Re: "error: static assertion failed: [...]"

[Martin Sebor <msebor at gmail dot com>]

On 07/13/2016 07:26 AM, Thomas Schwinge wrote:
> Hi!
>
> I had recently noticed that given:
>
>      #ifndef __cplusplus /* C */
>      _Static_assert(0, "foo");
>      #else /* C++ */
>      static_assert(0, "foo");
>      #endif
>
> ..., for C we diagnose:
>
>      [...]:2:1: error: static assertion failed: "foo"
>       _Static_assert(0, "foo");
>       ^~~~~~~~~~~~~~
>
> ..., and for C++ we diagnost:
>
>      [...]:4:1: error: static assertion failed: foo
>       static_assert(0, "foo");
>       ^~~~~~~~~~~~~
>
> ("foo" quoted vs. un-quoted.)  Assuming this difference between C and C++
> diagnostics is not intentional, which one should we settle on?  I thought
> I'd like the un-quoted version better, but judging by Martin's recent
> wiki change (see below), "foo" is a string constant, so should be quoted
> in diagnostics?  If yes, OK to commit to trunk the obvious changes (plus
> any testsuite updates)?

I hadn't thought of this case.  I don't have a personal preference
but I can provide a few data points to help with the decision (or
maybe muddy the waters).

Neither the C nor the C++ standard specifies whether or not to
include the quotes.  Both simply require that

  ...the implementation shall produce a diagnostic message that
  includes the text of the string literal, ...

Of the compilers I tried (Clang, EDG eccp, IBM XLC, Microsoft
Visual C++, and Oracle CC), more include the quotes in both
languages than not.  IBM XLC only quotes the C++ text, the
opposite of G++.  Visual C++ doesn't quote the C++ text and
doesn't understand the C11 _Static_assert.

From other similar constructs, C and C++ specify that the #error
directive include the preprocessing tokens that follow it (i.e.,
including quotes).

GCC doesn't include the quotes when printing the string argument
in attribute error.

Martin

> For reference:
>
> On Tue, 12 Jul 2016 22:34:17 -0000, GCC Wiki <noreply@gcc.gnu.org> wrote:
> > The "DiagnosticsGuidelines" page has been changed by MartinSebor:
> > https://gcc.gnu.org/wiki/DiagnosticsGuidelines?action=diff&rev1=7&rev2=8
> >
> > Comment:
> > Added a table of contents and a Quoting section.
>
> > + === Quoting ===
> > +
> > + The following elements should be quoted in GCC diagnostics, either using the {{{q}}} modifier in a directive such as {{{%qE}}}, or by enclosing the quoted text in a pair of {{{%<}}} and {{{%>}}} directives:
> > +
> > +  * Language keywords.
> > +  * Tokens.
> > +  * Boolean, numerical, character, and string constants that appear in the source code.
> > +  * Identifiers, including function, macro, type, and variable names.
> > +
> > + Other elements such as numbers that do no refer to numeric constants that appear in the source code should not be quoted.  For example, in the message:
> > + {{{#!highlight c++ numbers=disable
> > + argument %d of %qE must be a pointer type
> > + }}}
> > + since the argument number does not refer to a numerical constant in the source code it should not be quoted.
>
>
> Grüße
>   Thomas