On Fri, Feb 05, 2021 at 05:28:07PM +0000, Anthony Sharp wrote:
> Hi Marek,
>
> > Pedantically, "Altered function." is not very good, it should say what
> > in enforce_access changed.
>
> I would normally 100% agree, but the changes are a bit too complicated
> to be concisely (and helpfully) described there. I think the patch
> description covers it well enough; not sure what I would say without
> having to write a big paragraph there.
I think at least something like "Improve private access checking." would
be better. No need to be verbose in the ChangeLog. :)
> > Let's move the test into g++.dg/cpp1z and call it using9.C.
>
> Okie dokie - it's a bit hard to know where stuff's supposed to go in
> that folder. I'll put a comment in the testcase mentioning pr19377
> just in case there's ever a regression.
Yeah, it's customary to start a test with
// PR c++/19377
> > I don't understand the "generate a diagnostic decl location". Maybe just
> > "generate a diagnostic?"
>
> get_class_access_diagnostic_decl returns a decl which is used as the
> location that the error-producing code points to as the source of the
> problem. It could be better - I will change it to say "Examine certain
> special cases to find the decl that is the source of the problem" to
> make it a bit clearer.
Oh, I see now.
> > These two comments can be merged into one.
>
> Technically yes ... but I like how it is since in a very subtle way it
> creates a sense of separation between the first two paragraphs and the
> third. The first two paras are sort of an introduction and the third
> begins to describe the code.
Fair enough.
> > I think for comparing a binfo with a type we should use SAME_BINFO_TYPE_P.
>
> Okay, I think that simplifies the code a bit aswell.
>
> > This first term doesn't need to be wrapped in ().
>
> I normally wouldn't use the (), but I think that's how Jason likes it
> so that's why I did it. I guess it makes it more readable.
>
> > This could be part of the if above.
>
> Oops - I forgot to change that when I modified the code.
>
> > Just "had" instead of "did had"?
>
> Good spot - that's a spelling mistake on my part. Should be "did have".
>
> > Looks like this line is indented too much (even in the newer patch).
>
> You're right (if you meant access_failure_reason = ak_private), I will change.
Yup, this one.
> If you mean get_class_access_diagnostic_decl (parent_binfo, diag_decl)
> then I donno, because Linux Text Editor says both are on column 64.
>
> To be honest, I'm sure there is a way to do it, but I'm not really
> sure how to consistently align code. Every text/code editor/browser
> seems to give different column numbers (and display it differently)
> since they seem to all treat whitespace differently.
Yeah, that can be a pain. Best if your editor does it for you. If you
use vim, you can use gcc/contrib/vimrc and then vim will do most of the
formatting for you.
> > We usually use dg-do compile.
>
> True, but wouldn't that technically be slower? I would agree if it
> were more than just error-handling code.
>
> > Best to replace both with
> > // { dg-do compile { target c++17 } }
>
> Okie dokie. I did see both being used and I wasn't sure which to go for.
>
> I'll probably send another patch over tomorrow.
Sounds good, thanks!
> On Fri, 5 Feb 2021 at 16:06, Marek Polacek <pola...@redhat.com> wrote:
> >
> > Hi,
> >
> > a few comments:
> >
> > On Fri, Feb 05, 2021 at 03:39:25PM +0000, Anthony Sharp via Gcc-patches
> > wrote:
> > > 2021-02-05 Anthony Sharp <anthonyshar...@gmail.com>
> > >
> > > * semantics.c (get_class_access_diagnostic_decl): New function.
> > > (enforce_access): Altered function.
> >
> > Pedantically, "Altered function." is not very good, it should say what
> > in enforce_access changed.
> >
> > > gcc/testsuite/ChangeLog:
> > >
> > > 2021-02-05 Anthony Sharp <anthonyshar...@gmail.com>
> > >
> > > * g++.dg/pr19377.C: New test.
> >
> > Let's move the test into g++.dg/cpp1z and call it using9.C.
> >
> > > gcc/cp/semantics.c | 89 ++++++++++++++++++++++++++--------
> > > gcc/testsuite/g++.dg/pr19377.C | 28 +++++++++++
> > > 2 files changed, 98 insertions(+), 19 deletions(-)
> > > create mode 100644 gcc/testsuite/g++.dg/pr19377.C
> > >
> > > diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> > > index 73834467fca..ffb627f08ea 100644
> > > --- a/gcc/cp/semantics.c
> > > +++ b/gcc/cp/semantics.c
> > > @@ -256,6 +256,58 @@ pop_to_parent_deferring_access_checks (void)
> > > }
> > > }
> > >
> > > +/* Called from enforce_access. A class has attempted (but failed) to
> > > access
> > > + DECL. It is already established that a baseclass of that class,
> > > + PARENT_BINFO, has private access to DECL. Examine certain special
> > > cases to
> > > + generate a diagnostic decl location. If no special cases are found,
> > > simply
> >
> > I don't understand the "generate a diagnostic decl location". Maybe just
> > "generate a diagnostic?"
> >
> > > + return DECL. */
> > > +
> > > +static tree
> > > +get_class_access_diagnostic_decl (tree parent_binfo, tree decl)
> > > +{
> > > + /* When a class is denied access to a decl in a baseclass, most of the
> > > + time it is because the decl itself was declared as private at the
> > > point
> > > + of declaration. So, by default, DECL is at fault.
> > > +
> > > + However, in C++, there are (at least) two situations in which a decl
> > > + can be private even though it was not originally defined as such.
> > > */
> > > +
> > > + /* These two situations only apply if a baseclass had private access to
> > > + DECL (this function is only called if that is the case). We must
> > > however
> > > + also ensure that the reason the parent had private access wasn't
> > > simply
> > > + because it was declared as private in the parent. */
> >
> > These two comments can be merged into one.
> >
> > > + if (context_for_name_lookup (decl) == BINFO_TYPE (parent_binfo))
> > > + return decl;
> >
> > I think for comparing a binfo with a type we should use SAME_BINFO_TYPE_P.
> >
> > > + /* 1. If the "using" keyword is used to inherit DECL within a
> > > baseclass,
> > > + this may cause DECL to be private, so we return the using statement
> > > as
> > > + the source of the problem.
> > > +
> > > + Scan the fields of PARENT_BINFO and see if there are any using
> > > decls. If
> > > + there are, see if they inherit DECL. If they do, that's where DECL
> > > was
> > > + truly declared private. */
> > > + for (tree parent_field = TYPE_FIELDS (BINFO_TYPE (parent_binfo));
> > > + parent_field;
> > > + parent_field = DECL_CHAIN (parent_field))
> > > + {
> > > + if ((TREE_CODE (parent_field) == USING_DECL)
> >
> > This first term doesn't need to be wrapped in ().
> >
> > > + && TREE_PRIVATE (parent_field))
> > > + {
> > > + if (DECL_NAME (decl) == DECL_NAME (parent_field))
> >
> > This could be part of the if above. And then we can drop the braces (in the
> > if and for both).
> >
> > > + return parent_field;
> > > + }
> > > + }
> > > +
> > > + /* 2. If decl was privately inherited by a baseclass of the current
> > > class,
> > > + then decl will be inaccessible, even though it may originally have
> > > + been accessible to deriving classes. In that case, the fault lies
> > > with
> > > + the baseclass that used a private inheritance, so we return the
> > > + baseclass type as the source of the problem.
> > > +
> > > + Since this is the last check, we just assume it's true. */
> > > + return TYPE_NAME (BINFO_TYPE (parent_binfo));
> > > +}
> > > +
> > > /* If the current scope isn't allowed to access DECL along
> > > BASETYPE_PATH, give an error, or if we're parsing a function or class
> > > template, defer the access check to be performed at instantiation
> > > time.
> > > @@ -317,34 +369,33 @@ enforce_access (tree basetype_path, tree decl, tree
> > > diag_decl,
> > > diag_decl = strip_inheriting_ctors (diag_decl);
> > > if (complain & tf_error)
> > > {
> > > - /* We will usually want to point to the same place as
> > > - diag_decl but not always. */
> > > + access_kind access_failure_reason = ak_none;
> > > +
> > > + /* By default, using the decl as the source of the problem will
> > > + usually give correct results. */
> > > tree diag_location = diag_decl;
> > > - access_kind parent_access = ak_none;
> > >
> > > - /* See if any of BASETYPE_PATH's parents had private access
> > > - to DECL. If they did, that will tell us why we don't. */
> > > + /* However, if a parent of BASETYPE_PATH had private access to
> > > decl,
> > > + then it actually might be the case that the source of the
> > > problem
> > > + is not DECL. */
> > > tree parent_binfo = get_parent_with_private_access (decl,
> > > -
> > > basetype_path);
> > > +
> > > basetype_path);
> > >
> > > - /* If a parent had private access, then the diagnostic
> > > - location DECL should be that of the parent class, since it
> > > - failed to give suitable access by using a private
> > > - inheritance. But if DECL was actually defined in the parent,
> > > - it wasn't privately inherited, and so we don't need to do
> > > - this, and complain_about_access will figure out what to
> > > - do. */
> > > - if (parent_binfo != NULL_TREE
> > > - && (context_for_name_lookup (decl)
> > > - != BINFO_TYPE (parent_binfo)))
> > > + /* So if a parent did had private access, then we need to do
> > > special
> >
> > Just "had" instead of "did had"?
> >
> > > + checks to obtain the best diagnostic location decl. */
> > > + if (parent_binfo != NULL_TREE)
> > > {
> > > - diag_location = TYPE_NAME (BINFO_TYPE (parent_binfo));
> > > - parent_access = ak_private;
> > > + diag_location = get_class_access_diagnostic_decl
> > > (parent_binfo,
> > > + diag_decl);
> > > +
> > > + /* We also at this point know that the reason access failed
> > > was
> > > + because decl was private. */
> > > + access_failure_reason = ak_private;
> >
> > Looks like this line is indented too much (even in the newer patch).
> >
> > >
> > > /* Finally, generate an error message. */
> > > complain_about_access (decl, diag_decl, diag_location, true,
> > > - parent_access);
> > > + access_failure_reason);
> > > }
> > > if (afi)
> > > afi->record_access_failure (basetype_path, decl, diag_decl);
> > > diff --git a/gcc/testsuite/g++.dg/pr19377.C
> > > b/gcc/testsuite/g++.dg/pr19377.C
> > > new file mode 100644
> > > index 00000000000..fb023a33f82
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/pr19377.C
> > > @@ -0,0 +1,28 @@
> > > +/* { dg-do assemble } */
> >
> > We usually use dg-do compile.
> >
> > > +// { dg-options "-std=c++17" }
> >
> > Best to replace both with
> >
> > // { dg-do compile { target c++17 } }
> >
> > > +class A
> > > +{
> > > + protected:
> > > + int i();
> > > +};
> > > +
> > > +class A2
> > > +{
> > > + protected:
> > > + int i(int a);
> > > +};
> > > +
> > > +class B:private A, private A2
> > > +{
> > > + // Comma separated list only officially supported in c++17 and later.
> > > + using A::i, A2::i; // { dg-message "declared" }
> > > +};
> > > +
> > > +class C:public B
> > > +{
> > > + void f()
> > > + {
> > > + i(); // { dg-error "private" }
> > > + }
> > > +};
> > > \ No newline at end of file
> > > --
> > > 2.25.1
> > >
> >
> > Marek
> >
>
Marek
