[Bug ada/18453] New: Legal instantiation rejected; illegal instantiation accepted

[ludovic dot brenta at insalien dot org]

(Debian bug #279893)

-- legal instantiation rejected; illegal instantiation accepted
-- adapted from John Woodruff c.l.a. post

generic
   type T1 is private;
package pak1 is
   subtype T3 is T1;
end pak1;


with pak1;
generic
   type T2 is private;
package pak2 is
   package the_pak1 is new pak1 (T1 => T2);
end pak2;


generic
   type T2 is access the_pak1.T3;
package pak2.pak3 is
end pak2.pak3;


with pak1;
with pak2.pak3;
package Test_129 is

   type T4 is null record;
   type T5 is null record;
   subtype T3 is T5; -- line 9: triggers the bug at line 16

   type T4_ptr is access T4;
   type T5_ptr is access T5;

   package new_pak2 is new pak2 (T2 => T4);
   package new_pak3a is new new_pak2.pak3(T2 => T4_ptr);  -- line 15: Legal
   package new_pak3b is new new_pak2.pak3(T2 => T5_ptr);  -- line 16: Illegal
end Test_129;


The instantiation at line 15 is legal because T4_ptr is an access to
T4, and the previous instantiations make it so that

T4 = new_pak2.T2 = new_pak2.the_pak1.T1 = pak2.the_pak1.T3.

In contrast, line 16 is illegal because T5 /= new_pak2.T2.

Thus, the expected output from gnat is:

test_129.ads:16:49: designated type of actual does not match that of formal "T2"
test_129.ads:16:49: instantiation abandoned
gnatmake: "test_129.ads" compilation error

The actual output from gnat is:

test_129.ads:15:49: designated type of actual does not match that of formal "T2"
test_129.ads:15:49: instantiation abandoned
gnatmake: "test_129.ads" compilation error

The subtype at line 9 happens to be a homograph of pak1.T3.  Removing
this line, or renaming Test_129.T3, causes the actual output to
become:

test_129.ads:15:49: designated type of actual does not match that of formal "T2"
test_129.ads:15:49: instantiation abandoned
test_129.ads:16:49: designated type of actual does not match that of formal "T2"
test_129.ads:16:49: instantiation abandoned
gnatmake: "test_129.ads" compilation error

-- 
           Summary: Legal instantiation rejected; illegal instantiation
                    accepted
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ludovic dot brenta at insalien dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18453