[PATCHv8] boost: Add support for building boost-asio as a shared library

[Gustav Lindberg <gustali@axis.com>]

This is needed to build boost asio as a shared library rather than a
header-only library, which is needed to save memory.

This can be enabled by adding `PACKAGECONFIG:append = " asio-shared"` to
`boost_%.bbappend`.

Signed-off-by: Gustav Lindberg <gustali@axis.com>
---
 meta/recipes-support/boost/boost.inc          | 25 +++++++++++++++++++
 .../boost/boost/boost_asio.cpp                |  1 +
 2 files changed, 26 insertions(+)
 create mode 100644 meta/recipes-support/boost/boost/boost_asio.cpp

diff --git a/meta/recipes-support/boost/boost.inc b/meta/recipes-support/boost/boost.inc
index 64a57ddfb2..0267d8e819 100644
--- a/meta/recipes-support/boost/boost.inc
+++ b/meta/recipes-support/boost/boost.inc
@@ -16,6 +16,7 @@ do_configure[cleandirs] = "${B}"
 
 BOOST_LIBS = "\
 	atomic \
+	asio \
 	charconv \
 	chrono \
 	container \
@@ -51,11 +52,14 @@ BOOST_LIBS = "\
 
 # optional libraries
 PACKAGECONFIG ??= "locale python"
+PACKAGECONFIG[asio-shared] = ",,"
 PACKAGECONFIG[locale] = ",,icu"
 PACKAGECONFIG[graph_parallel] = ",,,boost-mpi mpich"
 PACKAGECONFIG[mpi] = ",,mpich"
 PACKAGECONFIG[python] = ",,python3"
 
+SRC_URI:append = " ${@bb.utils.contains('PACKAGECONFIG', 'asio-shared', 'file://boost_asio.cpp', '', d)}"
+
 inherit python3-dir
 PYTHON_ROOT = "${STAGING_DIR_HOST}/${prefix}"
 
@@ -198,6 +202,20 @@ do_compile() {
 		--debug-configuration
 }
 
+do_compile:append() {
+	if ${@bb.utils.contains('PACKAGECONFIG', 'asio-shared', 'true', 'false', d)}; then
+		${CXX} ${CPPFLAGS} ${CXXFLAGS} \
+			-DBOOST_ASIO_DYN_LINK=1 \
+			-I${S} \
+			-fPIC \
+			-shared \
+			-Wl,-soname,libboost_asio.so.${PV} \
+			${UNPACKDIR}/boost_asio.cpp \
+			${LDFLAGS} \
+			-o ${B}/libboost_asio.so.${PV}
+	fi
+}
+
 do_install() {
 	cd ${S}
 	b2 ${BJAM_OPTS} \
@@ -220,4 +238,11 @@ do_install() {
 
 }
 
+do_install:append() {
+	if ${@bb.utils.contains('PACKAGECONFIG', 'asio-shared', 'true', 'false', d)}; then
+		install -Dm 0755 ${B}/libboost_asio.so.${PV} ${D}${libdir}/libboost_asio.so.${PV}
+		ln -sf libboost_asio.so.${PV} ${D}${libdir}/libboost_asio.so
+	fi
+}
+
 BBCLASSEXTEND = "native nativesdk"
diff --git a/meta/recipes-support/boost/boost/boost_asio.cpp b/meta/recipes-support/boost/boost/boost_asio.cpp
new file mode 100644
index 0000000000..eb3b7262c3
--- /dev/null
+++ b/meta/recipes-support/boost/boost/boost_asio.cpp
@@ -0,0 +1 @@
+#include <boost/asio/impl/src.hpp>
\ No newline at end of file
-- 
2.43.0

Rename `asio` packageconfig flag to `asio-shared` and include asio in BOOST_LIBS unconditionally.

> No custom compiler executions please. Building a shared library should
> be done by the boost build system itself, and enabled via a flag to it
> during do_configure (e.g. via PACKAGECONFIG_CONFARGS or BJAM_EXTRA).
> You probably need to patch boost to do this, and send the needed patch
> upstream.

I spent a day trying to get that to work, but it doesn't seem to be possible. Everything I tried either breaks
the header-only version or doesn't build the shared library.