dotnet · vzarytovskii · Jul 17, 2024 · May 24, 2023 · May 24, 2023 · May 24, 2023
@@ -127,3 +127,6 @@ nCrunchTemp_*
 tests/FSharp.Compiler.Service.Tests/FSharp.CompilerService.SurfaceArea.netstandard.actual
 *.vsp
 /tests/AheadOfTime/Trimming/output.txt
+*.svclog
+micro.exe
+positive.exe
diff --git a/VisualFSharp.sln b/VisualFSharp.sln
@@ -187,7 +187,6 @@ Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "FSharp.Editor.Tests", "vsin
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "FSharp.Editor.IntegrationTests", "vsintegration\tests\FSharp.Editor.IntegrationTests\FSharp.Editor.IntegrationTests.csproj", "{E31F9B59-FCF1-4D04-8762-C7BB60285A7B}"
 EndProject
-Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "nullness", "tests\adhoc\nullness\nullness.fsproj", "{6992D926-AB1C-4CD4-94D5-0319D14DB54B}"
 Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "FSharp.Benchmarks.Common", "tests\benchmarks\FSharp.Benchmarks.Common\FSharp.Benchmarks.Common.fsproj", "{6734FC6F-B5F3-45E1-9A72-720378BB49C9}"
 EndProject
 Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "MicroPerf", "tests\benchmarks\CompiledCodeBenchmarks\MicroPerf\MicroPerf.fsproj", "{601CD5C1-EAFA-4AE3-8FB9-F667B5728213}"
@@ -984,18 +983,6 @@ Global
 		{E31F9B59-FCF1-4D04-8762-C7BB60285A7B}.Release|Any CPU.Build.0 = Release|Any CPU
 		{E31F9B59-FCF1-4D04-8762-C7BB60285A7B}.Release|x86.ActiveCfg = Release|Any CPU
 		{E31F9B59-FCF1-4D04-8762-C7BB60285A7B}.Release|x86.Build.0 = Release|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Debug|x86.Build.0 = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Proto|Any CPU.ActiveCfg = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Proto|Any CPU.Build.0 = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Proto|x86.ActiveCfg = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Proto|x86.Build.0 = Debug|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Release|Any CPU.Build.0 = Release|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Release|x86.ActiveCfg = Release|Any CPU
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B}.Release|x86.Build.0 = Release|Any CPU
 		{6734FC6F-B5F3-45E1-9A72-720378BB49C9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{6734FC6F-B5F3-45E1-9A72-720378BB49C9}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6734FC6F-B5F3-45E1-9A72-720378BB49C9}.Debug|x86.ActiveCfg = Debug|Any CPU
@@ -1109,7 +1096,6 @@ Global
 		{39CDF34B-FB23-49AE-AB27-0975DA379BB5} = {DFB6ADD7-3149-43D9-AFA0-FC4A818B472B}
 		{CBC96CC7-65AB-46EA-A82E-F6A788DABF80} = {F7876C9B-FB6A-4EFB-B058-D6967DB75FB2}
 		{E31F9B59-FCF1-4D04-8762-C7BB60285A7B} = {F7876C9B-FB6A-4EFB-B058-D6967DB75FB2}
-		{6992D926-AB1C-4CD4-94D5-0319D14DB54B} = {CFE3259A-2D30-4EB0-80D5-E8B5F3D01449}
 		{6734FC6F-B5F3-45E1-9A72-720378BB49C9} = {DFB6ADD7-3149-43D9-AFA0-FC4A818B472B}
 		{601CD5C1-EAFA-4AE3-8FB9-F667B5728213} = {DFB6ADD7-3149-43D9-AFA0-FC4A818B472B}
 		{9F9DD315-37DA-4413-928E-1CFC6924B64F} = {DFB6ADD7-3149-43D9-AFA0-FC4A818B472B}

diff --git a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
@@ -1,5 +1,6 @@
 ### Fixed
 
+
 * Fix a false positive of the `[<TailCall>]` analysis in combination with async. ([Issue #17237](https://github.com/dotnet/fsharp/issues/17237), [PR #17241](https://github.com/dotnet/fsharp/pull/17241))
 * Extended #help directive in fsi to show documentation in the REPL. ([PR #17140](https://github.com/dotnet/fsharp/pull/17140))
 * Fix internal error when dotting into delegates with multiple type parameters. ([PR #17227](https://github.com/dotnet/fsharp/pull/17227))

diff --git a/docs/release-notes/.FSharp.Core/8.0.400.md b/docs/release-notes/.FSharp.Core/8.0.400.md
@@ -12,3 +12,4 @@
 ### Breaking Changes
 
 * Fixed argument exception throwing inconsistency - accessing an out-of-bounds collection index will now throw `ArgumentOutOfRangeException` instead of `ArgumentException` ([#17328](https://github.com/dotnet/fsharp/pull/17328))
+
diff --git a/eng/Versions.props b/eng/Versions.props
@@ -39,7 +39,7 @@
     <FSharpCompilerServiceReleaseNotesVersion>$(FCSMajorVersion)$(FCSMinorVersion)$(FCSBuildVersion)</FSharpCompilerServiceReleaseNotesVersion>
     <!-- -->
     <!-- The current published nuget package -->
-    <FSharpCoreShippedPackageVersionValue>8.0.200</FSharpCoreShippedPackageVersionValue>
+    <FSharpCoreShippedPackageVersionValue>8.0.300</FSharpCoreShippedPackageVersionValue>
     <!-- -->
     <!-- The pattern for specifying the preview package -->
     <FSharpCorePreviewPackageVersionValue>$(FSCorePackageVersionValue)-$(PreReleaseVersionLabel).*</FSharpCorePreviewPackageVersionValue>

@@ -931,7 +931,6 @@ let mkCacheGeneric lowMem _inbase _nm (sz: int) =
         (fun f x -> f x)
     else
         let mutable cache = null
-
 #if STATISTICS
         let mutable _count = 0
 

@@ -483,8 +483,9 @@ let UnifyOverallType (cenv: cenv) (env: TcEnv) m overallTy actualTy =
     match overallTy with
     | MustConvertTo(isMethodArg, reqdTy) when g.langVersion.SupportsFeature LanguageFeature.AdditionalTypeDirectedConversions ->
         let actualTy = tryNormalizeMeasureInType g actualTy
-        let reqdTy = tryNormalizeMeasureInType g reqdTy
-        if AddCxTypeEqualsTypeUndoIfFailed env.DisplayEnv cenv.css m reqdTy actualTy then
+        let reqdTy = tryNormalizeMeasureInType g reqdTy       
+        let reqTyForUnification = reqTyForArgumentNullnessInference g actualTy reqdTy           
+        if AddCxTypeEqualsTypeUndoIfFailed env.DisplayEnv cenv.css m reqTyForUnification actualTy then
             ()
         else
             // try adhoc type-directed conversions
@@ -1040,6 +1041,7 @@ let TcAddNullnessToType (warn: bool) (cenv: cenv) (env: TcEnv) nullness innerTyC
 
             if not g.compilingFSharpCore || not (isTyparTy g innerTyC) then 
                 AddCxTypeDefnNotSupportsNull env.DisplayEnv cenv.css m NoTrace innerTyC
+                AddCxTypeIsReferenceType env.DisplayEnv cenv.css m NoTrace innerTyC
 
             if not g.compilingFSharpCore && isTyparTy g innerTyC then
                 // A typar might be later infered into a type not supporting `| null|, like tuple or anon.
@@ -2995,7 +2997,7 @@ let TcRuntimeTypeTest isCast isOperator (cenv: cenv) denv m tgtTy srcTy =
         else
             error(Error(FSComp.SR.tcTypeTestErased(NicePrint.minimalStringOfType denv tgtTy, NicePrint.minimalStringOfType denv (stripTyEqnsWrtErasure EraseAll g tgtTy)), m))
     else
-        for ety in getErasedTypes g tgtTy do
+        for ety in getErasedTypes g tgtTy true do
             if isMeasureTy g ety then
                 warning(Error(FSComp.SR.tcTypeTestLosesMeasures(NicePrint.minimalStringOfType denv ety), m))
             else
@@ -5203,6 +5205,7 @@ and TcPatLongIdentActivePatternCase warnOnUpper (cenv: cenv) (env: TcEnv) vFlags
                         | TyparConstraint.IsDelegate _
                         | TyparConstraint.IsEnum _
                         | TyparConstraint.IsNonNullableStruct _
+                        | TyparConstraint.NotSupportsNull _
                         | TyparConstraint.IsUnmanaged _
                         | TyparConstraint.RequiresDefaultConstructor _
                         | TyparConstraint.SimpleChoice _
@@ -5340,6 +5343,7 @@ and TcExprFlex (cenv: cenv) flex compat (desiredTy: TType) (env: TcEnv) tpenv (s
 
     if flex then
         let argTy = NewInferenceType g
+        (destTyparTy g argTy).SetSupportsNullFlex(true)
         if compat then
             (destTyparTy g argTy).SetIsCompatFlex(true)
 
@@ -9627,7 +9631,8 @@ and TcEventItemThen (cenv: cenv) overallTy env tpenv mItem mExprAndItem objDetai
     | None, false -> error (Error (FSComp.SR.tcEventIsNotStatic nm, mItem))
     | _ -> ()
 
-    let delTy = einfo.GetDelegateType(cenv.amap, mItem)
+    // The F# wrappers around events are null safe (impl is in FSharp.Core). Therefore, from an F# perspective, the type of the delegate can be considered Not Null.
+    let delTy = einfo.GetDelegateType(cenv.amap, mItem) |> replaceNullnessOfTy KnownWithoutNull 
     let (SigOfFunctionForDelegate(delInvokeMeth, delArgTys, _, _)) = GetSigOfFunctionForDelegate cenv.infoReader delTy mItem ad
     let objArgs = Option.toList (Option.map fst objDetails)
     MethInfoChecks g cenv.amap true None objArgs env.eAccessRights mItem delInvokeMeth

@@ -308,6 +308,9 @@ type ConstraintSolverEnv =
       // Is this speculative, with a trace allowing undo, and trial method overload resolution 
       IsSpeculativeForMethodOverloading: bool
 
+      // Can this ignore the 'must support null' constraint, e.g. in a mutable assignment scenario
+      IsSupportsNullFlex: bool
+
       /// Indicates that when unifying ty1 = ty2, only type variables in ty1 may be solved. Constraints
       /// can't be added to type variables in ty2
       MatchingOnly: bool
@@ -344,6 +347,7 @@ let MakeConstraintSolverEnv contextInfo css m denv =
       EquivEnv = TypeEquivEnv.Empty 
       DisplayEnv = denv
       IsSpeculativeForMethodOverloading = false
+      IsSupportsNullFlex = false
       ExtraRigidTypars = emptyFreeTypars
     }
 
@@ -953,6 +957,13 @@ let rec SolveTyparEqualsTypePart1 (csenv: ConstraintSolverEnv) m2 (trace: Option
         // Record the solution before we solve the constraints, since 
         // We may need to make use of the equation when solving the constraints. 
         // Record a entry in the undo trace if one is provided 
+
+        //let ty1AllowsNull = r.Constraints |> List.exists (function | TyparConstraint.SupportsNull _ -> true | _ -> false )
+        //let tyAllowsNull() = TypeNullIsExtraValueNew csenv.g m2 ty
+        //if ty1AllowsNull && not (tyAllowsNull()) then
+        //     trace.Exec (fun () -> r.typar_solution <- Some (ty |> replaceNullnessOfTy csenv.g.knownWithNull)) (fun () -> r.typar_solution <- None)
+        //else
+        //    trace.Exec (fun () -> r.typar_solution <- Some ty) (fun () -> r.typar_solution <- None)
         trace.Exec (fun () -> r.typar_solution <- Some ty) (fun () -> r.typar_solution <- None)
     }  
 
@@ -1051,8 +1062,7 @@ and SolveNullnessEquiv (csenv: ConstraintSolverEnv) m2 (trace: OptionalTrace) ty
         // Warn for 'strict "must pass null"` APIs like Option.ofObj
         | NullnessInfo.WithNull, NullnessInfo.WithoutNull when shouldWarnUselessNullCheck csenv -> 
             WarnD(Error(FSComp.SR.tcPassingWithoutNullToANullableExpectingFunc (csenv.SolverState.WarnWhenUsingWithoutNullOnAWithNullTarget.Value),m2))    
-        // Allow expected of WithNull and actual of WithoutNull
-        // TODO NULLNESS:  this is not sound in contravariant cases etc. It is assuming covariance.
+        // Allow expected of WithNull and actual of WithoutNull except for specially marked APIs (handled above)        
         | NullnessInfo.WithNull, NullnessInfo.WithoutNull -> CompleteD
         | _ -> 
             if csenv.g.checkNullness then 
@@ -1070,6 +1080,8 @@ and SolveNullnessSubsumesNullness (csenv: ConstraintSolverEnv) m2 (trace: Option
         SolveNullnessSubsumesNullness csenv m2 trace ty1 ty2 nv1.Solution nullness2
     | _, Nullness.Variable nv2 when nv2.IsSolved -> 
         SolveNullnessSubsumesNullness csenv m2 trace ty1 ty2 nullness1 nv2.Solution
+    | Nullness.Variable _nv1, Nullness.Known NullnessInfo.WithoutNull  -> 
+        CompleteD
     | Nullness.Variable nv1, _ -> 
         trace.Exec (fun () ->   nv1.Set nullness2) (fun () -> nv1.Unset())
         CompleteD
@@ -1218,6 +1230,12 @@ and SolveTypeEqualsType (csenv: ConstraintSolverEnv) ndeep m2 (trace: OptionalTr
     let sty1 = stripTyEqnsA csenv.g canShortcut ty1
     let sty2 = stripTyEqnsA csenv.g canShortcut ty2
 
+    let csenv = 
+        match ty1 with 
+        | TType.TType_var(r,_) when r.typar_flags.IsSupportsNullFlex -> 
+            { csenv with IsSupportsNullFlex = true}
+        | _ -> csenv
+
     match sty1, sty2 with
     // type vars inside forall-types may be alpha-equivalent 
     | TType_var (tp1, nullness1), TType_var (tp2, nullness2) when typarEq tp1 tp2 || (match aenv.EquivTypars.TryFind tp1 with | Some tpTy1 when typeEquiv g tpTy1 ty2 -> true | _ -> false) ->
@@ -1273,6 +1291,15 @@ and SolveTypeEqualsType (csenv: ConstraintSolverEnv) ndeep m2 (trace: OptionalTr
         // Unifying 'T1? and 'T2? 
         | ValueSome NullnessInfo.WithNull, ValueSome NullnessInfo.WithNull ->
             SolveTyparEqualsType csenv ndeep m2 trace sty1 (replaceNullnessOfTy g.knownWithoutNull sty2)
+        | ValueSome NullnessInfo.WithoutNull, ValueSome NullnessInfo.WithoutNull when 
+            csenv.IsSupportsNullFlex && 
+            isAppTy g sty2 && 
+            tp1.Constraints |> List.exists (function TyparConstraint.SupportsNull _ -> true | _ -> false) ->
+                let tpNew = NewCompGenTypar(TyparKind.Type, TyparRigidity.Flexible, TyparStaticReq.None, TyparDynamicReq.No, false)               
+                trackErrors {                    
+                    do! SolveTypeEqualsType csenv ndeep m2 trace cxsln (TType_var(tpNew, g.knownWithoutNull)) sty2
+                    do! SolveTypeEqualsType csenv ndeep m2 trace cxsln ty1 (TType_var(tpNew, g.knownWithNull))
+                }
         // Unifying 'T1 % and 'T2 % 
         //| ValueSome NullnessInfo.AmbivalentToNull, ValueSome NullnessInfo.AmbivalentToNull ->
         //    SolveTyparEqualsType csenv ndeep m2 trace sty1 (replaceNullnessOfTy g.knownWithoutNull sty2) 
@@ -1386,8 +1413,8 @@ and SolveTypeEqualsTypeEqns csenv ndeep m2 trace cxsln origl1 origl2 =
 
 and SolveFunTypeEqn csenv ndeep m2 trace cxsln domainTy1 domainTy2 rangeTy1 rangeTy2 =
     trackErrors {
-        // TODO NULLNESS: consider whether flipping the actual and expected in argument position
-        // causes other problems, e.g. better/worse diagnostics
+        let g = csenv.g
+        let domainTy2 = reqTyForArgumentNullnessInference g domainTy1 domainTy2
         do! SolveTypeEqualsTypeKeepAbbrevsWithCxsln csenv ndeep m2 trace cxsln domainTy2 domainTy1
         return! SolveTypeEqualsTypeKeepAbbrevsWithCxsln csenv ndeep m2 trace cxsln rangeTy1 rangeTy2
     }
@@ -2354,6 +2381,10 @@ and EnforceConstraintConsistency (csenv: ConstraintSolverEnv) ndeep m2 trace ret
         | TyparConstraint.IsNonNullableStruct _, TyparConstraint.IsReferenceType _
         | TyparConstraint.IsReferenceType _, TyparConstraint.IsNonNullableStruct _   ->
             return! ErrorD (Error(FSComp.SR.csStructConstraintInconsistent(), m))
+
+        | TyparConstraint.SupportsNull _, TyparConstraint.NotSupportsNull _
+        | TyparConstraint.NotSupportsNull _, TyparConstraint.SupportsNull _   ->
+            return! ErrorD (Error(FSComp.SR.csNullNotNullConstraintInconsistent(), m))
 
         | TyparConstraint.IsUnmanaged _, TyparConstraint.IsReferenceType _
         | TyparConstraint.IsReferenceType _, TyparConstraint.IsUnmanaged _ ->
@@ -2534,16 +2565,18 @@ and SolveTypeUseSupportsNull (csenv: ConstraintSolverEnv) ndeep m2 trace ty =
                 return! ErrorD (ConstraintSolverError(FSComp.SR.csNullableTypeDoesNotHaveNull(NicePrint.minimalStringOfType denv ty), m, m2))
             else
                 match tryDestTyparTy g ty with
-                | ValueSome tp ->
+                | ValueSome tp ->                    
                     let nullness = nullnessOfTy g ty
                     match nullness.TryEvaluate() with
                     // NULLNESS TODO: This rule means turning on checkNullness changes type inference results for the cases
                     // mentioned in the comment above. THat's OK but needs to be documented in the RFC.
                     | ValueNone when not g.checkNullness ->
-                        return! AddConstraint csenv ndeep m2 trace tp (TyparConstraint.SupportsNull m)
-                    | ValueSome NullnessInfo.WithoutNull ->
+                        return! AddConstraint csenv ndeep m2 trace tp (TyparConstraint.SupportsNull m)                    
+                    | ValueSome NullnessInfo.WithoutNull ->                      
                         return! AddConstraint csenv ndeep m2 trace tp (TyparConstraint.SupportsNull m)
                     | _ ->
+                        if tp.Constraints |> List.exists (function | TyparConstraint.IsReferenceType _ -> true | _ -> false) |> not then
+                            do! AddConstraint csenv ndeep m2 trace tp (TyparConstraint.IsReferenceType m)
                         return! SolveNullnessSupportsNull csenv ndeep m2 trace ty nullness
                 | _ ->
                     let nullness = nullnessOfTy g ty
@@ -2580,9 +2613,10 @@ and SolveNullnessSupportsNull (csenv: ConstraintSolverEnv) ndeep m2 (trace: Opti
             match n1 with 
             | NullnessInfo.AmbivalentToNull -> ()
             | NullnessInfo.WithNull -> ()
-            | NullnessInfo.WithoutNull -> 
+            | NullnessInfo.WithoutNull ->   
                 if g.checkNullness then 
-                    return! WarnD(ConstraintSolverNullnessWarningWithType(denv, ty, n1, m, m2)) 
+                    // TODO nullness: Shouldn't this be an error? We have a 'must support null' situation which is not being met.
+                    return! WarnD(ConstraintSolverNullnessWarningWithType(denv, ty, n1, m, m2))
     }
 
 and SolveTypeUseNotSupportsNull (csenv: ConstraintSolverEnv) ndeep m2 trace ty =
@@ -2635,7 +2669,9 @@ and SolveTypeCanCarryNullness (csenv: ConstraintSolverEnv)  ty nullness =
         let m = csenv.m
         let strippedTy = stripTyEqnsA g true ty
         match tryAddNullnessToTy nullness strippedTy with
-        | Some _ -> ()
+        | Some _ -> 
+            if isTyparTy g strippedTy && not (isReferenceTyparTy g strippedTy) then
+                return! AddConstraint csenv 0 m NoTrace (destTyparTy g strippedTy) (TyparConstraint.IsReferenceType m)
         | None -> 
             let tyString = NicePrint.minimalStringOfType csenv.DisplayEnv strippedTy
             return! ErrorD(Error(FSComp.SR.tcTypeDoesNotHaveAnyNull(tyString), m))

@@ -480,7 +480,7 @@ let MakeCalledArgs amap m (minfo: MethInfo) minst =
         IsOutArg=isOutArg
         ReflArgInfo=reflArgInfo
         NameOpt=nmOpt
-        CalledArgumentType=calledArgTy })
+        CalledArgumentType= changeWithNullReqTyToVariable amap.g calledArgTy})
 
 /// <summary>
 /// Represents the syntactic matching between a caller of a method and the called method.

@@ -2555,7 +2555,7 @@ let CheckEntityDefn cenv env (tycon: Entity) =
                 // Check if it's marked unsafe
                 let zeroInitUnsafe = TryFindFSharpBoolAttribute g g.attrib_DefaultValueAttribute f.FieldAttribs
                 if zeroInitUnsafe = Some true then
-                    if not (TypeHasDefaultValue g m ty) then
+                    if not (TypeHasDefaultValue g m f.FormalType) then
                         errorR(Error(FSComp.SR.chkValueWithDefaultValueMustHaveDefaultValue(), m))
 
         // Check type abbreviations
Original file line number	Diff line number	Diff line change
Expand Up		@@ -12,3 +12,4 @@
		### Breaking Changes

		* Fixed argument exception throwing inconsistency - accessing an out-of-bounds collection index will now throw `ArgumentOutOfRangeException` instead of `ArgumentException` ([#17328](https://github.com/dotnet/fsharp/pull/17328))