Allow object expression without overrides

docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

@@ -20,6 +20,7 @@
 * Sink: report function domain type ([PR #17470](https://github.com/dotnet/fsharp/pull/17470))
 * Allow access modifies to auto properties getters and setters ([Language suggestion #430](https://github.com/fsharp/fslang-suggestions/issues/430), [PR 16687](https://github.com/dotnet/fsharp/pull/16687), [PR 16861](https://github.com/dotnet/fsharp/pull/16861), [PR 17522](https://github.com/dotnet/fsharp/pull/17522))
 * Render C# nullable-analysis attributes in tooltips ([PR #17485](https://github.com/dotnet/fsharp/pull/17485))
+* Allow object expression without overrides. ([Language suggestion #632](https://github.com/fsharp/fslang-suggestions/issues/632), [PR #17387](https://github.com/dotnet/fsharp/pull/17387))
 
 ### Changed
 

docs/release-notes/.Language/preview.md

@@ -11,6 +11,8 @@
 * Allow #nowarn to support the FS prefix on error codes to disable warnings ([Issue #17206](https://github.com/dotnet/fsharp/issues/16447), [PR #17209](https://github.com/dotnet/fsharp/pull/17209))
 * Allow ParsedHashDirectives to have argument types other than strings ([Issue #17240](https://github.com/dotnet/fsharp/issues/16447), [PR #17209](https://github.com/dotnet/fsharp/pull/17209))
 * Support empty-bodied computation expressions. ([Language suggestion #1232](https://github.com/fsharp/fslang-suggestions/issues/1232), [PR #17352](https://github.com/dotnet/fsharp/pull/17352))
+* Allow object expression without overrides. ([Language suggestion #632](https://github.com/fsharp/fslang-suggestions/issues/632), [PR #17387](https://github.com/dotnet/fsharp/pull/17387))
+
 
 ### Fixed
 

src/Compiler/Checking/Expressions/CheckExpressions.fs

@@ -6791,7 +6791,8 @@ and TcRecordConstruction (cenv: cenv) (overallTy: TType) isObjExpr env tpenv wit
     UnifyTypes cenv env m overallTy objTy
 
     // Types with implicit constructors can't use record or object syntax: all constructions must go through the implicit constructor
-    if tycon.MembersOfFSharpTyconByName |> NameMultiMap.existsInRange (fun v -> v.IsIncrClassConstructor) then
+    let supportsObjectExpressionWithoutOverrides = isObjExpr && g.langVersion.SupportsFeature(LanguageFeature.AllowObjectExpressionWithoutOverrides)
+    if not supportsObjectExpressionWithoutOverrides && tycon.MembersOfFSharpTyconByName |> NameMultiMap.existsInRange (fun v -> v.IsIncrClassConstructor) then
         errorR(Error(FSComp.SR.tcConstructorRequiresCall(tycon.DisplayName), m))
 
     let fspecs = tycon.TrueInstanceFieldsAsList
@@ -7139,7 +7140,8 @@ and TcObjectExpr (cenv: cenv) env tpenv (objTy, realObjTy, argopt, binds, extraI
     let isRecordTy = tcref.IsRecordTycon
     let isInterfaceTy = isInterfaceTy g objTy
     let isFSharpObjModelTy = isFSharpObjModelTy g objTy
-    let isOverallTyAbstract = HasFSharpAttribute g g.attrib_AbstractClassAttribute tcref.Attribs
+    let isOverallTyAbstract = HasFSharpAttribute g g.attrib_AbstractClassAttribute tcref.Attribs || isAbstractTycon tcref.Deref
+
     if not isRecordTy && not isInterfaceTy && isSealedTy g objTy then errorR(Error(FSComp.SR.tcCannotCreateExtensionOfSealedType(), mNewExpr))
 
     CheckSuperType cenv objTy mObjTy
@@ -7206,8 +7208,9 @@ and TcObjectExpr (cenv: cenv) env tpenv (objTy, realObjTy, argopt, binds, extraI
 
         let overridesAndVirts, tpenv = ComputeObjectExprOverrides cenv env tpenv impls
 
-        // 2. check usage conditions
-        overridesAndVirts |> List.iter (fun (m, implTy, dispatchSlots, dispatchSlotsKeyed, availPriorOverrides, overrides) ->
+        // 2. check usage conditions 
+        for ovd in overridesAndVirts do
+            let (m, implTy, dispatchSlots, dispatchSlotsKeyed, availPriorOverrides, overrides) = ovd
             let overrideSpecs = overrides |> List.map fst
             let hasStaticMembers = dispatchSlots |> List.exists (fun reqdSlot -> not reqdSlot.MethodInfo.IsInstance)
             if hasStaticMembers then
@@ -7217,7 +7220,6 @@ and TcObjectExpr (cenv: cenv) env tpenv (objTy, realObjTy, argopt, binds, extraI
 
             if not hasStaticMembers then
                 DispatchSlotChecking.CheckDispatchSlotsAreImplemented (env.DisplayEnv, cenv.infoReader, m, env.NameEnv, cenv.tcSink, isOverallTyAbstract, true, implTy, dispatchSlots, availPriorOverrides, overrideSpecs) |> ignore
-            )
 
         // 3. create the specs of overrides
         let allTypeImpls =
@@ -7249,8 +7251,9 @@ and TcObjectExpr (cenv: cenv) env tpenv (objTy, realObjTy, argopt, binds, extraI
         let objtyR, overrides' = allTypeImpls.Head
         assert (typeEquiv g objTy objtyR)
         let extraImpls = allTypeImpls.Tail
-
-        if not isInterfaceTy && (isOverallTyAbstract && overrides'.IsEmpty) && extraImpls.IsEmpty then
+        let supportsObjectExpressionWithoutOverrides = g.langVersion.SupportsFeature(LanguageFeature.AllowObjectExpressionWithoutOverrides)
+
+        if not supportsObjectExpressionWithoutOverrides && not isInterfaceTy && overrides'.IsEmpty && extraImpls.IsEmpty then
            errorR (Error(FSComp.SR.tcInvalidObjectExpressionSyntaxForm (), mWholeExpr))
 
         // 4. Build the implementation

src/Compiler/FSComp.txt

@@ -1778,3 +1778,4 @@ featureEmptyBodiedComputationExpressions,"Support for computation expressions wi
 3870,parsExpectingUnionCaseField,"Expecting union case field"
 featureAllowAccessModifiersToAutoPropertiesGettersAndSetters,"Allow access modifiers to auto properties getters and setters"
 3871,tcAccessModifiersNotAllowedInSRTPConstraint,"Access modifiers cannot be applied to an SRTP constraint."
+featureAllowObjectExpressionWithoutOverrides,"Allow object expressions without overrides"

src/Compiler/Facilities/LanguageFeatures.fs

@@ -93,6 +93,7 @@ type LanguageFeature =
     | LowerSimpleMappingsInComprehensionsToFastLoops
     | ParsedHashDirectiveArgumentNonQuotes
     | EmptyBodiedComputationExpressions
+    | AllowObjectExpressionWithoutOverrides
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -217,6 +218,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.EnforceAttributeTargets, previewVersion // not enabled because: https://github.com/dotnet/fsharp/issues/17514
                 LanguageFeature.FromEndSlicing, previewVersion // Unfinished features --- needs work
                 LanguageFeature.AllowAccessModifiersToAutoPropertiesGettersAndSetters, previewVersion
+                LanguageFeature.AllowObjectExpressionWithoutOverrides, previewVersion
             ]
 
     static let defaultLanguageVersion = LanguageVersion("default")
@@ -372,6 +374,7 @@ type LanguageVersion(versionText) =
             FSComp.SR.featureLowerSimpleMappingsInComprehensionsToFastLoops ()
         | LanguageFeature.ParsedHashDirectiveArgumentNonQuotes -> FSComp.SR.featureParsedHashDirectiveArgumentNonString ()
         | LanguageFeature.EmptyBodiedComputationExpressions -> FSComp.SR.featureEmptyBodiedComputationExpressions ()
+        | LanguageFeature.AllowObjectExpressionWithoutOverrides -> FSComp.SR.featureAllowObjectExpressionWithoutOverrides ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -84,6 +84,7 @@ type LanguageFeature =
     | LowerSimpleMappingsInComprehensionsToFastLoops
     | ParsedHashDirectiveArgumentNonQuotes
     | EmptyBodiedComputationExpressions
+    | AllowObjectExpressionWithoutOverrides
 
 /// LanguageVersion management
 type LanguageVersion =