[Buildroot] [PATCH 19/29 v2] package/boost: headers-only libs are always installed

[Yann E. MORIN]

The headers-only libraries are an entry like the others for the boost
build system, and are reported in the list of libraries when it is
queried:

    $ ./bootstrap.sh --show-libraries
    [--SNIP--]
    The Boost libraries requiring separate building and installation are:
        [...]
        - headers
        [...]

However, they are always "built" and installed, and can't be disabled,
even using the --without-headers flag.

In a followup change, we'll make sure that the sets of libs provided by
Boost on one hand, and known to Buildroot on the other, are identical,
so we'll want to have 'headers' be present in the list known to
Buildroot.

Add an Kconfig symbol to represent that library. To inform the user that
the headers library is installed, we expose it with a prompt; we however
make sure the symbol can't be disabled when Boost is enabled. Since it
is a "special' library, we list if first, not in alphabetical order.

Signed-off-by: Yann E. MORIN <yann.morin.1998 at free.fr>
Cc: Michael Nosthoff <buildroot at heine.tech>
Cc: Yegor Yefremov <yegorslists at googlemail.com>
---
 package/boost/Config.in | 7 +++++++
 package/boost/boost.mk  | 1 +
 2 files changed, 8 insertions(+)

diff --git a/package/boost/Config.in b/package/boost/Config.in
index f37efd129b..784c40278b 100644
--- a/package/boost/Config.in
+++ b/package/boost/Config.in
@@ -9,6 +9,7 @@ config BR2_PACKAGE_BOOST
 	# let's depend on threads.
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_USE_WCHAR
+	select BR2_PACKAGE_BOOST_HEADERS
 	help
 	  A general purpose C++ library
 
@@ -16,6 +17,12 @@ config BR2_PACKAGE_BOOST
 
 if BR2_PACKAGE_BOOST
 
+# Headers-only libraries are always installed by Boost's buildsystem
+config BR2_PACKAGE_BOOST_HEADERS
+	bool "boost-headers"
+	help
+	  Headers-only libraries; those are always installed.
+
 config BR2_PACKAGE_BOOST_ATOMIC
 	bool "boost-atomic"
 	depends on BR2_TOOLCHAIN_SUPPORTS_ALWAYS_LOCKFREE_ATOMIC_INTS
diff --git a/package/boost/boost.mk b/package/boost/boost.mk
index 2b952baaac..e849f902f2 100644
--- a/package/boost/boost.mk
+++ b/package/boost/boost.mk
@@ -25,6 +25,7 @@ BOOST_ALL_LIBS = \
 	filesystem \
 	graph \
 	graph_parallel \
+	headers \
 	iostreams \
 	json \
 	locale \
-- 
2.47.0