Don't suggest names for errors in normal IDE usage

src/fsharp/CompileOps.fs

@@ -602,7 +602,7 @@ let getErrorString key = SR.GetString key
 
 let (|InvalidArgument|_|) (exn:exn) = match exn with :? ArgumentException as e -> Some e.Message | _ -> None
 
-let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
+let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) (suggestNames: bool) =
 
     let rec OutputExceptionR (os:StringBuilder) error = 
 
@@ -827,9 +827,10 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
 
       | UndefinedName(_, k, id, suggestionsF) ->
           os.Append(k (DecompileOpName id.idText)) |> ignore
-          let filtered = ErrorResolutionHints.FilterPredictions id.idText suggestionsF
-          if List.isEmpty filtered |> not then
-              os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
+          if suggestNames then
+              let filtered = ErrorResolutionHints.FilterPredictions suggestionsF id.idText 
+              if List.isEmpty filtered |> not then
+                  os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
 
 
       | InternalUndefinedItemRef(f, smr, ccuName, s) ->  
@@ -1367,9 +1368,10 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
 
       | ErrorWithSuggestions ((_, s), _, idText, suggestionF) -> 
           os.Append(DecompileOpName s) |> ignore
-          let filtered = ErrorResolutionHints.FilterPredictions idText suggestionF
-          if List.isEmpty filtered |> not then
-              os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
+          if suggestNames then
+              let filtered = ErrorResolutionHints.FilterPredictions suggestionF idText
+              if List.isEmpty filtered |> not then
+                  os.Append(ErrorResolutionHints.FormatPredictions DecompileOpName filtered) |> ignore
 
       | NumberedError ((_, s), _) -> os.Append(s) |> ignore
 
@@ -1585,10 +1587,10 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
 
 
 // remove any newlines and tabs 
-let OutputPhasedDiagnostic (os:System.Text.StringBuilder) (err:PhasedDiagnostic) (flattenErrors:bool) = 
+let OutputPhasedDiagnostic (os:System.Text.StringBuilder) (err:PhasedDiagnostic) (flattenErrors:bool) (suggestNames: bool) = 
     let buf = new System.Text.StringBuilder()
 
-    OutputPhasedErrorR buf err
+    OutputPhasedErrorR buf err suggestNames
     let s = if flattenErrors then ErrorLogger.NormalizeErrorString (buf.ToString()) else buf.ToString()
 
     os.Append(s) |> ignore
@@ -1638,7 +1640,7 @@ type Diagnostic =
     | Long of bool * DiagnosticDetailedInfo
 
 /// returns sequence that contains Diagnostic for the given error + Diagnostic for all related errors
-let CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorStyle, isError, err:PhasedDiagnostic) = 
+let CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorStyle, isError, err:PhasedDiagnostic, suggestNames: bool) = 
     let outputWhere (showFullPaths, errorStyle) m : DiagnosticLocation = 
         if Range.equals m rangeStartup || Range.equals m rangeCmdArgs then 
             { Range = m; TextRepresentation = ""; IsEmpty = true; File = "" }
@@ -1711,7 +1713,7 @@ let CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorSt
             let canonical = OutputCanonicalInformation(err.Subcategory(), GetDiagnosticNumber mainError)
             let message = 
                 let os = System.Text.StringBuilder()
-                OutputPhasedDiagnostic os mainError flattenErrors
+                OutputPhasedDiagnostic os mainError flattenErrors suggestNames
                 os.ToString()
 
             let entry : DiagnosticDetailedInfo = { Location = where; Canonical = canonical; Message = message }
@@ -1726,15 +1728,15 @@ let CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorSt
                     let relCanonical = OutputCanonicalInformation(err.Subcategory(), GetDiagnosticNumber mainError) // Use main error for code
                     let relMessage = 
                         let os = System.Text.StringBuilder()
-                        OutputPhasedDiagnostic os err flattenErrors
+                        OutputPhasedDiagnostic os err flattenErrors suggestNames
                         os.ToString()
 
                     let entry : DiagnosticDetailedInfo = { Location = relWhere; Canonical = relCanonical; Message = relMessage}
                     errors.Add( Diagnostic.Long (isError, entry) )
 
                 | _ -> 
                     let os = System.Text.StringBuilder()
-                    OutputPhasedDiagnostic os err flattenErrors
+                    OutputPhasedDiagnostic os err flattenErrors suggestNames
                     errors.Add( Diagnostic.Short(isError, os.ToString()) )
 
             relatedErrors |> List.iter OutputRelatedError
@@ -1755,7 +1757,8 @@ let CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorSt
 /// prints error and related errors to the specified StringBuilder
 let rec OutputDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorStyle, isError) os (err:PhasedDiagnostic) = 
 
-    let errors = CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorStyle, isError, err)
+    // 'true' for "suggestNames" is passed last here because we want to report suggestions in fsc.exe and fsi.exe, just not in regular IDE usage.
+    let errors = CollectDiagnostic (implicitIncludeDir, showFullPaths, flattenErrors, errorStyle, isError, err, true)
     for e in errors do
         Printf.bprintf os "\n"
         match e with

src/fsharp/CompileOps.fsi

@@ -83,7 +83,7 @@ val GetDiagnosticNumber: PhasedDiagnostic -> int
 val SplitRelatedDiagnostics: PhasedDiagnostic -> PhasedDiagnostic * PhasedDiagnostic list
 
 /// Output an error to a buffer
-val OutputPhasedDiagnostic: StringBuilder -> PhasedDiagnostic -> flattenErrors: bool -> unit
+val OutputPhasedDiagnostic: StringBuilder -> PhasedDiagnostic -> flattenErrors: bool -> suggestNames: bool -> unit
 
 /// Output an error or warning to a buffer
 val OutputDiagnostic: implicitIncludeDir:string * showFullPaths: bool * flattenErrors: bool * errorStyle: ErrorStyle *  isError:bool -> StringBuilder -> PhasedDiagnostic -> unit
@@ -120,7 +120,7 @@ type Diagnostic =
     | Long of bool * DiagnosticDetailedInfo
 
 /// Part of LegacyHostedCompilerForTesting
-val CollectDiagnostic: implicitIncludeDir:string * showFullPaths: bool * flattenErrors: bool * errorStyle: ErrorStyle *  warning:bool * PhasedDiagnostic -> seq<Diagnostic>
+val CollectDiagnostic: implicitIncludeDir:string * showFullPaths: bool * flattenErrors: bool * errorStyle: ErrorStyle *  warning:bool * PhasedDiagnostic * suggestNames: bool -> seq<Diagnostic>
 
 //----------------------------------------------------------------------------
 // Resolve assembly references 

src/fsharp/ErrorResolutionHints.fs

@@ -24,7 +24,7 @@ let IsInEditDistanceProximity idText suggestion =
     editDistance <= threshold
 
 /// Filters predictions based on edit distance to the given unknown identifier.
-let FilterPredictions (idText:string) (suggestionF:ErrorLogger.Suggestions) =    
+let FilterPredictions (suggestionF:ErrorLogger.Suggestions) (idText:string) =    
     let uppercaseText = idText.ToUpperInvariant()
     let allSuggestions = suggestionF()
 

src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj

@@ -634,6 +634,12 @@
     <Compile Include="..\service\service.fs">
       <Link>Service/service.fs</Link>
     </Compile>
+    <Compile Include="..\service\ServiceErrorResolutionHints.fsi">
+      <Link>Service/ServiceErrorResolutionHints.fsi</Link>
+    </Compile>
+    <Compile Include="..\service\ServiceErrorResolutionHints.fs">
+      <Link>Service/ServiceErrorResolutionHints.fs</Link>
+    </Compile>
     <Compile Include="..\service\ServiceInterfaceStubGenerator.fsi">
       <Link>Service/ServiceInterfaceStubGenerator.fsi</Link>
     </Compile>

src/fsharp/fsc.fs

@@ -132,8 +132,9 @@ type InProcErrorLoggerProvider() =
            member log.CreateErrorLoggerUpToMaxErrors(tcConfigBuilder, exiter) =
             { new ErrorLoggerUpToMaxErrors(tcConfigBuilder, exiter, "InProcCompilerErrorLoggerUpToMaxErrors") with
                     member this.HandleTooManyErrors(text) = warnings.Add(Diagnostic.Short(false, text))
-                    member this.HandleIssue(tcConfigBuilder, err, isError) = 
-                        let errs = CollectDiagnostic(tcConfigBuilder.implicitIncludeDir, tcConfigBuilder.showFullPaths, tcConfigBuilder.flatErrors, tcConfigBuilder.errorStyle, isError, err)
+                    member this.HandleIssue(tcConfigBuilder, err, isError) =
+                        // 'true' is passed for "suggestNames", since we want to suggest names with fsc.exe runs and this doesn't affect IDE perf
+                        let errs = CollectDiagnostic(tcConfigBuilder.implicitIncludeDir, tcConfigBuilder.showFullPaths, tcConfigBuilder.flatErrors, tcConfigBuilder.errorStyle, isError, err, true)
                         let container = if isError then errors else warnings 
                         container.AddRange(errs) } 
             :> ErrorLogger }

src/fsharp/fsi/fsi.fs

@@ -2594,7 +2594,8 @@ type FsiEvaluationSession (fsi: FsiEvaluationSessionHostConfig, argv:string[], i
             | Choice2Of2 None -> Choice2Of2 (System.Exception "Operation could not be completed due to earlier error")
             | Choice2Of2 (Some userExn) -> Choice2Of2 userExn
 
-        userRes, ErrorHelpers.CreateErrorInfos (errorOptions, true, scriptFile, errs)
+        // 'true' is passed for "suggestNames" because we want the FSI session to suggest names for misspellings and it won't affect IDE perf much
+        userRes, ErrorHelpers.CreateErrorInfos (errorOptions, true, scriptFile, errs, true)
 
     let dummyScriptFileName = "input.fsx"
 

src/fsharp/service/IncrementalBuild.fs

@@ -1741,7 +1741,7 @@ type IncrementalBuilder(tcGlobals, frameworkTcImports, nonFrameworkAssemblyInput
 
     /// CreateIncrementalBuilder (for background type checking). Note that fsc.fs also
     /// creates an incremental builder used by the command line compiler.
-    static member TryCreateBackgroundBuilderForProjectOptions (ctok, legacyReferenceResolver, defaultFSharpBinariesDir, frameworkTcImportsCache: FrameworkImportsCache, loadClosureOpt:LoadClosure option, sourceFiles:string list, commandLineArgs:string list, projectReferences, projectDirectory, useScriptResolutionRules, keepAssemblyContents, keepAllBackgroundResolutions, maxTimeShareMilliseconds, tryGetMetadataSnapshot) =
+    static member TryCreateBackgroundBuilderForProjectOptions (ctok, legacyReferenceResolver, defaultFSharpBinariesDir, frameworkTcImportsCache: FrameworkImportsCache, loadClosureOpt:LoadClosure option, sourceFiles:string list, commandLineArgs:string list, projectReferences, projectDirectory, useScriptResolutionRules, keepAssemblyContents, keepAllBackgroundResolutions, maxTimeShareMilliseconds, tryGetMetadataSnapshot, suggestNamesForErrors) =
       let useSimpleResolutionSwitch = "--simpleresolution"
 
       cancellable {
@@ -1874,7 +1874,7 @@ type IncrementalBuilder(tcGlobals, frameworkTcImports, nonFrameworkAssemblyInput
                 errorLogger.GetErrors() |> Array.map (fun (d, severity) -> d, severity = FSharpErrorSeverity.Error)
             | _ ->
                 Array.ofList delayedLogger.Diagnostics
-            |> Array.map (fun (d, isError) -> FSharpErrorInfo.CreateFromException(d, isError, range.Zero))
+            |> Array.map (fun (d, isError) -> FSharpErrorInfo.CreateFromException(d, isError, range.Zero, suggestNamesForErrors))
 
         return builderOpt, diagnostics
       }

src/fsharp/service/IncrementalBuild.fsi

@@ -162,7 +162,7 @@ type internal IncrementalBuilder =
       /// This may be a marginally long-running operation (parses are relatively quick, only one file needs to be parsed)
       member GetParseResultsForFile : CompilationThreadToken * filename:string -> Cancellable<Ast.ParsedInput option * Range.range * string * (PhasedDiagnostic * FSharpErrorSeverity)[]>
 
-      static member TryCreateBackgroundBuilderForProjectOptions : CompilationThreadToken * ReferenceResolver.Resolver * defaultFSharpBinariesDir: string * FrameworkImportsCache * scriptClosureOptions:LoadClosure option * sourceFiles:string list * commandLineArgs:string list * projectReferences: IProjectReference list * projectDirectory:string * useScriptResolutionRules:bool * keepAssemblyContents: bool * keepAllBackgroundResolutions: bool * maxTimeShareMilliseconds: int64 * tryGetMetadataSnapshot: ILBinaryReader.ILReaderTryGetMetadataSnapshot -> Cancellable<IncrementalBuilder option * FSharpErrorInfo[]>
+      static member TryCreateBackgroundBuilderForProjectOptions : CompilationThreadToken * ReferenceResolver.Resolver * defaultFSharpBinariesDir: string * FrameworkImportsCache * scriptClosureOptions:LoadClosure option * sourceFiles:string list * commandLineArgs:string list * projectReferences: IProjectReference list * projectDirectory:string * useScriptResolutionRules:bool * keepAssemblyContents: bool * keepAllBackgroundResolutions: bool * maxTimeShareMilliseconds: int64 * tryGetMetadataSnapshot: ILBinaryReader.ILReaderTryGetMetadataSnapshot * suggestNamesForErrors: bool -> Cancellable<IncrementalBuilder option * FSharpErrorInfo[]>
 
       /// Increment the usage count on the IncrementalBuilder by 1. This initial usage count is 0 so immediately after creation 
       /// a call to KeepBuilderAlive should be made. The returns an IDisposable which will 

src/fsharp/service/ServiceErrorResolutionHints.fs

@@ -0,0 +1,14 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.FSharp.Compiler.SourceCodeServices
+
+open System.Collections.Generic
+
+open Microsoft.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

src/fsharp/service/ServiceErrorResolutionHints.fsi

@@ -0,0 +1,9 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.FSharp.Compiler.SourceCodeServices
+
+/// Exposes the string distance algorithm used to suggest names for mistyped identifiers.
+module ErrorResolutionHints =
+    /// Given a set of names, uses and a string representing an unresolved identifier,
+    /// returns a list of suggested names if there are any feasible candidates.
+    val getSuggestedNames: symbolUses: string[] -> unresolvedIdentifier: string -> string list option