modref.NestedTyconRef kv.Value))
                     |> Seq.collect (fun e -> [e.Value.DisplayName; e.Value.DemangledModuleOrNamespaceName])
-                    |> HashSet
                 raze (UndefinedName(depth, FSComp.SR.undefinedNameNamespaceOrModule, id, suggestPossibleModules))
 
         let tyconSearch =
@@ -2916,7 +2905,6 @@ let rec private ResolveTypeLongIdentInModuleOrNamespace sink nenv (ncenv: NameRe
                 let suggestTypes() =
                     modref.ModuleOrNamespaceType.TypesByDemangledNameAndArity id.idRange
                     |> Seq.map (fun e -> e.Value.DisplayName)
-                    |> HashSet
 
                 raze (UndefinedName(depth, FSComp.SR.undefinedNameType, id, suggestTypes))
 
@@ -2959,7 +2947,6 @@ let rec ResolveTypeLongIdentPrim sink (ncenv: NameResolver) occurence first full
                                  if e.Value.DisplayName.EndsWithOrdinal("Attribute") then
                                      yield e.Value.DisplayName.Replace("Attribute", "")]
                             | _ -> [e.Value.DisplayName; e.Value.DemangledModuleOrNamespaceName])
-                        |> HashSet
 
                     raze (UndefinedName(0, FSComp.SR.undefinedNameType, id, suggestPossibleTypes))
         | id2 :: rest2 ->
@@ -3116,7 +3103,7 @@ let SuggestLabelsOfRelatedRecords g (nenv: NameResolutionEnv) (id: Ident) (allFi
                 labelsOfPossibleRecords.ExceptWith givenFields
                 labelsOfPossibleRecords
 
-        if fullyQualfied.Count > 0 then fullyQualfied else
+        if fullyQualfied.Count > 0 then fullyQualfied :> seq<_> else
 
         // check if the user forgot to use qualified access
         nenv.eTyconsByDemangledNameAndArity
@@ -3130,7 +3117,6 @@ let SuggestLabelsOfRelatedRecords g (nenv: NameResolutionEnv) (id: Ident) (allFi
                 else
                     None)
         |> Seq.map (fun t -> t.DisplayName + "." + id.idText)
-        |> HashSet
 
     UndefinedName(0, FSComp.SR.undefinedNameRecordLabel, id, suggestLabels)
 
@@ -3159,7 +3145,7 @@ let ResolveFieldPrim sink (ncenv: NameResolver) nenv ad ty (mp, id: Ident) allFi
             | _ ->
                 if isRecdTy g ty then
                     // record label doesn't belong to record type -> suggest other labels of same record
-                    let suggestLabels() = SuggestOtherLabelsOfSameRecordType g nenv ty id allFields
+                    let suggestLabels() = SuggestOtherLabelsOfSameRecordType g nenv ty id allFields :> seq<_>
                     let typeName = NicePrint.minimalStringOfType nenv.eDisplayEnv ty
                     let errorText = FSComp.SR.nrRecordDoesNotContainSuchLabel(typeName, id.idText)
                     error(ErrorWithSuggestions(errorText, m, id.idText, suggestLabels))

src/fsharp/TypeChecker.fs

@@ -4555,9 +4555,9 @@ and TcTyparOrMeasurePar optKind cenv (env: TcEnv) newOk tpenv (Typar(id, _, _) a
                         elements
                         |> Seq.map (fun p -> "'" + p.Key)
 
-                [ yield! predictions1 
-                  yield! predictions2 ]
-                |> HashSet
+                seq {
+                  yield! predictions1 
+                  yield! predictions2 }
 
             let reportedId = Ident("'" + id.idText, id.idRange)
             error (UndefinedName(0, FSComp.SR.undefinedNameTypeParameter, reportedId, predictTypeParameters))
@@ -6550,8 +6550,7 @@ and FreshenObjExprAbstractSlot cenv (env: TcEnv) (implty: TType) virtNameAndArit
 
             let suggestVirtualMembers() =
                 virtNameAndArityPairs
-                |> List.map (fst >> fst)
-                |> HashSet
+                |> Seq.map (fst >> fst)
 
             if containsNonAbstractMemberWithSameName then
                 errorR(ErrorWithSuggestions(FSComp.SR.tcMemberFoundIsNotAbstractOrVirtual(tcref.DisplayName, bindName), mBinding, bindName, suggestVirtualMembers))

src/fsharp/service/ServiceErrorResolutionHints.fs

@@ -8,7 +8,8 @@ open FSharp.Compiler.ErrorResolutionHints
 
 module ErrorResolutionHints =
     let getSuggestedNames (namesToCheck: string[]) (unresolvedIdentifier: string) =
-        let res = FilterPredictions (fun () -> HashSet<string>(namesToCheck)) unresolvedIdentifier |> List.map snd
-        match res with
-        | [] -> None
-        | _ -> Some res
+        let res = FilterPredictions (fun () -> namesToCheck :> seq<_>) unresolvedIdentifier
+        if Seq.isEmpty res then
+            None
+        else
+            Some(Array.toList res)