Inline Hints for F# (#12927)

Note the following behavior:

* Type hints are at definition/binding, not use
* Type hints do not show if something already has an annotation
* Parameter name hints appear for F# functions and methods, using the named argument syntax
* Named parameters get no hints
* Lambdas that are let-bound will have a type hint, but other let-bound F# functions will not

Out of scope:

* Type hints for "normal" function declarations.
  * It just looks bad and there isn't a good way to play hints without getting smushed together with the type hint for the last parameter.
  * Lambda function declarations, yes.
* Show inferred types for _ in a pattern
  * Note - this can be done orthogonally and also support quickinfo
* Add QuickInfo -
  * Note, this can be done orthogonally.
  * We need a way to resolve the symbol we're showing the type for and get quickinfo from
  * No such API exists in the compiler today

Author: baronfel

src/fsharp/NicePrint.fs

@@ -1105,7 +1105,18 @@ module PrintTypes =
 
     let prettyLayoutOfTypeNoConstraints denv ty = 
         let ty, _cxs = PrettyTypes.PrettifyType denv.g ty
-        layoutTypeWithInfoAndPrec denv SimplifyTypes.typeSimplificationInfo0 5 ty 
+        layoutTypeWithInfoAndPrec denv SimplifyTypes.typeSimplificationInfo0 5 ty
+
+    let layoutOfValReturnType denv (v: ValRef) =
+        match v.ValReprInfo with 
+        | None ->
+            let _, tau = v.TypeScheme
+            let _argtysl, rty = stripFunTy denv.g tau
+            layoutReturnType denv SimplifyTypes.typeSimplificationInfo0 rty
+        | Some (ValReprInfo(_typars, argInfos, _retInfo)) -> 
+            let tau = v.TauType
+            let _c, rty = GetTopTauTypeInFSharpForm denv.g argInfos tau Range.range0
+            layoutReturnType denv SimplifyTypes.typeSimplificationInfo0 rty
 
     let layoutAssemblyName _denv (ty: TType) =
         ty.GetAssemblyName()
@@ -2435,7 +2446,9 @@ let prettyLayoutOfValOrMember denv infoReader typarInst v = PrintTastMemberOrVal
 
 let prettyLayoutOfValOrMemberNoInst denv infoReader v = PrintTastMemberOrVals.prettyLayoutOfValOrMemberNoInst denv infoReader v
 
-let prettyLayoutOfMemberNoInstShort denv v = PrintTastMemberOrVals.prettyLayoutOfMemberNoInstShort denv v 
+let prettyLayoutOfMemberNoInstShort denv v = PrintTastMemberOrVals.prettyLayoutOfMemberNoInstShort denv v
+
+let layoutOfValReturnType denv v = v |> PrintTypes.layoutOfValReturnType denv
 
 let prettyLayoutOfInstAndSig denv x = PrintTypes.prettyLayoutOfInstAndSig denv x
 

src/fsharp/NicePrint.fsi

@@ -109,6 +109,8 @@ val prettyLayoutOfValOrMemberNoInst: denv:DisplayEnv -> infoReader:InfoReader ->
 
 val prettyLayoutOfMemberNoInstShort: denv:DisplayEnv -> v:Val -> Layout
 
+val layoutOfValReturnType: denv:DisplayEnv -> v:ValRef -> Layout
+
 val prettyLayoutOfInstAndSig: denv:DisplayEnv -> TyparInst * TTypes * TType -> TyparInst * (TTypes * TType) * (Layout list * Layout) * Layout
 
 val minimalStringsOfTwoTypes: denv:DisplayEnv -> t1:TType -> t2:TType -> string * string * string

src/fsharp/service/ServiceParamInfoLocations.fs

@@ -8,8 +8,19 @@ open FSharp.Compiler.Text.Range
 open FSharp.Compiler.Syntax
 open FSharp.Compiler.SyntaxTreeOps
 
+type TupledArgumentLocation = { IsNamedArgument: bool; ArgumentRange: range }
+
 [<Sealed>]
-type ParameterLocations(longId: string list, longIdRange: range, openParenLocation: pos,  tupleEndLocations: pos list, isThereACloseParen: bool, namedParamNames: string option list) =
+type ParameterLocations
+    (
+        longId: string list,
+        longIdRange: range,
+        openParenLocation: pos,
+        argRanges: TupledArgumentLocation list, 
+        tupleEndLocations: pos list,
+        isThereACloseParen: bool,
+        namedParamNames: string option list
+    ) =
 
     let tupleEndLocations = Array.ofList tupleEndLocations
     let namedParamNames = Array.ofList namedParamNames
@@ -30,6 +41,7 @@ type ParameterLocations(longId: string list, longIdRange: range, openParenLocati
     member this.TupleEndLocations = tupleEndLocations
     member this.IsThereACloseParen = isThereACloseParen
     member this.NamedParamNames = namedParamNames
+    member this.ArgumentLocations = argRanges |> Array.ofList
 
 [<AutoOpen>]
 module internal ParameterLocationsImpl =
@@ -54,7 +66,7 @@ module internal ParameterLocationsImpl =
         | _ -> None
 
     type FindResult = 
-        | Found of openParen: pos * commasAndCloseParen: (pos * string option) list * hasClosedParen: bool
+        | Found of openParen: pos * argRanges: TupledArgumentLocation list * commasAndCloseParen: (pos * string option) list * hasClosedParen: bool
         | NotFound
 
     let digOutIdentFromStaticArg (StripParenTypes synType) =
@@ -90,7 +102,8 @@ module internal ParameterLocationsImpl =
         match inner with
         | None ->
             if SyntaxTraversal.rangeContainsPosLeftEdgeExclusiveAndRightEdgeInclusive parenRange pos then
-                Found (parenRange.Start, [(parenRange.End, getNamedParamName synExpr)], rpRangeOpt.IsSome), None
+                let argRanges = [{ IsNamedArgument = (getNamedParamName synExpr).IsSome; ArgumentRange = synExpr.Range }]
+                Found (parenRange.Start, argRanges, [(parenRange.End, getNamedParamName synExpr)], rpRangeOpt.IsSome), None
             else
                 NotFound, None
         | _ -> NotFound, None
@@ -107,8 +120,12 @@ module internal ParameterLocationsImpl =
             match inner with
             | None ->
                 if SyntaxTraversal.rangeContainsPosLeftEdgeExclusiveAndRightEdgeInclusive parenRange pos then
+                    // argRange, isNamed
+                    let argRanges =
+                        synExprList
+                        |> List.map (fun e -> { IsNamedArgument = (getNamedParamName e).IsSome; ArgumentRange = e.Range })
                     let commasAndCloseParen = ((synExprList, commaRanges@[parenRange]) ||> List.map2 (fun e c -> c.End, getNamedParamName e))
-                    let r = Found (parenRange.Start, commasAndCloseParen, rpRangeOpt.IsSome)
+                    let r = Found (parenRange.Start, argRanges, commasAndCloseParen, rpRangeOpt.IsSome)
                     r, None
                 else
                     NotFound, None
@@ -127,14 +144,14 @@ module internal ParameterLocationsImpl =
 
         | SynExpr.ArbitraryAfterError (_debugStr, range) -> // single argument when e.g. after open paren you hit EOF
             if SyntaxTraversal.rangeContainsPosEdgesExclusive range pos then
-                let r = Found (range.Start, [(range.End, None)], false)
+                let r = Found (range.Start, [], [(range.End, None)], false)
                 r, None
             else
                 NotFound, None
 
         | SynExpr.Const (SynConst.Unit, unitRange) ->
             if SyntaxTraversal.rangeContainsPosEdgesExclusive unitRange pos then
-                let r = Found (unitRange.Start, [(unitRange.End, None)], true)
+                let r = Found (unitRange.Start, [], [(unitRange.End, None)], true)
                 r, None
             else
                 NotFound, None
@@ -145,7 +162,7 @@ module internal ParameterLocationsImpl =
             | None ->
                 if SyntaxTraversal.rangeContainsPosEdgesExclusive e.Range pos then
                     // any other expression doesn't start with parens, so if it was the target of an App, then it must be a single argument e.g. "f x"
-                    Found (e.Range.Start, [ (e.Range.End, None) ], false), Some inner
+                    Found (e.Range.Start, [], [ (e.Range.End, None) ], false), Some inner
                 else
                     NotFound, Some inner
             | _ -> NotFound, Some inner
@@ -157,7 +174,7 @@ module internal ParameterLocationsImpl =
             let betweenTheBrackets = mkRange wholem.FileName openm.Start wholem.End
             if SyntaxTraversal.rangeContainsPosEdgesExclusive betweenTheBrackets pos && args |> List.forall isStaticArg then
                 let commasAndCloseParen = [ for c in commas -> c.End ] @ [ wholem.End ]
-                Some (ParameterLocations(pathOfLid lid, lidm, openm.Start, commasAndCloseParen, closemOpt.IsSome, args |> List.map digOutIdentFromStaticArg))
+                Some (ParameterLocations(pathOfLid lid, lidm, openm.Start, [], commasAndCloseParen, closemOpt.IsSome, args |> List.map digOutIdentFromStaticArg))
             else
                 None
         | _ ->
@@ -173,9 +190,9 @@ module internal ParameterLocationsImpl =
             | SynExpr.New (_, synType, synExpr, _) -> 
                 let constrArgsResult, cacheOpt = searchSynArgExpr traverseSynExpr pos synExpr
                 match constrArgsResult, cacheOpt with
-                | Found(parenLoc, args, isThereACloseParen), _ ->
+                | Found(parenLoc, argRanges, commasAndCloseParen, isThereACloseParen), _ ->
                     let typeName = getTypeName synType
-                    Some (ParameterLocations(typeName, synType.Range, parenLoc, args |> List.map fst, isThereACloseParen, args |> List.map snd))
+                    Some (ParameterLocations(typeName, synType.Range, parenLoc, argRanges, commasAndCloseParen |> List.map fst, isThereACloseParen, commasAndCloseParen |> List.map snd))
                 | NotFound, Some cache ->
                     cache
                 | _ ->
@@ -194,7 +211,7 @@ module internal ParameterLocationsImpl =
                     if SyntaxTraversal.rangeContainsPosEdgesExclusive typeArgsm pos then
                         // We found it, dig out ident
                         match digOutIdentFromFuncExpr synExpr with
-                        | Some(lid, lidRange) -> Some (ParameterLocations(lid, lidRange, op.idRange.Start, [ wholem.End ], false, []))
+                        | Some(lid, lidRange) -> Some (ParameterLocations(lid, lidRange, op.idRange.Start, [], [ wholem.End ], false, []))
                         | None -> None
                     else
                         None
@@ -209,7 +226,7 @@ module internal ParameterLocationsImpl =
                     // Search the argument
                     let xResult, cacheOpt = searchSynArgExpr traverseSynExpr pos synExpr2
                     match xResult, cacheOpt with
-                    | Found(parenLoc, args, isThereACloseParen), _ ->
+                    | Found(parenLoc, argRanges, commasAndCloseParen, isThereACloseParen), _ ->
                         // We found it, dig out ident
                         match digOutIdentFromFuncExpr synExpr with
                         | Some(lid, lidRange) -> 
@@ -219,7 +236,7 @@ module internal ParameterLocationsImpl =
                                 // For now, we don't support infix operators.
                                 None
                             else
-                                Some (ParameterLocations(lid, lidRange, parenLoc, args |> List.map fst, isThereACloseParen, args |> List.map snd))
+                                Some (ParameterLocations(lid, lidRange, parenLoc, argRanges, commasAndCloseParen |> List.map fst, isThereACloseParen, commasAndCloseParen |> List.map snd))
                         | None -> None
                     | NotFound, Some cache -> cache
                     | _ -> traverseSynExpr synExpr2
@@ -232,7 +249,8 @@ module internal ParameterLocationsImpl =
                     let typeArgsm = mkRange openm.FileName openm.Start wholem.End 
                     if SyntaxTraversal.rangeContainsPosEdgesExclusive typeArgsm pos && tyArgs |> List.forall isStaticArg then
                         let commasAndCloseParen = [ for c in commas -> c.End ] @ [ wholem.End ]
-                        let r = ParameterLocations(["dummy"], synExpr.Range, openm.Start, commasAndCloseParen, closemOpt.IsSome, tyArgs |> List.map digOutIdentFromStaticArg)
+                        let argRanges = tyArgs |> List.map (fun tyarg -> { IsNamedArgument = false; ArgumentRange = tyarg.Range })
+                        let r = ParameterLocations(["dummy"], synExpr.Range, openm.Start, argRanges, commasAndCloseParen, closemOpt.IsSome, tyArgs |> List.map digOutIdentFromStaticArg)
                         Some r
                     else
                         None
@@ -253,10 +271,10 @@ module internal ParameterLocationsImpl =
                     // inherit ty(expr)    ---   treat it like an application (constructor call)
                     let xResult, _cacheOpt = searchSynArgExpr defaultTraverse pos expr
                     match xResult with
-                    | Found(parenLoc, args, isThereACloseParen) ->
+                    | Found(parenLoc, argRanges, commasAndCloseParen, isThereACloseParen) ->
                         // we found it, dig out ident
                         let typeName = getTypeName ty
-                        let r = ParameterLocations(typeName, ty.Range, parenLoc, args |> List.map fst, isThereACloseParen, args |> List.map snd)
+                        let r = ParameterLocations(typeName, ty.Range, parenLoc, argRanges, commasAndCloseParen |> List.map fst, isThereACloseParen, commasAndCloseParen |> List.map snd)
                         Some r
                     | NotFound -> None
                 else None
@@ -276,7 +294,6 @@ type ParameterLocations with
             r
         | _ -> None
 
-
 module internal SynExprAppLocationsImpl =
     let rec private searchSynArgExpr traverseSynExpr expr ranges =
         match expr with

src/fsharp/service/ServiceParamInfoLocations.fsi

@@ -10,6 +10,9 @@ namespace FSharp.Compiler.EditorServices
 open FSharp.Compiler.Syntax
 open FSharp.Compiler.Text
 
+/// Represents the location of a tupled argument, which can optionally be a named argument.
+type TupledArgumentLocation = { IsNamedArgument: bool; ArgumentRange: range }
+
 /// Represents the locations relevant to activating parameter info in an IDE
 [<Sealed>]
 type public ParameterLocations =
@@ -33,7 +36,10 @@ type public ParameterLocations =
     member IsThereACloseParen : bool   
 
     /// Either empty or a name if an actual named parameter; f(0,a=4,?b=None) would be [|None; Some "a"; Some "b"|]
-    member NamedParamNames : string option []  
+    member NamedParamNames : string option []
+
+    /// Array of locations for each argument, and a flag if that argument is named
+    member ArgumentLocations: TupledArgumentLocation []
 
     /// Find the information about parameter info locations at a particular source location
     static member Find : pos * ParsedInput -> ParameterLocations option