[perl #123327] [PATCH] define and use STATIC_ASSERT for compile-time invariants

# New Ticket Created by  l.mai@web.de 
# Please include the string:  [perl #123327]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=123327 >


This is a bug report for perl from l.mai@web.de,
generated with the help of perlbug 1.40 running under perl 5.20.1.


-----------------------------------------------------------------
[Please describe your issue here]

Hi,

while reading commit de06ff5a50f29 I spotted the statement
'assert(SVt_NULL == 0);', i.e. using a runtime check to verify a compile-time
property. I thought it would be better if we could make compilation fail if the
condition doesn't hold (instead of triggering a runtime error in DEBUGGING
builds).

The attached patch does this by defining and using STATIC_ASSERT_GLOBAL (at
global scope) and STATIC_ASSERT_STMT (at function scope).

Things to note:

1) perl.h now always includes <assert.h>.
Previously it would only include <assert.h> in DEBUGGING builds and define
assert(x) away otherwise. I changed it to always include <assert.h> but define
NDEBUG if DEBUGGING is not set, which also makes assert(x) a no-op.
Reason: Modern <assert.h>s provide not just assert but also a static_assert
macro that I want to use where available.

2) perl.h defines STATIC_ASSERT_GLOBAL.
This can be used to enforce compile-time invariants outside of a function. A
fallback implementation is provided in case static_assert isn't defined.

3) perl.h defines STATIC_ASSERT_STMT.
Like STATIC_ASSERT_GLOBAL, but can be used inside functions. In theory you can
also use STATIC_ASSERT_GLOBAL in a function, but it expands to a declaration,
so in C90 builds it has to occur at the beginning of a block (before any
statements). And even in C99+ you can't attach a label to a declaration, so
something like 'case FOO: STATIC_ASSERT_GLOBAL(1);' is a syntax error.


Aside:
Some compile-time invariants can be checked with
#if !COND
#  error "bad"
#endif

But this only works for things the preprocessor knows about. In particular, it
can't be used with 'sizeof' or enum values (such as SVt_NULL, my motivating
example).

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
    Type=Patch
    PatchStatus=HasPatch
---
Site configuration information for perl 5.20.1:

Configured by mauke at Thu Nov  6 21:08:16 CET 2014.

Summary of my perl5 (revision 5 version 20 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=3.17.1-1-arch, archname=i686-linux
    uname='linux simplicio 3.17.1-1-arch #1 smp preempt wed oct 15 15:36:07 cest 2014 i686 gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.9.1 20140903 (prerelease)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/i686-pc-linux-gnu/4.9.1/include-fixed /usr/lib /lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.20.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.20'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector'


---
@INC for perl 5.20.1:
    /home/mauke/usr/lib/perl5/site_perl/5.20.1/i686-linux
    /home/mauke/usr/lib/perl5/site_perl/5.20.1
    /home/mauke/usr/lib/perl5/5.20.1/i686-linux
    /home/mauke/usr/lib/perl5/5.20.1
    .

---
Environment for perl 5.20.1:
    HOME=/home/mauke
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=POSIX
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/mauke/perl5/perlbrew/bin:/home/mauke/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
    PERLBREW_BASHRC_VERSION=0.69
    PERLBREW_HOME=/home/mauke/.perlbrew
    PERLBREW_ROOT=/home/mauke/perl5/perlbrew
    PERL_BADLANG (unset)
    SHELL=/bin/bash

• [perl #123327] [PATCH] define and use STATIC_ASSERT for compile-time invariants by Father Chrysostomos via RT
• Re: [perl #123327] [PATCH] define and use STATIC_ASSERT for compile-timeinvariants by Lukas Mai
• [perl #123327] [PATCH] define and use STATIC_ASSERT for compile-time invariants by Father Chrysostomos via RT
• Re: [perl #123327] [PATCH] define and use STATIC_ASSERT forcompile-time invariants by Dave Mitchell
• [perl #123327] [PATCH] define and use STATIC_ASSERT for compile-time invariants by l . mai @ web . de