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The MCS makefiles (-*- outline -*-)
Peter Williams <peter@newton.cx>

The new makefiles try to abstract building on Windows and Linux. They
try to provide a consistent set of ways to express the things that our
build system needs to let us do, specifically:

      * Build recursively
      * Build libraries and executables easily
      * Let developers use different runtimes and class libaries
      * Make distributions easily
      * Provide a framework for testing
      * Build platform-independently whenever possible





** Makefile structure

A general makefile looks like this:

========================================
thisdir = class/Mono.My.Library
SUBDIRS =
include ../../build/rules.make

all-local:
        do some stuff

install-local:
        $(MKINSTALLDIRS) $(DESTDIR)$(prefix)/share/
        $(INSTALL_DATA) myfile.txt $(DESTDIR)$(prefix)/share/myfiledir

clean-local:
        rm -f my-generated-file

test-local: my_test_program.exe

run-test-local:
        $(RUNTIME) my_test_program.exe

run-test-ondotnet-local:
        $(RUNTIME) my_test_program.exe

DISTFILES = myfile.txt my_test_source.cs

dist-local: dist-default

my_test_program.exe: my_test_source.cs
        $(CSCOMPILE) /target:exe /out:$@ $<
========================================

Each makefile follows the same pattern: it does some setup, includes
the standard make rules, and provides rules for seven standard targets:
all, install, test, run-test, clean, and dist.

"Some setup" is defining two variables: $(thisdir) and
$(SUBDIRS). $(thisdir) is the directory that the makefile lives in,
relative to the top directory (ie, class/corlib) and $(SUBDIRS)
defines the subdirectories that should be built in.

The seven targets do the following:

        * all-local builds whatever someone would expect to be built
when they just type 'make'. Most likely Foo.dll or Foo.exe

        * install-local installs whatever got built by all-local.

        * test-local _builds_ the test programs or libraries but does
_not_ run them.

        * run-test-local actually runs the tests. It shouldn't
necessarily exit in an error if the test fails, but should make that
situation obvious. It should only run tests that take care of
themselves automatically; interactive tests should have an individual
target. The idea is that 'make run-test' from the toplevel should be
able to proceed unsupervised and test everything that can be tested in
such a manner.

        * run-test-ondotnet-local is a variant of run-test-local. It is used only to validate if our tests themselves works fine under Microsoft runtime (on Windows). Basically, in this target, we should not use $(TEST_RUNTIME) to test our libraries.

        * clean-local removes built files; 'make clean' should leave
only files that go into a distribution tarball. (But it is not necessarily
true that all files that go into a tarball need to be left after a make clean.)

        * dist-local copies files into the distribution tree, which is
given by the variable $(distdir). dist-local always depends on the
target 'dist-default'. See ** 'make dist' below.





** Build configuration

In general, MCS needs to be able to build relying only on the
existence of a runtime and core libraries (corlib, System,
System.Xml). So there shouldn't be any checking for libraries or
whatnot; MCS should be able to build out of the box. We try to keep
platform detection and feature testing (ie, for HP/UX echo) inside
the makefiles; right now, there's no configuration script, and it'd
be nice to keep it that way. (I am told that some people build on
both Windows and Linux in the same tree, which would be impossible to
do if we cached platform-related configury values.)

That being said, it's very convenient for developers to be able to
customize their builds to suit their needs. To allow this, the
Makefile rules are set up to allow people to override pretty much any
important variable.

Configuration variables are given defaults in `config-default.make';
`rules.make' optionally includes `$(topdir)/build/config.make', so you
can customize your build without CVS trying to commit your modified
`config-default.make' all the time.  Platform-specific variables are
defined in `$(topdir)/build/platforms/$(PLATFORM).make', where
$(PLATFORM) is detected in config-default.make. (Currently, the only
choices are linux.make and win32.make.)

The best way to learn what the configuration variables are is to read
`config.make' and `platform.make'. There aren't too many and hopefully
they should be self-explanatory; see the numerous examples below for
more information if you're confused.






** Recommendations for platform specifics

If you find yourself needing a platform-specific customization, try
and express it in terms of a feature, rather than a platform test. In
other words, this is good:

========================================
run-test-local: my-test.exe
ifdef PLATFORM_NEEDS_CRAZY_CRAP
        crazy-crap
endif
        $(RUNTIME) my-test.exe
========================================

and this is bad:

========================================
run-test-local: my-test.exe
ifdef WINDOWS
        crazy-crap
else
ifdef AMIGA
        crazy-crap
endif
endif
        $(RUNTIME) my-test.exe
========================================

The latter accumulates and gets unpleasant and it sucks. Granted,
right now we only have two platforms, so it's not a big deal, but it's
good form to get used to and practice. Anyway, take a look at how we
do the various corlib building hacks for examples of how we've done
platform-specificity. It certainly isn't pretty, but at least it's a
little structured.






** Saving effort

        The point of the build system is to abstract things and take
care of all the easy stuff. So if you find yourself writing a
Makefile, know that there's probably already infrastructure to do what
you want. Here are all the common cases I can think of ...






* Compiling C# code? use:

========================================
my-program.exe: my-source.cs
         $(CSCOMPILE) /target:exe /out:$@ $^
========================================

        or

========================================
my-lib.dll: my-source.cs
         $(CSCOMPILE) /target:library /out:$@ $^
========================================

Note the '$@' and '$^' variables. The former means "the name of the
file that I am trying to make" and the latter means "all the
dependencies of the file I am trying to make." USE THESE VARIABLES
AGGRESSIVELY. Say that you add a new source to your program:

========================================
my-program.exe: my-source.cs my-new-source.cs
         $(CSCOMPILE) /target:exe /out:$@ $^
========================================

Because of the $^ variable, you don't need to remember to add another
file to the command line. Similarly, if you rename your program, you
won't need to remember to change the rule:

========================================
MonoVaporizer.exe: my-source.cs my-new-source.cs
         $(CSCOMPILE) /target:exe /out:$@ $^
========================================

will still work. Another useful variable is $<, which means "the first
dependency of whatever I'm building." If you order your dependencies
carefully it can be extremely useful.





* Just building an executable? use:

========================================
PROGRAM = myprogram.exe
LOCAL_MCS_FLAGS = /r:System.Xml.dll

include ../build/executable.make
========================================

executable.make builds a program in the current directory. Its name is
held in $(PROGRAM), and its sources are listed in the file
$(PROGRAM).sources. It might seem to make more sense to just list the
program's sources in the Makefile, but when we build on Windows we
need to change slashes around, which is much easier to do if the
sources are listed in a file. The variable $(LOCAL_MCS_FLAGS) changes
the flags given to the compiler; it is included in $(CSCOMPILE) so you
don't need to worry about it.

executable.make does a lot for you: it builds the program in 'make
all-local', installs the program in $(prefix)/bin, distributes the
sources, and defines empty test targets. Now, if your program has a
test, set the variable HAS_TEST:

========================================
PROGRAM = myprogram.exe
LOCAL_MCS_FLAGS = /r:System.Xml.dll
HAS_TEST = yes
include ../build/executable.make

test-local: mytester.exe

run-test-local: mytester.exe
        $(RUNTIME) $<

mytester.exe: mytester.cs
        $(CSCOMPILE) /target:exe /out:$@ mytester.cs
========================================

If your program has 'built sources', that is, source files generated
from other files (say, generated by jay), define a variable called
BUILT_SOURCES and do *not* list the sources in $(PROGRAM).sources:

========================================
PROGRAM = myprogram.exe
LOCAL_MCS_FLAGS = /r:System.Xml.dll
BUILT_SOURCES = parser.cs
CLEAN_FILES = y.output

include ../build/executable.make

parser.cs: parser.jay
        $(topdir)/jay/jay $< > $@
========================================

executable.make will automatically delete the $(BUILT_SOURCES) files
on 'make clean'. Since this situation is a common occurrence and jay
happens to leave behind y.output files, you can also define a variable
called $(CLEAN_FILES) that lists extra files to be deleted when 'make clean' is
called. (That's in addition to your executable and the built sources).






* Buildling a library? Use

========================================
LIBRARY = Mono.MyLib.dll
LIB_MCS_FLAGS = /unsafe
TEST_MCS_FLAGS = /r:System.Xml.dll

include ../../build/library.make
========================================

Where you library is called $(LIBRARY); it will be put into
$(topdir)/class/lib. LIB_MCS_FLAGS is the set of MCS flags to use when
compiling the library; in addition, a global set of flags called
$(LIBRARY_FLAGS) is added (that variable is defined in
config-defaults.make), as well as the usual $(LOCAL_MCS_FLAGS).

As in executable.make, the sources for your library are listed in
$(LIBRARY).sources. Note: these source lists should have Unix forward
slashes and Unix newlines (\n, not \r\n.) If you get an error about
"touch: need a filename", that means your .sources file doesn't end in
a newline. It should.

Now library.make also assumes that your library has an NUnit2 test
harness. The files should be in a subdirectory called Test/, and if
your library is called Mono.Foo.dll, they should be listed in
Mono.Foo_test.dll.sources. The names in that files should *not* have
the Test/ prefix. 'make test' will build Mono.Foo_test.dll in the
current directory, automatically supplying the flags to reference the
original library and NUnit.Framework.dll. 

If you don't have a test, just do this:

========================================
LIBRARY = Mono.MyLib.dll
LIB_MCS_FLAGS = /unsafe
NO_TEST = yes

include ../../build/library.make
========================================

and feel ashamed. Every good library has a test suite!

Extra flags needed to compile the test library should be listed in
$(TEST_MCS_FLAGS); often you will have a line like this:

========================================
TEST_MCS_FLAGS = $(LIB_MCS_FLAGS)
========================================

Again, library.make does a lot for you: it builds the dll, it
generates makefile fragments to track the dependencies, it installs
the library, it builds the test dll on 'make test', it runs
$(TEST_HARNESS) on it on 'make run-test', it removes the appropriate
files on 'make clean', and it distributes all the source files on
'make dist'. (TEST_HARNESS defaults to be nunit-console.exe but it may
be overridden to, say, nunit-gtk). If you have extra files to
distribute when using either library.make or executable.make, use the
variable $(EXTRA_DISTFILES):

========================================
EXTRA_DISTFILES = \
        Test/testcase1.in               \
        Test/testcase1.out              \
        README
========================================

Again, library.make and executable.make do the right things so that we
can build on Windows, doing some trickery to invert slashes and
overcome command-line length limitations. Use them unless you have a
really good reason not to. If you're building a bunch of small
executables, check out tools/Makefile or tools/security/Makefile; if
all the files are in the current directory, changing slashes isn't a
big deal, and command-line lengths won't be a problem, so
executable.make isn't necessary (and indeed it won't work, since it
can only build one .exe in a directory).

If you're building a library, library.make is highly recommended; the
only DLL that doesn't use it is corlib, because building corlib is a
fair bit more complicated than it should be. Oh well.






* Running a C# program? Use $(RUNTIME)

========================================
run-test-local: myprog.exe
        $(RUNTIME) myprog.exe
========================================

$(RUNTIME) might be empty (if you're on windows), so don't expect to
be able to give it any arguments. If you're on a platform which has an
interpreter or jitter, $(RUNTIME_FLAGS) is included in $(RUNTIME), so
set that variable.

$(TEST_RUNTIME) is the runtime to use when running tests. Right now it's
just "mono --debug".



* Calling the compiler directly? Use $(MCS).

Really, you should use $(CSCOMPILE) whenever possible, but $(MCS) is
out there. $(BOOTSTRAP_MCS) is the C# compiler that we use to build
mcs.exe; on Linux, we then use mcs.exe to build everything else, but
on Windows, we use csc.exe to build everything. Only use
$(BOOTSTRAP_MCS) if you know what you're doing.





* Compiling C code? Use $(CCOMPILE)

To give it flags, set $(LOCAL_CFLAGS). As with compiling C#, the
variable $(CFLAGS) will automatically be included on the command line.





* Installing files? Use $(MKINSTALLDIRS), $(INSTALL_DATA) or
$(INSTALL_BIN), $(prefix), and $(DESTDIR).

Every time a file is installed the commands should look like this:

========================================
install-local:
        $(MKINSTALLDIRS) $(DESTDIR)$(prefix)/my/dir
        $(INSTALL_DATA) myfile $(DESTDIR)$(prefix)/my/dir
========================================

This way the directory is created recursively if needed (admittedly, we could
probably rely on mkdir -p), the file is given the correct permissions,
the user can override $(MKINSTALLDIRS) and $(INSTALL) if they need to,
and we can support $(DESTDIR) installs. We use $(DESTDIR) to make
monocharge tarballs, and it's useful otherwise, so try and use it
consistently.





* 'make dist'? Use $(DISTFILES)

The 'dist-default' target will copy the files listed in $(DISTFILES)
into the distribution directory, as well as Makefile and ChangeLog if
they exist. This is almost always all that you need, so ideally your
make dist support should only be:

========================================
DISTFILES = README Test/thoughts.txt

dist-local: dist-default
========================================

DISTFILES will cope correctly with files in subdirectories, by the
way. Note that if you put a nonexistant file or a directory in
DISTFILES it will *not* complain; it will just ignore it.

If you want to test your 'make dist' code, you can try

========================================
$ cd class/Mono.MyClass
$ make dist-local distdir=TEST
========================================

And your files should be copied into TEST/ in the current directory.
There is a toplevel 'make distcheck' target, which will build a dist
tarball, try to build it, install files to a temporary prefix, make
clean it, make a distribution, and compare the files left over to the
files originally in the tarball: they should be the same. But this
takes about 15 minutes to run on my 1.1 Ghz computer, so it's not for
the faint of heart.





* Lots of files? Use $(wildcard *.foo)

When specifying the sources to a library or executable, wildcards are
not encouraged; in fact they're not allowed if you use library.make or
executable.make. But there are times when they're useful, eg:

========================================
DISTFILES = $(wildcard Test/*.in) $(wildcard Test/*.out)
========================================

Just so you know that 'make' has this feature.






* Referencing files in other directories? Use $(topdir).

$(topdir) is the path to the top directory from the current build
directory. Basically it's a sequence of ../.. computed from the value
that you give $(thisdir) at the top of your Makefile. Try to reference
things from $(topdir), so your code can be moved or cut-and-pasted
around with a minimum of fuss.






* Conditional building? Use ifdef/ifndef/endif

Now in general we want to avoid conditional building, but sometimes
something doesn't work on Linux or already exists on Windows or
whatnot. (See below on recommended form for how to build
platform-specifically.) GNU Make supports the following construction:

========================================
BUILD_EXPERIMENTAL = yes

ifdef BUILD_EXPERIMENTAL
experimental_stuff = my-experiment.exe
else
experimental_stuff = 
endif

all-local: my-sane.exe $(experimental_stuff)
========================================

'ifdef' means 'if the variable is set to nonempty', so you could have 

========================================
BUILD_EXPERIMENTAL = colorless green ideas sleep furiously
========================================

and Make would be happy. I hope that the meaning of 'ifndef' should be
obvious. If you want to only sometimes build a target, the above
construction is the recommended way to go about it; it's nice to have
the rules exist in a Makefile even if they aren't invoked.

If you want to see why conditionals aren't nice, take a look at
library.make or class/corlib/Makefile.





* 'Private' directories that shouldn't be built by default? Use DIST_ONLY_SUBDIRS

Several of the MCS class libraries have demo or experimental
implementations that depend on things not included with MCS (say,
Gtk#). We don't want to build them by default, because the user might
not have those dependencies installed, but it's nice to have a
Makefile for them to be built nicely.

First of all, there's nothing stopping you from writing a Makefile for
such a directory; just don't put it in the SUBDIRS line of its parent
directory. That way, you can do all the normal build things like 'make
all' or 'make clean' in that directory, but people trying to bootstrap
their system won't run into problems.

At the same time you probably want to include this directory in the
distribution so that people can use your demo or experimental code if
they know what they're doing. Hence the variable
$(DIST_ONLY_SUBDIRS). As you might guess, it's like the SUBDIRS
variable: it lists subdirectories that a regular shouldn't recurse
into, but should have their 'make dist' rules invoked. 

Say you've written Mono.MyFancyLib.dll and you have
a demo app using Gtk# called MyFancyDemo. The Makefile rules might
look like this:

class/Mono.MyFancyLib/Makefile
========================================
thisdir = class/Mono.MyFancyLib
SUBDIRS =
DIST_ONLY_SUBDIRS = MyFancyDemo
include ../../build/rules.make

LIBRARY = Mono.MyFancyLib.dll
LIB_MCS_FLAGS = /r:System.dll
TEST_MCS_FLAGS = $(LIB_MCS_FLAGS)

include ../../build/library.make
========================================

class/Mono.MyFancyLib/MyFancyDemo/Makefile
========================================
thisdir = class/Mono.MyFancyLib/MyFancyDemo
SUBDIRS =
include ../../../build/rules.make

PROGRAM = FancyDemo.exe
LOCAL_MCS_FLAGS = /r:gtk-sharp.dll

include ../../../build/executable.make
========================================




* Special recursion needs?

By default, rules.make defines the all, install, clean, etc. targets
to look something like this:

   all: all-recursive
        $(MAKE) all-local

Sometimes that doesn't cut it; say for example you want to check for
something before doing a lengthy recursive build (see
$(topdir)/Makefile) or you have a something like this

        class/MyLibrary:
                Build MyLibrary.dll
        class/MyLibrary/Test:
                Build TestMyLibrary.exe

'make clean test' will fail here, because the build will happen in
the Test subdirectory first, so there will be no MyLibrary.dll to link
against. (Unless you write a nasty evil relative path rule which is
strongly discouraged.)

Anyway, to solve this problem you can do

========================================
thisdir = class/MyLibrary
SUBDIRS = Test
include ../../build/rules.make

# Normally, make runs 'all-recursive' first, and then 'all-local'
# With this, we ensure that 'all-local' is executed first.
all-recursive: all-local

test-recursive: test-local
...
========================================





** A few implementation details

The way rules.make does its recursion is very standard; it maps
{all,install,clean, dist,test} to $@-recursive, which executes that rule
in each directory in $(SUBDIRS), and then calls $@-local in the current
directory. So something that gets built in a subdirectory cannot rely on
something that gets built in its parent directory. If this is a problem,
see the previous section.  Note that the recursive rule for 'dist' is
different; it makes dist-recursive in subdirectories, so you at least
have to define that rule.

Note that even a directory that doesn't, for example, have any tests
must still define test-local; otherwise 'make test' run from the
toplevel directory will break.






** Flags for Tools

We want to make it so that the user can specify certain flags to
always be given to a tool, so there's a general way of implementing
FLAGS variables:

        * $(foo_FLAGS) remains unset or defaulted to something
          sensible; the user can provide overrides this way.

        * $(LOCAL_foo_FLAGS) is set in a specific Makefile to
          provide necessary values.

        * $(PLATFORM_foo_FLAGS) is set in the platform configuration
          to provide platform-specific values.

        * $(PROFILE_foo_FLAGS) is set in the profile configuration
          to provide profile-specific values.

        * $(USE_foo_FLAGS) is defined to be the combination of all of
          the above, and it's what is actually passed to $(foo).

$(MCS_FLAGS) and $(CFLAGS) follow this model. If you end up finding
that another tool is used commonly (hm, jay...), please follow this form.






** Portability tips

Always use the icky Windows /argument way of passing parameters to the C#
compiler so that csc can be used.

Always use /r:foo.dll, not /r:foo. Windows requires the former.

Use /r:$(corlib), not /r:corlib.

If you're writing shell script code as part of a make rule, remember
that Windows has command-line length limits. So something like

========================================
mytool $(all_the_sources_to_corlib)
========================================

Is probably going to cause problems. As I understand it, 

========================================
for f in  $(all_the_sources_to_corlib) ; do ...
========================================

is ok, since the shell itself doesn't have those limitations. Other
than that, you should still try to write fairly portable shell
script. Linux and Cygwin both use the GNU utilities, but there's at
least one hardy soul trying to build Mono on HP/UX, and no doubt there
will be ports to more Unices as time goes on.






** Misc

We still don't use /d:NET_1_1 ; it causes some build problems right
now.

There's a hack in class/System.Data/Makefile to work around a very
strange crash in the runtime with some custom attribute stuff. It'd be
nice to fix it.

Also, there's a /lib:$(prefix)/lib in the System.dll Makefile, which
is for some reason necessary if System.Xml.dll hasn't been built yet.
(Well, it's necessary because of the /r:System.Xml.dll, but that
should be in the search path, it seems.)

A lot of the weird targets in the old makefiles have been dropped; I
have a feeling that a lot of them are archaic and not needed anymore.

I'd really like to write a build tool in C#. It would be nice to have
something really extensible and well-designed and clean. NAnt is,
IMHO, an apalling abomination and a tragically bad attempt at solving
the software building problem. Just so you know.

(On the other hand, NUnit is really neat.)

Peter