package/pkg-golang.mk: implement Go vendoring support

This commit introduces the download post-process script
support/download/go-post-process, and hooks it into the Go package
infrastructure.

The -modcacherw flag is added to ensure that the Go cache is
read/write, and can be deleted properly upon "make clean".

The <pkg>_LICENSE variable of golang packages is expanded with ",
vendored dependencies licenses probably not listed" as currently for
all packages, the licenses of the vendored dependencies are not taken
into account.

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

package/pkg-golang.mk

@@ -42,12 +42,13 @@ define inner-golang-package
 
 $(2)_BUILD_OPTS += \
 	-ldflags "$$($(2)_LDFLAGS)" \
+	-modcacherw \
 	-tags "$$($(2)_TAGS)" \
 	-trimpath \
 	-p $(PARALLEL_JOBS)
 
 # Target packages need the Go compiler on the host.
-$(2)_DEPENDENCIES += host-go
+$(2)_DOWNLOAD_DEPENDENCIES += host-go
 
 $(2)_BUILD_TARGETS ?= .
 
@@ -81,6 +82,16 @@ define $(2)_GEN_GOMOD
 endef
 $(2)_POST_PATCH_HOOKS += $(2)_GEN_GOMOD
 
+$(2)_DOWNLOAD_POST_PROCESS = go
+$(2)_DL_ENV = \
+	$(HOST_GO_COMMON_ENV) \
+	GOPROXY=direct \
+	BR_GOMOD=$$($(2)_GOMOD)
+
+# Due to vendoring, it is pretty likely that not all licenses are
+# listed in <pkg>_LICENSE.
+$(2)_LICENSE += , vendored dependencies licenses probably not listed
+
 # Build step. Only define it if not already defined by the package .mk
 # file.
 ifndef $(2)_BUILD_CMDS

support/download/go-post-process

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -e
+set -o pipefail
+
+. "${0%/*}/helpers"
+
+# Parse our options
+while getopts "n:o:" OPT; do
+    case "${OPT}" in
+    o)  output="${OPTARG}";;
+    n)  base_name="${OPTARG}";;
+    :)  error "option '%s' expects a mandatory argument\n" "${OPTARG}";;
+    \?) error "unknown option '%s'\n" "${OPTARG}";;
+    esac
+done
+
+# Already vendored tarball, nothing to do
+if tar tf "${output}" | grep -q "^[^/]*/vendor" ; then
+    exit 0
+fi
+
+post_process_unpack "${base_name}" "${output}"
+
+# Do the Go vendoring
+pushd "${base_name}" > /dev/null
+
+if [ ! -f go.mod ]; then
+    echo "ERROR: no vendor/ folder and no go.mod, aborting"
+    exit 1
+fi
+
+go mod vendor -v -modcacherw
+popd > /dev/null
+
+post_process_repack $(pwd) "${base_name}" "${output}"