Merge pull request #16060 from dotnet/merges/release/dev17.8-to-relea…

…se/dev17.9

src/Compiler/Checking/CheckDeclarations.fs

@@ -1840,7 +1840,10 @@ let TcMutRecDefns_Phase2 (cenv: cenv) envInitial mBinds scopem mutRecNSInfo (env
           | SynMemberDefn.ImplicitCtor _ :: _ -> ()
           | _ ->
             if not tcref.IsFSharpEnumTycon && not tcref.IsFSharpDelegateTycon && not tcref.IsFSharpException && not tcref.IsTypeAbbrev then
-                TyconBindingDefn(containerInfo, newslotsOK, declKind, None, tcref.Range)
+                if members |> List.exists (function | SynMemberDefn.LetBindings(isStatic=true) -> true | _ -> false ) then
+                    // Introduction of this member has caused the regression #16009, due to a missed Lazy<>.Force access from a member to a value in recursive module
+                    // Minimizing the impact by only yielding in case of actually emitting static let bindings.
+                    TyconBindingDefn(containerInfo, newslotsOK, declKind, None, tcref.Range)
 
           // Yield the other members
           for memb in members do

src/Compiler/Checking/CheckIncrementalClasses.fs

@@ -756,7 +756,6 @@ let MakeCtorForIncrClassConstructionPhase2C(
     /// binding in the implicit class construction sequence 
     let TransTrueDec isCtorArg (reps: IncrClassReprInfo) dec = 
             match dec with 
-            // Pokud to neni staticke, a zaroven to nema construktor info, tak zkusit vyhnout se TransBind mozna?
             | IncrClassBindingGroup(binds, isStatic, isRec) ->
                 let actions, reps, methodBinds = 
                     let reps = (reps, binds) ||> List.fold (fun rep bind -> rep.ChooseAndAddRepresentation(cenv, env, isStatic, isCtorArg, staticCtorInfo, ctorInfoOpt, staticForcedFieldVars, instanceForcedFieldVars, bind)) // extend

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/StaticLet/StaticLetInUnionsAndRecords.fs

@@ -561,4 +561,86 @@ Console.Write(MyTypes.X.GetX)
     IL_0019:  ret
   } 
 
-}"""]
+}"""]
+
+[<Theory>]
+[<InlineData("preview")>]
+let ``Regression 16009 - module rec does not initialize let bindings`` langVersion =
+    let moduleWithBinding = """
+module rec Module
+
+open System
+
+let binding = 
+    do Console.WriteLine("Asked for Module.binding")
+    let b = Foo.StaticMember
+    do Console.Write("isNull b in Module.binding after the call to Foo.StaticMember? ")
+    do Console.WriteLine(isNull b)
+    b
+
+module NestedModule =
+    let Binding =         
+        do Console.WriteLine("Asked for NestedModule.Binding, before creating obj()")
+        let b = new obj()
+        do Console.Write("isNull b in NestedModule.Binding after 'new obj()'? ")
+        do Console.WriteLine(isNull b)
+        b
+
+type Foo =
+    static member StaticMember = 
+        do Console.WriteLine("Asked for Foo.StaticMember")
+        let b = NestedModule.Binding
+        do Console.Write("isNull b in Foo.StaticMember after access to NestedModule.Binding? ")
+        do Console.WriteLine(isNull b)
+        b
+"""
+
+    let program = """
+open Module
+open System
+
+do Console.WriteLine("Right before calling binding.ToString() in program.fs")
+let b = binding
+b.ToString() |> ignore
+"""
+
+    FSharp moduleWithBinding
+    |> withAdditionalSourceFiles [SourceCodeFileKind.Create("program.fs", program)]
+    |> withLangVersion langVersion
+    |> asExe
+    |> ignoreWarnings
+    |> compileAndRun
+    |> shouldSucceed 
+
+
+[<Theory>]
+[<InlineData("preview")>]
+let ``Regression 16009 - as a single file program`` langVersion =
+    let code = """
+namespace MyProgram
+
+module rec Module = 
+
+    open System
+
+    let binding = Foo.StaticMember
+
+    module NestedModule =
+        let Binding = new obj()
+
+    type Foo =
+        static member StaticMember = NestedModule.Binding
+            
+module ActualProgram = 
+    open Module
+    open System
+    
+    binding.ToString() |> Console.WriteLine
+"""
+
+    FSharp code
+    |> withLangVersion langVersion
+    |> asExe
+    |> ignoreWarnings
+    |> compileAndRun
+    |> shouldSucceed  

tests/fsharp/typecheck/sigs/neg04.bsl

@@ -45,16 +45,12 @@ neg04.fs(70,21,70,36): typecheck error FS0064: This construct causes code to be
 
 neg04.fs(70,12,70,14): typecheck error FS0663: This type parameter has been used in a way that constrains it to always be 'c<string>'
 
-neg04.fs(70,12,70,14): typecheck error FS0660: This code is less generic than required by its annotations because the explicit type variable 'a' could not be generalized. It was constrained to be 'c<string>'.
-
 neg04.fs(76,19,76,26): typecheck error FS0698: Invalid constraint: the type used for the constraint is sealed, which means the constraint could only be satisfied by at most one solution
 
 neg04.fs(76,19,76,26): typecheck error FS0064: This construct causes code to be less generic than indicated by the type annotations. The type variable 'a has been constrained to be type 'd'.
 
 neg04.fs(76,10,76,12): typecheck error FS0663: This type parameter has been used in a way that constrains it to always be 'd'
 
-neg04.fs(76,10,76,12): typecheck error FS0660: This code is less generic than required by its annotations because the explicit type variable 'a' could not be generalized. It was constrained to be 'd'.
-
 neg04.fs(81,58,81,61): typecheck error FS0001: This expression was expected to have type
     'int'    
 but here has type