On Wed, 31 Aug 2022, Qing Zhao via Gcc-patches wrote:

> > "a GNU extension" suggests a particular language feature, but I think 
> > you're actually referring here to a whole language version rather than an 
> > individual feature.
> 
> Is “not supported by GNU extension GNU89” better?

There are no existing diagnostics referring to GNU89 at all.  I don't 
think "GNU extension" needs to be mentioned in that diagnostic, but I also 
think that having that diagnostic at all is ill-conceived.

> > In any case, -std=gnu89 supports flexible array members.
> 
> Yes, but only [0],[1] are supported as flexible array members.  The C99 
> flexible array member [] is not supported by GNU89, right?

C99 flexible array members are fully supported in GNU89 mode.  In general, 
any feature from a new language version that doesn't affect code that was 
valid in previous versions is likely to be accepted as an extension with 
options for older language versions.

-- 
Joseph S. Myers
joseph@codesourcery.com