=head1 NAME

makepp_builtin -- Built in rules for makepp

=for vc $Id: makepp_builtin.pod,v 1.12 2012/02/07 22:26:15 pfeiffer Exp $

=head1 DESCRIPTION

Makepp may be able to figure out how to compile and link your program even if
you specify no rules at all (or if you don't even have a Makeppfile).  After
every Makeppfile is loaded, makepp also loads a set of default rules.  (These
rules are special in that they do not override any other rules in the
Makeppfile.)  The default rule database is stored in the file
C<makepp_builtin_rules.mk> in the makepp distribution or library directory, so
you can always look at that to see exactly what the default rules are.

Makepp's builtin rules are almost the same as the rules in GNU make, except
that it has no rules for some of the rare languages that GNU make has rules
for.  (This is deliberate; I often ran into trouble with GNU make on several
projects that accidentally reused some of the suffixes that GNU make assigned to
those rare languages.)  The rules use the same variables as GNU make, with
some possibly useful additions.  Makepp is smarter than GNU make about
inferring which compiler to use, and which other objects and libraries to link
in.

=head2 Default variable values

Makepp supplies default values for a number of variables.  Most of these are
typically used in rules, and are indeed used in the default rules.  Their
values can be overridden by assigning to these variables in your Makeppfile or
on the command line.

These variables are documented in L<makepp_variables/Predefined Variables>.
If you have any questions about what any variable evaluates to, you can
always put a line like either of these lines in your Makeppfile:

    dummy := $(print $(CC))
    &echo -- $(CC)		# Must be indented less than previous rule.

which simply prints the value of the C<$(CC)> variable when the Makeppfile
is loaded.  (Incidentally, this is a useful way to debug any expression
that you're not sure is right.)

=head2 Compilation rules

In simplified form, here is approximately what the compilation rules
look like.  If you change the values of any of the indicated variables,
the compilation command is changed as expected.

    #
    # For C programs:
    #
    %.o: %.c
 	$(CC) $(CFLAGS) $(CPPFLAGS) -c $(input) -o $(output)
 
    #
    # For C++ programs:
    #
    %.o: %.cxx # and also %.cc, %.cpp, %.c++, and %.C
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $(input) -o $(output)
 
    #
    # For Fortran programs:
    #
    %.o: %.f
 	$(FC) $(FFLAGS) -c $(input) -o $(output)
 
    #
    # Yacc and lex:
    #
    %.c: %.y
 	$(YACC) $(YFLAGS) $(input)
 	&mv -f y.tab.c $(output)
 
    %.c: %.l
 	$(LEX) $(LFLAGS) -t $(input) -o $(output)

If you're curious about the exact details, you can look in the file
F<makepp_builtin_rules.mk> in the makepp distribution.

=head2 Link rules

Makepp also knows how to link programs, too.  Makepp attempts to be more
clever than the standard Unix make when it comes to figuring out a link
command.  Suppose you are trying to build the target program C<xyz>.
Makepp will try to build this from C<xyz.o>, and (unlike the standard
Unix make) it will also attempt to infer whether any other objects or
libraries need to be linked in.

The link rule looks something like this:

    xyz: $(infer_objects xyz.o, *.o)
 	$(infer_linker $(inputs)) $(inputs) $(LDFLAGS) $(LDLIBS) $(LIBS) -o $(output)

L<C<$(infer_objects)>|makepp_functions/infer_objects_file1_file2_pattern>
attempts to infer what other C<.o> files need to be linked in based on what
C<.h> files are included.

The "inferred linker" is a special bit of magic that turns into C<$(CC)>
if all the sources are C code, C<$(CXX)> if any of the sources are C++,
or C<$(F77)> if any of the sources are Fortran.

=head2 Turning off the built-in rules

If you don't like the built-in rules, don't use them.  If they don't
work for you, your built is probably sufficiently complicated that you
need your own custom Makeppfile anyway.

X<makepp_no_builtin>To turn off the builtin rules, you can add a line like
this to your Makeppfile:

    makepp_no_builtin = 1

X<makepp_no_builtin_linker>If you do use them, but not the fairly expensive
builtin linker rules, you can turn those off with:

    makepp_no_builtin_linker = 1

For backward compatibility, makepp also turns off its default rules if
you include this line somewhere in your Makeppfile:

    .SUFFIXES:

You can turn off builtin rules for every Makeppfile in the entire build by
specifying the C<--no-builtin-rules> option on the command line.
