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Bugfix: Warn when upcast drops nullness via FindUniqueFeasibleSupertype #18261

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Merged
merged 4 commits into from
Feb 4, 2025
Merged

Bugfix: Warn when upcast drops nullness via FindUniqueFeasibleSupertype #18261

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434a568
Warn when upcast drops nullness via FindUniqueFeasibleSupertype
T-Gro Jan 23, 2025
278e3b7
temporary null shutuops before `use` is softened
T-Gro Feb 3, 2025
f945bea
notes added
T-Gro Feb 3, 2025
784318c
Merge branch 'main' into 18232-nullness-issue---typenullinterface-sub…
T-Gro Feb 3, 2025
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1 change: 1 addition & 0 deletions docs/release-notes/.FSharp.Compiler.Service/9.0.300.md
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Expand Up @@ -3,6 +3,7 @@
* Fix optimizer internal error for records with static fields ([Issue #18165](https://github.com/dotnet/fsharp/issues/18165), [PR #18280](https://github.com/dotnet/fsharp/pull/18280))
* Fix internal error when missing measure attribute in an unsolved measure typar. ([Issue #7491](https://github.com/dotnet/fsharp/issues/7491), [PR #18234](https://github.com/dotnet/fsharp/pull/18234)==
* Set `Cancellable.token` from async computation ([Issue #18235](https://github.com/dotnet/fsharp/issues/18235), [PR #18238](https://github.com/dotnet/fsharp/pull/18238))
* Fix missing nullness warning when static upcast dropped nullness ([Issue #18232](https://github.com/dotnet/fsharp/issues/18232), [PR #18261](https://github.com/dotnet/fsharp/pull/18261))
* Cancellable: only cancel on OCE with own token ([PR #18277](https://github.com/dotnet/fsharp/pull/18277))

### Added
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12 changes: 10 additions & 2 deletions src/Compiler/Checking/TypeRelations.fs
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Expand Up @@ -341,5 +341,13 @@ let IteratedAdjustLambdaToMatchValReprInfo g amap valReprInfo lambdaExpr =
/// "Single Feasible Type" inference
/// Look for the unique supertype of ty2 for which ty2 :> ty1 might feasibly hold
let FindUniqueFeasibleSupertype g amap m ty1 ty2 =
let supertypes = Option.toList (GetSuperTypeOfType g amap m ty2) @ (GetImmediateInterfacesOfType SkipUnrefInterfaces.Yes g amap m ty2)
supertypes |> List.tryFind (TypeFeasiblySubsumesType 0 g amap m ty1 NoCoerce)
let n2 = nullnessOfTy g ty2
let nullify t = addNullnessToTy n2 t

let supertypes =
Option.toList (GetSuperTypeOfType g amap m ty2) @
(GetImmediateInterfacesOfType SkipUnrefInterfaces.Yes g amap m ty2)

supertypes
|> List.tryFind (TypeFeasiblySubsumesType 0 g amap m ty1 NoCoerce)
|> Option.map nullify
6 changes: 3 additions & 3 deletions src/Compiler/Utilities/Activity.fs
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Expand Up @@ -93,14 +93,14 @@ module internal Activity =
let activity = activitySource.CreateActivity(name, ActivityKind.Internal)

match activity with
| null -> activity
| null -> !!activity //TODO change retTy to |null after PR #18262 is merged!!
| activity ->
for key, value in tags do
activity.AddTag(key, value) |> ignore

activity.Start()

let startNoTags (name: string) : IDisposable = activitySource.StartActivity name
let startNoTags (name: string) : IDisposable = !! (activitySource.StartActivity name) //TODO change retTy to |null after PR #18262 is merged!!

let addEvent name =
match Activity.Current with
Expand All @@ -122,7 +122,7 @@ module internal Activity =

let private profiledSource = new ActivitySource(ActivityNames.ProfiledSourceName)

let startAndMeasureEnvironmentStats (name: string) : IDisposable = profiledSource.StartActivity(name)
let startAndMeasureEnvironmentStats (name: string) : IDisposable = !!(profiledSource.StartActivity(name)) //TODO change retTy to |null after PR #18262 is merged!!

type private GCStats = int[]

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14 changes: 14 additions & 0 deletions tests/FSharp.Compiler.ComponentTests/Language/Nullness/NullableReferenceTypesTests.fs
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Expand Up @@ -17,6 +17,20 @@ let typeCheckWithStrictNullness cu =
|> withNullnessOptions
|> typecheck

[<Fact>]
let ``Warning on nullness hidden behind interface upcast`` () =
FSharp """module Test

open System.IO
open System

// This is bad - input is nullable, output is not = must warn
let whatisThis (s:Stream|null) : IDisposable =
s"""
|> asLibrary
|> typeCheckWithStrictNullness
|> shouldFail
|> withDiagnostics [Error 3261, Line 8, Col 5, Line 8, Col 6, "Nullness warning: The types 'IDisposable' and 'IDisposable | null' do not have compatible nullability."]

[<FSharp.Test.FactForNETCOREAPPAttribute>]
let ``Report warning when applying anon record to a nullable generic return value`` () =
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