C99 Features

[Greg Hudson]

On 06/15/2015 09:06 PM, Nathaniel McCallum wrote:
> So how about it? Can MIT start using C99 features?

There are four questions here:

1. Can we reasonably require MSVC 2013 for the Windows build?  I don't
know of a compelling reason why we can't, but there may be reasons I
don't know about.

2. Can we abandon MSVC for the Windows build in favor of mingw or clang,
in order to get VLA support?  I think the practical answer here is no,
in that we don't expect to commit the resources to investigate this
possibility in the near future.

3. Should we allow MSVC-unsupported C99 features in code we don't
currently build on Windows?  (This includes the KDC, KDB library,
PKINIT, and everything related to kadmin including gssrpc.)  I don't
really feel strongly either way, but it doesn't buy us a lot to allow it
in just a few places, and the inconsistency could be confusing.

4. Are there any C99 features we don't want to use, because they don't
mesh with our BSD KNF-inspired style or for other reasons?  Going over
the specific features you mentioned:

* Designated initializers and compound literals don't seem to present
any stylistic or practical issues.  VLAs also don't seem to present
issues except for the lack of MSVC support.

* Does _Bool present any issues if it creeps into public ABIs?  I found
http://yarchive.net/comp/linux/bool.html but it's from 2009, and might
be specific to the kernel.  It might also just be confusing to have
"krb5_boolean" and "bool" in the same code base when they aren't
generally the same size (krb5_boolean is a typedef for unsigned int).

* Our style guide discourages declaring variables in interior scope.
The justification (which predates my involvement) has to do with
debugging convenience and limiting function complexity; I personally
find that code is a little easier to read if it doesn't have type
declarations mixed in with statements.  If there are good reasons to
avoid interior scope declarations, those reasons may also apply to mixed
declarations and code.
http://k5wiki.kerberos.org/wiki/Coding_style/Practices#Local_variables