Jarkko's How to build Configure tweaked by Nick and Merijn.

The Configure script and config_h.SH file in the Perl distribution are
generated by a program called metaconfig.  Metaconfig was originally 
written by Larry Wall, and was subsequently enhanced and maintained
by Raphael Manfredi. The binary that invokes the generation of the
Configure file is called mconfig.

As sort order and filenaming are vital in this process, make sure you
are working on a case-sensitive file system! (Case preserving is not
sufficient).

You have presumably obtained the metaconfig from the repository e.g.

  $ git clone git://perl5.git.perl.org/metaconfig.git metaconfig

or some other way to obtain this file, like a complete compressed archive
from the previous pumpkin.

Normally this directory and perl directory are next to each other
so ../perl will get you to perl and ../perl/../metaconfig will get you
back here.

Contents of this directory:

    README:	This file.
    U:		Metaconfig units used for building Perl's Configure
    U.check:	Sample directory used for testing new metaconfig units.
    		see U.check/README for more information.
    dist-git:
		a git clone of "dist". Optionally present. See (a) below.
		This is where dist/meta resides as of 2016-04-01
    dist:
		a symlink to the lib you actually use. For Merijn that is
		metaconfig/dist -> ../lib/dist

(a) You need to have dist installed so that you have metalint and metaconfig
    in your $PATH. As dist/meta binaries are now included in the git chackout,
    you do NOT need to install dist/meta itself.

    If you also want to play with or compare to the original meta/dit, you can
    checkout that too.

    The dist version used for perl is dist-3.5-20 in this directory, which is
    a slightly modified version of the original, which you can get at GITHUB
    repository https://github.com/rmanfredi/dist.git. If you'd like to keep
    up to date with changes in dist, you can use git to create your own clone.
    For git, that would be something like:

    $ git clone https://github.com/rmanfredi/dist.git dist-git

    Unsurprisingly 'dist' uses (its) Configure to generate itself:

    $ cd dist-3.5-20	# or dist-git
    $ chmod -R +w .     # We have derived files in git :-(
    $ ./Configure
    $ make
    $ make install

    After make install, remove lib/U/d_debugging.U in your target lib, as perl
    uses its own way to set/define debugging (see INSTALL)

    the dist-3.5-20 installation as used by Merijn is available on his CPAN as
    perl-meta-3.5-20.tgz

    dist's 'Configure' is similar to perl's but perhaps not quite as polished.

    There are some perl specific "dist units" in the 'U' directory.
    The U directory also contains some patches to 'dist' which have already
    been applied to dist-3.5-20 directory.
    We have not yet arranged for metaconfig to use perl's versions of the
    'units' by default so you need some housekeeping in the perl directory...

(aa)

    If you plan to make changes to mconfig or mlint locally (and you probably
    want to, as both are written for perl4), consider installing mconfig and
    mlint from the cmon subdirectory into your $PATH too. These are the
    non-autoloading versions and can easily be changed. Here is what I added
    at the beginning of mconfig:

    --8<---
    BEGIN { $ENV{LC_ALL} = "C"; }
    chdir "/pro/3gl/CPAN/perl";
    {   my @Cc = qw( Configure config_h.SH );
	system "chown merijn @Cc";
	chmod 0775, @Cc;
	#-d "merijn" or mkdir "merijn";
	#system "cp -f Configure config_h.SH Porting/Glossary Porting/config.sh merijn/";
	system "ls", "-l", @Cc;
	}
    -->8---

    I also added the first two lines of that patch to mlint

(b) You need to be in a/the Perl directory, i.e. either something from
    //depot/perl/... or one of its branches
    (e.g. Nick I-S is usually in //depot/perlio/...)
    and you need:
     1) have a symlink to ../metaconfig/U called U
     2) have a symlink to ../metaconfig/.package called .package
     3) have a symlink to MANIFEST called MANIFEST.new
     4) chmod +w Configure config_h.SH Porting/Glossary Porting/config*

(c) Write the new unit as U/perl/d_bar.U ('perl' can also be 'modified',
    'compline' or any other existing folder, except for 'all'). Choose
    the best appropriate subdir of U.  See U/README for a description of
    the various subdirectories.)

(d) Run metalint (or mlint) to see nits: as opposed to lint, the gripings
    of metalint are usually serious :-) and need fixing

    Exceptions are lots of
      Your private U/modified/issymlink.U overrides the public one.
    due to the perl special units

    an alias to something like
    $ metalint      |& grep -v -e '^    Your private U/'
    will make the process silence up on that (of course you can add an
    option to mlint to disable that warning (which is already disabled
    by the undocumented and forgotten -s option, but that also suppresses
    other warnings)

    and

    "End.U": stale ?MAKE: dependency '$W'.

    which is apparently normal ...

-- the next steps are in the perl folder

(e) chmod +w Configure config_h.SH

(f) mconfig -m -O to regenerate Configure and config_h.SH

    Make *sure* your mconfig is the correct one in your $PATH, as the mono-web
    package will install /usr/bin/mconfig which will do something completely
    different.

(g) metaconfig does not deal with depends in config_h.SH, so some
    reorganization is needed.

    perl Porting/config_h.SH

    will fix the ordering
    
(h) The messy not-yet-automated part is that the knowledge of the new symbol
    needs to be propagated to non-Configure lands like Win32, WinCE, Netware,
    VMS, VOS, EPOC, ...  see previous Configure changes to see which are these
    heathen lands.  Files to take care of are
    {win32,wince,NetWare}/config_[hH]*, (Win32, WinCE, NetWare),
    configure.com (VMS), VOS/config* (since 5.9 VOS uses Configure, though),
    epoc/config.sh (EPOC).  Depending on the kind of patch djgpp/config*
    might also need adjusting (for example when adding/changing the list
    of extensions)

    For Win32 the process is semi-automated - if you have a Win32
    machine to run dmake on ...

(i) Edit U/mkglossary (right near the top) to point to where you keep
    dist's standard metaconfig units as well as your perl-specific ones.

(j) Run U/mksample to freshen the Porting/config* and Porting/Glossary.
    Adjust the various compile-time options (e.g. 64bit, threads) as
    you see fit.
    You can skip this phase, it's not essential, just good housekeeping.

(k) Run the perl build chain

    make veryclean
    sh ./Configure -des -Dusedevel

    The dependency for uconfig.h isn't carved in stone, so you might
    need to regenerate it

    perl regen/uconfig_h.pl

    Then make and make test or make test_harness (with TEST_JOBS=5)

    make all test_harness

    Before you start committing, make sure that the other developers
    are happy and run

    make test_porting

-- the next steps are in the metaconfig folder again

(l) git add U/perl/foo/bar.U when you are ready ...

(m) git commit -m "Your commit description"

(n) When all patches are applied, tested and committed, and you are happy,
    git push

    Merijn prefers to do steps (l) through (n) in git-gui