Compiler error when using instance let-bindings on static class

src/Compiler/Checking/CheckDeclarations.fs

@@ -1665,7 +1665,9 @@ let private ReportErrorOnStaticClass (synMembers: SynMemberDefn list) =
         | SynMemberDefn.Member(SynBinding(valData = SynValData(memberFlags = Some memberFlags)), m) when memberFlags.MemberKind = SynMemberKind.Constructor ->
             errorR(Error(FSComp.SR.chkAdditionalConstructorOnStaticClasses(), m))
         | SynMemberDefn.Member(SynBinding(valData = SynValData(memberFlags = Some memberFlags)), m) when memberFlags.MemberKind = SynMemberKind.Member && memberFlags.IsInstance ->
-            errorR(Error(FSComp.SR.chkInstanceMemberOnStaticClasses(), m));
+            errorR(Error(FSComp.SR.chkInstanceMemberOnStaticClasses(), m))
+        | SynMemberDefn.LetBindings(isStatic = false; range = range) ->
+            errorR(Error(FSComp.SR.chkInstanceLetBindingOnStaticClasses(), range))
         | _ -> ()
 
 /// Check and generalize the interface implementations, members, 'let' definitions in a mutually recursive group of definitions.

src/Compiler/FSComp.txt

@@ -1669,3 +1669,4 @@ featureEscapeBracesInFormattableString,"Escapes curly braces before calling Form
 3552,chkConstructorWithArgumentsOnStaticClasses,"If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Constructor with arguments is not allowed."
 3553,chkAdditionalConstructorOnStaticClasses,"If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Additional constructor is not allowed."
 3554,chkInstanceMemberOnStaticClasses,"If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Instance members are not allowed."
+3555,chkInstanceLetBindingOnStaticClasses,"If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Instance let bindings are not allowed."

src/Compiler/xlf/FSComp.txt.cs.xlf

@@ -72,6 +72,11 @@
         <target state="translated">Použití incr z knihovny F# je zastaralé. Více informací: https://aka.ms/fsharp-refcell-ops. Změňte prosím například incr cell na cell.Value &lt;- cell.Value + 1.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.de.xlf

@@ -72,6 +72,11 @@
         <target state="translated">Die Verwendung von "incr" aus der F#-Bibliothek ist veraltet. Siehe https://aka.ms/fsharp-refcell-ops. Ändern Sie z. B. "incr cell" in "cell.Value &lt;- cell.Value + 1".</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.es.xlf

@@ -72,6 +72,11 @@
         <target state="translated">El uso de "incr" de la biblioteca de F# está en desuso. Vea https://aka.ms/fsharp-refcell-ops. Por ejemplo, cambie "incr cell" a "cell.Value &lt;- cell.Value + 1".</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.fr.xlf

@@ -72,6 +72,11 @@
         <target state="translated">L’utilisation de « incr » à partir de la bibliothèque F# est déconseillée. Voir https://aka.ms/fsharp-refcell-ops. Par exemple, veuillez remplacer « incr cell » par « cell.Value &lt;- cell.Value + 1 ».</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.it.xlf

@@ -72,6 +72,11 @@
         <target state="translated">L'uso di 'incr' dalla libreria F # è deprecato. Vedere https://aka.ms/fsharp-refcell-ops. Ad esempio, modificare 'incr cell' in 'cell.Value &lt;- cell.Value + 1'.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.ja.xlf

@@ -72,6 +72,11 @@
         <target state="translated">F# ライブラリからの 'incr' の使用は非推奨です。https://aka.ms/fsharp-refcell-ops を参照してください。たとえば、'incr cell' を 'cell.Value &lt;- cell.Value +1' に変更してください。</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.ko.xlf

@@ -72,6 +72,11 @@
         <target state="translated">F# 라이브러리의 'incr' 사용은 더 이상 사용되지 않습니다. https://aka.ms/fsharp-refcell-ops를 참조하세요. 예를 들어 'incr cell'을 'cell.Value &lt;- cell.Value + 1'로 변경하세요.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.pl.xlf

@@ -72,6 +72,11 @@
         <target state="translated">Użycie elementu „incr” z biblioteki języka F# jest przestarzałe. Sprawdź stronę https://aka.ms/fsharp-refcell-ops. Na przykład zmień wyrażenie „incr cell” na „cell.Value &lt;- cell.Value + 1”.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.pt-BR.xlf

@@ -72,6 +72,11 @@
         <target state="translated">O uso de 'incr' da biblioteca F# foi preterido. Consulte https://aka.ms/fsharp-refcell-ops. Por exemplo, altere a célula 'incr cell' para 'cell.Value &lt;- cell.Value + 1'.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.ru.xlf

@@ -72,6 +72,11 @@
         <target state="translated">Использование "incr" из библиотеки F# является нерекомендуемым. См. https://aka.ms/fsharp-refcell-ops. Например, замените "incr cell" на "cell.Value &lt;- cell.Value + 1".</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.tr.xlf

@@ -72,6 +72,11 @@
         <target state="translated">F# kitaplığından gelen 'incr' kullanımı kullanım dışı. https://aka.ms/fsharp-refcell-ops’a bakın. Örneğin, lütfen 'incr cell' ifadesini 'cell.Value &lt;- cell.Value + 1' olarak değiştirin.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.zh-Hans.xlf

@@ -72,6 +72,11 @@
         <target state="translated">已弃用 F# 库中的“incr”。请参阅 https://aka.ms/fsharp-refcell-ops。 例如，请将“incr cell”更改为“cell.Value &lt;- cell.Value + 1”。</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

src/Compiler/xlf/FSComp.txt.zh-Hant.xlf

@@ -72,6 +72,11 @@
         <target state="translated">透過 F# 程式庫使用 'incr' 的方式已淘汰。請參閱 https://aka.ms/fsharp-refcell-ops。舉例來說，請將 'incr cell' 變更為 'cell.Value &lt;- cell.Value + 1'。</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkInstanceLetBindingOnStaticClasses">
+        <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</source>
+        <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance let bindings are not allowed.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkInstanceMemberOnStaticClasses">
         <source>If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</source>
         <target state="new">If a type uses both [&lt;Sealed&gt;] and [&lt;AbstractClass&gt;] attributes, it means it is static. Instance members are not allowed.</target>

tests/FSharp.Compiler.ComponentTests/Language/StaticClassTests.fs

@@ -249,6 +249,108 @@ type T() =
 type T() =
     static member M() = ()
     static member X = T.M()
+        """
+         |> withLangVersionPreview
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass on a type with static and non static let bindings in lang 70`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    let a = 1
+    static let x = 1
+        """
+         |> withLangVersion70
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass on a type with static and non static recursive let bindings in lang 70`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    let rec a = 1
+    static let x = 1
+        """
+         |> withLangVersion70
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass on a type with static let bindings in lang 70`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    static let a = 1
+    static let x = a
+        """
+         |> withLangVersion70
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass on a type with recursive static let bindings in lang 70`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    static let rec a = 1
+    static let x = a
+        """
+         |> withLangVersion70
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass with static and non static let bindings in lang preview`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    let a = 1
+    static let X = 1
+        """
+         |> withLangVersionPreview
+         |> compile
+         |> shouldFail
+         |> withDiagnostics [
+             (Error 3555, Line 4, Col 5, Line 4, Col 14, "If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Instance let bindings are not allowed.")
+         ]
+
+    [<Fact>]
+    let ``Sealed and AbstractClass with static and non static recursive let bindings in lang preview`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    let rec a = 1
+    static let X = 1
+        """
+         |> withLangVersionPreview
+         |> compile
+         |> shouldFail
+         |> withDiagnostics [
+             (Error 3555, Line 4, Col 5, Line 4, Col 18, "If a type uses both [<Sealed>] and [<AbstractClass>] attributes, it means it is static. Instance let bindings are not allowed.")
+         ]
+
+    [<Fact>]
+    let ``Sealed and AbstractClass with static let bindings in lang preview`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    static let a = 1
+    static let X = a
+        """
+         |> withLangVersionPreview
+         |> compile
+         |> shouldSucceed
+
+    [<Fact>]
+    let ``Sealed and AbstractClass with recursive static let bindings in lang preview`` () =
+        Fsx """
+[<Sealed; AbstractClass>]
+type C() =
+    static let rec a = 1
+    static let X = a
         """
          |> withLangVersionPreview
          |> compile