[Ada] Implement AI12-0109 (prohibit some "early" derivations)
2019-12-13 Steve Baird <baird@adacore.com> gcc/ada/ * einfo.ads: Correct comment for Derived_Type_Link to reflect that fact that this function is now used for more than just generation of warnings. * sem_ch3.adb (Build_Derived_Type): Do not call Set_Derived_Type_Link if the derived type and the parent type are in different compilation units. Such a derivation cannot be a problematic "early" derivation (identifying these is what the Derived_Type_Link attribute is used for) and we don't like inter-unit references that go in the opposite direction of semantic dependencies. * sem_ch13.adb (Is_Type_Related_Rep_Item): A new function, analogous to the existing function Is_Operational_Item. (Rep_Item_Too_Late): Generate a hard error (with same text as the warning that was previously being generated) if the AI12-0109 legality rule is violated. From-SVN: r279355
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Steve Baird
Pierre-Marie de Rodat
parent
63e21a7237
commit
cfedf3e51b
4 changed files with 128 additions and 24 deletions
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@ -1,3 +1,21 @@
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2019-12-13 Steve Baird <baird@adacore.com>
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* einfo.ads: Correct comment for Derived_Type_Link to reflect
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that fact that this function is now used for more than just
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generation of warnings.
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* sem_ch3.adb (Build_Derived_Type): Do not call
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Set_Derived_Type_Link if the derived type and the parent type
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are in different compilation units. Such a derivation cannot be
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a problematic "early" derivation (identifying these is what the
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Derived_Type_Link attribute is used for) and we don't like
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inter-unit references that go in the opposite direction of
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semantic dependencies.
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* sem_ch13.adb (Is_Type_Related_Rep_Item): A new function,
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analogous to the existing function Is_Operational_Item.
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(Rep_Item_Too_Late): Generate a hard error (with same text as
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the warning that was previously being generated) if the
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AI12-0109 legality rule is violated.
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2019-12-13 Eric Botcazou <ebotcazou@adacore.com>
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* doc/gnat_rm/implementation_defined_pragmas.rst: Minor tweak to
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@ -929,12 +929,12 @@ package Einfo is
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--
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-- In this case, if primitive operations have been declared for R, at
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-- the point of declaration of G, then the Derived_Type_Link of R is set
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-- to point to the entity for G. This is used to generate warnings for
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-- rep clauses that appear later on for R, which might result in an
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-- unexpected implicit conversion operation.
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-- to point to the entity for G. This is used to generate warnings and
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-- errors for rep clauses that appear later on for R, which might result
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-- in an unexpected (or illegal) implicit conversion operation.
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--
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-- Note: if there is more than one such derived type, the link will point
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-- to the last one (this is only used in generating warning messages).
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-- to the last one.
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-- Designated_Type (synthesized)
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-- Applies to access types. Returns the designated type. Differs from
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@ -154,6 +154,10 @@ package body Sem_Ch13 is
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-- that do not specify a representation characteristic are operational
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-- attributes.
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function Is_Type_Related_Rep_Item (N : Node_Id) return Boolean;
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-- Returns True for a representation clause/pragma that specifies a
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-- type-related representation (as opposed to operational) aspect.
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function Is_Predicate_Static
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(Expr : Node_Id;
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Nam : Name_Id) return Boolean;
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@ -12282,6 +12286,59 @@ package body Sem_Ch13 is
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end if;
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end Is_Predicate_Static;
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------------------------------
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-- Is_Type_Related_Rep_Item --
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------------------------------
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function Is_Type_Related_Rep_Item (N : Node_Id) return Boolean is
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begin
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case Nkind (N) is
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when N_Attribute_Definition_Clause =>
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declare
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Id : constant Attribute_Id := Get_Attribute_Id (Chars (N));
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-- See AARM 13.1(8.f-8.x) list items that end in "clause"
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-- ???: include any GNAT-defined attributes here?
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begin
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return Id = Attribute_Component_Size
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or else Id = Attribute_Bit_Order
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or else Id = Attribute_Storage_Pool
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or else Id = Attribute_Stream_Size
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or else Id = Attribute_Machine_Radix;
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end;
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when N_Pragma =>
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case Get_Pragma_Id (N) is
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-- See AARM 13.1(8.f-8.x) list items that start with "pragma"
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-- ???: include any GNAT-defined pragmas here?
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when Pragma_Pack
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| Pragma_Import
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| Pragma_Export
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| Pragma_Convention
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| Pragma_Atomic
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| Pragma_Independent
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| Pragma_Volatile
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| Pragma_Atomic_Components
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| Pragma_Independent_Components
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| Pragma_Volatile_Components
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| Pragma_Discard_Names
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=>
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return True;
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when others =>
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null;
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end case;
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when N_Enumeration_Representation_Clause
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| N_Record_Representation_Clause
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=>
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return True;
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when others =>
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null;
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end case;
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return False;
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end Is_Type_Related_Rep_Item;
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---------------------
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-- Kill_Rep_Clause --
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---------------------
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@ -12964,7 +13021,7 @@ package body Sem_Ch13 is
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end if;
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-- No error, but one more warning to consider. The RM (surprisingly)
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-- allows this pattern:
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-- allows this pattern in some cases:
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-- type S is ...
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-- primitive operations for S
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@ -12973,7 +13030,7 @@ package body Sem_Ch13 is
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-- Meaning that calls on the primitive operations of S for values of
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-- type R may require possibly expensive implicit conversion operations.
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-- This is not an error, but is worth a warning.
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-- So even when this is not an error, it is still worth a warning.
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if not Relaxed_RM_Semantics and then Is_Type (T) then
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declare
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@ -12981,26 +13038,47 @@ package body Sem_Ch13 is
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begin
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if Present (DTL)
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and then Has_Primitive_Operations (Base_Type (T))
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-- For now, do not generate this warning for the case of aspect
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-- specification using Ada 2012 syntax, since we get wrong
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-- messages we do not understand. The whole business of derived
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-- types and rep items seems a bit confused when aspects are
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-- used, since the aspects are not evaluated till freeze time.
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-- For now, do not generate this warning for the case of
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-- aspect specification using Ada 2012 syntax, since we get
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-- wrong messages we do not understand. The whole business
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-- of derived types and rep items seems a bit confused when
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-- aspects are used, since the aspects are not evaluated
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-- till freeze time. However, AI12-0109 confirms (in an AARM
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-- ramification) that inheritance in this case is required
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-- to work.
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and then not From_Aspect_Specification (N)
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then
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Error_Msg_Sloc := Sloc (DTL);
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Error_Msg_N
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("representation item for& appears after derived type "
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& "declaration#??", N);
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Error_Msg_NE
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("\may result in implicit conversions for primitive "
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& "operations of&??", N, T);
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Error_Msg_NE
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("\to change representations when called with arguments "
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& "of type&??", N, DTL);
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if Is_By_Reference_Type (T)
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and then not Is_Tagged_Type (T)
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and then Is_Type_Related_Rep_Item (N)
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and then (Ada_Version >= Ada_2012
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or else Has_Primitive_Operations (Base_Type (T)))
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then
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-- Treat as hard error (AI12-0109, binding interpretation).
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-- Implementing a change of representation is not really
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-- an option in the case of a by-reference type, so we
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-- take this path for all Ada dialects if primitive
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-- operations are present.
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Error_Msg_Sloc := Sloc (DTL);
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Error_Msg_N
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("representation item for& appears after derived type "
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& "declaration#", N);
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elsif Has_Primitive_Operations (Base_Type (T)) then
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Error_Msg_Sloc := Sloc (DTL);
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Error_Msg_N
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("representation item for& appears after derived type "
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& "declaration#??", N);
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Error_Msg_NE
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("\may result in implicit conversions for primitive "
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& "operations of&??", N, T);
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Error_Msg_NE
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("\to change representations when called with arguments "
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& "of type&??", N, DTL);
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end if;
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end if;
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end;
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end if;
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@ -9741,9 +9741,17 @@ package body Sem_Ch3 is
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(Derived_Type, No_Tagged_Streams_Pragma (Parent_Type));
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end if;
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-- If the parent has primitive routines, set the derived type link
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-- If the parent has primitive routines and may have not-seen-yet aspect
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-- specifications (e.g., a Pack pragma), then set the derived type link
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-- in order to later diagnose "early derivation" issues. If in different
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-- compilation units, then "early derivation" cannot be an issue (and we
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-- don't like interunit references that go in the opposite direction of
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-- semantic dependencies).
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if Has_Primitive_Operations (Parent_Type) then
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if Has_Primitive_Operations (Parent_Type)
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and then Enclosing_Comp_Unit_Node (Parent_Type) =
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Enclosing_Comp_Unit_Node (Derived_Type)
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then
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Set_Derived_Type_Link (Parent_Base, Derived_Type);
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end if;
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