Regenerate using a command sequence like
"aclocal-1.7 && autoconf-2.59 && autoheader-2.59
&& automake-1.7" as needed. And/or configure with
--enable-maintainer-mode. The version numbers will vary depending on
the current
requirements and your vendor's choice of installation names.
Until that glorious day when we can use AC_TRY_LINK with a cross-compiler,
we have to hardcode the results of what the tests would have shown if
they could be run. So we have an inflexible mess like crossconfig.m4.
Wouldn't it be nice if we could store that information in files like
configure.host, which can be modified without needing to regenerate
anything, and can even be tweaked without really knowing how the configury
all works? Perhaps break the pieces of crossconfig.m4 out and place them in
their appropriate config/{cpu,os} directory.
Alas, writing macros like "AC_DEFINE(HAVE_A_NICE_DAY)" can
only be done inside files which are passed through autoconf. Files which
are pure shell script can be source'd at configure time. Files which
contain autoconf macros must be processed with autoconf. We could still
try breaking the pieces out into "config/*/cross.m4" bits, for instance,
but then we would need arguments to aclocal/autoconf to properly find
them all when generating configure. I would discourage that.
Lots of stuff got thrown out because the new autotools kindly generate
the same (or better) shell code for us.
Most comments should use {octothorpes, shibboleths, hash marks, pound
signs, whatevers} rather than "dnl". Nearly all comments in configure.ac
should. Comments inside macros written in ancilliary .m4 files should.
About the only comments which should not use #, but use dnl
instead, are comments outside our own macros in the ancilliary
files. The difference is that # comments show up in configure
(which is most helpful for debugging), while dnl'd lines just vanish.
Since the macros in ancilliary files generate code which appears in odd
places, their "outside" comments tend to not be useful while reading
configure.
Do not use any $target* variables, such as
$target_alias. The single exception is in configure.ac,
for automake+dejagnu's sake.
The nice thing about acinclude.m4/aclocal.m4 is that macros aren't actually
performed/called/expanded/whatever here, just loaded. So we can arrange
the contents however we like. As of this writing, acinclude.m4 is arranged
as follows:
Next come extra compiler/linker feature tests. Wide character support
was placed here because I couldn't think of another place for it. It will
probably get broken apart like the math tests, because we're still disabling
wchars on systems which could actually support them.
All the GLIBCXX_ENABLE_FOO macros use a common helper, GLIBCXX_ENABLE.
(You don't have to use it, but it's easy.) The helper does two things
for us:
Builds the call to the AC_ARG_ENABLE macro, with --help text properly
quoted and aligned. (Death to changequote!)
Checks the result against a list of allowed possibilities, and signals
a fatal error if there's no match. This means that the rest of the
GLIBCXX_ENABLE_FOO macro doesn't need to test for strange arguments,
nor do we need to protect against empty/whitespace strings with the
"x$foo" = "xbar" idiom.
Doing these things correctly takes some extra autoconf/autom4te code,
which made our macros nearly illegible. So all the ugliness is factored
out into this one helper macro.
Many of the macros take an argument, passed from when they are expanded
in configure.ac. The argument controls the default value of the
enable/disable switch. Previously, the arguments themselves had defaults.
Now they don't, because that's extra complexity with zero gain for us.
There are three "overloaded signatures". When reading the descriptions
below, keep in mind that the brackets are autoconf's quotation characters,
and that they will be stripped. Examples of just about everything occur
in acinclude.m4, if you want to look.
FEATURE is the string that follows --enable. The results of the test
(such as it is) will be in the variable $enable_FEATURE, where FEATURE
has been squashed. Example: [extra-foo], controlled by the
--enable-extra-foo option and stored in $enable_extra_foo.
DEFAULT is the value to store in $enable_FEATURE if the user does not
pass --enable/--disable. It should be one of the permitted values
passed later. Examples: [yes], or [bar], or
[$1] (which passes the argument given to the
GLIBCXX_ENABLE_FOO macro as the default).
For cases where we need to probe for particular models
of things, it is useful to have an undocumented "auto" value here (see
GLIBCXX_ENABLE_CLOCALE for an example).
HELP-ARG is any text to append to the option string itself in the
--help output. Examples: [] (i.e., an empty string,
which appends nothing),
[=BAR], which produces
--enable-extra-foo=BAR, and
[@<:@=BAR@:>@], which produces
--enable-extra-foo[=BAR]. See the difference? See what
it implies to the user?
If you're wondering what that line noise in the last example was,
that's how you embed autoconf special characters in output text.
They're called
quadrigraphs
and you should use them whenever necessary.
HELP-STRING is what you think it is. Do not include the "default"
text like we used to do; it will be done for you by GLIBCXX_ENABLE.
By convention, these are not full English sentences.
Example: [turn on extra foo]
With no other arguments, only the standard autoconf patterns are
allowed: "--{enable,disable}-foo[={yes,no}]" The
$enable_FEATURE variable is guaranteed to equal either "yes" or "no"
after the macro. If the user tries to pass something else, an
explanatory error message will be given, and configure will halt.
The second signature takes a fifth argument,
"[permit a|b|c|...]"
This allows a or b or ... after the equals sign in the
option, and $enable_FEATURE is guaranteed to equal one of them after the
macro. Note that if you want to allow plain --enable/--disable with no
"=whatever", you must include "yes" and "no" in the list of permitted
values. Also note that whatever you passed as DEFAULT must be in the list.
If the user tries to pass something not on the list, a semi-explanatory
error message will be given, and configure will halt.
Example: [permit generic|gnu|ieee_1003.1-2001|yes|no|auto]
The third signature takes a fifth argument. It is arbitrary shell code
to execute if the user actually passes the enable/disable option. (If
the user does not, the default is used. Duh.) No argument checking at
all is done in this signature. See GLIBCXX_ENABLE_CXX_FLAGS for an
example of handling, and an error message.
