[RFC FS-1043] Extension members visible to trait constraints

fcs/FSharp.Compiler.Service/FSharp.Compiler.Service.fsproj

@@ -460,6 +460,12 @@
     <Compile Include="$(FSharpSourcesRoot)/fsharp/PatternMatchCompilation.fs">
       <Link>Logic/PatternMatchCompilation.fs</Link>
     </Compile>
+    <Compile Include="$(FSharpSourcesRoot)/fsharp/FindUnsolved.fsi">
+      <Link>Logic/FindUnsolved.fsi</Link>
+    </Compile>
+    <Compile Include="$(FSharpSourcesRoot)/fsharp/FindUnsolved.fs">
+      <Link>Logic/FindUnsolved.fs</Link>
+    </Compile>
     <Compile Include="$(FSharpSourcesRoot)/fsharp/ConstraintSolver.fsi">
       <Link>Logic/ConstraintSolver.fsi</Link>
     </Compile>
@@ -472,12 +478,6 @@
     <Compile Include="$(FSharpSourcesRoot)/fsharp/CheckFormatStrings.fs">
       <Link>Logic/CheckFormatStrings.fs</Link>
     </Compile>
-    <Compile Include="$(FSharpSourcesRoot)/fsharp/FindUnsolved.fsi">
-      <Link>Logic/FindUnsolved.fsi</Link>
-    </Compile>
-    <Compile Include="$(FSharpSourcesRoot)/fsharp/FindUnsolved.fs">
-      <Link>Logic/FindUnsolved.fs</Link>
-    </Compile>
     <Compile Include="$(FSharpSourcesRoot)/fsharp/QuotationTranslator.fsi">
       <Link>Logic/QuotationTranslator.fsi</Link>
     </Compile>

src/fsharp/AccessibilityLogic.fs

@@ -38,6 +38,8 @@ type AccessorDomain =
     /// An AccessorDomain which returns all items
     | AccessibleFromSomewhere 
 
+    interface ITraitAccessorDomain
+
     // Hashing and comparison is used for the memoization tables keyed by an accessor domain.
     // It is dependent on a TcGlobals because of the TyconRef in the data structure
     static member CustomGetHashCode(ad:AccessorDomain) = 
@@ -46,6 +48,7 @@ type AccessorDomain =
         | AccessibleFromEverywhere -> 2
         | AccessibleFromSomeFSharpCode  -> 3
         | AccessibleFromSomewhere  -> 4
+
     static member CustomEquals(g:TcGlobals, ad1:AccessorDomain, ad2:AccessorDomain) = 
         match ad1, ad2 with 
         | AccessibleFrom(cs1, tc1), AccessibleFrom(cs2, tc2) -> (cs1 = cs2) && (match tc1, tc2 with None, None -> true | Some tc1, Some tc2 -> tyconRefEq g tc1 tc2 | _ -> false)

src/fsharp/CheckFormatStrings.fs

@@ -16,7 +16,7 @@ open FSharp.Compiler.TcGlobals
 type FormatItem = Simple of TType | FuncAndVal 
 
 let copyAndFixupFormatTypar m tp = 
-    let _,_,tinst = FreshenAndFixupTypars m TyparRigidity.Flexible [] [] [tp]
+    let _,_,tinst = FreshenAndFixupTypars traitCtxtNone m TyparRigidity.Flexible [] [] [tp]
     List.head tinst
 
 let lowestDefaultPriority = 0 (* See comment on TyparConstraint.DefaultsTo *)

src/fsharp/CompileOps.fs

@@ -5408,14 +5408,13 @@ module ScriptPreprocessClosure =
                                         yield! loop subSource
                                 else
                                     yield ClosureFile(subFile, m, None, [], [], []) 
+
                             yield ClosureFile(filename, m, Some parsedScriptAst, parseDiagnostics, errorLogger.Diagnostics, noWarns)
 
                         | None -> 
-                            printfn "yielding source %s (failed parse)" filename
                             yield ClosureFile(filename, m, None, parseDiagnostics, [], [])
                     else 
                         // Don't traverse into .fs leafs.
-                        printfn "yielding non-script source %s" filename
                         yield ClosureFile(filename, m, None, [], [], []) ]
 
         closureSources |> List.collect loop, tcConfig

src/fsharp/CompileOptions.fs

@@ -1055,7 +1055,7 @@ let internalFlags (tcConfigB:TcConfigBuilder) =
   [
     CompilerOption
        ("stamps", tagNone,
-        OptionUnit ignore,
+        OptionSet DebugPrint.layoutStamps,
         Some(InternalCommandLineOption("--stamps", rangeCmdArgs)), None)
 
     CompilerOption

src/fsharp/ConstraintSolver.fsi

@@ -10,6 +10,7 @@ open FSharp.Compiler.Import
 open FSharp.Compiler.Infos
 open FSharp.Compiler.InfoReader
 open FSharp.Compiler.MethodCalls
+open FSharp.Compiler.NameResolution
 open FSharp.Compiler.Range
 open FSharp.Compiler.SyntaxTree
 open FSharp.Compiler.TcGlobals
@@ -36,16 +37,19 @@ val NewInferenceTypes: 'a list -> TType list
 
 /// Given a set of formal type parameters and their constraints, make new inference type variables for
 /// each and ensure that the constraints on the new type variables are adjusted to refer to these.
-val FreshenAndFixupTypars: range -> TyparRigidity -> Typars -> TType list -> Typars -> Typars * TyparInst * TType list
+val FreshenAndFixupTypars : ITraitContext option -> range -> TyparRigidity -> Typars -> TType list -> Typars -> Typars * TyparInst * TType list
 
-val FreshenTypeInst: range -> Typars -> Typars * TyparInst * TType list
+/// Make new type inference variables for the use of a generic construct at a particular location
+val FreshenTypeInst : ITraitContext option -> range -> Typars -> Typars * TyparInst * TType list
 
-val FreshenTypars: range -> Typars -> TType list
+/// Make new type inference variables for the use of a generic construct at a particular location
+val FreshenTypars : ITraitContext option -> range -> Typars -> TType list
 
-val FreshenMethInfo: range -> MethInfo -> TType list
+/// Make new type inference variables for the use of a method at a particular location
+val FreshenMethInfo : ITraitContext option -> range -> MethInfo -> TType list
 
 [<RequireQualifiedAccess>] 
-/// Information about the context of a type equation.
+/// Information about the context of a type equation, for better error reporting
 type ContextInfo =
 
     /// No context was given.
@@ -205,6 +209,13 @@ val CodegenWitnessesForTraitWitness : TcValF -> TcGlobals -> ImportMap -> range
 /// to its constraints and applies that solution by using a constraint.
 val ChooseTyparSolutionAndSolve : ConstraintSolverState -> DisplayEnv -> Typar -> unit
 
-val IsApplicableMethApprox: TcGlobals -> ImportMap -> range -> MethInfo -> TType -> bool
+/// Apply defaults arising from 'default' constraints in FSharp.Core
+/// for any unsolved free inference type variables.
+val ApplyDefaultsForUnsolved: ConstraintSolverState -> DisplayEnv -> Typar list -> unit
 
-val CanonicalizePartialInferenceProblem:  ConstraintSolverState -> DisplayEnv -> range -> Typars -> unit
+/// Choose solutions for any remaining unsolved free inference type variables.
+val ChooseSolutionsForUnsolved: ConstraintSolverState -> DisplayEnv -> Typar list -> unit
+
+val IsApplicableMethApprox: TcGlobals -> ImportMap -> range -> ITraitContext option -> MethInfo -> TType -> bool
+
+val CanonicalizePartialInferenceProblem:  ConstraintSolverState -> DisplayEnv -> range -> Typars -> bool -> unit

src/fsharp/FSComp.txt

@@ -305,9 +305,9 @@ csExpectedArguments,"Expected arguments to an instance member"
 csIndexArgumentMismatch,"This indexer expects %d arguments but is here given %d"
 csExpectTypeWithOperatorButGivenFunction,"Expecting a type supporting the operator '%s' but given a function type. You may be missing an argument to a function."
 csExpectTypeWithOperatorButGivenTuple,"Expecting a type supporting the operator '%s' but given a tuple type"
-csTypesDoNotSupportOperator,"None of the types '%s' support the operator '%s'"
+csTypesDoNotSupportOperator,"The types '%s' do not support the operator '%s'"
 csTypeDoesNotSupportOperator,"The type '%s' does not support the operator '%s'"
-csTypesDoNotSupportOperatorNullable,"None of the types '%s' support the operator '%s'. Consider opening the module 'Microsoft.FSharp.Linq.NullableOperators'."
+csTypesDoNotSupportOperatorNullable,"The types '%s' do not support the operator '%s'. Consider opening the module 'Microsoft.FSharp.Linq.NullableOperators'."
 csTypeDoesNotSupportOperatorNullable,"The type '%s' does not support the operator '%s'. Consider opening the module 'Microsoft.FSharp.Linq.NullableOperators'."
 csTypeDoesNotSupportConversion,"The type '%s' does not support a conversion to the type '%s'"
 csMethodFoundButIsStatic,"The type '%s' has a method '%s' (full name '%s'), but the method is static"
@@ -1512,4 +1512,5 @@ featureFixedIndexSlice3d4d,"fixed-index slice 3d/4d"
 featureAndBang,"applicative computation expressions"
 featureNullableOptionalInterop,"nullable optional interop"
 featureDefaultInterfaceMemberConsumption,"default interface member consumption"
+featureExtensionConstraintSolutions,"extension constraint solutions"
 featureWitnessPassing,"witness passing"

src/fsharp/FSharp.Compiler.Private/FSharp.Compiler.Private.fsproj

@@ -462,6 +462,12 @@
     <Compile Include="..\PatternMatchCompilation.fs">
       <Link>Logic\PatternMatchCompilation.fs</Link>
     </Compile>
+    <Compile Include="..\FindUnsolved.fsi">
+      <Link>Logic\FindUnsolved.fsi</Link>
+    </Compile>
+    <Compile Include="..\FindUnsolved.fs">
+      <Link>Logic\FindUnsolved.fs</Link>
+    </Compile>
     <Compile Include="..\ConstraintSolver.fsi">
       <Link>Logic\ConstraintSolver.fsi</Link>
     </Compile>
@@ -474,12 +480,6 @@
     <Compile Include="..\CheckFormatStrings.fs">
       <Link>Logic\CheckFormatStrings.fs</Link>
     </Compile>
-    <Compile Include="..\FindUnsolved.fsi">
-      <Link>Logic\FindUnsolved.fsi</Link>
-    </Compile>
-    <Compile Include="..\FindUnsolved.fs">
-      <Link>Logic\FindUnsolved.fs</Link>
-    </Compile>
     <Compile Include="..\QuotationTranslator.fsi">
       <Link>Logic\QuotationTranslator.fsi</Link>
     </Compile>

src/fsharp/FSharp.Core/prim-types.fs

@@ -81,6 +81,11 @@ namespace Microsoft.FSharp.Core
         member x.Value = value
         new () = new AllowNullLiteralAttribute(true)
 
+    [<AttributeUsage(AttributeTargets.Method, AllowMultiple=false)>]
+    [<Sealed>]
+    type AllowOverloadByReturnTypeAttribute() =
+        inherit System.Attribute()
+
     [<AttributeUsage(AttributeTargets.Field, AllowMultiple=false)>]
     [<Sealed>]
     type VolatileFieldAttribute() =

src/fsharp/FSharp.Core/prim-types.fsi

@@ -232,6 +232,16 @@ namespace Microsoft.FSharp.Core
         /// <summary>The value of the attribute, indicating whether the type allows the null literal or not</summary>
         member Value: bool
 
+    /// <summary>Adding this attribute to a method allows that method to be overloaded by return type.</summary>
+    [<AttributeUsage (AttributeTargets.Method,AllowMultiple=false)>]  
+    [<Sealed>]
+    type AllowOverloadByReturnTypeAttribute =
+        inherit Attribute
+
+        /// <summary>Creates an instance of the attribute</summary>
+        /// <returns>AllowOverloadByReturnTypeAttribute</returns>
+        new : unit -> AllowOverloadByReturnTypeAttribute
+
     /// <summary>Adding this attribute to a value causes it to be compiled as a CLI constant literal.</summary>
     [<AttributeUsage (AttributeTargets.Field,AllowMultiple=false)>]  
     [<Sealed>]

src/fsharp/FindUnsolved.fs

@@ -145,7 +145,7 @@ and accOp cenv env (op, tyargs, args, _m) =
         accTypeInst cenv env tys
     | _ ->    ()
 
-and accTraitInfo cenv env (TTrait(tys, _nm, _, argtys, rty, _sln)) =
+and accTraitInfo cenv env (TTrait(tys, _nm, _, argtys, rty, _sln, _traitCtxt)) =
     argtys |> accTypeInst cenv env 
     rty |> Option.iter (accTy cenv env)
     tys |> List.iter (accTy cenv env)
@@ -282,4 +282,13 @@ let UnsolvedTyparsOfModuleDef g amap denv (mdef, extraAttribs) =
    accAttribs cenv Nix extraAttribs
    List.rev cenv.unsolved
 
+let UnsolvedTyparsOfExpr g amap denv expr =
+   let cenv = 
+      { g =g  
+        amap=amap 
+        denv=denv 
+        unsolved = [] }
+   accExpr cenv Nix expr
+   List.rev cenv.unsolved
+
 

src/fsharp/FindUnsolved.fsi

@@ -10,3 +10,6 @@ open FSharp.Compiler.Import
 
 /// Find all unsolved inference variables after type inference for an entire file
 val UnsolvedTyparsOfModuleDef: g: TcGlobals -> amap: ImportMap -> denv: DisplayEnv -> mdef : ModuleOrNamespaceExpr * extraAttribs: Attrib list -> Typar list
+
+/// Find all unsolved inference variables after adhoc generation of witness
+val UnsolvedTyparsOfExpr: g: TcGlobals -> amap: ImportMap -> denv: DisplayEnv -> expr: Expr -> Typar list

src/fsharp/IlxGen.fs

@@ -391,7 +391,7 @@ let ComputeTypeAccess (tref: ILTypeRef) hidden =
 type TypeReprEnv(reprs: Map<Stamp, uint16>, count: int) =
 
     /// Lookup a type parameter
-    member __.Item (tp: Typar, m: range) =
+    member __.LookupTyparRepr (tp: Typar, m: range) =
         try reprs.[tp.Stamp]
         with :? KeyNotFoundException ->
           errorR(InternalError("Undefined or unsolved type variable: " + showL(typarL tp), m))
@@ -542,7 +542,7 @@ and GenTypeAux amap m (tyenv: TypeReprEnv) voidOK ptrsOK ty =
         if tps.IsEmpty then GenTypeAux amap m tyenv VoidNotOK ptrsOK tau
         else EraseClosures.mkILTyFuncTy g.ilxPubCloEnv
 
-    | TType_var tp -> mkILTyvarTy tyenv.[tp, m]
+    | TType_var tp -> mkILTyvarTy (tyenv.LookupTyparRepr(tp, m))
 
     | TType_measure _ -> g.ilg.typ_Int32
 
@@ -4565,7 +4565,7 @@ and GenGenericParams cenv eenv tps =
     tps |> DropErasedTypars |> List.map (GenGenericParam cenv eenv)
 
 and GenGenericArgs m (tyenv: TypeReprEnv) tps =
-    tps |> DropErasedTypars |> List.map (fun c -> (mkILTyvarTy tyenv.[c, m]))
+    tps |> DropErasedTypars |> List.map (fun c -> mkILTyvarTy (tyenv.LookupTyparRepr(c, m)))
 
 /// Generate the closure class for a function
 and GenLambdaClosure cenv (cgbuf: CodeGenBuffer) eenv isLocalTypeFunc thisVars expr =

src/fsharp/LanguageFeatures.fs

@@ -32,6 +32,7 @@ type LanguageFeature =
     | NullableOptionalInterop
     | DefaultInterfaceMemberConsumption
     | WitnessPassing
+    | ExtensionConstraintSolutions
 
 /// LanguageVersion management
 type LanguageVersion (specifiedVersionAsString) =
@@ -65,6 +66,7 @@ type LanguageVersion (specifiedVersionAsString) =
             LanguageFeature.NameOf, previewVersion
             LanguageFeature.OpenStaticClasses, previewVersion
             LanguageFeature.PackageManagement, previewVersion
+            LanguageFeature.ExtensionConstraintSolutions, previewVersion
             LanguageFeature.AndBang, previewVersion
             LanguageFeature.NullableOptionalInterop, previewVersion
             LanguageFeature.DefaultInterfaceMemberConsumption, previewVersion
@@ -138,6 +140,7 @@ type LanguageVersion (specifiedVersionAsString) =
         | LanguageFeature.NullableOptionalInterop -> FSComp.SR.featureNullableOptionalInterop()
         | LanguageFeature.DefaultInterfaceMemberConsumption -> FSComp.SR.featureDefaultInterfaceMemberConsumption()
         | LanguageFeature.WitnessPassing -> FSComp.SR.featureWitnessPassing()
+        | LanguageFeature.ExtensionConstraintSolutions -> FSComp.SR.featureExtensionConstraintSolutions()
 
     /// Get a version string associated with the given feature.
     member _.GetFeatureVersionString feature =

src/fsharp/LanguageFeatures.fsi

@@ -20,6 +20,7 @@ type LanguageFeature =
     | NullableOptionalInterop
     | DefaultInterfaceMemberConsumption
     | WitnessPassing
+    | ExtensionConstraintSolutions
 
 /// LanguageVersion management
 type LanguageVersion =