Index: Mk/Uses/go.mk
===================================================================
--- Mk/Uses/go.mk
+++ Mk/Uses/go.mk
@@ -93,6 +93,9 @@
 GOARM?=		${ARCH:C/armv//}
 .endif
 
+GO_GOPROXY?=	https://proxy.golang.org
+GO_GOSUMDB?=	sum.golang.org
+
 # Read-only variables
 
 GO_CMD=		${LOCALBASE}/bin/go
@@ -103,14 +106,31 @@
 		GOARM=${GOARM}
 
 .if ${go_ARGS:Mmodules}
-GO_BUILDFLAGS+=	-mod=vendor
-GO_TESTFLAGS+=	-mod=vendor
 GO_WRKSRC=	${WRKSRC}
-GO_ENV+=	GOPATH="" \
+GO_ENV+=	GOPATH="${DISTDIR}/go/${PKGORIGIN}" \
 		GOBIN="${GO_WRKDIR_BIN}" \
 		GO111MODULE=on \
-		GOPROXY=off \
-		GO_NO_VENDOR_CHECKS=1
+		GOFLAGS=-modcacherw \
+		GOSUMDB=${GO_GOSUMDB}
+.  if defined(GO_MODULE)
+GO_BUILDFLAGS+=	-mod=readonly
+GO_TESTFLAGS+=	-mod=readonly
+GO_MODNAME=	${GO_MODULE:C/^([^@]*)(@([^@]*)?)/\1/}
+GO_MODVERSION=	${GO_MODULE:C/^([^@]*)(@([^@]*)?)/\2/:M@*:S/^@//:S/^$/${DISTVERSIONFULL}/}
+GO_MODFILE=	${GO_MODVERSION}.mod
+GO_DISTFILE=	${GO_MODVERSION}.zip
+DIST_SUBDIR=	go/${PKGORIGIN}/${DISTNAME}
+MASTER_SITES=	${GO_GOPROXY}/${GO_MODNAME}/@v/
+DISTFILES=	${GO_MODFILE} ${GO_DISTFILE}
+EXTRACT_ONLY=	${GO_DISTFILE}
+WRKSRC=		${WRKDIR}/${GO_MODNAME}@${GO_MODVERSION}
+USES+=		zip
+.  else
+GO_BUILDFLAGS+=	-mod=vendor
+GO_TESTFLAGS+=	-mod=vendor
+GO_ENV+=	GO_NO_VENDOR_CHECKS=1 \
+		GOPROXY=off
+.  endif
 .else
 GO_WRKSRC=	${WRKDIR}/src/${GO_PKGNAME}
 GO_ENV+=	GOPATH="${WRKDIR}" \
@@ -121,6 +141,7 @@
 GO_PORT?=	lang/go
 
 BUILD_DEPENDS+=	${GO_CMD}:${GO_PORT}
+FETCH_DEPENDS+=	${GO_CMD}:${GO_PORT}
 .if ${go_ARGS:Mrun}
 RUN_DEPENDS+=	${GO_CMD}:${GO_PORT}
 .endif
@@ -131,6 +152,14 @@
 .if defined(_POSTMKINCLUDED) && !defined(_INCLUDE_USES_GO_POST_MK)
 _INCLUDE_USES_GO_POST_MK=	yes
 
+.if !target(post-fetch) && ${go_ARGS:Mmodules} && defined(GO_MODULE)
+post-fetch:
+	@${ECHO_MSG} "===> Fetching ${GO_MODNAME} dependencies";
+	@(cd ${DISTDIR}/${DIST_SUBDIR}; \
+		${RLN} ${GO_MODFILE} go.mod; \
+		${SETENV} ${GO_ENV} ${GO_CMD} mod download -x)
+.endif
+
 .if !target(post-extract) && empty(go_ARGS)
 post-extract:
 	@${MKDIR} ${GO_WRKSRC:H}
@@ -176,6 +205,16 @@
 	done)
 .endif
 
+gomod-clean:
+	@${ECHO_MSG} "===>  Cleaning Go module cache"
+	@${SETENV} ${GO_ENV} ${GO_CMD} clean -modcache
+
+# Hook up to distclean
+.if !make(clean)
+post-clean: gomod-clean
+	@${RM} -r ${DISTDIR}/${DIST_SUBDIR}
+.endif
+
 # Helper targets for port maintainers
 
 .if ${go_ARGS:Mmodules}
@@ -189,11 +228,11 @@
 	fi
 
 gomod-vendor: gomod-vendor-deps patch
-	@cd ${WRKSRC}; ${SETENV} GOPATH=${WRKDIR}/.gopath GOFLAGS=-modcacherw ${GO_CMD} mod vendor; \
+	@cd ${WRKSRC}; ${SETENV} ${GO_ENV:NGOPROXY*} ${GO_CMD} mod vendor; \
 	[ -r vendor/modules.txt ] && ${_MODULES2TUPLE_CMD} vendor/modules.txt
 
 gomod-vendor-diff: gomod-vendor-deps patch
-	@cd ${WRKSRC}; ${SETENV} GOPATH=${WRKDIR}/.gopath GOFLAGS=-modcacherw ${GO_CMD} mod vendor; \
+	@cd ${WRKSRC}; ${SETENV} ${GO_ENV:NGOPROXY*} ${GO_CMD} mod vendor; \
 	[ -r vendor/modules.txt ] && ${_MODULES2TUPLE_CMD} vendor/modules.txt | ${SED} 's|GH_TUPLE=|	|; s| \\$$||' | ${GREP} -v '		\\' > ${WRKDIR}/GH_TUPLE-new.txt && \
 	echo ${GH_TUPLE} | ${TR} -s " " "\n" | ${SED} "s|^|		|" > ${WRKDIR}/GH_TUPLE-old.txt && \
 	${DIFF} ${WRKDIR}/GH_TUPLE-old.txt ${WRKDIR}/GH_TUPLE-new.txt || exit 0