Use ordinal string comparison in string manipulation methods (#4912)

* Use ordinal string comparison in string manipulation methods

StartsWith, EndsWith, Compare, etc

* Add StartsWithOrdinal, EndsWithOrdinal extension methods

fcs/FSharp.Compiler.Service.ProjectCrackerTool/Program.fs

@@ -10,8 +10,8 @@ module Program =
     let addMSBuildv14BackupResolution () =
         let onResolveEvent = new ResolveEventHandler(fun sender evArgs ->
             let requestedAssembly = AssemblyName(evArgs.Name)
-            if requestedAssembly.Name.StartsWith("Microsoft.Build") &&
-                not (requestedAssembly.Name.EndsWith(".resources")) && 
+            if requestedAssembly.Name.StartsWith("Microsoft.Build", StringComparison.Ordinal) &&
+                not (requestedAssembly.Name.EndsWith(".resources", StringComparison.Ordinal)) && 
                 not (requestedAssembly.Version.ToString().Contains("12.0.0.0")) 
             then
                 // If the version of MSBuild that we're using wasn't present on the machine, then 

src/absil/il.fs

@@ -356,8 +356,7 @@ type AssemblyRefData =
 let AssemblyRefUniqueStampGenerator = new UniqueStampGenerator<AssemblyRefData>()
 
 let isMscorlib data =
-    if System.String.Compare(data.assemRefName, "mscorlib") = 0 then true 
-    else false
+    data.assemRefName = "mscorlib"
 
 [<Sealed>]
 type ILAssemblyRef(data)  =

src/absil/illib.fs

@@ -445,6 +445,13 @@ module ValueOption =
     let inline ofOption x = match x with Some x -> ValueSome x | None -> ValueNone
     let inline bind f x = match x with ValueSome x -> f x | ValueNone -> ValueNone
 
+type String with
+    member inline x.StartsWithOrdinal(value) =
+        x.StartsWith(value, StringComparison.Ordinal)
+
+    member inline x.EndsWithOrdinal(value) =
+        x.EndsWith(value, StringComparison.Ordinal)
+
 module String = 
     let indexNotFound() = raise (new KeyNotFoundException("An index for the character was not found in the string"))
 
@@ -524,7 +531,7 @@ module String =
     let (|StartsWith|_|) pattern value =
         if String.IsNullOrWhiteSpace value then
             None
-        elif value.StartsWith pattern then
+        elif value.StartsWithOrdinal(pattern) then
             Some()
         else None
 
@@ -542,7 +549,7 @@ module String =
         while not (isNull !line) do
             yield !line
             line := reader.ReadLine()
-        if str.EndsWith("\n") then
+        if str.EndsWithOrdinal("\n") then
             // last trailing space not returned
             // http://stackoverflow.com/questions/19365404/stringreader-omits-trailing-linebreak
             yield String.Empty

src/absil/ilreflect.fs

@@ -1296,7 +1296,7 @@ let rec emitInstr cenv (modB : ModuleBuilder) emEnv (ilG:ILGenerator) instr =
         ignore src
         ()
 #else
-        if cenv.generatePdb && not (src.Document.File.EndsWith("stdin", StringComparison.Ordinal)) then
+        if cenv.generatePdb && not (src.Document.File.EndsWithOrdinal("stdin")) then
             let guid x = match x with None -> Guid.Empty | Some g -> Guid(g:byte[]) in
             let symDoc = modB.DefineDocumentAndLog(src.Document.File, guid src.Document.Language, guid src.Document.Vendor, guid src.Document.DocumentType)
             ilG.MarkSequencePointAndLog(symDoc, src.Line, src.Column, src.EndLine, src.EndColumn)

src/fsharp/CompileOps.fs

@@ -695,7 +695,7 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
           | ContextInfo.TupleInRecordFields ->
                 os.Append(ErrorFromAddingTypeEquation1E().Format t2 t1 tpcs) |> ignore
                 os.Append(System.Environment.NewLine + FSComp.SR.commaInsteadOfSemicolonInRecord()) |> ignore
-          | _ when t2 = "bool" && t1.EndsWith " ref" ->
+          | _ when t2 = "bool" && t1.EndsWithOrdinal(" ref") ->
                 os.Append(ErrorFromAddingTypeEquation1E().Format t2 t1 tpcs) |> ignore
                 os.Append(System.Environment.NewLine + FSComp.SR.derefInsteadOfNot()) |> ignore
           | _ -> os.Append(ErrorFromAddingTypeEquation1E().Format t2 t1 tpcs) |> ignore
@@ -1604,7 +1604,7 @@ let SanitizeFileName fileName implicitIncludeDir =
         let currentDir = implicitIncludeDir
         
         // if the file name is not rooted in the current directory, return the full path
-        if not(fullPath.StartsWith(currentDir)) then
+        if not(fullPath.StartsWithOrdinal(currentDir)) then
             fullPath
         // if the file name is rooted in the current directory, return the relative path
         else
@@ -1796,7 +1796,7 @@ type private TypeInThisAssembly = class end
 let GetDefaultSystemValueTupleReference () =
     try
         let asm = typeof<System.ValueTuple<int, int>>.Assembly 
-        if asm.FullName.StartsWith "System.ValueTuple" then  
+        if asm.FullName.StartsWithOrdinal("System.ValueTuple") then  
             Some asm.Location
         else
             let location = Path.GetDirectoryName(typeof<TypeInThisAssembly>.Assembly.Location)
@@ -2025,7 +2025,7 @@ let GetWarningNumber(m, s:string) =
         //      therefore if we have warning id that starts with a numeric digit we convert it to Some (int32)
         //      anything else is ignored None
         if Char.IsDigit(s.[0]) then Some (int32 s)
-        elif s.StartsWith("FS", StringComparison.Ordinal) = true then raise (new ArgumentException())
+        elif s.StartsWithOrdinal("FS") = true then raise (new ArgumentException())
         else None
     with err ->
         warning(Error(FSComp.SR.buildInvalidWarningNumber(s), m))
@@ -3748,28 +3748,29 @@ type TcAssemblyResolutions(tcConfig: TcConfig, results: AssemblyResolution list,
 //--------------------------------------------------------------------------
 
 let IsSignatureDataResource         (r: ILResource) = 
-    r.Name.StartsWith FSharpSignatureDataResourceName ||
-    r.Name.StartsWith FSharpSignatureDataResourceName2
+    r.Name.StartsWithOrdinal(FSharpSignatureDataResourceName) ||
+    r.Name.StartsWithOrdinal(FSharpSignatureDataResourceName2)
 
 let IsOptimizationDataResource      (r: ILResource) = 
-    r.Name.StartsWith FSharpOptimizationDataResourceName || 
-    r.Name.StartsWith FSharpOptimizationDataResourceName2
+    r.Name.StartsWithOrdinal(FSharpOptimizationDataResourceName)|| 
+    r.Name.StartsWithOrdinal(FSharpOptimizationDataResourceName2)
 
 let GetSignatureDataResourceName    (r: ILResource) = 
-    if r.Name.StartsWith FSharpSignatureDataResourceName then 
+    if r.Name.StartsWithOrdinal(FSharpSignatureDataResourceName) then 
         String.dropPrefix r.Name FSharpSignatureDataResourceName
-    elif r.Name.StartsWith FSharpSignatureDataResourceName2 then 
+    elif r.Name.StartsWithOrdinal(FSharpSignatureDataResourceName2) then 
         String.dropPrefix r.Name FSharpSignatureDataResourceName2
     else failwith "GetSignatureDataResourceName"
 
 let GetOptimizationDataResourceName (r: ILResource) = 
-    if r.Name.StartsWith FSharpOptimizationDataResourceName then 
+    if r.Name.StartsWithOrdinal(FSharpOptimizationDataResourceName) then 
         String.dropPrefix r.Name FSharpOptimizationDataResourceName
-    elif r.Name.StartsWith FSharpOptimizationDataResourceName2 then 
+    elif r.Name.StartsWithOrdinal(FSharpOptimizationDataResourceName2) then 
         String.dropPrefix r.Name FSharpOptimizationDataResourceName2
     else failwith "GetOptimizationDataResourceName"
 
-let IsReflectedDefinitionsResource  (r: ILResource) = r.Name.StartsWith QuotationPickler.SerializedReflectedDefinitionsResourceNameBase
+let IsReflectedDefinitionsResource (r: ILResource) =
+    r.Name.StartsWithOrdinal(QuotationPickler.SerializedReflectedDefinitionsResourceNameBase)
 
 let MakeILResource rname bytes = 
     { Name = rname

src/fsharp/CompileOptions.fs

@@ -188,7 +188,7 @@ module ResponseFile =
         let parseLine (l: string) =
             match l with
             | s when String.IsNullOrWhiteSpace(s) -> None
-            | s when l.StartsWith("#") -> Some (ResponseFileLine.Comment (s.TrimStart('#')))
+            | s when l.StartsWithOrdinal("#") -> Some (ResponseFileLine.Comment (s.TrimStart('#')))
             | s -> Some (ResponseFileLine.CompilerOptionSpec (s.Trim()))
 
         try
@@ -224,7 +224,7 @@ let ParseCompilerOptions (collectOtherArgument : string -> unit, blocks: Compile
       if opt.Length = 2 || isSlashOpt opt then
         opt <- opt.[1 ..]
       // else, it should be a non-abbreviated option starting with "--"
-      elif opt.Length > 3 && opt.StartsWith("--") then
+      elif opt.Length > 3 && opt.StartsWithOrdinal("--") then
         opt <- opt.[2 ..]
       else
         opt <- ""
@@ -247,19 +247,19 @@ let ParseCompilerOptions (collectOtherArgument : string -> unit, blocks: Compile
   
   let getSwitchOpt (opt : string) =
     // if opt is a switch, strip the  '+' or '-'
-    if opt <> "--" && opt.Length > 1 && (opt.EndsWith("+",StringComparison.Ordinal) || opt.EndsWith("-",StringComparison.Ordinal)) then
+    if opt <> "--" && opt.Length > 1 && (opt.EndsWithOrdinal("+") || opt.EndsWithOrdinal("-")) then
       opt.[0 .. opt.Length - 2]
     else
       opt
       
   let getSwitch (s: string) = 
     let s = (s.Split([|':'|])).[0]
-    if s <> "--" && s.EndsWith("-",StringComparison.Ordinal) then OptionSwitch.Off else OptionSwitch.On
+    if s <> "--" && s.EndsWithOrdinal("-") then OptionSwitch.Off else OptionSwitch.On
 
   let rec processArg args =    
     match args with 
     | [] -> ()
-    | ((rsp: string) :: t) when rsp.StartsWith("@") ->
+    | ((rsp: string) :: t) when rsp.StartsWithOrdinal("@") ->
         let responseFileOptions =
             let fullpath =
                 try
@@ -555,7 +555,7 @@ let inputFileFlagsFsc tcConfigB = inputFileFlagsBoth tcConfigB
 //---------------------------------
 
 let errorsAndWarningsFlags (tcConfigB: TcConfigBuilder) = 
-    let trimFS (s:string) = if s.StartsWith("FS", StringComparison.Ordinal) = true then s.Substring(2) else s
+    let trimFS (s:string) = if s.StartsWithOrdinal("FS") = true then s.Substring(2) else s
     let trimFStoInt (s:string) =
         try
             Some (int32 (trimFS s))

src/fsharp/ConstraintSolver.fs

@@ -1241,8 +1241,8 @@ and SolveMemberConstraint (csenv:ConstraintSolverEnv) ignoreUnresolvedOverload p
 
           // First look for a solution by a record property
           let recdPropSearch = 
-              let isGetProp = nm.StartsWith "get_" 
-              let isSetProp = nm.StartsWith "set_" 
+              let isGetProp = nm.StartsWithOrdinal("get_") 
+              let isSetProp = nm.StartsWithOrdinal("set_") 
               if argtys.IsEmpty && isGetProp || isSetProp then 
                   let propName = nm.[4..]
                   let props = 

src/fsharp/ErrorResolutionHints.fs

@@ -4,6 +4,7 @@
 module internal Microsoft.FSharp.Compiler.ErrorResolutionHints
 
 open Internal.Utilities
+open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library
 
 let maxSuggestions = 5
 let minThresholdForSuggestions = 0.7
@@ -28,17 +29,18 @@ let FilterPredictions (idText:string) (suggestionF:ErrorLogger.Suggestions) =
     let allSuggestions = suggestionF()
 
     let demangle (nm:string) =
-        if nm.StartsWith "( " && nm.EndsWith " )" then
+        if nm.StartsWithOrdinal("( ") && nm.EndsWithOrdinal(" )") then
             let cleanName = nm.[2..nm.Length - 3]
             cleanName
         else nm
 
     /// Returns `true` if given string is an operator display name, e.g. ( |>> )
     let IsOperatorName (name: string) =
-        if not (name.StartsWith "( " && name.EndsWith " )") then false else
-        let name =  name.[2..name.Length - 3]
-        let res = name |> Seq.forall (fun c -> c <> ' ')
-        res        
+        if not (name.StartsWithOrdinal("( ") && name.EndsWithOrdinal(" )")) then
+            false
+        else
+            let name = name.[2..name.Length - 3]
+            name |> Seq.forall (fun c -> c <> ' ')
 
     if allSuggestions.Contains idText then [] else // some other parsing error occurred
     allSuggestions
@@ -47,11 +49,11 @@ let FilterPredictions (idText:string) (suggestionF:ErrorLogger.Suggestions) =
         // 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.StartsWith "_" then None else
+        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.EndsWith ("." + idText) then
+        if similarity >= highConfidenceThreshold || suggestion.EndsWithOrdinal("." + idText) then
             Some(similarity, suggestion)
         elif similarity < minThresholdForSuggestions && suggestedText.Length > minStringLengthForThreshold then
             None

src/fsharp/IlxGen.fs

@@ -5281,9 +5281,9 @@ and GenMethodForBinding
 
         let mdef = 
             if // operator names
-               mdef.Name.StartsWith("op_",System.StringComparison.Ordinal) || 
+               mdef.Name.StartsWithOrdinal("op_") || 
                // active pattern names
-               mdef.Name.StartsWith("|",System.StringComparison.Ordinal) ||
+               mdef.Name.StartsWithOrdinal("|") ||
                // event add/remove method
                v.val_flags.IsGeneratedEventVal then
                 mdef.WithSpecialName

src/fsharp/MethodCalls.fs

@@ -1300,7 +1300,8 @@ let MethInfoChecks g amap isInstance tyargsOpt objArgs ad m (minfo:MethInfo)  =
     if not (IsTypeAndMethInfoAccessible amap m adOriginal ad minfo) then 
       error (Error (FSComp.SR.tcMethodNotAccessible(minfo.LogicalName), m))
 
-    if isAnyTupleTy g minfo.ApparentEnclosingType && not minfo.IsExtensionMember && (minfo.LogicalName.StartsWith "get_Item" || minfo.LogicalName.StartsWith "get_Rest") then
+    if isAnyTupleTy g minfo.ApparentEnclosingType && not minfo.IsExtensionMember &&
+        (minfo.LogicalName.StartsWithOrdinal("get_Item") || minfo.LogicalName.StartsWithOrdinal("get_Rest")) then
       warning (Error (FSComp.SR.tcTupleMemberNotNormallyUsed(), m))
 
     CheckMethInfoAttributes g m tyargsOpt minfo |> CommitOperationResult

src/fsharp/NameResolution.fs

@@ -2890,7 +2890,7 @@ let rec ResolveTypeLongIdentPrim sink (ncenv:NameResolver) occurence first fully
                             | ItemOccurence.UseInAttribute -> 
                                 [yield e.Value.DisplayName
                                  yield e.Value.DemangledModuleOrNamespaceName
-                                 if e.Value.DisplayName.EndsWith "Attribute" then
+                                 if e.Value.DisplayName.EndsWithOrdinal("Attribute") then
                                      yield e.Value.DisplayName.Replace("Attribute","")]
                             | _ -> [e.Value.DisplayName; e.Value.DemangledModuleOrNamespaceName])
                         |> HashSet
@@ -3598,7 +3598,7 @@ let ResolveCompletionsInType (ncenv: NameResolver) nenv (completionTargets: Reso
                 if methsWithStaticParams.IsEmpty then minfos
                 else minfos |> List.filter (fun minfo -> 
                         let nm = minfo.LogicalName
-                        not (nm.Contains "," && methsWithStaticParams |> List.exists (fun m -> nm.StartsWith(m))))
+                        not (nm.Contains "," && methsWithStaticParams |> List.exists (fun m -> nm.StartsWithOrdinal(m))))
 #endif
 
             minfos 
@@ -4227,7 +4227,7 @@ let ResolveCompletionsInTypeForItem (ncenv: NameResolver) nenv m ad statics ty (
                         if methsWithStaticParams.IsEmpty then minfos
                         else minfos |> List.filter (fun minfo -> 
                                 let nm = minfo.LogicalName
-                                not (nm.Contains "," && methsWithStaticParams |> List.exists (fun m -> nm.StartsWith(m))))
+                                not (nm.Contains "," && methsWithStaticParams |> List.exists (fun m -> nm.StartsWithOrdinal(m))))
         #endif
         
                     minfos 

src/fsharp/NicePrint.fs

@@ -71,7 +71,7 @@ module internal PrintUtilities =
                     tcref.DisplayName // has no static params
                 else
                     tcref.DisplayName+"<...>" // shorten
-            if isAttribute && name.EndsWith "Attribute" then
+            if isAttribute && name.EndsWithOrdinal("Attribute") then
                 String.dropSuffix name "Attribute"
             else 
                 name
@@ -655,7 +655,7 @@ module private PrintTypes =
         | ILAttrib ilMethRef -> 
             let trimmedName = 
                 let name = ilMethRef.DeclaringTypeRef.Name
-                if name.EndsWith "Attribute" then
+                if name.EndsWithOrdinal("Attribute") then
                     String.dropSuffix name "Attribute"
                 else
                     name

src/fsharp/PostInferenceChecks.fs

@@ -4,6 +4,7 @@
 /// is complete.
 module internal Microsoft.FSharp.Compiler.PostTypeCheckSemanticChecks
 
+open System
 open System.Collections.Generic
 
 open Microsoft.FSharp.Compiler
@@ -153,7 +154,7 @@ let BindVal cenv env (v:Val) =
        cenv.reportErrors && 
        not v.HasBeenReferenced && 
        not v.IsCompiledAsTopLevel && 
-       not (v.DisplayName.StartsWith("_", System.StringComparison.Ordinal)) && 
+       not (v.DisplayName.StartsWithOrdinal("_")) && 
        not v.IsCompilerGenerated then 
 
         match v.BaseOrThisInfo with 
@@ -1478,14 +1479,14 @@ let CheckModuleBinding cenv env (TBind(v,e,_) as bind) =
 
                 // Default augmentation contains the nasty 'Case<UnionCase>' etc.
                 let prefix = "New"
-                if nm.StartsWith prefix then
+                if nm.StartsWithOrdinal(prefix) then
                     match tcref.GetUnionCaseByName(nm.[prefix.Length ..]) with 
                     | Some(uc) -> error(NameClash(nm,kind,v.DisplayName,v.Range, FSComp.SR.chkUnionCaseCompiledForm(),uc.DisplayName,uc.Range))
                     | None -> ()
 
                 // Default augmentation contains the nasty 'Is<UnionCase>' etc.
                 let prefix = "Is"
-                if nm.StartsWith prefix && hasDefaultAugmentation then
+                if nm.StartsWithOrdinal(prefix) && hasDefaultAugmentation then
                     match tcref.GetUnionCaseByName(nm.[prefix.Length ..]) with 
                     | Some(uc) -> error(NameClash(nm,kind,v.DisplayName,v.Range, FSComp.SR.chkUnionCaseDefaultAugmentation(),uc.DisplayName,uc.Range))
                     | None -> ()

src/fsharp/PrettyNaming.fs

@@ -136,13 +136,15 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
 
     /// Returns `true` if given string is an operator display name, e.g. ( |>> )
     let IsOperatorName (name: string) =
-        let name = if name.StartsWith "( " && name.EndsWith " )" then name.[2..name.Length - 3] else name
+        let name =
+            if name.StartsWithOrdinal("( ") && name.EndsWithOrdinal(" )") then
+                name.[2 .. name.Length - 3]
+            else name
         // there is single operator containing a space - range operator with step: `.. ..`
-        let res = name = ".. .." || name |> Seq.forall (fun c -> c <> ' ' && opCharSet.Contains c)
-        res
+        name = ".. .." || name |> Seq.forall (fun c -> c <> ' ' && opCharSet.Contains c)
 
     let IsMangledOpName (n:string) =
-        n.StartsWith (opNamePrefix, StringComparison.Ordinal)
+        n.StartsWithOrdinal(opNamePrefix)
 
     /// Compiles a custom operator into a mangled operator name.
     /// For example, "!%" becomes "op_DereferencePercent".
@@ -427,7 +429,7 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
         // This function recognises these "infix operator" names.
         let s = DecompileOpName s
         let skipIgnoredChars = s.TrimStart(ignoredChars)
-        let afterSkipStartsWith prefix   = skipIgnoredChars.StartsWith(prefix,StringComparison.Ordinal)
+        let afterSkipStartsWith prefix   = skipIgnoredChars.StartsWithOrdinal(prefix)
         let afterSkipStarts     prefixes = Array.exists afterSkipStartsWith prefixes
         // The following conditions follow the declExpr infix clauses.
         // The test corresponds to the lexer definition for the token.
@@ -468,7 +470,7 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
         if IsCompilerGeneratedName nm then nm else nm+compilerGeneratedMarker
 
     let GetBasicNameOfPossibleCompilerGeneratedName (name:string) =
-            match name.IndexOf compilerGeneratedMarker with 
+            match name.IndexOf(compilerGeneratedMarker, StringComparison.Ordinal) with 
             | -1 | 0 -> name
             | n -> name.[0..n-1]
 
@@ -518,13 +520,13 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
     let TryChopPropertyName (s: string) =
         // extract the logical name from any mangled name produced by MakeMemberDataAndMangledNameForMemberVal
         if s.Length <= 4 then None else
-        if s.StartsWith("get_", StringComparison.Ordinal) ||
-           s.StartsWith("set_", StringComparison.Ordinal)
+        if s.StartsWithOrdinal("get_") ||
+           s.StartsWithOrdinal("set_")
         then Some (s.Substring(4, s.Length - 4))
         else
         let s = chopStringTo s '.'
-        if s.StartsWith("get_", StringComparison.Ordinal) ||
-           s.StartsWith("set_", StringComparison.Ordinal)
+        if s.StartsWithOrdinal("get_") ||
+           s.StartsWithOrdinal("set_")
         then Some (s.Substring(4, s.Length - 4))
         else None
 
@@ -537,7 +539,7 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
         | Some res -> res
 
     let SplitNamesForILPath (s : string) : string list = 
-        if s.StartsWith("``",StringComparison.Ordinal) && s.EndsWith("``",StringComparison.Ordinal) && s.Length > 4 then [s.Substring(2, s.Length-4)] // identifier is enclosed in `` .. ``, so it is only a single element (this is very approximate)
+        if s.StartsWithOrdinal("``") && s.EndsWithOrdinal("``") && s.Length > 4 then [s.Substring(2, s.Length-4)] // identifier is enclosed in `` .. ``, so it is only a single element (this is very approximate)
         else s.Split [| '.' ; '`' |] |> Array.toList      // '.' chops members / namespaces / modules; '`' chops generic parameters for .NET types
         
     /// Return a string array delimited by the given separator.

src/fsharp/QuotationTranslator.fs

@@ -161,7 +161,7 @@ let (|ObjectInitializationCheck|_|) g expr =
            [| TTarget([], Expr.App(Expr.Val(failInitRef, _, _), _, _, _, _), _); _ |], _, resultTy
         ) when 
             IsCompilerGeneratedName name &&
-            name.StartsWith "init" &&
+            name.StartsWithOrdinal("init") &&
             selfRef.BaseOrThisInfo = MemberThisVal &&
             valRefEq g failInitRef (ValRefForIntrinsic g.fail_init_info) &&
             isUnitTy g resultTy -> Some()
@@ -562,8 +562,8 @@ and private ConvExprCore cenv (env : QuotationTranslationEnv) (expr: Expr) : QP.
              let methArgTypesR = List.map (ConvILType cenv env m) ilMethRef.ArgTypes
              let methRetTypeR = ConvILType cenv env m ilMethRef.ReturnType
              let methName = ilMethRef.Name
-             let isPropGet = isProp && methName.StartsWith("get_",System.StringComparison.Ordinal)
-             let isPropSet = isProp && methName.StartsWith("set_",System.StringComparison.Ordinal)
+             let isPropGet = isProp && methName.StartsWithOrdinal("get_")
+             let isPropSet = isProp && methName.StartsWithOrdinal("set_")
              let tyargs = (enclTypeArgs@methTypeArgs)
              ConvObjectModelCall cenv env m (isPropGet,isPropSet,isNewObj,parentTyconR,methArgTypesR,methRetTypeR,methName,tyargs,methTypeArgs.Length,callArgs)
 

src/fsharp/SimulatedMSBuildReferenceResolver.fs

@@ -103,7 +103,7 @@ let internal SimulatedMSBuildResolver =
 #if !FX_RESHAPED_MSBUILD
                 // For this one we need to get the version search exactly right, without doing a load
                 try 
-                    if not found && r.StartsWith("FSharp.Core, Version=")  && Environment.OSVersion.Platform = PlatformID.Win32NT then 
+                    if not found && r.StartsWithOrdinal("FSharp.Core, Version=") && Environment.OSVersion.Platform = PlatformID.Win32NT then 
                         let n = AssemblyName(r)
                         let fscoreDir0 = 
                             let PF = 

src/fsharp/TypeChecker.fs

@@ -623,7 +623,7 @@ let TryStripPrefixPath (g:TcGlobals) (enclosingNamespacePath: Ident list) =
     | p::rest when
         g.isInteractive &&
         not (isNil rest) &&
-        p.idText.StartsWith(FsiDynamicModulePrefix, System.StringComparison.Ordinal) && 
+        p.idText.StartsWithOrdinal(FsiDynamicModulePrefix) && 
         p.idText.[FsiDynamicModulePrefix.Length..] |> String.forall System.Char.IsDigit 
         -> Some(p, rest)
     | _ -> None
@@ -762,7 +762,7 @@ let ReportImplicitlyIgnoredBoolExpression denv m ty expr =
                         UnitTypeExpectedWithEquality (denv, ty, m)
                 else
                     UnitTypeExpectedWithEquality (denv, ty, m)
-            | Expr.Op(TOp.ILCall(_, _, _, _, _, _, _, methodRef, _, _, _), _, Expr.Val(vf, _, _) :: _, _) :: _ when methodRef.Name.StartsWith "get_"->
+            | Expr.Op(TOp.ILCall(_, _, _, _, _, _, _, methodRef, _, _, _), _, Expr.Val(vf, _, _) :: _, _) :: _ when methodRef.Name.StartsWithOrdinal("get_") ->
                 UnitTypeExpectedWithPossiblePropertySetter (denv, ty, vf.DisplayName, PrettyNaming.ChopPropertyName(methodRef.Name), m)
             | Expr.Val(vf, _, _) :: _ -> 
                 UnitTypeExpectedWithPossibleAssignment (denv, ty, vf.IsMutable, vf.DisplayName, m)
@@ -5125,7 +5125,7 @@ and TcPatBindingName cenv env id ty isMemberThis vis1 topValData (inlineFlag, de
         // isLeftMost indicates we are processing the left-most path through a disjunctive or pattern.
         // For those binding locations, CallNameResolutionSink is called in MakeAndPublishValue, like all other bindings
         // For non-left-most paths, we register the name resolutions here
-        if not isLeftMost && not vspec.IsCompilerGenerated && not (vspec.LogicalName.StartsWith "_") then 
+        if not isLeftMost && not vspec.IsCompilerGenerated && not (vspec.LogicalName.StartsWithOrdinal("_")) then 
             let item = Item.Value(mkLocalValRef vspec)
             CallNameResolutionSink cenv.tcSink (id.idRange, env.NameEnv, item, item, emptyTyparInst, ItemOccurence.Binding, env.DisplayEnv, env.eAccessRights)
 
@@ -9678,7 +9678,7 @@ and TcMethodApplication
                 match unrefinedItem with 
                 | Item.MethodGroup(_, overridenMeths, _) -> overridenMeths |> List.map (fun minfo -> minfo, None)
                 | Item.Property(_, pinfos) -> 
-                    if result.Method.LogicalName.StartsWith ("set_") then 
+                    if result.Method.LogicalName.StartsWithOrdinal("set_") then 
                         SettersOfPropInfos pinfos
                     else 
                         GettersOfPropInfos pinfos
@@ -12219,7 +12219,7 @@ let TcOpenDecl tcSink (g:TcGlobals) amap m scopem env (longId : Ident list)  =
         let p = 
             match p with 
             | [] -> []
-            | (h, _):: t -> if h.StartsWith(FsiDynamicModulePrefix, System.StringComparison.Ordinal) then t else p
+            | (h, _):: t -> if h.StartsWithOrdinal(FsiDynamicModulePrefix) then t else p
 
         // See https://fslang.uservoice.com/forums/245727-f-language/suggestions/6107641-make-microsoft-prefix-optional-when-using-core-f
         let isFSharpCoreSpecialCase =
@@ -12487,7 +12487,7 @@ module IncrClassChecking =
                 nm, takenFieldNames.Add(nm)
                  
             let reportIfUnused() = 
-                if not v.HasBeenReferenced && not v.IsCompiledAsTopLevel && not (v.DisplayName.StartsWith "_") && not v.IsCompilerGenerated then 
+                if not v.HasBeenReferenced && not v.IsCompiledAsTopLevel && not (v.DisplayName.StartsWithOrdinal("_")) && not v.IsCompilerGenerated then 
                     warning (Error(FSComp.SR.chkUnusedValue(v.DisplayName), v.Range))
 
             let repr = 
@@ -15994,7 +15994,7 @@ module TcDeclarations =
                   | None -> 
                         //false
                         // There is a special case we allow when compiling FSharp.Core.dll which permits interface implementations across namespace fragments
-                        (cenv.g.compilingFslib && tcref.LogicalName.StartsWith("Tuple`"))
+                        (cenv.g.compilingFslib && tcref.LogicalName.StartsWithOrdinal("Tuple`"))
         
             let nReqTypars = reqTypars.Length
 

src/fsharp/ast.fs

@@ -100,7 +100,7 @@ type XmlDoc =
             | (lineA::rest) as lines ->
                 let lineAT = lineA.TrimStart([|' '|])
                 if lineAT = "" then processLines rest
-                else if lineAT.StartsWith "<" then lines
+                else if lineAT.StartsWithOrdinal("<") then lines
                 else ["<summary>"] @
                      (lines |> List.map (fun line -> Microsoft.FSharp.Core.XmlAdapters.escape(line))) @
                      ["</summary>"]

src/fsharp/fsi/fsi.fs

@@ -2343,7 +2343,7 @@ type internal FsiInteractionProcessor
 
         let nItems = NameResolution.ResolvePartialLongIdent ncenv nenv (ConstraintSolver.IsApplicableMethApprox istate.tcGlobals amap rangeStdin) rangeStdin ad lid false
         let names  = nItems |> List.map (fun d -> d.DisplayName) 
-        let names  = names |> List.filter (fun name -> name.StartsWith(stem,StringComparison.Ordinal)) 
+        let names  = names |> List.filter (fun name -> name.StartsWithOrdinal(stem)) 
         names
 
     member __.ParseAndCheckInteraction (ctok, legacyReferenceResolver, checker, istate, text:string) =

src/fsharp/lexhelp.fs

@@ -355,7 +355,10 @@ module Keywords =
 
     /// Quote identifier with double backticks if needed, remove unnecessary double backticks quotation.
     let NormalizeIdentifierBackticks (s : string) : string =
-        let s = if s.StartsWith "``" && s.EndsWith "``" then s.[2..s.Length - 3] else s
+        let s =
+            if s.StartsWithOrdinal("``") && s.EndsWithOrdinal("``") then
+                s.[2..s.Length - 3]
+            else s
         QuoteIdentifierIfNeeded s
 
     /// Keywords paired with their descriptions. Used in completion and quick info.

src/fsharp/range.fs

@@ -3,6 +3,7 @@
 /// Anything to do with special names of identifiers and other lexical rules 
 module Microsoft.FSharp.Compiler.Range
 
+open System
 open System.IO
 open System.Collections.Generic
 open Microsoft.FSharp.Core.Printf
@@ -177,7 +178,7 @@ type range(code:int64) =
             |> Seq.skip (r.StartLine - 1)
             |> Seq.take (r.EndLine - r.StartLine + 1)
             |> String.concat "\n"
-            |> fun s -> s.Substring(startCol + 1, s.LastIndexOf("\n") + 1 - startCol + endCol)
+            |> fun s -> s.Substring(startCol + 1, s.LastIndexOf("\n", StringComparison.Ordinal) + 1 - startCol + endCol)
         with e ->
             e.ToString()        
 #endif

src/fsharp/service/IncrementalBuild.fs

@@ -1745,7 +1745,7 @@ type IncrementalBuilder(tcGlobals, frameworkTcImports, nonFrameworkAssemblyInput
             let tcConfigB, sourceFilesNew = 
 
                 let getSwitchValue switchstring =
-                    match commandLineArgs |> Seq.tryFindIndex(fun s -> s.StartsWith(switchstring)) with
+                    match commandLineArgs |> Seq.tryFindIndex(fun s -> s.StartsWithOrdinal(switchstring)) with
                     | Some idx -> Some(commandLineArgs.[idx].Substring(switchstring.Length))
                     | _ -> None
 

src/fsharp/service/QuickParse.fs

@@ -3,6 +3,7 @@
 namespace Microsoft.FSharp.Compiler
 
 open System
+open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library
 open Microsoft.FSharp.Compiler.SourceCodeServices
 
 /// Qualified long name.
@@ -46,7 +47,8 @@ module QuickParse =
     // Adjusts the token tag for the given identifier
     // - if we're inside active pattern name (at the bar), correct the token TAG to be an identifier
     let CorrectIdentifierToken (tokenText: string) (tokenTag: int) = 
-        if tokenText.EndsWith "|" then Microsoft.FSharp.Compiler.Parser.tagOfToken (Microsoft.FSharp.Compiler.Parser.token.IDENT tokenText)
+        if tokenText.EndsWithOrdinal("|") then
+            Microsoft.FSharp.Compiler.Parser.tagOfToken (Microsoft.FSharp.Compiler.Parser.token.IDENT tokenText)
         else tokenTag
 
     let rec isValidStrippedName (name:string) idx = 
@@ -61,9 +63,7 @@ module QuickParse =
     let private isValidActivePatternName (name: string) = 
 
       // Strip the surrounding bars (e.g. from "|xyz|_|") to get "xyz"
-      match name.StartsWith("|", System.StringComparison.Ordinal), 
-            name.EndsWith("|_|", System.StringComparison.Ordinal), 
-            name.EndsWith("|", System.StringComparison.Ordinal) with
+      match name.StartsWithOrdinal("|"), name.EndsWithOrdinal("|_|"), name.EndsWithOrdinal("|") with
       | true, true, _ when name.Length > 4 -> isValidStrippedName (name.Substring(1, name.Length - 4)) 0
       | true, _, true when name.Length > 2 -> isValidStrippedName (name.Substring(1, name.Length - 2)) 0
       | _ -> false

src/fsharp/service/ServiceAssemblyContent.fs

@@ -66,7 +66,7 @@ module Extensions =
             try x.MembersFunctionsAndValues with _ -> [||] :> _
 
     let isOperator (name: string) =
-        name.StartsWith "( " && name.EndsWith " )" && name.Length > 4
+        name.StartsWithOrdinal("( ") && name.EndsWithOrdinal(" )") && name.Length > 4
             && name.Substring (2, name.Length - 4) 
                |> String.forall (fun c -> c <> ' ' && not (Char.IsLetter c))
 
@@ -1007,7 +1007,8 @@ module ParsedInput =
                 if ctx.Pos.Line > 1 then
                     // it's an implicit module without any open declarations    
                     let line = getLineStr (ctx.Pos.Line - 2)
-                    let isImpliciteTopLevelModule = not (line.StartsWith "module" && not (line.EndsWith "="))
+                    let isImpliciteTopLevelModule =
+                        not (line.StartsWithOrdinal("module") && not (line.EndsWithOrdinal("=")))
                     if isImpliciteTopLevelModule then 1 else ctx.Pos.Line
                 else 1
             | ScopeKind.Namespace ->
@@ -1016,7 +1017,7 @@ module ParsedInput =
                     [0..ctx.Pos.Line - 1]
                     |> List.mapi (fun i line -> i, getLineStr line)
                     |> List.tryPick (fun (i, lineStr) -> 
-                        if lineStr.StartsWith "namespace" then Some i
+                        if lineStr.StartsWithOrdinal("namespace") then Some i
                         else None)
                     |> function
                         // move to the next line below "namespace" and convert it to F# 1-based line number

src/fsharp/service/ServiceDeclarationLists.fs

@@ -11,7 +11,6 @@ open Microsoft.FSharp.Compiler
 open Microsoft.FSharp.Compiler.AbstractIL.IL 
 open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library  
 open Microsoft.FSharp.Compiler.AbstractIL.Diagnostics 
-
 open Microsoft.FSharp.Compiler.AccessibilityLogic
 open Microsoft.FSharp.Compiler.ErrorLogger
 open Microsoft.FSharp.Compiler.Layout
@@ -642,7 +641,7 @@ type FSharpDeclarationListInfo(declarations: FSharpDeclarationListItem[], isForT
                     let glyph = GlyphOfItem(denv, item.Item)
 
                     let name, nameInCode =
-                        if displayName.StartsWith "( " && displayName.EndsWith " )" then
+                        if displayName.StartsWithOrdinal("( ") && displayName.EndsWithOrdinal(" )") then
                             let cleanName = displayName.[2..displayName.Length - 3]
                             cleanName, 
                             if IsOperatorName displayName then cleanName else "``" + cleanName + "``"
@@ -655,7 +654,7 @@ type FSharpDeclarationListInfo(declarations: FSharpDeclarationListItem[], isForT
                     let isAttributeItem = lazy (SymbolHelpers.IsAttribute infoReader item.Item)
 
                     let cutAttributeSuffix (name: string) =
-                        if isAttributeApplicationContext && name <> "Attribute" && name.EndsWith "Attribute" && isAttributeItem.Value then
+                        if isAttributeApplicationContext && name <> "Attribute" && name.EndsWithOrdinal("Attribute") && isAttributeItem.Value then
                             name.[0..name.Length - "Attribute".Length - 1]
                         else name
 

src/fsharp/service/ServiceInterfaceStubGenerator.fs

@@ -289,8 +289,8 @@ module internal InterfaceStubGenerator =
     /// Convert a getter/setter to its canonical form
     let internal normalizePropertyName (v: FSharpMemberOrFunctionOrValue) =
         let displayName = v.DisplayName
-        if (v.IsPropertyGetterMethod && displayName.StartsWith("get_")) || 
-            (v.IsPropertySetterMethod && displayName.StartsWith("set_")) then
+        if (v.IsPropertyGetterMethod && displayName.StartsWithOrdinal("get_")) || 
+            (v.IsPropertySetterMethod && displayName.StartsWithOrdinal("set_")) then
             displayName.[4..]
         else displayName
 
@@ -308,7 +308,7 @@ module internal InterfaceStubGenerator =
                 | _  -> formatArgsUsage ctx verboseMode v argInfos
              
             if String.IsNullOrWhiteSpace(args) then "" 
-            elif args.StartsWith("(") then args
+            elif args.StartsWithOrdinal("(") then args
             elif v.CurriedParameterGroups.Count > 1 && (not verboseMode) then " " + args
             else sprintf "(%s)" args
             , namesWithIndices
@@ -321,7 +321,7 @@ module internal InterfaceStubGenerator =
                 | _, _, ".ctor", _ -> "new" + parArgs
                 // Properties (skipping arguments)
                 | _, true, _, name when v.IsPropertyGetterMethod || v.IsPropertySetterMethod -> 
-                    if name.StartsWith("get_") || name.StartsWith("set_") then name.[4..] else name
+                    if name.StartsWithOrdinal("get_") || name.StartsWithOrdinal("set_") then name.[4..] else name
                 // Ordinary instance members
                 | _, true, _, name -> name + parArgs
                 // Ordinary functions or values
@@ -509,10 +509,10 @@ module internal InterfaceStubGenerator =
     let internal (|MemberNameAndRange|_|) = function
         | Binding(_access, _bindingKind, _isInline, _isMutable, _attrs, _xmldoc, SynValData(Some mf, _, _), LongIdentPattern(name, range), 
                     _retTy, _expr, _bindingRange, _seqPoint) when mf.MemberKind = MemberKind.PropertyGet ->
-            if name.StartsWith("get_") then Some(name, range) else Some("get_" + name, range)
+            if name.StartsWithOrdinal("get_") then Some(name, range) else Some("get_" + name, range)
         | Binding(_access, _bindingKind, _isInline, _isMutable, _attrs, _xmldoc, SynValData(Some mf, _, _), LongIdentPattern(name, range), 
                     _retTy, _expr, _bindingRange, _seqPoint) when mf.MemberKind = MemberKind.PropertySet ->
-            if name.StartsWith("set_") then Some(name, range) else Some("set_" + name, range)
+            if name.StartsWithOrdinal("set_") then Some(name, range) else Some("set_" + name, range)
         | Binding(_access, _bindingKind, _isInline, _isMutable, _attrs, _xmldoc, _valData, LongIdentPattern(name, range), 
                     _retTy, _expr, _bindingRange, _seqPoint) ->
             Some(name, range)
@@ -535,8 +535,8 @@ module internal InterfaceStubGenerator =
 
     let internal normalizeEventName (m: FSharpMemberOrFunctionOrValue) =
         let name = m.DisplayName
-        if name.StartsWith("add_") then name.[4..]
-        elif name.StartsWith("remove_")  then name.[7..]
+        if name.StartsWithOrdinal("add_") then name.[4..]
+        elif name.StartsWithOrdinal("remove_")  then name.[7..]
         else name
 
     /// Ideally this info should be returned in error symbols from FCS. 

src/fsharp/service/ServiceLexing.fs

@@ -6,8 +6,10 @@
 
 namespace Microsoft.FSharp.Compiler.SourceCodeServices
 
+open System
 open System.Collections.Generic
 open Microsoft.FSharp.Compiler.AbstractIL.Internal  
+open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library  
 open Microsoft.FSharp.Compiler 
 open Microsoft.FSharp.Compiler.Parser
 open Microsoft.FSharp.Compiler.Range
@@ -511,7 +513,7 @@ type FSharpLineTokenizer(lexbuf: UnicodeLexing.Lexbuf,
 
     // Process: anywhite* #<directive>
     let processDirective (str:string) directiveLength delay cont =
-        let hashIdx = str.IndexOf("#")
+        let hashIdx = str.IndexOf("#", StringComparison.Ordinal)
         if (hashIdx <> 0) then delay(WHITESPACE cont, 0, hashIdx - 1)
         delay(HASH_IF(range0, "", cont), hashIdx, hashIdx + directiveLength)
         hashIdx + directiveLength + 1
@@ -623,34 +625,34 @@ type FSharpLineTokenizer(lexbuf: UnicodeLexing.Lexbuf,
                           delayToken(greaters.[i] false, leftc + i, rightc - opstr.Length + i + 1)
                       false, (greaters.[0] false, leftc, rightc - opstr.Length + 1)
                   // break up any operators that start with '.' so that we can get auto-popup-completion for e.g. "x.+1"  when typing the dot
-                  | INFIX_STAR_STAR_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_STAR_STAR_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_STAR_STAR_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | PLUS_MINUS_OP opstr when opstr.StartsWith(".") ->
+                  | PLUS_MINUS_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(PLUS_MINUS_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | INFIX_COMPARE_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_COMPARE_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_COMPARE_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | INFIX_AT_HAT_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_AT_HAT_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_AT_HAT_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | INFIX_BAR_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_BAR_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_BAR_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | PREFIX_OP opstr when opstr.StartsWith(".") ->
+                  | PREFIX_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(PREFIX_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | INFIX_STAR_DIV_MOD_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_STAR_DIV_MOD_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_STAR_DIV_MOD_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | INFIX_AMP_OP opstr when opstr.StartsWith(".") ->
+                  | INFIX_AMP_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(INFIX_AMP_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | ADJACENT_PREFIX_OP opstr when opstr.StartsWith(".") ->
+                  | ADJACENT_PREFIX_OP opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(ADJACENT_PREFIX_OP(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
-                  | FUNKY_OPERATOR_NAME opstr when opstr.StartsWith(".") ->
+                  | FUNKY_OPERATOR_NAME opstr when opstr.StartsWithOrdinal(".") ->
                       delayToken(FUNKY_OPERATOR_NAME(opstr.Substring(1)), leftc+1, rightc)
                       false, (DOT, leftc, leftc)
                   | _ -> false, (token, leftc, rightc)

src/fsharp/service/ServiceStructure.fs

@@ -2,8 +2,9 @@
 
 namespace Microsoft.FSharp.Compiler.SourceCodeServices
 
-open Microsoft.FSharp.Compiler.Ast
 open System.Collections.Generic
+open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library
+open Microsoft.FSharp.Compiler.Ast
 open Microsoft.FSharp.Compiler
 open Microsoft.FSharp.Compiler.Range
 
@@ -624,8 +625,8 @@ module Structure =
 
         /// Determine if a line is a single line or xml docummentation comment
         let (|Comment|_|) (line: string) =
-            if line.StartsWith "///" then Some XmlDoc
-            elif line.StartsWith "//" then Some SingleLine
+            if line.StartsWithOrdinal("///") then Some XmlDoc
+            elif line.StartsWithOrdinal("//") then Some SingleLine
             else None
 
         let getCommentRanges (lines: string[]) =

src/fsharp/service/ServiceUntypedParse.fs

@@ -1358,7 +1358,7 @@ module UntypedParseImpl =
                       else None)
              else
                 // Paired [< and >] were not found, try to determine that we are after [< without closing >]
-                match lineStr.LastIndexOf "[<" with
+                match lineStr.LastIndexOf("[<", StringComparison.Ordinal) with
                 | -1 -> None
                 | openParenIndex when pos.Column >= openParenIndex + 2 -> 
                     let str = lineStr.[openParenIndex + 2..pos.Column - 1].TrimStart()

src/fsharp/service/ServiceXmlDocParser.fs

@@ -165,7 +165,7 @@ module XmlDocComment =
         Some (res, pos + (s.Length - res.Length))
 
     let private str (prefix: string) (s: string, pos) =
-        match s.StartsWith prefix with
+        match s.StartsWithOrdinal(prefix) with
         | true -> 
             let res = s.Substring prefix.Length
             Some (res, pos + (s.Length - res.Length))

src/fsharp/symbols/Exprs.fs

@@ -183,7 +183,7 @@ module FSharpExprConvert =
         rfref.RecdField.IsCompilerGenerated && 
         rfref.RecdField.IsStatic &&
         rfref.RecdField.IsMutable &&
-        rfref.RecdField.Name.StartsWith "init" 
+        rfref.RecdField.Name.StartsWithOrdinal("init") 
 
         // Match "if [AI_clt](init@41, 6) then IntrinsicFunctions.FailStaticInit () else ()"
     let (|StaticInitializationCheck|_|) e = 
@@ -857,8 +857,8 @@ module FSharpExprConvert =
     and ConvILCall (cenv:SymbolEnv) env (isNewObj, valUseFlags, ilMethRef, enclTypeArgs, methTypeArgs, callArgs, m) =
         let isNewObj = (isNewObj || (match valUseFlags with CtorValUsedAsSuperInit | CtorValUsedAsSelfInit -> true | _ -> false))
         let methName = ilMethRef.Name
-        let isPropGet = methName.StartsWith("get_", System.StringComparison.Ordinal)
-        let isPropSet = methName.StartsWith("set_", System.StringComparison.Ordinal)
+        let isPropGet = methName.StartsWithOrdinal("get_")
+        let isPropSet = methName.StartsWithOrdinal("set_")
         let isProp = isPropGet || isPropSet
         
         let tcref, subClass = 
@@ -916,8 +916,8 @@ module FSharpExprConvert =
                         let vr = VRefLocal v
                         makeFSCall isMember vr
                     | [] ->
-                        let isPropGet = vName.StartsWith("get_", System.StringComparison.Ordinal)
-                        let isPropSet = vName.StartsWith("set_", System.StringComparison.Ordinal)
+                        let isPropGet = vName.StartsWithOrdinal("get_")
+                        let isPropSet = vName.StartsWithOrdinal("set_")
                         if isPropGet || isPropSet then
                             let name = PrettyNaming.ChopPropertyName vName          
                             let findByName =
@@ -956,12 +956,12 @@ module FSharpExprConvert =
                     if vName = "GetTag" || vName = "get_Tag" then
                         let objR = ConvExpr cenv env callArgs.Head
                         E.UnionCaseTag(objR, typR) 
-                    elif vName.StartsWith("New") then
+                    elif vName.StartsWithOrdinal("New") then
                         let name = vName.Substring(3)
                         let mkR = ConvUnionCaseRef cenv (UCRef(tcref, name))
                         let argsR = ConvExprs cenv env callArgs
                         E.NewUnionCase(typR, mkR, argsR)
-                    elif vName.StartsWith("Is") then
+                    elif vName.StartsWithOrdinal("Is") then
                         let name = vName.Substring(2)
                         let mkR = ConvUnionCaseRef cenv (UCRef(tcref, name))
                         let objR = ConvExpr cenv env callArgs.Head

src/fsharp/symbols/SymbolPatterns.fs

@@ -5,8 +5,9 @@ namespace Microsoft.FSharp.Compiler.SourceCodeServices
 /// Patterns over FSharpSymbol and derivatives.
 [<RequireQualifiedAccess>]
 module Symbol =
-    open System.Text.RegularExpressions
     open System
+    open System.Text.RegularExpressions
+    open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library
 
     let isAttribute<'T> (attribute: FSharpAttribute) =
         // CompiledName throws exception on DataContractAttribute generated by SQLProvider
@@ -36,7 +37,7 @@ module Symbol =
             |> Option.isSome
 
     let isOperator (name: string) =
-        name.StartsWith "( " && name.EndsWith " )" && name.Length > 4
+        name.StartsWithOrdinal("( ") && name.EndsWithOrdinal(" )") && name.Length > 4
             && name.Substring (2, name.Length - 4) 
                 |> String.forall (fun c -> c <> ' ' && not (Char.IsLetter c))
 

src/fsharp/symbols/Symbols.fs

@@ -1550,7 +1550,7 @@ and FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
     member __.IsEventAddMethod = 
         if isUnresolved() then false else 
         match d with 
-        | M m when m.LogicalName.StartsWith("add_") -> 
+        | M m when m.LogicalName.StartsWithOrdinal("add_") -> 
             let eventName = m.LogicalName.[4..]
             let entityTy = generalizedTyconRef m.DeclaringTyconRef
             not (isNil (cenv.infoReader.GetImmediateIntrinsicEventsOfType (Some eventName, AccessibleFromSomeFSharpCode, range0, entityTy))) ||
@@ -1564,7 +1564,7 @@ and FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
     member __.IsEventRemoveMethod = 
         if isUnresolved() then false else 
         match d with 
-        | M m when m.LogicalName.StartsWith("remove_") -> 
+        | M m when m.LogicalName.StartsWithOrdinal("remove_") -> 
             let eventName = m.LogicalName.[7..]
             let entityTy = generalizedTyconRef m.DeclaringTyconRef
             not (isNil (cenv.infoReader.GetImmediateIntrinsicEventsOfType (Some eventName, AccessibleFromSomeFSharpCode, range0, entityTy))) ||
@@ -1591,7 +1591,7 @@ and FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
     member __.IsPropertyGetterMethod = 
         if isUnresolved() then false else 
         match d with 
-        | M m when m.LogicalName.StartsWith("get_") -> 
+        | M m when m.LogicalName.StartsWithOrdinal("get_") -> 
             let propName = PrettyNaming.ChopPropertyName(m.LogicalName) 
             let declaringTy = generalizedTyconRef m.DeclaringTyconRef
             not (isNil (GetImmediateIntrinsicPropInfosOfType (Some propName, AccessibleFromSomeFSharpCode) cenv.g cenv.amap range0 declaringTy))
@@ -1602,7 +1602,7 @@ and FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
         if isUnresolved() then false else 
         match d with 
         // Look for a matching property with the right name. 
-        | M m when m.LogicalName.StartsWith("set_") -> 
+        | M m when m.LogicalName.StartsWithOrdinal("set_") -> 
             let propName = PrettyNaming.ChopPropertyName(m.LogicalName) 
             let declaringTy = generalizedTyconRef m.DeclaringTyconRef
             not (isNil (GetImmediateIntrinsicPropInfosOfType (Some propName, AccessibleFromSomeFSharpCode) cenv.g cenv.amap range0 declaringTy))

src/utils/filename.fs

@@ -14,7 +14,7 @@ let checkPathForIllegalChars  =
             if chars.Contains c then raise(IllegalFileNameChar(path, c)))
 
 // Case sensitive (original behaviour preserved).
-let checkSuffix (x:string) (y:string) = x.EndsWith(y,System.StringComparison.Ordinal) 
+let checkSuffix (x:string) (y:string) = x.EndsWithOrdinal(y) 
 
 let hasExtensionWithValidate (validate:bool) (s:string) = 
     if validate then (checkPathForIllegalChars s) |> ignore

tests/service/Common.fs

 module internal FSharp.Compiler.Service.Tests.Common
 
+open System
 open System.IO
 open System.Collections.Generic
 open Microsoft.FSharp.Compiler
@@ -36,7 +37,7 @@ let readRefs (folder : string) (projectFile: string) =
     match result with
     | Ok(Dotnet.ProjInfo.Inspect.GetResult.FscArgs x) ->
         x
-        |> List.filter (fun s -> s.StartsWith("-r:"))
+        |> List.filter (fun s -> s.StartsWith("-r:", StringComparison.Ordinal))
         |> List.map (fun s -> s.Replace("-r:", ""))
     | _ -> []
 #endif

tests/service/ExprTests.fs

@@ -183,7 +183,7 @@ module internal Utils =
 
     let printGenericParameter (p: FSharpGenericParameter) =
         let name = 
-            if p.Name.StartsWith "?" then "_"
+            if p.Name.StartsWith("?", StringComparison.Ordinal) then "_"
             elif p.IsSolveAtCompileTime then "^" + p.Name 
             else "'" + p.Name
         let constraints =