Remove always-on OpenTypeDeclaration language feature flag

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -157,6 +157,7 @@
 
 ### Changed
 
+* Removed the always-on `OpenTypeDeclaration` language feature flag; `open type` declarations are unconditional and `--disableLanguageFeature:OpenTypeDeclaration` is no longer a recognized feature name. ([Issue #20148](https://github.com/dotnet/fsharp/issues/20148), [PR #20215](https://github.com/dotnet/fsharp/pull/20215))
 * Improvements in error and warning messages: new error FS3885 when `let!`/`use!` is the final expression in a computation expression; new warning FS3886 when a list literal contains a single tuple element (likely missing `;` separator); improved wording for FS0003, FS0025, FS0039, FS0072, FS0247, FS0597, FS0670, FS3082, and SRTP operator-not-in-scope hints. ([PR #19398](https://github.com/dotnet/fsharp/pull/19398))
 * Exception field serialization (`GetObjectData` and field-restoring constructor) is now gated behind `langversion:11` (`LanguageFeature.ExceptionFieldSerializationSupport`). With langversion ≤10, exception codegen is unchanged from pre-#19342 behavior. ([PR #19746](https://github.com/dotnet/fsharp/pull/19746))
 * Lower string-typed interpolated strings to `System.String.Concat` rather than the reflection-based `printf` engine, making them trim- and NativeAOT-compatible. This generalizes and ungates the previous all-string `String.Concat` optimization, so it now applies to every string-typed interpolation. ([Language suggestion #1108](https://github.com/fsharp/fslang-suggestions/issues/1108), [PR #19971](https://github.com/dotnet/fsharp/pull/19971))

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

@@ -12,6 +12,7 @@
 
 ### Changed
 
+* Removed the always-on `OpenTypeDeclaration` language feature flag; `open type` declarations are unconditional and `--disableLanguageFeature:OpenTypeDeclaration` is no longer a recognized feature name. ([Issue #20148](https://github.com/dotnet/fsharp/issues/20148), [PR #20215](https://github.com/dotnet/fsharp/pull/20215))
 * Direct delegate construction ([PR #19993](https://github.com/dotnet/fsharp/pull/19993))
   * A delegate built from a method or function now points straight at that method instead of an intermediate closure, so `delegate.Method` is the real target and no closure class is generated.
   * Two delegates built from the same method and target now compare equal, where the previous closure form produced distinct instances; this also makes `Delegate.Remove` (and `-=` on events) match and remove such a delegate that it previously left in place.

src/Compiler/Checking/CheckDeclarations.fs

@@ -782,11 +782,9 @@ let TcOpenModuleOrNamespaceDecl tcSink g amap scopem env (longId, m) =
     let env = OpenModuleOrNamespaceRefs tcSink g amap scopem false env modrefs openDecl
     env, [openDecl]
 
-let TcOpenTypeDecl (cenv: cenv) mOpenDecl scopem env (synType: SynType, m) =
+let TcOpenTypeDecl (cenv: cenv) scopem env (synType: SynType, m) =
     let g = cenv.g
 
-    checkLanguageFeatureAndRecover g.langVersion LanguageFeature.OpenTypeDeclaration mOpenDecl
-
     let ty, _tpenv = TcType cenv NoNewTypars CheckCxs ItemOccurrence.Open WarnOnIWSAM.Yes env emptyUnscopedTyparEnv synType
 
     if not (isAppTy g ty) then
@@ -799,14 +797,14 @@ let TcOpenTypeDecl (cenv: cenv) mOpenDecl scopem env (synType: SynType, m) =
     let env = OpenTypeContent cenv.tcSink g cenv.amap scopem env ty openDecl
     env, [openDecl]
 
-let TcOpenDecl (cenv: cenv) mOpenDecl scopem env target = 
+let TcOpenDecl (cenv: cenv) scopem env target = 
     let g = cenv.g
     match target with
     | SynOpenDeclTarget.ModuleOrNamespace (longId, m) ->
         TcOpenModuleOrNamespaceDecl cenv.tcSink g cenv.amap scopem env (longId.LongIdent, m)
 
     | SynOpenDeclTarget.Type (synType, m) ->
-        TcOpenTypeDecl cenv mOpenDecl scopem env (synType, m)
+        TcOpenTypeDecl cenv scopem env (synType, m)
 
 let MakeSafeInitField (cenv: cenv) env m isStatic = 
     let id =
@@ -1852,8 +1850,8 @@ module MutRecBindingChecking =
 
                 // Process the 'open' declarations                
                 let envForDecls =
-                    (envForDecls, opens) ||> List.fold (fun env (target, m, moduleRange, openDeclsRef) ->
-                        let env, openDecls = TcOpenDecl cenv m moduleRange env target
+                    (envForDecls, opens) ||> List.fold (fun env (target, _, moduleRange, openDeclsRef) ->
+                        let env, openDecls = TcOpenDecl cenv moduleRange env target
                         openDeclsRef.Value <- openDecls
                         env)
 
@@ -2824,8 +2822,8 @@ module EstablishTypeDefinitionCores =
             use _holder = TemporarilySuspendReportingTypecheckResultsToSink cenv.tcSink
             (env, shapes) ||> List.fold (fun env shape ->
                 match shape with
-                | MutRecShape.Open(MutRecDataForOpen(SynOpenDeclTarget.ModuleOrNamespace _ as target, openm, moduleRange, _)) ->
-                    let env, _ = TcOpenDecl cenv openm moduleRange env target
+                | MutRecShape.Open(MutRecDataForOpen(SynOpenDeclTarget.ModuleOrNamespace _ as target, _, moduleRange, _)) ->
+                    let env, _ = TcOpenDecl cenv moduleRange env target
                     env
                 | _ -> env))
 
@@ -5261,7 +5259,7 @@ let rec TcSignatureElementNonMutRec (cenv: cenv) parent typeNames endm (env: TcE
 
         | SynModuleSigDecl.Open (target, m) -> 
             let scopem = unionRanges m.EndRange endm
-            let env, _openDecl = TcOpenDecl cenv m scopem env target
+            let env, _openDecl = TcOpenDecl cenv scopem env target
             return env
 
         | SynModuleSigDecl.Val (vspec, m) -> 
@@ -5667,7 +5665,7 @@ let rec TcModuleOrNamespaceElementNonMutRec (cenv: cenv) parent typeNames scopem
 
       | SynModuleDecl.Open (target, m) -> 
           let scopem = unionRanges m.EndRange scopem
-          let env, openDecls = TcOpenDecl cenv m scopem env target
+          let env, openDecls = TcOpenDecl cenv scopem env target
           let defns =
               match openDecls with
               | [] -> []

src/Compiler/Checking/NameResolution.fs

@@ -1374,7 +1374,6 @@ and private AddStaticPartsOfTyconRefToNameEnv bulkAddMode ownDefinition g amap m
         eUnindexedExtensionMembers = eUnindexedExtensionMembers }
 
 and private CanAutoOpenTyconRef (g: TcGlobals) (tcref: TyconRef) =
-    g.langVersion.SupportsFeature LanguageFeature.OpenTypeDeclaration &&
     not tcref.IsILTycon &&
     EntityHasWellKnownAttribute g WellKnownEntityAttributes.AutoOpenAttribute tcref.Deref &&
     tcref.Typars |> List.isEmpty

src/Compiler/FSComp.txt

@@ -1568,7 +1568,6 @@ featureWildCardInForLoop,"wild card in for loop"
 featureRelaxWhitespace,"whitespace relaxation"
 featureNameOf,"nameof"
 featureImplicitYield,"implicit yield"
-featureOpenTypeDeclaration,"open type declaration"
 featureDotlessFloat32Literal,"dotless float32 literal"
 featurePackageManagement,"package management"
 featureFromEndSlicing,"from-end slicing"

src/Compiler/Facilities/LanguageFeatures.fs

@@ -22,7 +22,6 @@ type LanguageFeature =
     | RelaxWhitespace2
     | NameOf
     | ImplicitYield
-    | OpenTypeDeclaration
     | DotlessFloat32Literal
     | PackageManagement
     | FromEndSlicing
@@ -163,7 +162,6 @@ type LanguageVersion(versionText, ?disabledFeaturesArray: LanguageFeature array)
                 LanguageFeature.AndBang, languageVersion50
                 LanguageFeature.NullableOptionalInterop, languageVersion50
                 LanguageFeature.DefaultInterfaceMemberConsumption, languageVersion50
-                LanguageFeature.OpenTypeDeclaration, languageVersion50
                 LanguageFeature.PackageManagement, languageVersion50
                 LanguageFeature.WitnessPassing, languageVersion50
                 LanguageFeature.InterfacesWithMultipleGenericInstantiation, languageVersion50
@@ -369,7 +367,6 @@ type LanguageVersion(versionText, ?disabledFeaturesArray: LanguageFeature array)
         | LanguageFeature.RelaxWhitespace2 -> FSComp.SR.featureRelaxWhitespace2 ()
         | LanguageFeature.NameOf -> FSComp.SR.featureNameOf ()
         | LanguageFeature.ImplicitYield -> FSComp.SR.featureImplicitYield ()
-        | LanguageFeature.OpenTypeDeclaration -> FSComp.SR.featureOpenTypeDeclaration ()
         | LanguageFeature.DotlessFloat32Literal -> FSComp.SR.featureDotlessFloat32Literal ()
         | LanguageFeature.PackageManagement -> FSComp.SR.featurePackageManagement ()
         | LanguageFeature.FromEndSlicing -> FSComp.SR.featureFromEndSlicing ()

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -12,7 +12,6 @@ type LanguageFeature =
     | RelaxWhitespace2
     | NameOf
     | ImplicitYield
-    | OpenTypeDeclaration
     | DotlessFloat32Literal
     | PackageManagement
     | FromEndSlicing