[Bug c++/115960] New: gcc throws an error when I use Optional in c++17.

[Bug c++/115960] New: gcc throws an error when I use Optional in c++17.

[noahmartinwilliams at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

            Bug ID: 115960
           Summary: gcc throws an error when I use Optional in c++17.
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: noahmartinwilliams at gmail dot com
  Target Milestone: ---

Created attachment 58686
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58686&action=edit
The requested files for the bug report.

See attached tarball file which contains the intermediate files that the
guidelines asked for, a minimal code example that triggers the bug, the error
message the compiler gave, and the exact commands used to replicate the
problem.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
llvm/include/llvm/ADT/Optional.h is not included so llvm::Optional is not
declared anywhere.

GCC's error message is correct.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Anyways this is not a GCC issue.

The   AttrBuilder::addAllocSizeAttr is declared in the preprocessed source as:
AttrBuilder &addAllocSizeAttr(unsigned ElemSizeArg,
                                const std::optional<unsigned> &NumElemsArg);

But the upstream is defined as:

  AttrBuilder &addAllocSizeAttr(unsigned ElemSizeArg,
                                const Optional<unsigned> &NumElemsArg);


https://github.com/hdoc/llvm-project/blob/a38b25fa77bdf1437c690494ae6d61179b3bb4f8/llvm/include/llvm/IR/Attributes.h#L1188


Also note
https://github.com/llvm/llvm-project/commit/125f4457a54a550846732763ee36b1447ec8d66e


Anyways this still not a GCC bug.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[noahmartinwilliams at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #3 from Noah Williams <noahmartinwilliams at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> Anyways this is not a GCC issue.
> 
> The   AttrBuilder::addAllocSizeAttr is declared in the preprocessed source
> as:
> AttrBuilder &addAllocSizeAttr(unsigned ElemSizeArg,
>                                 const std::optional<unsigned> &NumElemsArg);
> 
> But the upstream is defined as:
> 
>   AttrBuilder &addAllocSizeAttr(unsigned ElemSizeArg,
>                                 const Optional<unsigned> &NumElemsArg);
> 
> 
> https://github.com/hdoc/llvm-project/blob/
> a38b25fa77bdf1437c690494ae6d61179b3bb4f8/llvm/include/llvm/IR/Attributes.
> h#L1188
> 
> 
> Also note
> https://github.com/llvm/llvm-project/commit/
> 125f4457a54a550846732763ee36b1447ec8d66e
> 
> 
> Anyways this still not a GCC bug.

Darn. I was hoping this was a gcc bug since that would make fixing the llvm-hs
project easier. :(

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> The problem seems to be that, despite passing "-std=c++17", it doesn't use c++17
> header files for the Optional identifier.

Why should it? The name "Optional" is not part of any C++ standard.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[noahmartinwilliams at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #5 from Noah Williams <noahmartinwilliams at gmail dot com> ---
(In reply to Jonathan Wakely from comment #4)
> > The problem seems to be that, despite passing "-std=c++17", it doesn't use c++17
> > header files for the Optional identifier.
> 
> Why should it? The name "Optional" is not part of any C++ standard.

It isn't? The library I was trying to compile included the "optional" header,
and I had looked it up and found it was part of C++ 17, so I thought it was
part of the standard.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Noah Williams from comment #5)
> It isn't? The library I was trying to compile included the "optional"
> header, and I had looked it up and found it was part of C++ 17, so I thought
> it was part of the standard.

std::optional is part of C++17 but Optional is not.
LLVM had its own Optional class which basically implemented what was included
in C++17 before they wrote LLVM in C++17. This is the whole confusing thing
with their code is that LLVM is compiled as C++17 but sometimes uses their own
Optional class and sometimes std::optional. But again this is not GCC related
issue and should be discussed in LLVM's developmental forms instead.

[Bug c++/115960] gcc throws an error when I use Optional in c++17.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115960

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #6)
> (In reply to Noah Williams from comment #5)
> > It isn't? The library I was trying to compile included the "optional"
> > header, and I had looked it up and found it was part of C++ 17, so I thought
> > it was part of the standard.
> 
> std::optional is part of C++17 but Optional is not.

And names in C++ are case sensitive. optional != Optional.