[Buildroot] [PATCH v3 1/6] package/go: implement go modules integration

[Christian Stewart]

This commit moves from the GOPATH mechanism to the new GO111MODULE approach for
Go based packages. Old Go packages compile with small tweaks.

The Go module system replaces the GOPATH mechanism by allowing the Go tool to
work with packages correctly without a GOPATH tree.

Reference: https://github.com/golang/go/wiki/Modules

Signed-off-by: Christian Stewart <christian at paral.in>

v2 -> v3:

 - cjs: cleaned up spelling and moved extract hook to configure step
 - cjs: applied fixes from vincent fazio related to host packages

Signed-off-by: Christian Stewart <christian at paral.in>
---
 package/go/go.mk      |  8 ++++++--
 package/pkg-golang.mk | 31 +++++++++++++++++++------------
 2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/package/go/go.mk b/package/go/go.mk
index 376c3db7f0..1291874b1d 100644
--- a/package/go/go.mk
+++ b/package/go/go.mk
@@ -15,6 +15,8 @@ HOST_GO_DEPENDENCIES = host-go-bootstrap
 HOST_GO_HOST_CACHE = $(HOST_DIR)/usr/share/host-go-cache
 HOST_GO_ROOT = $(HOST_DIR)/lib/go
 HOST_GO_TARGET_CACHE = $(HOST_DIR)/usr/share/go-cache
+# used for go module downloads
+HOST_GO_GOPATH = $(DL_DIR)/go-module
 
 ifeq ($(BR2_PACKAGE_HOST_GO_TARGET_ARCH_SUPPORTS),y)
 
@@ -43,13 +45,15 @@ else ifeq ($(BR2_mips64el),y)
 GO_GOARCH = mips64le
 endif
 
-# For the convienience of target packages.
+# For the convenience of target packages.
 HOST_GO_TOOLDIR = $(HOST_GO_ROOT)/pkg/tool/linux_$(GO_GOARCH)
 HOST_GO_TARGET_ENV = \
-	GO111MODULE=off \
+	GO111MODULE=on \
 	GOARCH=$(GO_GOARCH) \
 	GOCACHE="$(HOST_GO_TARGET_CACHE)" \
+	GOPROXY=off \
 	GOROOT="$(HOST_GO_ROOT)" \
+	GOPATH="$(HOST_GO_GOPATH)" \
 	CC="$(TARGET_CC)" \
 	CXX="$(TARGET_CXX)" \
 	GOTOOLDIR="$(HOST_GO_TOOLDIR)"
diff --git a/package/pkg-golang.mk b/package/pkg-golang.mk
index 2494ce028c..7b5c263806 100644
--- a/package/pkg-golang.mk
+++ b/package/pkg-golang.mk
@@ -35,8 +35,16 @@ GO_TARGET_ENV = \
 	$(GO_COMMON_ENV)
 
 GO_HOST_ENV = \
+	CC=$(HOSTCC_NOCCACHE) \
+	CXX=$(HOSTCXX_NOCCACHE) \
 	CGO_CFLAGS="$(HOST_CFLAGS)" \
 	CGO_LDFLAGS="$(HOST_LDFLAGS)" \
+	GO111MODULE=on \
+	GOCACHE="$(HOST_GO_TARGET_CACHE)" \
+	GOPROXY=off \
+	GOROOT="$(HOST_GO_ROOT)" \
+	GOPATH="$(HOST_GO_GOPATH)" \
+	GOTOOLDIR="$(HOST_GO_TOOLDIR)" \
 	$(GO_COMMON_ENV)
 
 ################################################################################
@@ -60,6 +68,7 @@ $(2)_WORKSPACE ?= _gopath
 
 $(2)_BUILD_OPTS += \
 	-ldflags "$$($(2)_LDFLAGS)" \
+	-mod=vendor \
 	-tags "$$($(2)_TAGS)" \
 	-trimpath \
 	-p $(PARALLEL_JOBS)
@@ -79,23 +88,23 @@ endif
 
 $(2)_INSTALL_BINS ?= $(1)
 
-# Source files in Go should be extracted in a precise folder in the hierarchy
-# of GOPATH. It usually resolves around domain/vendor/software. By default, we
-# derive domain/vendor/software from the upstream URL of the project, but we
-# allow $(2)_SRC_SUBDIR to be overridden if needed.
+# Source files in Go usually use an import path resolved around
+# domain/vendor/software. We infer domain/vendor/software from the upstream URL
+# of the project. $(2)_GOMOD can be overridden.
 $(2)_SRC_DOMAIN = $$(call domain,$$($(2)_SITE))
 $(2)_SRC_VENDOR = $$(word 1,$$(subst /, ,$$(call notdomain,$$($(2)_SITE))))
 $(2)_SRC_SOFTWARE = $$(word 2,$$(subst /, ,$$(call notdomain,$$($(2)_SITE))))
+$(2)_SRC_PATH = $$(@D)
 
-$(2)_SRC_SUBDIR ?= $$($(2)_SRC_DOMAIN)/$$($(2)_SRC_VENDOR)/$$($(2)_SRC_SOFTWARE)
-$(2)_SRC_PATH = $$(@D)/$$($(2)_WORKSPACE)/src/$$($(2)_SRC_SUBDIR)
+$(2)_GOMOD ?= $$($(2)_SRC_DOMAIN)/$$($(2)_SRC_VENDOR)/$$($(2)_SRC_SOFTWARE)
 
 # Configure step. Only define it if not already defined by the package .mk
 # file.
 ifndef $(2)_CONFIGURE_CMDS
 define $(2)_CONFIGURE_CMDS
-	mkdir -p $$(dir $$($(2)_SRC_PATH))
-	ln -sf $$(@D) $$($(2)_SRC_PATH)
+	if [ ! -f $$($(2)_SRC_PATH)/go.mod ] && [ -n "$$($(2)_GOMOD)" ]; then \
+		printf "module $$($(2)_GOMOD)\n" > $$($(2)_SRC_PATH)/go.mod; \
+	fi
 endef
 endif
 
@@ -113,11 +122,10 @@ define $(2)_BUILD_CMDS
 	$$(foreach d,$$($(2)_BUILD_TARGETS),\
 		cd $$($(2)_SRC_PATH); \
 		$$(GO_TARGET_ENV) \
-			GOPATH="$$(@D)/$$($(2)_WORKSPACE)" \
 			$$($(2)_GO_ENV) \
 			$$(GO_BIN) build -v $$($(2)_BUILD_OPTS) \
 			-o $$(@D)/bin/$$(or $$($(2)_BIN_NAME),$$(notdir $$(d))) \
-			./$$(d)
+			$$(d)
 	)
 endef
 else
@@ -126,11 +134,10 @@ define $(2)_BUILD_CMDS
 	$$(foreach d,$$($(2)_BUILD_TARGETS),\
 		cd $$($(2)_SRC_PATH); \
 		$$(GO_HOST_ENV) \
-			GOPATH="$$(@D)/$$($(2)_WORKSPACE)" \
 			$$($(2)_GO_ENV) \
 			$$(GO_BIN) build -v $$($(2)_BUILD_OPTS) \
 			-o $$(@D)/bin/$$(or $$($(2)_BIN_NAME),$$(notdir $$(d))) \
-			./$$(d)
+			$$(d)
 	)
 endef
 endif
-- 
2.25.1