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Re: [libcpp] Issue a pedantic warning for UCNs outside UCS codespace

On Thu, 26 Sep 2019, Eric Botcazou wrote:

> > For C, I think such UCNs violate the Semantics but not the Constraints on
> > UCNs, so no diagnostic is actually required in C, although it is permitted
> > as a pedwarn / error.
> > 
> > However, while C++ doesn't have that Semantics / Constraints division,
> > it's also the case that before C++2a, C++ only has a dated normative
> > reference to ISO/IEC 10646-1:1993 (C++2a adds an undated reference and
> > says the dated one is only for deprecated features, as well as explicitly
> > making such UCNs outside the ISO 10646 code point range ill-formed).  So I
> > think that for C++, this is only correct as an error / pedwarn in the
> > C++2a case.
> OK, thanks for the exegesis. ;-)  Revision version attached.

Checking "CPP_OPTION (pfile, lang) == CLK_CXX2A" is problematic because 
future versions later than C++2a should be handled the same as C++2a.

The only place I see doing something similar (outside of init.c, most 
version conditionals are handled via language flags set there) does 
"CPP_OPTION (pfile, lang) > CLK_CXX11" (for "In C++14 and up these 
suffixes are in the standard library, so treat them as user-defined 
literals.", two places doing the same comparison).  So I think that 
"CPP_OPTION (pfile, lang) > CLK_CXX17" is the right thing to replace the 
comparisons against CLK_CXX2A and CLK_GNUCXX2A.

The patch is OK with that change.

Joseph S. Myers

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