An implicit dereference of an access to constrained unchecked union subtype has inferable discriminants. This change fixes the Has_Inferable_Discriminants function to take this case into account properly. The following program must compile quietly and display "OK" when executed:
with Ada.Text_IO; use Ada.Text_IO; procedure UU_Subtype_Eq is type UncU (Disc : Boolean := False) is record case Disc is when False => CC : Character; when True => BC : Boolean; end case; end record; pragma Unchecked_Union (UncU); subtype UncU1 is UncU (Disc => False); type UncA is access all UncU1; X1, Y1 : aliased UncU1; task Tester is entry Test (Y : UncU1; Res : out Boolean); end Tester; task body Tester is begin accept Test (Y : UncU1; Res : out Boolean) do declare Local_Y : constant UncU1 := Y; begin if X1 = Y then Res := True; else Res := False; end if; end; end Test; end Tester; Res : Boolean; begin X1.CC := 'X'; Y1.CC := 'Y'; Tester.Test (Y1, Res); if Res then Put_Line ("KO"); else Put_Line ("OK"); end if; end UU_Subtype_Eq; Tested on x86_64-pc-linux-gnu, committed on trunk 2012-06-12 Thomas Quinot <qui...@adacore.com> * exp_ch4.adb (Has_Inferable_Discriminants): Reorganize code to treat implicit dereferences with a constrained unchecked union nominal subtype as having inferable discriminants.
Index: exp_ch4.adb =================================================================== --- exp_ch4.adb (revision 188428) +++ exp_ch4.adb (working copy) @@ -10048,11 +10048,12 @@ -------------------------------- function Prefix_Is_Formal_Parameter (N : Node_Id) return Boolean is - Sel_Comp : Node_Id := N; + Sel_Comp : Node_Id; begin -- Move to the left-most prefix by climbing up the tree + Sel_Comp := N; while Present (Parent (Sel_Comp)) and then Nkind (Parent (Sel_Comp)) = N_Selected_Component loop @@ -10065,20 +10066,12 @@ -- Start of processing for Has_Inferable_Discriminants begin - -- For identifiers and indexed components, it is sufficient to have a - -- constrained Unchecked_Union nominal subtype. - - if Nkind_In (N, N_Identifier, N_Indexed_Component) then - return Is_Unchecked_Union (Base_Type (Etype (N))) - and then - Is_Constrained (Etype (N)); - -- For selected components, the subtype of the selector must be a -- constrained Unchecked_Union. If the component is subject to a -- per-object constraint, then the enclosing object must have inferable -- discriminants. - elsif Nkind (N) = N_Selected_Component then + if Nkind (N) = N_Selected_Component then if Has_Per_Object_Constraint (Entity (Selector_Name (N))) then -- A small hack. If we have a per-object constrained selected @@ -10087,19 +10080,20 @@ if Prefix_Is_Formal_Parameter (N) then return True; - end if; -- Otherwise, check the enclosing object and the selector - return Has_Inferable_Discriminants (Prefix (N)) - and then - Has_Inferable_Discriminants (Selector_Name (N)); - end if; + else + return Has_Inferable_Discriminants (Prefix (N)) + and then Has_Inferable_Discriminants (Selector_Name (N)); + end if; -- The call to Has_Inferable_Discriminants will determine whether -- the selector has a constrained Unchecked_Union nominal type. - return Has_Inferable_Discriminants (Selector_Name (N)); + else + return Has_Inferable_Discriminants (Selector_Name (N)); + end if; -- A qualified expression has inferable discriminants if its subtype -- mark is a constrained Unchecked_Union subtype. @@ -10107,9 +10101,14 @@ elsif Nkind (N) = N_Qualified_Expression then return Is_Unchecked_Union (Etype (Subtype_Mark (N))) and then Is_Constrained (Etype (Subtype_Mark (N))); - end if; - return False; + -- For all other names, it is sufficient to have a constrained + -- Unchecked_Union nominal subtype. + + else + return Is_Unchecked_Union (Base_Type (Etype (N))) + and then Is_Constrained (Etype (N)); + end if; end Has_Inferable_Discriminants; -------------------------------