Index: head/Mk/Uses/go.mk
===================================================================
--- head/Mk/Uses/go.mk	(revision 508837)
+++ head/Mk/Uses/go.mk	(revision 508838)
@@ -1,129 +1,142 @@
 # $FreeBSD$
 #
 # This file contains logic to ease porting of Go binaries using the
 # `go` command.
 #
 # Feature:	go
 # Usage:	USES=go
 # Valid ARGS:	(none), modules, no_targets, run
 #
 # (none)	Setup GOPATH and build in GOPATH mode.
 # modules	If the upstream uses Go modules, this can be set to build
 #		in modules-aware mode.
 # no_targets	Indicates that Go is needed at build time as a part of
 #		make/CMake build.  This will setup build environment like
 #		GO_ENV, GO_BUILDFLAGS but will not create post-extract, do-build
 #		and do-install targets.
 # run		Indicates that Go is needed at run time and adds it to
 #		RUN_DEPENDS.
 #
 # You can set the following variables to control the process.
 #
 # GO_PKGNAME
 #	The name of the package. When building in GOPATH mode, this is
 #	the directory that will be created in GOPATH/src and seen by the
 #	`go` command. When building in modules-aware mode, no directories
 #	will be created and GO_PKGNAME value will be only used as a default
 #	for GO_TARGET. If not set explicitly and GH_SUBDIR is present,
 #	GO_PKGNAME will be inferred from GH_SUBDIR.
 #
 # GO_TARGET
 #	The names of the package(s) to build. If not set explicitly,
 #	defaults to GO_PKGNAME.
 #
 # CGO_CFLAGS
 #	Addional CFLAGS variables to be passed to the C compiler by the `go`
 #	command
 #
 # CGO_LDFLAGS
 #	Addional LDFLAGS variables to be passed to the C compiler by the `go`
 #	command
 #
 # GO_BUILDFLAGS
 #	Additional build arguments to be passed to the `go install` command
 #
 # GO_PORT
 #	The Go port to use.  By default this is lang/go but can be set
 #	to lang/go-devel in make.conf for testing with future Go versions.
 #
 #	This variable must not be set by individual ports!
 #
 # MAINTAINER: dg@syrec.org
 
 .if !defined(_INCLUDE_USES_GO_MK)
 _INCLUDE_USES_GO_MK=	yes
 
 .if !empty(go_ARGS:Nmodules:Nno_targets:Nrun)
 IGNORE=	USES=go has invalid arguments: ${go_ARGS:Nmodules:Nno_targets:Nrun}
 .endif
 
 # Settable variables
 .if empty(GO_PKGNAME)
 .  if !empty(GH_SUBDIR)
 GO_PKGNAME=	${GH_SUBDIR:S|^src/||}
 .  else
 GO_PKGNAME=	${PORTNAME}
 .  endif
 .endif
 GO_TARGET?=	${GO_PKGNAME}
 GO_BUILDFLAGS+=	-v -buildmode=exe
 CGO_ENABLED?=	1
 CGO_CFLAGS+=	-I${LOCALBASE}/include
 CGO_LDFLAGS+=	-L${LOCALBASE}/lib
 .if ${ARCH} == armv6 || ${ARCH} == armv7
 GOARM?=		${ARCH:C/armv//}
 .endif
 
 # Read-only variables
 GO_CMD=		${LOCALBASE}/bin/go
 GO_WRKDIR_BIN=	${WRKDIR}/bin
 
 GO_ENV+=	CGO_ENABLED=${CGO_ENABLED} \
 		CGO_CFLAGS="${CGO_CFLAGS}" \
 		CGO_LDFLAGS="${CGO_LDFLAGS}" \
 		GOARM=${GOARM}
 
 .if ${go_ARGS:Mmodules}
 GO_BUILDFLAGS+=	-mod=vendor
 GO_WRKSRC=	${WRKSRC}
 GO_ENV+=	GOPATH="" \
 		GOBIN="${GO_WRKDIR_BIN}"
 .else
 GO_WRKDIR_SRC=	${WRKDIR}/src
 GO_WRKSRC=	${GO_WRKDIR_SRC}/${GO_PKGNAME}
 GO_ENV+=	GOPATH="${WRKDIR}" \
 		GOBIN=""
 .endif
 
 GO_PORT?=	lang/go
 BUILD_DEPENDS+=	${GO_CMD}:${GO_PORT}
 .if ${go_ARGS:Mrun}
 RUN_DEPENDS+=	${GO_CMD}:${GO_PORT}
 .endif
 
 _USES_POST+=	go
 .endif # !defined(_INCLUDE_USES_GO_MK)
 
 .if defined(_POSTMKINCLUDED) && !defined(_INCLUDE_USES_GO_POST_MK)
 _INCLUDE_USES_GO_POST_MK=	yes
 
 .if !target(post-extract) && empty(go_ARGS)
 post-extract:
 	@${MKDIR} ${GO_WRKSRC:H}
 	@${LN} -sf ${WRKSRC} ${GO_WRKSRC}
 .endif
 
 .if !target(do-build) && empty(go_ARGS:Mno_targets)
 do-build:
 	(cd ${GO_WRKSRC}; \
 		${SETENV} ${MAKE_ENV} ${GO_ENV} ${GO_CMD} install ${GO_BUILDFLAGS} ${GO_TARGET:S/^${PORTNAME}$/./})
 .endif
 
 .if !target(do-install) && empty(go_ARGS:Mno_targets)
 do-install:
 .for _TARGET in ${GO_TARGET}
 	${INSTALL_PROGRAM} ${GO_WRKDIR_BIN}/${_TARGET:T:S/^.$/${PORTNAME}/} ${STAGEDIR}${PREFIX}/bin
 .endfor
 .endif
 
+# Helper targets for port maintainers
+
+.if ${go_ARGS:Mmodules}
+_MODULES2TUPLE_CMD=	modules2tuple
+gomod-vendor: patch
+	@if type ${_MODULES2TUPLE_CMD} > /dev/null 2>&1; then \
+		cd ${WRKSRC}; ${GO_CMD} mod vendor; \
+		[ -r vendor/modules.txt ] && ${_MODULES2TUPLE_CMD} vendor/modules.txt; \
+	else \
+		${ECHO_MSG} "===> Please install \"ports-mgmt/modules2tuple\""; \
+	fi
+.endif
+
 .endif # defined(_POSTMKINCLUDED) && !defined(_INCLUDE_USES_GO_POST_MK)