Re: "error: static assertion failed: [...]" (was: [GCC Wiki] Update of "DiagnosticsGuidelines" by MartinSebor)

[Manuel López-Ibáñez <lopezibanez at gmail dot com>]

On 13/07/16 14:26, 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)?


From a diagnostics point-of-view, neither version is quoted:

c/c-parser.c: error_at (assert_loc, "static assertion failed: %E", string);

cp/semantics.c: error ("static assertion failed: %s",

To be "quoted", it would need to use either %q or %<%>. Note that %qs would 
produce `foo' not "foo". Nevertheless, we probably want to print 'x' for 
character literals and not `'x'' and "string" for string literals and not 
`string'. Thus, the wiki should probably be amended to clarify this.

Also, there is a substantial difference between %E and %s when the string 
contains control characters such as \n \t \u etc. Clang uses something similar 
to %E.

For comparison, we use %s to print

test.c:1:9: note: #pragma message:
string
#pragma message "\nstring"
^

Cheers,
	Manuel.