kumquat-buildroot/docs/manual/adding-packages-meson.txt
Peter Seiderer 74e574c8a6 infra/pkg-meson: allow packages to pass custom compiler/linker flags
Meson does not allow to pass CFLAGS/LDFLAGS/CXXFLAGS via the environment
or via command-line arguments or options (instead, those flags from the
environment are passed to the host compiler, which is seldom what we
need). The only way to pas those flags is via the cross-compilation.conf
file.

Add LIBFOO_CFLAGS, LIBFOO_LDFLAGS and LIBFOO_CXXFLAGS variables to allow
packages to provide their own flags, possibly overriding the generic
ones entirely, as we allow for other infras. Those per-package flags will
then be used to generate the per-package cross-compilation.conf.

This means that the meson infra is the first and only infra for which
FOO_CFLAGS, FOO_LDFLAGS, and FOO_CXXFLAGS are meaningful, while for the
other infras, they are just variables private to the package itself.
Instead of naming those variables after the meson infra (e.g.
FOO_MESON_CFLAGS), we name them with a generic name, as maybe, just
maybe, we could also change the other infras to also recognise those
variables.

Just like for the HOST_MESON_SED_CFLAGS etc., we need to add auxiliary
variables to do convert the shell-formatted argument list into the
JSON-formatted list that meson expects. We can't use a pure-make
construct because the CFLAGS can contain quoting that needs to be
expanded by the shell. Similarly, we need a condition on the strip'ed
variable to avoid passing empty arguments.

To mimic this feature for packages that are built from the SDK, we also
install a templatised version of cross-compilation.conf, with three new
placeholders for custom flags. If a user wants to build a package that
needs custom flags, they can use that template to generate a per-package
cross-compilation.conf.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Adam Duskett <aduskett@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Tested-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
2019-07-01 09:51:16 +02:00

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// -*- mode:doc; -*-
// vim: set syntax=asciidoc:
=== Infrastructure for Meson-based packages
[[meson-package-tutorial]]
==== +meson-package+ tutorial
http://mesonbuild.com[Meson] is an open source build system meant to be both
extremely fast, and, even more importantly, as user friendly as possible. It
uses https://ninja-build.org[Ninja] as a companion tool to perform the actual
build operations.
Let's see how to write a +.mk+ file for a Meson-based package, with an example:
------------------------------
01: ################################################################################
02: #
03: # foo
04: #
05: ################################################################################
06:
07: FOO_VERSION = 1.0
08: FOO_SOURCE = foo-$(FOO_VERSION).tar.gz
09: FOO_SITE = http://www.foosoftware.org/download
10: FOO_LICENSE = GPL-3.0+
11: FOO_LICENSE_FILES = COPYING
12: FOO_INSTALL_STAGING = YES
13:
14: FOO_DEPENDENCIES = host-pkgconf bar
15:
16: ifeq ($(BR2_PACKAGE_BAZ),y)
17: FOO_CONF_OPTS += -Dbaz=true
18: FOO_DEPENDENCIES += baz
19: else
20: FOO_CONF_OPTS += -Dbaz=false
21: endif
22:
23: $(eval $(meson-package))
--------------------------------
The Makefile starts with the definition of the standard variables for package
declaration (lines 7 to 11).
On line line 23, we invoke the +meson-package+ macro that generates all the
Makefile rules that actually allows the package to be built.
In the example, +host-pkgconf+ and +bar+ are declared as dependencies in
+FOO_DEPENDENCIES+ at line 14 because the Meson build file of +foo+ uses
`pkg-config` to determine the compilation flags and libraries of package +bar+.
Note that it is not necessary to add +host-meson+ in the +FOO_DEPENDENCIES+
variable of a package, since this basic dependency is automatically added as
needed by the Meson package infrastructure.
If the "baz" package is selected, then support for the "baz" feature in "foo" is
activated by adding +-Dbaz=true+ to +FOO_CONF_OPTS+ at line 17, as specified in
the +meson_options.txt+ file in "foo" source tree. The "baz" package is also
added to +FOO_DEPENDENCIES+. Note that the support for +baz+ is explicitly
disabled at line 20, if the package is not selected.
To sum it up, to add a new meson-based package, the Makefile example can be
copied verbatim then edited to replace all occurences of +FOO+ with the
uppercase name of the new package and update the values of the standard
variables.
[[meson-package-reference]]
==== +meson-package+ reference
The main macro of the Meson package infrastructure is +meson-package+. It is
similar to the +generic-package+ macro. The ability to have target and host
packages is also available, with the +host-meson-package+ macro.
Just like the generic infrastructure, the Meson infrastructure works by defining
a number of variables before calling the +meson-package+ macro.
First, all the package metadata information variables that exist in the generic
infrastructure also exist in the Meson infrastructure: +FOO_VERSION+,
+FOO_SOURCE+, +FOO_PATCH+, +FOO_SITE+, +FOO_SUBDIR+, +FOO_DEPENDENCIES+,
+FOO_INSTALL_STAGING+, +FOO_INSTALL_TARGET+.
A few additional variables, specific to the Meson infrastructure, can also be
defined. Many of them are only useful in very specific cases, typical packages
will therefore only use a few of them.
* +FOO_SUBDIR+ may contain the name of a subdirectory inside the
package that contains the main meson.build file. This is useful,
if for example, the main meson.build file is not at the root of
the tree extracted by the tarball. If +HOST_FOO_SUBDIR+ is not
specified, it defaults to +FOO_SUBDIR+.
* +FOO_CONF_ENV+, to specify additional environment variables to pass to
+meson+ for the configuration step. By default, empty.
* +FOO_CONF_OPTS+, to specify additional options to pass to +meson+ for the
configuration step. By default, empty.
* +FOO_CFLAGS+, to specify compiler arguments added to the package specific
+cross-compile.conf+ file +c_args+ property. By default, the value of
+TARGET_CFLAGS+.
* +FOO_CXXFLAGS+, to specify compiler arguments added to the package specific
+cross-compile.conf+ file +cpp_args+ property. By default, the value of
+TARGET_CXXFLAGS+.
* +FOO_LDFLAGS+, to specify compiler arguments added to the package specific
+cross-compile.conf+ file +c_link_args+ and +cpp_link_args+ properties. By
default, the value of +TARGET_LDFLAGS+.
* +FOO_NINJA_ENV+, to specify additional environment variables to pass to
+ninja+, meson companion tool in charge of the build operations. By default,
empty.
* +FOO_NINJA_OPTS+, to specify a space-separated list of targets to build. By
default, empty, to build the default target(s).