Use dict instead if mutable Map (#9113)

* Use dict instead if mutable Map

* open namespace

* cleanup

* Further cleanup

* small cleanup

src/fsharp/service/ServiceNavigation.fs

@@ -7,6 +7,7 @@
 
 namespace FSharp.Compiler.SourceCodeServices
 
+open System.Collections.Generic
 open FSharp.Compiler.Range
 open FSharp.Compiler.SyntaxTree
 open FSharp.Compiler.SyntaxTreeOps
@@ -78,9 +79,9 @@ module NavigationImpl =
         else unionRanges r1 r2
     
     let rangeOfDecls2 f decls = 
-      match (decls |> List.map (f >> (fun (d:FSharpNavigationDeclarationItem) -> d.bodyRange))) with 
-      | hd :: tl -> tl |> List.fold unionRangesChecked hd
-      | [] -> range.Zero
+        match decls |> List.map (f >> (fun (d:FSharpNavigationDeclarationItem) -> d.bodyRange)) with 
+        | hd :: tl -> tl |> List.fold unionRangesChecked hd
+        | [] -> range.Zero
     
     let rangeOfDecls = rangeOfDecls2 fst
 
@@ -98,15 +99,18 @@ module NavigationImpl =
     /// Get information for implementation file      
     let getNavigationFromImplFile (modules: SynModuleOrNamespace list) =
         // Map for dealing with name conflicts
-        let mutable nameMap = Map.empty 
+        let names = Dictionary()
 
         let addItemName name = 
-            let count = defaultArg (nameMap |> Map.tryFind name) 0
-            nameMap <- (Map.add name (count + 1) (nameMap))
-            (count + 1)
+            let count =
+                match names.TryGetValue name with
+                | true, count -> count + 1
+                | _ -> 1
+            names.[name] <- count
+            count
         
         let uniqueName name idx = 
-            let total = Map.find name nameMap
+            let total = names.[name]
             sprintf "%s_%d_of_%d" name idx total
 
         // Create declaration (for the left dropdown)                
@@ -195,8 +199,11 @@ module NavigationImpl =
                 | SynTypeDefnSimpleRepr.Record(_, fields, mb) ->
                     let fields = 
                         [ for (Field(_, _, id, _, _, _, _, m)) in fields do
-                            if (id.IsSome) then
-                              yield createMember(id.Value, FieldDecl, FSharpGlyph.Field, m, FSharpEnclosingEntityKind.Record, false, access) ]
+                            match id with
+                            | Some ident -> 
+                                yield createMember(ident, FieldDecl, FSharpGlyph.Field, m, FSharpEnclosingEntityKind.Record, false, access)
+                            | _ -> 
+                                () ]
                     let nested = fields@topMembers
                     [ createDeclLid(baseName, lid, TypeDecl, FSharpGlyph.Type, m, bodyRange mb nested, nested, FSharpEnclosingEntityKind.Record, false, access) ]
                 | SynTypeDefnSimpleRepr.TypeAbbrev(_, _, mb) ->
@@ -244,7 +251,7 @@ module NavigationImpl =
                      | _ -> [])) 
             
             (members |> Seq.map fst |> Seq.fold unionRangesChecked range.Zero),
-            (members |> List.map snd |> List.concat)
+            (members |> List.collect snd)
 
         // Process declarations in a module that belong to the right drop-down (let bindings)
         let processNestedDeclarations decls = decls |> List.collect (function
@@ -364,8 +371,11 @@ module NavigationImpl =
                 | SynTypeDefnSimpleRepr.Record(_, fields, mb) ->
                     let fields = 
                         [ for (Field(_, _, id, _, _, _, _, m)) in fields do
-                            if (id.IsSome) then
-                              yield createMember(id.Value, FieldDecl, FSharpGlyph.Field, m, FSharpEnclosingEntityKind.Record, false, access) ]
+                            match id with
+                            | Some ident ->
+                                yield createMember(ident, FieldDecl, FSharpGlyph.Field, m, FSharpEnclosingEntityKind.Record, false, access)
+                            | _ ->
+                                () ]
                     let nested = fields@topMembers
                     [ createDeclLid(baseName, lid, TypeDecl, FSharpGlyph.Type, m, bodyRange mb nested, nested, FSharpEnclosingEntityKind.Record, false, access) ]
                 | SynTypeDefnSimpleRepr.TypeAbbrev(_, _, mb) ->
@@ -393,14 +403,16 @@ module NavigationImpl =
 
         // Process declarations nested in a module that should be displayed in the left dropdown
         // (such as type declarations, nested modules etc.)                            
-        let rec processFSharpNavigationTopLevelSigDeclarations(baseName, decls) = decls |> List.collect (function
+        let rec processFSharpNavigationTopLevelSigDeclarations(baseName, decls) = 
+            decls 
+            |> List.collect (function
             | SynModuleSigDecl.ModuleAbbrev(id, lid, m) ->
                 [ createDecl(baseName, id, ModuleDecl, FSharpGlyph.Module, m, rangeOfLid lid, [], FSharpEnclosingEntityKind.Module, false, None) ]
                 
             | SynModuleSigDecl.NestedModule(ComponentInfo(_, _, _, lid, _, _, access, _), _, decls, m) ->                
                 // Find let bindings (for the right dropdown)
                 let nested = processNestedSigDeclarations(decls)
-                let newBaseName = (if (baseName = "") then "" else baseName+".") + (textOfLid lid)
+                let newBaseName = (if baseName = "" then "" else baseName + ".") + (textOfLid lid)
                 
                 // Get nested modules and types (for the left dropdown)
                 let other = processFSharpNavigationTopLevelSigDeclarations(newBaseName, decls)