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Warn when obj is inferred (#13298)
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Co-authored-by: Tomas Grosup <tomasgrosup@microsoft.com>
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Smaug123 and T-Gro authored Jul 21, 2023
1 parent 7b5e128 commit fd80552
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Showing 3 changed files with 165 additions and 16 deletions.
41 changes: 25 additions & 16 deletions src/Compiler/Checking/TypeRelations.fs
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
/// constraint solving and method overload resolution.
module internal FSharp.Compiler.TypeRelations

open FSharp.Compiler.Features
open Internal.Utilities.Collections
open Internal.Utilities.Library
open FSharp.Compiler.DiagnosticsLogger
Expand Down Expand Up @@ -134,50 +135,58 @@ let rec TypeFeasiblySubsumesType ndeep g amap m ty1 canCoerce ty2 =
/// Here x gets a generalized type "list<'T>".
let ChooseTyparSolutionAndRange (g: TcGlobals) amap (tp:Typar) =
let m = tp.Range
let maxTy, m =
let (maxTy, isRefined), m =
let initialTy =
match tp.Kind with
| TyparKind.Type -> g.obj_ty
| TyparKind.Measure -> TType_measure Measure.One
// Loop through the constraints computing the lub
((initialTy, m), tp.Constraints) ||> List.fold (fun (maxTy, _) tpc ->
(((initialTy, false), m), tp.Constraints) ||> List.fold (fun ((maxTy, isRefined), _) tpc ->
let join m x =
if TypeFeasiblySubsumesType 0 g amap m x CanCoerce maxTy then maxTy
elif TypeFeasiblySubsumesType 0 g amap m maxTy CanCoerce x then x
else errorR(Error(FSComp.SR.typrelCannotResolveImplicitGenericInstantiation((DebugPrint.showType x), (DebugPrint.showType maxTy)), m)); maxTy
if TypeFeasiblySubsumesType 0 g amap m x CanCoerce maxTy then maxTy, isRefined
elif TypeFeasiblySubsumesType 0 g amap m maxTy CanCoerce x then x, true
else errorR(Error(FSComp.SR.typrelCannotResolveImplicitGenericInstantiation((DebugPrint.showType x), (DebugPrint.showType maxTy)), m)); maxTy, isRefined
// Don't continue if an error occurred and we set the value eagerly
if tp.IsSolved then maxTy, m else
if tp.IsSolved then (maxTy, isRefined), m else
match tpc with
| TyparConstraint.CoercesTo(x, m) ->
join m x, m
| TyparConstraint.MayResolveMember(_traitInfo, m) ->
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.SimpleChoice(_, m) ->
errorR(Error(FSComp.SR.typrelCannotResolveAmbiguityInPrintf(), m))
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.SupportsNull m ->
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.SupportsComparison m ->
join m g.mk_IComparable_ty, m
| TyparConstraint.SupportsEquality m ->
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.IsEnum(_, m) ->
errorR(Error(FSComp.SR.typrelCannotResolveAmbiguityInEnum(), m))
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.IsDelegate(_, _, m) ->
errorR(Error(FSComp.SR.typrelCannotResolveAmbiguityInDelegate(), m))
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.IsNonNullableStruct m ->
join m g.int_ty, m
| TyparConstraint.IsUnmanaged m ->
errorR(Error(FSComp.SR.typrelCannotResolveAmbiguityInUnmanaged(), m))
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.RequiresDefaultConstructor m ->
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.IsReferenceType m ->
maxTy, m
(maxTy, isRefined), m
| TyparConstraint.DefaultsTo(_priority, _ty, m) ->
maxTy, m)
(maxTy, isRefined), m)

if g.langVersion.SupportsFeature LanguageFeature.DiagnosticForObjInference then
match tp.Kind with
| TyparKind.Type ->
if not isRefined then
informationalWarning(Error(FSComp.SR.typrelNeverRefinedAwayFromTop(), m))
| TyparKind.Measure -> ()

maxTy, m

let ChooseTyparSolution g amap tp =
Expand Down
139 changes: 139 additions & 0 deletions tests/FSharp.Compiler.ComponentTests/ConstraintSolver/ObjInference.fs
Original file line number Diff line number Diff line change
@@ -0,0 +1,139 @@
namespace FSharp.Compiler.ComponentTests.ConstraintSolver

open Xunit
open FSharp.Test.Compiler

module ObjInference =

let message = "A type has been implicitly inferred as 'obj', which may be unintended. Consider adding explicit type annotations. You can disable this warning by using '#nowarn \"3559\"' or '--nowarn:3559'."

let quotableWarningCases =
[
"""System.Object.ReferenceEquals(null, "hello") |> ignore""", 1, 31, 1, 35
"""System.Object.ReferenceEquals("hello", null) |> ignore""", 1, 40, 1, 44
"([] = []) |> ignore", 1, 7, 1, 9
"<@ [] = [] @> |> ignore", 1, 9, 1, 11
"let _ = Unchecked.defaultof<_> in ()", 1, 29, 1, 30
]
|> List.map (fun (str, line1, col1, line2, col2) -> [| box str ; line1 ; col1 ; line2 ; col2 |])

let unquotableWarningCases =
[
"let f() = ([] = [])", 1, 17, 1, 19
"""let f<'b> (x : 'b) : int = failwith ""
let deserialize<'v> (s : string) : 'v = failwith ""
let x = deserialize "" |> f""", 3, 9, 3, 28
"let f = typedefof<_>", 1, 19, 1, 20
"""let f<'b> () : 'b = (let a = failwith "" in unbox a)""", 1, 26, 1, 27
]
|> List.map (fun (str, line1, col1, line2, col2) -> [| box str ; line1 ; col1 ; line2 ; col2 |])

let warningCases =
quotableWarningCases @ unquotableWarningCases

[<Theory>]
[<MemberData(nameof(warningCases))>]
let ``Warning is emitted when type Obj is inferred``(code: string, line1: int, col1: int, line2: int, col2: int) =
FSharp code
|> withErrorRanges
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldFail
|> withSingleDiagnostic (Information 3559, Line line1, Col col1, Line line2, Col col2, message)

let quotableNoWarningCases =
[
"let a = 5 |> unbox<obj> in let b = a in ()" // explicit obj annotation
"let add x y = x + y in ()" // inferred as int
"let f() = ([] = ([] : obj list)) in ()" // obj is inferred, but is annotated
"let f() = (([] : obj list) = []) in ()" // obj is inferred, but is annotated
"let f () : int = Unchecked.defaultof<_> in ()" // explicitly int
"let f () = Unchecked.defaultof<int> in ()" // explicitly int
]
|> List.map Array.singleton

let unquotableNoWarningCases =
[
"let add x y = x + y" // inferred as int
"let inline add x y = x + y" // inferred with SRTP
"let inline add< ^T when ^T : (static member (+) : ^T * ^T -> ^T)> (x : ^T) (y : ^T) : ^T = x + y" // with SRTP
"let f x = string x" // inferred as generic 'a -> string
"let f() = ([] = ([] : obj list))" // obj is inferred, but is annotated
"let f() = (([] : obj list) = [])" // obj is inferred, but is annotated
"""let x<[<Measure>]'m> : int<'m> = failwith ""
let f () = x = x |> ignore""" // measure is inferred as 1, but that's not covered by this warning
"let f () : int = Unchecked.defaultof<_>" // explicitly int
"let f () = Unchecked.defaultof<int>" // explicitly int
"let f () = Unchecked.defaultof<_>" // generic
]
|> List.map Array.singleton

let noWarningCases = quotableNoWarningCases @ unquotableNoWarningCases

[<Theory>]
[<MemberData(nameof(noWarningCases))>]
let ``Warning does not fire unless required``(code: string) =
FSharp code
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldSucceed

let nullNoWarningCases =
[
"""System.Object.ReferenceEquals("hello", (null: string))"""
"""System.Object.ReferenceEquals((null: string), "hello")"""
]
|> List.map Array.singleton

[<Theory>]
[<MemberData(nameof(nullNoWarningCases))>]
let ``Don't warn on an explicitly annotated null``(expr: string) =
sprintf "%s |> ignore" expr
|> FSharp
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldSucceed

[<Theory>]
[<MemberData(nameof(nullNoWarningCases))>]
let ``Don't warn on an explicitly annotated null, inside quotations``(expr: string) =
sprintf "<@ %s @> |> ignore" expr
|> FSharp
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldSucceed

[<Theory>]
[<MemberData(nameof(quotableWarningCases))>]
let ``Warn also inside quotations of acceptable code``(expr: string, line1: int, col1: int, line2: int, col2: int) =
sprintf "<@ %s @> |> ignore" expr
|> FSharp
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldFail
|> withSingleDiagnostic (Information 3559, Line line1, Col (col1 + 3), Line line2, Col (col2 + 3), message)

[<Theory>]
[<MemberData(nameof(quotableNoWarningCases))>]
let ``Don't warn inside quotations of acceptable code``(expr: string) =
sprintf "<@ %s @> |> ignore" expr
|> FSharp
|> withWarnOn 3559
|> withLangVersionPreview
|> typecheck
|> shouldSucceed

[<Theory>]
[<MemberData(nameof(warningCases))>]
let ``Warning is off by default``(expr: string, _: int, _: int, _: int, _: int) =
expr
|> FSharp
|> withLangVersionPreview
|> withOptions ["--warnaserror"]
|> typecheck
|> shouldSucceed
Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@
<Compile Include="Language\CopyAndUpdateTests.fs" />
<Compile Include="ConstraintSolver\PrimitiveConstraints.fs" />
<Compile Include="ConstraintSolver\MemberConstraints.fs" />
<Compile Include="ConstraintSolver\ObjInference.fs" />
<Compile Include="Interop\DeeplyNestedCSharpClasses.fs" />
<Compile Include="Interop\SimpleInteropTests.fs" />
<Compile Include="Interop\RequiredAndInitOnlyProperties.fs" />
Expand Down

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