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Bugfix :: Nullness :: Unsafe cast no longer requires generic type to be not null typar #18343

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merged 4 commits into from
Feb 28, 2025
Merged

Bugfix :: Nullness :: Unsafe cast no longer requires generic type to be not null typar #18343

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f6d53e2
ways of casting obj to T - tests
T-Gro Feb 25, 2025
4d21ee7
Merge branch 'main' into 18275-nullness-issue---unsafe-cast-requires-…
T-Gro Feb 25, 2025
da38c2b
Make ' obj downcast to T' work without insisting on notnull constraint
T-Gro Feb 27, 2025
057da85
notes
T-Gro Feb 28, 2025
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8 changes: 3 additions & 5 deletions src/Compiler/Checking/Expressions/CheckExpressions.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -2976,11 +2976,9 @@ let TcRuntimeTypeTest isCast isOperator (cenv: cenv) denv m tgtTy srcTy =
if isSealedTy g srcTy then
error(RuntimeCoercionSourceSealed(denv, srcTy, m))

if isSealedTy g tgtTy || isTyparTy g tgtTy || not (isInterfaceTy g srcTy) then
if isCast then
AddCxTypeMustSubsumeType (ContextInfo.RuntimeTypeTest isOperator) denv cenv.css m NoTrace srcTy tgtTy
else
AddCxTypeMustSubsumeType ContextInfo.NoContext denv cenv.css m NoTrace srcTy tgtTy
if (isSealedTy g tgtTy || isTyparTy g tgtTy || not (isInterfaceTy g srcTy)) && not (isObjTyAnyNullness g srcTy) then
let context = if isCast then ContextInfo.RuntimeTypeTest isOperator else ContextInfo.NoContext
AddCxTypeMustSubsumeType context denv cenv.css m NoTrace srcTy tgtTy

if isErasedType g tgtTy then
if isCast then
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16 changes: 14 additions & 2 deletions tests/FSharp.Compiler.ComponentTests/Language/Nullness/NullableReferenceTypesTests.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -150,10 +150,8 @@ let doNotWarnOnDowncastRepeatedNestedNullable(o:objnull) = o :? list<((AB | null
|> shouldFail
|> withDiagnostics
[ Error 3264, Line 4, Col 39, Line 4, Col 47, "Nullness warning: Downcasting from 'objnull' into 'AB' can introduce unexpected null values. Cast to 'AB|null' instead or handle the null before downcasting."
Error 3261, Line 5, Col 42, Line 5, Col 59, "Nullness warning: The types 'obj' and 'AB | null' do not have compatible nullability."
Error 3060, Line 5, Col 42, Line 5, Col 59, "This type test or downcast will erase the provided type 'AB | null' to the type 'AB'"
Error 3060, Line 6, Col 41, Line 6, Col 55, "This type test or downcast will erase the provided type 'AB | null' to the type 'AB'"
Error 3261, Line 7, Col 51, Line 7, Col 97, "Nullness warning: The types 'obj' and 'AB | null array | null list | null' do not have compatible nullability."
Error 3060, Line 7, Col 51, Line 7, Col 97, "This type test or downcast will erase the provided type 'List<AB | null array | null> | null' to the type 'List<AB array>'"]


Expand Down Expand Up @@ -1381,6 +1379,20 @@ dict["ok"] <- 42
|> typeCheckWithStrictNullness
|> shouldSucceed

[<InlineData("t :?> 'T")>]
[<InlineData("(downcast t) : 'T")>]
[<InlineData("t |> unbox<'T>")>]
[<InlineData("(t : objnull) :?> 'T")>]
[<Theory>]
let ``Unsafe cast should not insist on not null constraint``(castOp:string) =

FSharp $"""module MyLibrary
let test<'T> () =
let t = obj()
{castOp}"""
|> asLibrary
|> typeCheckWithStrictNullness
|> shouldSucceed


[<InlineData("null")>]
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