In Ada 2012, if a subtype has predicates, a predicate check must be applied to
the expression in a type conversion to the subtype. Furthermore, if the
expression is a scalar static constant, the predicate must be evluated at
compile-time, and the program must be rejected if the predicate is false.
Compiling
gcc -c -gnat12 -gnata main.adb
must yield:
main.adb:6:16: static expression fails static predicate check on "T"
---
procedure Main is
subtype T is Integer
with Static_Predicate => T >= 10;
V : T := 10;
begin
V := 1000 / T (9);
end Main;
Tested on x86_64-pc-linux-gnu, committed on trunk
2012-10-01 Ed Schonberg <schonb...@adacore.com>
* checks.adb (Apply_Predicate_Check): If the predicate is a
static one and the operand is static, evaluate the predicate at
compile time.
* sem_eval.ads, sem_eval.adb (Eval_Static_Predicate_Check): new
procedure, to evaluate a static predicate check whenever possible.
* sem_res.adb (Resolve_Type_Conversion): Apply predicate check
on the conversion if the target type has predicates.
Index: checks.adb
===================================================================
--- checks.adb (revision 191920)
+++ checks.adb (working copy)
@@ -2337,6 +2337,23 @@
(Sloc (N), Reason => SE_Infinite_Recursion));
else
+
+ -- If the predicate is a static predicate and the operand is
+ -- static, the predicate must be evaluated statically. If the
+ -- evaluation fails this is a static constraint error.
+
+ if Is_OK_Static_Expression (N) then
+ if Present (Static_Predicate (Typ)) then
+ if Eval_Static_Predicate_Check (N, Typ) then
+ return;
+ else
+ Error_Msg_NE
+ ("static expression fails static predicate check on&",
+ N, Typ);
+ end if;
+ end if;
+ end if;
+
Insert_Action (N,
Make_Predicate_Check (Typ, Duplicate_Subexpr (N)));
end if;
Index: sem_res.adb
===================================================================
--- sem_res.adb (revision 191920)
+++ sem_res.adb (working copy)
@@ -9713,6 +9713,22 @@
end if;
end;
end if;
+
+ -- Ada 2012: if target type has predicates, the result requires a
+ -- predicate check. If the context is a call to another predicate
+ -- check we must prevent infinite recursion.
+
+ if Has_Predicates (Target_Typ) then
+ if Nkind (Parent (N)) = N_Function_Call
+ and then Present (Name (Parent (N)))
+ and then Has_Predicates (Entity (Name (Parent (N))))
+ then
+ null;
+
+ else
+ Apply_Predicate_Check (N, Target_Typ);
+ end if;
+ end if;
end Resolve_Type_Conversion;
----------------------
Index: sem_eval.adb
===================================================================
--- sem_eval.adb (revision 191895)
+++ sem_eval.adb (working copy)
@@ -3249,6 +3249,37 @@
end if;
end Eval_Slice;
+ ---------------------------------
+ -- Eval_Static_Predicate_Check --
+ ---------------------------------
+
+ function Eval_Static_Predicate_Check
+ (N : Node_Id;
+ Typ : Entity_Id) return Boolean
+ is
+ Loc : constant Source_Ptr := Sloc (N);
+ Pred : constant List_Id := Static_Predicate (Typ);
+ Test : Node_Id;
+ begin
+ if No (Pred) then
+ return True;
+ end if;
+
+ -- The static predicate is a list of alternatives in the proper format
+ -- for an Ada 2012 membership test. If the argument is a literal, the
+ -- membership test can be evaluated statically. The caller transforms
+ -- a result of False into a static contraint error.
+
+ Test := Make_In (Loc,
+ Left_Opnd => New_Copy_Tree (N),
+ Right_Opnd => Empty,
+ Alternatives => Pred);
+ Analyze_And_Resolve (Test, Standard_Boolean);
+
+ return Nkind (Test) = N_Identifier
+ and then Entity (Test) = Standard_True;
+ end Eval_Static_Predicate_Check;
+
-------------------------
-- Eval_String_Literal --
-------------------------
Index: sem_eval.ads
===================================================================
--- sem_eval.ads (revision 191888)
+++ sem_eval.ads (working copy)
@@ -317,6 +317,11 @@
procedure Eval_Unary_Op (N : Node_Id);
procedure Eval_Unchecked_Conversion (N : Node_Id);
+ function Eval_Static_Predicate_Check
+ (N : Node_Id;
+ Typ : Entity_Id) return Boolean;
+ -- Evaluate a static predicate check applied to a scalar literal.
+
procedure Fold_Str (N : Node_Id; Val : String_Id; Static : Boolean);
-- Rewrite N with a new N_String_Literal node as the result of the compile
-- time evaluation of the node N. Val is the resulting string value from
