[Bug fortran/57360] Implement a warning for implied save

[kargl at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57360

--- Comment #7 from kargl at gcc dot gnu.org ---
Upon some additional thinking, I wonder how useful this will be compared
to the possible volume of warning messages from modern Fortran.  Consider
this code:

module foo
   integer :: j = 2
   type a
      integer :: k = 3
   end type
   type(a) :: b = a(4)
   integer, target :: n
   integer, pointer :: m => n
end module foo

subroutine t()
 integer :: i=1
 write(6,*) i
 i=i+1
end subroutine t

 call t()
 call t()
end

with the patch at the end of this email, I see

% gfcx -c -Wsurprising -Wall a.f90
a.f90:2:14:

    2 |    integer :: j = 2
      |              1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:6:14:

    6 |    type(a) :: b = a(4)
      |              1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:7:22:

    7 |    integer, target :: n
      |                      1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:8:23:

    8 |    integer, pointer :: m => n
      |                       1
Warning: Entity at (1) has an implicit SAVE attribute [-Wsurprising]
a.f90:12:13:

   12 |  integer :: i=1
      |             1
Warning: ‘i’ at (1) has an implicit SAVE attribute [-Wsurprising]


diff --git a/gcc/fortran/decl.cc b/gcc/fortran/decl.cc
index 503ecb8d9b5..d6ef37e51f2 100644
--- a/gcc/fortran/decl.cc
+++ b/gcc/fortran/decl.cc
@@ -2278,7 +2278,12 @@ add_init_expr_to_sym (const char *name, gfc_expr
**initp, locus *var_locus)

       sym->value = init;
       if (sym->attr.save == SAVE_NONE)
-       sym->attr.save = SAVE_IMPLICIT;
+       {
+         sym->attr.save = SAVE_IMPLICIT;
+         if (warn_surprising)
+           gfc_warning (OPT_Wsurprising, "%qs at %L has an implicit SAVE "
+                     "attribute", sym->name, &sym->declared_at);
+       }
       *initp = NULL;
     }

@@ -5868,7 +5873,12 @@ match_attr_spec (void)
        || gfc_current_state () == COMP_SUBMODULE)
       && !current_attr.save
       && (gfc_option.allow_std & GFC_STD_F2008) != 0)
-    current_attr.save = SAVE_IMPLICIT;
+    {
+      current_attr.save = SAVE_IMPLICIT;
+      if (warn_surprising)
+       gfc_warning (OPT_Wsurprising, "Entity at %C has an implicit SAVE "
+                    "attribute");
+    }

   colon_seen = 1;
   return MATCH_YES;