package/pkg-rebar: new infrastructure

Ease the development of packages that use the erlang rebar tool as
their build system.

Signed-off-by: Johan Oudinet <johan.oudinet@gmail.com>
[yann.morin.1998@free.fr: split the patch into semantically separated
patches; large rewrites of the rest]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

[Thomas, with help from Yann and Arnout:
 - Fix the comment about the symlink used to make sure rebar does not
   download dependencies. The comment was not up-to-date with where
   the symlink is actually created.
 - Make <pkg>_USE_BUNDLED_REBAR and <pkg>_USE_AUTOCONF be inherited by
   host packages from their corresponding target package.
 - Make sure host dependencies are inherited from the corresponding
   target packages dependencies. This requires copying some logic from
   inner-autotools-package and inner-generic-package, just like
   inner-autotools-package duplicates some logic from
   inner-generic-package.
 - Fix host variant of $(2)_BUILD_CMDS indentation, use double quotes
   instead of simple quotes. So that it matches the target
   $(2)_BUILD_CMDS, and what we do elsewhere in Buildroot.]

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/Makefile.in

@@ -416,3 +416,4 @@ include package/pkg-python.mk
 include package/pkg-virtual.mk
 include package/pkg-generic.mk
 include package/pkg-kconfig.mk
+include package/pkg-rebar.mk

package/pkg-rebar.mk

@@ -0,0 +1,253 @@
+################################################################################
+# rebar package infrastructure for Erlang packages
+#
+# This file implements an infrastructure that eases development of
+# package .mk files for rebar packages.  It should be used for all
+# packages that use rebar as their build system.
+#
+# In terms of implementation, this rebar infrastructure requires the
+# .mk file to only specify metadata information about the package:
+# name, version, download URL, etc.
+#
+# We still allow the package .mk file to override what the different
+# steps are doing, if needed. For example, if <PKG>_BUILD_CMDS is
+# already defined, it is used as the list of commands to perform to
+# build the package, instead of the default rebar behaviour. The
+# package can also define some post operation hooks.
+#
+################################################################################
+
+# Directories to store rebar dependencies in.
+#
+# These directories actually only contain symbolic links to Erlang
+# applications in either $(HOST_DIR) or $(STAGING_DIR).  One needs
+# them to avoid rebar complaining about missing dependencies, as this
+# infrastructure tells rebar to NOT download dependencies during
+# the build stage.
+#
+REBAR_HOST_DEPS_DIR = $(HOST_DIR)/usr/share/rebar/deps
+REBAR_TARGET_DEPS_DIR = $(STAGING_DIR)/usr/share/rebar/deps
+
+# Tell rebar where to find the dependencies
+#
+REBAR_HOST_DEPS_ENV = \
+	ERL_COMPILER_OPTIONS='{i, "$(REBAR_HOST_DEPS_DIR)"}' \
+	ERL_EI_LIBDIR=$(HOST_DIR)/usr/lib/erlang/lib/erl_interface-$(ERLANG_EI_VSN)/lib
+REBAR_TARGET_DEPS_ENV = \
+	ERL_COMPILER_OPTIONS='{i, "$(REBAR_TARGET_DEPS_DIR)"}' \
+	ERL_EI_LIBDIR=$(STAGING_DIR)/usr/lib/erlang/lib/erl_interface-$(ERLANG_EI_VSN)/lib
+
+################################################################################
+# Helper functions
+################################################################################
+
+# Install an Erlang application from $(@D).
+#
+# i.e., define a recipe that installs the "ebin priv $(2)" directories
+# from $(@D) to $(1)$($(PKG)_ERLANG_LIBDIR).
+#
+#  argument 1 should typically be $(HOST_DIR), $(TARGET_DIR),
+#	      or $(STAGING_DIR).
+#  argument 2 is typically empty when installing in $(TARGET_DIR) and
+#             "include" when installing in $(HOST_DIR) or
+#             $(STAGING_DIR).
+#
+# Note: calling this function must be done with $$(call ...) because it
+# expands package-related variables.
+#
+define install-erlang-directories
+	$(INSTALL) -d $(1)/$($(PKG)_ERLANG_LIBDIR)
+	for dir in ebin priv $(2); do                                   \
+		if test -d $(@D)/$$dir; then                            \
+			cp -r $(@D)/$$dir $(1)$($(PKG)_ERLANG_LIBDIR);  \
+		fi;                                                     \
+	done
+endef
+
+# Setup a symbolic link in rebar's deps_dir to the actual location
+# where an Erlang application is installed.
+#
+# i.e., define a recipe that creates a symbolic link
+# from $($(PKG)_REBAR_DEPS_DIR)/$($(PKG)_ERLANG_APP)
+# to $(1)$($(PKG)_ERLANG_LIBDIR).
+#
+# For target packages for example, one uses this to setup symbolic
+# links from $(STAGING_DIR)/usr/share/rebar/deps/<erlang-app> to
+# $(STAGING_DIR)/usr/lib/erlang/lib/<erlang-app>-<version>. This
+# infrastructure points rebar at the former in order to tell rebar do
+# NOT download dependencies during the build stage, and instead use
+# the already available dependencies.
+#
+# Therefore,
+#  argument 1 is $(HOST_DIR) (for host packages) or
+#	      $(STAGING_DIR) (for target packages).
+#
+#  argument 2 is HOST (for host packages) or
+#	      TARGET (for target packages).
+#
+# Note: calling this function must be done with $$(call ...) because it
+# expands package-related variables.
+#
+define install-rebar-deps
+	$(INSTALL) -d $(REBAR_$(2)_DEPS_DIR)
+	ln -f -s $(1)/$($(PKG)_ERLANG_LIBDIR) \
+		$(REBAR_$(2)_DEPS_DIR)/$($(PKG)_ERLANG_APP)
+endef
+
+################################################################################
+# inner-rebar-package -- defines how the configuration, compilation
+# and installation of a rebar package should be done, implements a few
+# hooks to tune the build process according to rebar specifities, and
+# calls the generic package infrastructure to generate the necessary
+# make targets.
+#
+#  argument 1 is the lowercase package name
+#  argument 2 is the uppercase package name, including a HOST_ prefix
+#             for host packages
+#  argument 3 is the uppercase package name, without the HOST_ prefix
+#             for host packages
+#  argument 4 is the type (target or host)
+#
+################################################################################
+
+define inner-rebar-package
+
+# Extract just the raw package name, lowercase without the leading
+# erlang- or host- prefix, as this is used by rebar to find the
+# dependencies a package specifies.
+#
+$(2)_ERLANG_APP = $(subst -,_,$(patsubst erlang-%,%,$(patsubst host-%,%,$(1))))
+
+# Path where to store the package's libs, relative to either $(HOST_DIR)
+# for host packages, or $(STAGING_DIR) for target packages.
+#
+$(2)_ERLANG_LIBDIR = \
+	/usr/lib/erlang/lib/$$($$(PKG)_ERLANG_APP)-$$($$(PKG)_VERSION)
+
+# If a host package, inherit <pkg>_USE_BUNDLED_REBAR from the target
+# package, if not explicitly defined. Otherwise, default to NO.
+ifndef $(2)_USE_BUNDLED_REBAR
+ ifdef $(3)_USE_BUNDLED_REBAR
+  $(2)_USE_BUNDLED_REBAR = $$($(3)_USE_BUNDLED_REBAR)
+ else
+  $(2)_USE_BUNDLED_REBAR ?= NO
+ endif
+endif
+
+# If a host package, inherit <pkg>_USE_AUTOCONF from the target
+# package, if not explicitly defined. Otherwise, default to NO.
+ifndef $(2)_USE_AUTOCONF
+ ifdef $(3)_USE_AUTOCONF
+  $(2)_USE_AUTOCONF = $$($(3)_USE_AUTOCONF)
+ else
+  $(2)_USE_AUTOCONF ?= NO
+ endif
+endif
+
+# Define the build and install commands
+#
+ifeq ($(4),target)
+
+# Target packages need the erlang interpreter on the target
+$(2)_DEPENDENCIES += erlang
+
+# Used only if the package uses autotools underneath; otherwise, ignored
+$(2)_CONF_ENV += $$(REBAR_TARGET_DEPS_ENV)
+
+ifndef $(2)_BUILD_CMDS
+define $(2)_BUILD_CMDS
+	(cd $$(@D); \
+		CC="$$(TARGET_CC)" \
+		CFLAGS="$$(TARGET_CFLAGS)" \
+		LDFLAGS="$$(TARGET_LDFLAGS)" \
+		$$(REBAR_TARGET_DEPS_ENV) \
+		$$(TARGET_MAKE_ENV) \
+		$$($$(PKG)_REBAR_ENV) $$($$(PKG)_REBAR) deps_dir=$$(REBAR_TARGET_DEPS_DIR) compile \
+	)
+endef
+endif
+
+# We need to double-$ the 'call' because it wants to expand
+# package-related variables
+ifndef $(2)_INSTALL_STAGING_CMDS
+define $(2)_INSTALL_STAGING_CMDS
+	$$(call install-erlang-directories,$$(STAGING_DIR),include)
+	$$(call install-rebar-deps,$$(STAGING_DIR),TARGET)
+endef
+endif
+
+# We need to double-$ the 'call' because it wants to expand
+# package-related variables
+ifndef $(2)_INSTALL_TARGET_CMDS
+define $(2)_INSTALL_TARGET_CMDS
+	$$(call install-erlang-directories,$$(TARGET_DIR))
+endef
+endif
+
+else # !target
+
+ifeq ($$($(2)_USE_AUTOCONF),YES)
+# This must be repeated from inner-autotools-package, otherwise we get
+# an empty _DEPENDENCIES if _AUTORECONF is YES or _USE_BUNDLED_REBAR
+# is NO.  Also filter the result of _AUTORECONF and _GETTEXTIZE away
+# from the non-host rule
+$(2)_DEPENDENCIES ?= $$(filter-out host-automake host-autoconf host-libtool \
+				host-gettext host-toolchain host-erlang-rebar $(1),\
+    $$(patsubst host-host-%,host-%,$$(addprefix host-,$$($(3)_DEPENDENCIES))))
+else
+# Same deal, if _USE_BUNLDED_REBAR is NO.
+$(2)_DEPENDENCIES ?= $$(filter-out  host-toolchain host-erlang-rebar $(1),\
+	$$(patsubst host-host-%,host-%,$$(addprefix host-,$$($(3)_DEPENDENCIES))))
+endif
+
+# Host packages need the erlang interpreter on the host
+$(2)_DEPENDENCIES += host-erlang
+
+# Used only if the package uses autotools underneath; otherwise, ignored
+$(2)_CONF_ENV += $$(REBAR_HOST_DEPS_ENV)
+
+ifndef $(2)_BUILD_CMDS
+define $(2)_BUILD_CMDS
+	(cd $$(@D); \
+		CC="$$(HOST_CC)" \
+		CFLAGS="$$(HOST_CFLAGS)" \
+		LDFLAGS="$$(HOST_LDFLAGS)" \
+		$$(REBAR_HOST_DEPS_ENV) \
+		$$(HOST_MAKE_ENV) \
+		$$($$(PKG)_REBAR_ENV) $$($$(PKG)_REBAR) deps_dir=$$(REBAR_HOST_DEPS_DIR) compile \
+	)
+endef
+endif
+
+# We need to double-$ the 'call' because it wants to expand
+# package-related variables
+ifndef $(2)_INSTALL_CMDS
+define $(2)_INSTALL_CMDS
+	$$(call install-erlang-directories,$$(HOST_DIR),include)
+	$$(call install-rebar-deps,$$(HOST_DIR),HOST)
+endef
+endif
+
+endif # !target
+
+# Whether to use the generic rebar or the package's bundled rebar
+#
+ifeq ($$($(2)_USE_BUNDLED_REBAR),YES)
+$(2)_REBAR = ./rebar
+else
+$(2)_REBAR = rebar
+$(2)_DEPENDENCIES += host-erlang-rebar
+endif
+
+# The package sub-infra to use
+#
+ifeq ($$($(2)_USE_AUTOCONF),YES)
+$(call inner-autotools-package,$(1),$(2),$(3),$(4))
+else
+$(call inner-generic-package,$(1),$(2),$(3),$(4))
+endif
+
+endef # inner-rebar-package
+
+rebar-package = $(call inner-rebar-package,$(pkgname),$(call UPPERCASE,$(pkgname)),$(call UPPERCASE,$(pkgname)),target)
+host-rebar-package = $(call inner-rebar-package,host-$(pkgname),$(call UPPERCASE,host-$(pkgname)),$(call UPPERCASE,$(pkgname)),host)