vlcrs: add autotools infra for build and linking Rust modules

The autotools suite (automake, libtool, ...) does not support Rust
neither Cargo (Rust package manager and build system) so we need to have
a custom system for using them. We do this by having "hacky" script that
does the build with cargo and output an .a archive in the .libs
directory. And with this and another cargo command we create the .la
with the right information so that the build system can continue as
usual.

modules/Makefile.am

@@ -13,6 +13,31 @@ TESTS =
 dist_noinst_SCRIPTS = module.rc.in
 EXTRA_LTLIBRARIES =
 
+if HAVE_RUST
+
+LIBTOOL_CARGO_EXE = $(srcdir)/libtool_cargo.sh
+
+CARGO_BUILD_ARGS = --target=@RUST_TARGET@ --release \
+	--crate-type=staticlib
+
+LIBTOOL_CARGO = \
+	TARGET_CC=$(CC) TARGET_AR=$(AR) \
+	TARGET_CFLAGS="$(CFLAGS)" \
+	RUSTTARGET="@RUST_TARGET@" \
+	RUSTFLAGS="-C panic=abort -C opt-level=z" \
+	CARGO_TARGET_DIR="target-rust" \
+	$(LIBTOOL_CARGO_EXE) $(CARGO) rustc $(CARGO_BUILD_ARGS)
+
+CARGO_PLUGINS_INV = ${LTLIBRARIES:%rs_plugin.la=%rs_plugin}
+CARGO_PLUGINS_CUT = ${CARGO_PLUGINS_INV:%.la=}
+CARGO_PLUGINS = ${CARGO_PLUGINS_CUT:%=%.la}
+
+CARGO_DEPS = ${CARGO_PLUGINS:%_plugin.la=${top_builddir}/modules/.libs/%.d}
+
+-include $(CARGO_DEPS)
+
+endif
+
 include common.am
 include access/Makefile.am
 include access/http/Makefile.am

modules/libtool_cargo.sh

@@ -0,0 +1,87 @@
+#!/bin/bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# Copyright (C) 2022 Loïc Branstett <loic@videolabs.io>
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation; either version 2.1 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+
+
+# This script generate a libtool convinence library from a Cargo (Rust project)
+
+set -e # Automaticly exit on error
+
+CARGO_RUSTC_CMD=${@:1:$#-2} # all other args
+MODULE_PROJECT_DIR=${@:$#-1:1} # second last argument
+LT_CONVENIENCE=${@:$#:1} # last argument
+
+# Build the project a first time without anything specitial)
+$CARGO_RUSTC_CMD --manifest-path="$MODULE_PROJECT_DIR/Cargo.toml"
+
+# "Build" the project a second time and fetch the native-static-libs to link with
+NATIVE_STATIC_LIBS=$($CARGO_RUSTC_CMD --manifest-path="$MODULE_PROJECT_DIR/Cargo.toml" --quiet -- --print native-static-libs 2>&1 | grep "native-static-libs" | sed "s/note: native-static-libs://" | sed "s/-lvlccore//")
+
+STATIC_LIB_NAME=$(echo $LT_CONVENIENCE | sed "s/\.la/\.a/")
+STATIC_LIB_DEP=$(echo $LT_CONVENIENCE | sed "s/\.la/\.d/")
+CARGO_STATIC_LIB_PATH="$CARGO_TARGET_DIR/$RUSTTARGET/release/$STATIC_LIB_NAME"
+CARGO_STATIC_DEP_PATH="$CARGO_TARGET_DIR/$RUSTTARGET/release/$STATIC_LIB_DEP"
+
+LT_VERSION=$(../libtool --version | grep "libtool")
+
+cat <<EOF > $LT_CONVENIENCE
+# $LT_CONVENIENCE - a libtool library file
+# Generated by $LT_VERSION
+
+# The name that we can dlopen(3).
+dlname=''
+
+# Names of this library.
+library_names=''
+
+# The name of the static archive.
+old_library='$STATIC_LIB_NAME'
+
+# Linker flags that cannot go in dependency_libs.
+inherited_linker_flags=''
+
+# Libraries that this one depends upon.
+dependency_libs=' $NATIVE_STATIC_LIBS'
+
+# Names of additional weak libraries provided by this library
+weak_library_names=''
+
+# Version information
+current=0
+age=0
+revision=0
+
+# Is this an already installed library?
+installed=no
+
+# Should we warn about portability when linking against -modules?
+shouldnotlink=no
+
+# Files to dlopen/dlpreopen
+dlopen=''
+dlpreopen=''
+
+# Directory that this library needs to be installed in:
+libdir=''
+EOF
+
+mkdir -p "./.libs"
+ln -sf "../$LT_CONVENIENCE" "./.libs/$LT_CONVENIENCE"
+cp "$CARGO_STATIC_LIB_PATH" "./.libs/$STATIC_LIB_NAME"
+
+echo -n "$LT_CONVENIENCE:" > "./.libs/$STATIC_LIB_DEP"
+cat "$CARGO_STATIC_DEP_PATH" | cut -d ':' -f2 >> "./.libs/$STATIC_LIB_DEP"