We only need to check for mangledGenericTypeNameSym once (#5633)

* We only need to check for mangledGenericTypeNameSym once

* ShortCut name checking

* Reduce number of LastIndexOf calls

* Reduce number of LastIndexOf calls

* Reduce number of LastIndexOf calls

* Incorporate feedback

* Use PrettyNaming.DemangleGenericTypeName instead of ungenericizeTypeName

* Remove couple of double checks

* Update illib.fs

src/absil/il.fs

@@ -154,12 +154,11 @@ let unsplitTypeName (ns, n) =
     | [] -> String.concat "." ns + "." + n 
     | _ -> n 
 
-let splitTypeNameRightAux nm = 
-    if String.contains nm '.' then 
-      let idx = String.rindex nm '.'
-      let s1, s2 = splitNameAt nm idx
-      Some s1, s2 
-    else None, nm
+let splitTypeNameRightAux (nm:string) = 
+    let idx = nm.LastIndexOf '.'
+    if idx = -1 then None, nm else
+    let s1, s2 = splitNameAt nm idx
+    Some s1, s2
 
 let splitTypeNameRight nm =
     memoizeNamespaceRightTable.GetOrAdd(nm, splitTypeNameRightAux)
@@ -4189,23 +4188,6 @@ let resolveILMethodRef td mref = resolveILMethodRefWithRescope id td mref
 let mkRefToILModule m =
   ILModuleRef.Create(m.Name, true, None)
 
-
-let ungenericizeTypeName n = 
-  let sym = '`'
-  if 
-    String.contains n sym && 
-      (* check what comes after the symbol is a number *)
-    (let m = String.rindex n sym
-     let res = ref (m < n.Length - 1)
-     for i = m + 1 to n.Length - 1 do
-       res := !res && n.[i] >= '0' && n.[i] <= '9'
-     !res)
-  then 
-      let pos = String.rindex n sym
-      String.sub n 0 pos
-  else n
-
-
 type ILEventRef =
     { erA: ILTypeRef; erB: string }
     static member Create(a, b) = {erA=a;erB=b}

src/absil/il.fsi

@@ -1540,9 +1540,6 @@ val typeNameForGlobalFunctions: string
 
 val isTypeNameForGlobalFunctions: string -> bool
 
-val ungenericizeTypeName: string -> string (* e.g. List`1 --> List *)
-
-
 // ====================================================================
 // PART 2
 // 

src/absil/illib.fs

@@ -452,23 +452,13 @@ type String with
     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"))
-
+module String =
     let make (n: int) (c: char) : string = new String(c, n)
 
     let get (str:string) i = str.[i]
 
     let sub (s:string) (start:int) (len:int) = s.Substring(start,len)
 
-    let index (s:string) (c:char) =  
-        let r = s.IndexOf(c) 
-        if r = -1 then indexNotFound() else r
-
-    let rindex (s:string) (c:char) =
-        let r =  s.LastIndexOf(c) 
-        if r = -1 then indexNotFound() else r
-
     let contains (s:string) (c:char) = s.IndexOf(c) <> -1
 
     let order = LanguagePrimitives.FastGenericComparer<string>

src/fsharp/CompileOps.fs

@@ -2609,13 +2609,13 @@ type TcConfigBuilder =
     member tcConfigB.RemoveReferencedAssemblyByPath (m, path) =
         tcConfigB.referencedDLLs <- tcConfigB.referencedDLLs |> List.filter (fun ar-> ar.Range <> m || ar.Text <> path)
     
-    static member SplitCommandLineResourceInfo ri = 
-        if String.contains ri ',' then 
-            let p = String.index ri ',' 
+    static member SplitCommandLineResourceInfo (ri:string) =
+        let p = ri.IndexOf ','
+        if p <> -1 then
             let file = String.sub ri 0 p 
             let rest = String.sub ri (p+1) (String.length ri - p - 1) 
-            if String.contains rest ',' then 
-                let p = String.index rest ',' 
+            let p = rest.IndexOf ',' 
+            if p <> -1 then
                 let name = String.sub rest 0 p+".resources" 
                 let pubpri = String.sub rest (p+1) (rest.Length - p - 1) 
                 if pubpri = "public" then file, name, ILResourceAccess.Public 

src/fsharp/NameResolution.fs

@@ -985,10 +985,8 @@ type TypeNameResolutionStaticArgsInfo =
 
     // Get the first possible mangled name of the type, assuming the args are generic args
     member x.MangledNameForType nm = 
-        if IsMangledGenericName nm || x.NumStaticArgs = 0 then nm
-        else nm+"`"+string x.NumStaticArgs
-
-
+        if x.NumStaticArgs = 0 || TryDemangleGenericNameAndPos nm <> ValueNone then nm
+        else nm + "`" + string x.NumStaticArgs
 
 [<NoEquality; NoComparison>]
 /// Represents information which guides name resolution of types.
@@ -1018,7 +1016,11 @@ let LookupTypeNameInEntityHaveArity nm (staticResInfo: TypeNameResolutionStaticA
 /// Unqualified lookups of type names where the number of generic arguments is known 
 /// from context, e.g. List<arg>.  Rebindings due to 'open' may have rebound identifiers.
 let LookupTypeNameInEnvHaveArity fq nm numTyArgs (nenv:NameResolutionEnv) = 
-    let key = if IsMangledGenericName nm then DecodeGenericTypeName nm else NameArityPair(nm,numTyArgs)
+    let key =
+        match TryDemangleGenericNameAndPos nm with
+        | ValueSome pos -> DecodeGenericTypeName pos nm
+        | _ -> NameArityPair(nm,numTyArgs)
+
     match nenv.TyconsByDemangledNameAndArity(fq).TryFind(key)  with
     | Some res -> Some res
     | None -> nenv.TyconsByAccessNames(fq).TryFind nm |> Option.map List.head
@@ -1041,15 +1043,17 @@ let LookupTypeNameInEnvHaveArity fq nm numTyArgs (nenv:NameResolutionEnv) =
 // also be used to qualify access if needed, though this is almost never needed.  
 
 let LookupTypeNameNoArity nm (byDemangledNameAndArity: LayeredMap<NameArityPair,_>) (byAccessNames: LayeredMultiMap<string,_>) = 
-    if IsMangledGenericName nm then 
-      match byDemangledNameAndArity.TryFind (DecodeGenericTypeName nm) with 
-      | Some res -> [res]
-      | None -> 
-          match byAccessNames.TryFind nm with
-          | Some res -> res
-          | None -> []
-    else 
-      byAccessNames.[nm]
+    match TryDemangleGenericNameAndPos nm with
+    | ValueSome pos -> 
+        let demangled = DecodeGenericTypeName pos nm
+        match byDemangledNameAndArity.TryFind demangled with 
+        | Some res -> [res]
+        | None ->
+            match byAccessNames.TryFind nm with
+            | Some res -> res
+            | None -> []
+    | _ ->
+        byAccessNames.[nm]
 
 /// Qualified lookup of type names in the environment
 let LookupTypeNameInEnvNoArity fq nm (nenv: NameResolutionEnv) = 

src/fsharp/NicePrint.fs

@@ -102,7 +102,7 @@ module private PrintIL =
     open Microsoft.FSharp.Compiler.AbstractIL.IL
         
     let fullySplitILTypeRef (tref:ILTypeRef) = 
-        (List.collect IL.splitNamespace (tref.Enclosing @ [IL.ungenericizeTypeName tref.Name])) 
+        (List.collect IL.splitNamespace (tref.Enclosing @ [PrettyNaming.DemangleGenericTypeName tref.Name])) 
 
     let layoutILTypeRefName denv path =
         let path = 
@@ -193,7 +193,7 @@ module private PrintIL =
         let args = signatur.ArgTypes |> List.map (layoutILType denv ilTyparSubst) 
         let res  = 
             match cons with
-            | Some className -> layoutILTypeRefName denv (SplitNamesForILPath (ungenericizeTypeName className)) ^^ (pruneParms className ilTyparSubst |> paramsL) // special case for constructor return-type (viz., the class itself)
+            | Some className -> layoutILTypeRefName denv (SplitNamesForILPath (PrettyNaming.DemangleGenericTypeName className)) ^^ (pruneParms className ilTyparSubst |> paramsL) // special case for constructor return-type (viz., the class itself)
             | None           -> signatur.ReturnType |> layoutILType denv ilTyparSubst
         match args with
         | []   -> WordL.structUnit ^^ WordL.arrow ^^ res
@@ -226,7 +226,7 @@ module private PrintIL =
         // return type be passed along as the `cons` parameter.)
         let res  = 
             match cons with
-            | Some className -> layoutILTypeRefName denv (SplitNamesForILPath (ungenericizeTypeName className)) ^^ (pruneParms className ilTyparSubst |> paramsL) // special case for constructor return-type (viz., the class itself)
+            | Some className -> layoutILTypeRefName denv (SplitNamesForILPath (PrettyNaming.DemangleGenericTypeName className)) ^^ (pruneParms className ilTyparSubst |> paramsL) // special case for constructor return-type (viz., the class itself)
             | None           -> retType |> layoutILType denv ilTyparSubst
         match parameters with
         | []   -> WordL.structUnit ^^ WordL.arrow ^^ res

src/fsharp/PrettyNaming.fs

@@ -484,30 +484,36 @@ module public Microsoft.FSharp.Compiler.PrettyNaming
      
     let [<Literal>] private mangledGenericTypeNameSym = '`'
 
-    let IsMangledGenericName (n:string) = 
-        n.IndexOf mangledGenericTypeNameSym <> -1 &&
+    let TryDemangleGenericNameAndPos (n:string) =
         (* check what comes after the symbol is a number *)
-        let m = n.LastIndexOf mangledGenericTypeNameSym
-        let mutable res = m < n.Length - 1
-        for i = m + 1 to n.Length - 1 do
-            res <- res && n.[i] >= '0' && n.[i] <= '9'
-        res
+        let pos = n.LastIndexOf mangledGenericTypeNameSym
+        if pos = -1 then ValueNone else
+        let mutable res = pos < n.Length - 1
+        let mutable i = pos + 1
+        while res && i < n.Length do
+            let char = n.[i]
+            if not (char >= '0' && char <= '9') then
+                res <- false
+            i <- i + 1
+        if res then
+            ValueSome pos
+        else
+            ValueNone
 
     type NameArityPair = NameArityPair of string * int
 
-    let DecodeGenericTypeName n = 
-        if IsMangledGenericName n then 
-            let pos = n.LastIndexOf mangledGenericTypeNameSym
-            let res = n.Substring(0,pos)
-            let num = n.Substring(pos+1,n.Length - pos - 1)
-            NameArityPair(res, int32 num)
-        else NameArityPair(n,0)
-
-    let DemangleGenericTypeName n = 
-        if  IsMangledGenericName n then 
-            let pos = n.LastIndexOf mangledGenericTypeNameSym
-            n.Substring(0,pos)
-        else n
+    let DecodeGenericTypeName pos (mangledName:string) =
+        let res = mangledName.Substring(0,pos)
+        let num = mangledName.Substring(pos+1,mangledName.Length - pos - 1)
+        NameArityPair(res, int32 num)
+
+    let DemangleGenericTypeNameWithPos pos (mangledName:string) =
+        mangledName.Substring(0,pos)
+
+    let DemangleGenericTypeName (mangledName:string) =
+        match TryDemangleGenericNameAndPos mangledName with
+        | ValueSome pos -> DemangleGenericTypeNameWithPos pos mangledName
+        | _ -> mangledName
 
     let private chopStringTo (s:string) (c:char) =
         match s.IndexOf c with

src/fsharp/tast.fs

@@ -480,10 +480,11 @@ let KeyTyconByDemangledNameAndArity nm (typars: _ list) x =
 
 /// Generic types can be accessed either by 'List' or 'List`1'. This lists both keys. The second form should really be deprecated.
 let KeyTyconByAccessNames nm x = 
-    if IsMangledGenericName nm then 
-        let dnm = DemangleGenericTypeName nm 
+    match TryDemangleGenericNameAndPos nm with
+    | ValueSome pos ->
+        let dnm = DemangleGenericTypeNameWithPos pos nm 
         [| KeyValuePair(nm,x); KeyValuePair(dnm,x) |]
-    else
+    | _ ->
         [| KeyValuePair(nm,x) |]
 
 type ModuleOrNamespaceKind =