Make ' obj downcast to T' work without insisting on notnull constraint

dotnet · Feb 27, 2025 · da38c2b · da38c2b
1 parent 4d21ee7
commit da38c2b
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Showing 2 changed files with 3 additions and 7 deletions.
diff --git a/src/Compiler/Checking/Expressions/CheckExpressions.fs b/src/Compiler/Checking/Expressions/CheckExpressions.fs
@@ -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

diff --git a/tests/FSharp.Compiler.ComponentTests/Language/Nullness/NullableReferenceTypesTests.fs b/tests/FSharp.Compiler.ComponentTests/Language/Nullness/NullableReferenceTypesTests.fs
@@ -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>'"]