[Buildroot] [RFC 1/1] br2-external: Alow to include toolchain from external tree

[Vadim Kochan]

Add possibility to select toolchain from br2-external tree which
allows to easy use custom external toolchains by selecting them via
menuconfig as if they were integrated into buildroot.

The br2-external tree should contain:

	${br2-external}/external-toolchain/Config.in

file to be included into external toolchains list.

All such picked toolchains are sourced in:

	toolchain/toolchain-external/Config.in

from auto-generated file ${O}/build/.br2-external.in.toolchain.

Added new '-t' option in support/scripts/br2-external to generate
kconfig for the found toolchains from the all specified external trees.

Signed-off-by: Vadim Kochan <vadim4j at gmail.com>
---

This is just PoC to rise the discussion about this concept.

 Makefile                               |  6 +++++-
 support/scripts/br2-external           | 36 ++++++++++++++++++++++++++++++++--
 toolchain/toolchain-external/Config.in |  2 ++
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 522c0b0606..4eceb88813 100644
--- a/Makefile
+++ b/Makefile
@@ -938,7 +938,7 @@ HOSTCFLAGS = $(CFLAGS_FOR_BUILD)
 export HOSTCFLAGS
 
 .PHONY: prepare-kconfig
-prepare-kconfig: outputmakefile $(BUILD_DIR)/.br2-external.in
+prepare-kconfig: outputmakefile $(BUILD_DIR)/.br2-external.in $(BUILD_DIR)/.br2-external.in.toolchain
 
 $(BUILD_DIR)/buildroot-config/%onf:
 	mkdir -p $(@D)/lxdialog
@@ -1042,6 +1042,10 @@ endif
 $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
 	$(Q)support/scripts/br2-external -k -o "$(@)" $(BR2_EXTERNAL)
 
+.PHONY: $(BUILD_DIR)/.br2-external.in.toolchain
+$(BUILD_DIR)/.br2-external.in.toolchain: $(BUILD_DIR)
+	$(Q)support/scripts/br2-external -t -o "$(@)" $(BR2_EXTERNAL)
+
 # printvars prints all the variables currently defined in our
 # Makefiles. Alternatively, if a non-empty VARS variable is passed,
 # only the variables matching the make pattern passed in VARS are
diff --git a/support/scripts/br2-external b/support/scripts/br2-external
index 00cb57d1ed..3ec332d93e 100755
--- a/support/scripts/br2-external
+++ b/support/scripts/br2-external
@@ -16,10 +16,11 @@ main() {
     local OPT OPTARG
     local br2_ext ofile ofmt
 
-    while getopts :hkmo: OPT; do
+    while getopts :htkmo: OPT; do
         case "${OPT}" in
         h)  help; exit 0;;
         o)  ofile="${OPTARG}";;
+        t)  ofmt="toolchain";;
         k)  ofmt="kconfig";;
         m)  ofmt="mk";;
         :)  error "option '%s' expects a mandatory argument\n" "${OPTARG}";;
@@ -30,7 +31,7 @@ main() {
     shift $((OPTIND-1))
 
     case "${ofmt}" in
-    mk|kconfig)
+    mk|kconfig|toolchain)
         ;;
     *)  error "no output format specified (-m/-k)\n";;
     esac
@@ -188,6 +189,37 @@ do_kconfig() {
     printf "endmenu # User-provided options\n"
 }
 
+# Generate the toolchain kconfig snippet for the br2-external tree.
+do_toolchain() {
+    local br2_name br2_ext
+
+    printf '#\n# Automatically generated file; DO NOT EDIT.\n#\n'
+    printf '\n'
+
+    if [ ${#BR2_EXT_NAMES[@]} -eq 0 ]; then
+        printf '# No br2-external tree defined.\n'
+        return
+    fi
+
+    for br2_name in "${BR2_EXT_NAMES[@]}"; do
+        eval br2_desc="\"\${BR2_EXT_DESCS_${br2_name}}\""
+        eval br2_ext="\"\${BR2_EXT_PATHS_${br2_name}}\""
+
+        if [ ! -f "${br2_ext}/toolchain-external/Config.in" ]; then
+            continue
+	fi
+
+        # we have to duplicate it here too because otherwise BR2_EXTERNAL_*
+	# is not evaluated in Config.in
+        printf 'config BR2_EXTERNAL_%s_PATH\n' "${br2_name}"
+        printf '\tstring\n'
+        printf '\tdefault "%s"\n' "${br2_ext}"
+
+        printf 'source "%s/toolchain-external/Config.in"\n' "${br2_ext}"
+        printf '\n'
+    done
+}
+
 help() {
     cat <<-_EOF_
 	Usage:
diff --git a/toolchain/toolchain-external/Config.in b/toolchain/toolchain-external/Config.in
index d234c1c552..70e8a89e5e 100644
--- a/toolchain/toolchain-external/Config.in
+++ b/toolchain/toolchain-external/Config.in
@@ -50,6 +50,8 @@ source "toolchain/toolchain-external/toolchain-external-codesourcery-amd64/Confi
 # architecture.
 source "toolchain/toolchain-external/toolchain-external-custom/Config.in"
 
+source "$BR2_BUILD_DIR/.br2-external.in.toolchain"
+
 endchoice
 
 choice
-- 
2.14.1