Remove List.headAndTail and some tuples (dotnet#9336)

Author: forki

src/absil/illib.fs

@@ -330,13 +330,6 @@ module List =
             | [] -> None
             | h :: t -> if f h then Some (h, List.rev acc @ t) else loop (h :: acc) t
         loop [] inp
-            
-    let headAndTail l =
-        match l with 
-        | [] -> 
-            Debug.Assert(false, "empty list")
-            failwith "List.headAndTail"
-        | h :: t -> h, t
 
     let zip4 l1 l2 l3 l4 = 
         List.zip l1 (List.zip3 l2 l3 l4) |> List.map (fun (x1, (x2, x3, x4)) -> (x1, x2, x3, x4))

src/fsharp/MethodCalls.fs

@@ -1867,12 +1867,15 @@ let GenWitnessExpr amap g m (traitInfo: TraitConstraintInfo) argExprs =
 
         // Fix bug 1281: If we resolve to an instance method on a struct and we haven't yet taken 
         // the address of the object then go do that 
-        if minfo.IsStruct && minfo.IsInstance && (match argExprs with [] -> false | h :: _ -> not (isByrefTy g (tyOfExpr g h))) then 
-            let h, t = List.headAndTail argExprs
-            let wrap, h', _readonly, _writeonly = mkExprAddrOfExpr g true false PossiblyMutates h None m 
-            Some (wrap (Expr.Op (TOp.TraitCall traitInfo, [], (h' :: t), m)))
+        if minfo.IsStruct && minfo.IsInstance then 
+            match argExprs with
+            | h :: t when not (isByrefTy g (tyOfExpr g h)) ->
+                let wrap, h', _readonly, _writeonly = mkExprAddrOfExpr g true false PossiblyMutates h None m 
+                Some (wrap (Expr.Op (TOp.TraitCall traitInfo, [], (h' :: t), m)))
+            | _ ->
+                Some (MakeMethInfoCall amap m minfo methArgTys argExprs)
         else        
-            Some (MakeMethInfoCall amap m minfo methArgTys argExprs )
+            Some (MakeMethInfoCall amap m minfo methArgTys argExprs)
 
     | Choice2Of5 (tinst, rfref, isSet) -> 
         match isSet, rfref.RecdField.IsStatic, argExprs.Length with 

src/fsharp/NicePrint.fs

@@ -1472,12 +1472,14 @@ module InfoMemberPrinting =
     let prettifyILMethInfo (amap: Import.ImportMap) m (minfo: MethInfo) typarInst ilMethInfo = 
         let (ILMethInfo(_, apparentTy, dty, mdef, _)) = ilMethInfo
         let (prettyTyparInst, prettyTys), _ = PrettyTypes.PrettifyInstAndTypes amap.g (typarInst, (apparentTy :: minfo.FormalMethodInst))
-        let prettyApparentTy, prettyFormalMethInst = List.headAndTail prettyTys
-        let prettyMethInfo = 
-            match dty with 
-            | None -> MethInfo.CreateILMeth (amap, m, prettyApparentTy, mdef)
-            | Some declaringTyconRef -> MethInfo.CreateILExtensionMeth(amap, m, prettyApparentTy, declaringTyconRef, minfo.ExtensionMemberPriorityOption, mdef)
-        prettyTyparInst, prettyMethInfo, prettyFormalMethInst
+        match prettyTys with
+        | prettyApparentTy :: prettyFormalMethInst ->
+            let prettyMethInfo = 
+                match dty with 
+                | None -> MethInfo.CreateILMeth (amap, m, prettyApparentTy, mdef)
+                | Some declaringTyconRef -> MethInfo.CreateILExtensionMeth(amap, m, prettyApparentTy, declaringTyconRef, minfo.ExtensionMemberPriorityOption, mdef)
+            prettyTyparInst, prettyMethInfo, prettyFormalMethInst
+        | _ -> failwith "prettifyILMethInfo - prettyTys empty"
 
     /// Format a method to a buffer using "standalone" display style. 
     /// For example, these are the formats used when printing signatures of methods that have not been overridden,

src/fsharp/TypeChecker.fs

@@ -9265,9 +9265,8 @@ and TcNameOfExpr cenv env tpenv (synArg: SynExpr) =
     let m = cleanSynArg.Range
     let rec check overallTyOpt expr (delayed: DelayedItem list) = 
         match expr with
-        | LongOrSingleIdent (false, (LongIdentWithDots(longId, _) as lidd), _, _) when longId.Length > 0 ->
+        | LongOrSingleIdent (false, (LongIdentWithDots((id::rest) as longId, _) as lidd), _, _) ->
             let ad = env.eAccessRights
-            let id, rest = List.headAndTail longId
             match ResolveLongIndentAsModuleOrNamespaceOrStaticClass cenv.tcSink ResultCollectionSettings.AllResults cenv.amap m false true OpenQualified env.eNameResEnv ad id rest true with 
             | Result modref when delayed.IsEmpty && modref |> List.exists (p23 >> IsEntityAccessible cenv.amap m ad) -> 
                 () // resolved to a module or namespace, done with checks

src/fsharp/fsi/fsi.fs

@@ -2266,10 +2266,15 @@ type internal FsiInteractionProcessor
 
                 // When the last declaration has a shape of DoExp (i.e., non-binding), 
                 // transform it to a shape of "let it = <exp>", so we can refer it.
-                let defsA = if defsA.Length <= 1 || not (List.isEmpty defsB) then defsA else
-                            match List.headAndTail (List.rev defsA) with
-                            | SynModuleDecl.DoExpr(_,exp,_), rest -> (rest |> List.rev) @ (fsiDynamicCompiler.BuildItBinding exp)
-                            | _ -> defsA
+                let defsA =                    
+                    if not (isNil defsB) then defsA else
+                    match defsA with
+                    | [] -> defsA
+                    | [_] -> defsA
+                    | _ ->
+                        match List.rev defsA with
+                        | SynModuleDecl.DoExpr(_,exp,_) :: rest -> (rest |> List.rev) @ (fsiDynamicCompiler.BuildItBinding exp)
+                        | _ -> defsA
 
                 Some (IDefns(defsA,m)),Some (IDefns(defsB,m)),istate