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


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



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