package/pkg-golang: use 'build' instead of 'install'

So far, we were using the 'go install' mechanism to build a package
and have its binary installed in
$$($(2)_WORKSPACE)/bin/linux_$$(GO_GOARCH). This worked fine when
building on x86-64 for ARM, but failed when building on x86-64 for
x86-64 because the binaries were installed in $$($(2)_WORKSPACE)/bin/.

Instead of doing some complicated logic to guess whether Go is going
to put our binaries in $$($(2)_WORKSPACE)/bin/ or in
$$($(2)_WORKSPACE)/bin/linux_$$(GO_GOARCH), we revert back to using
"go build", as it was done before the introduction of the golang
package infrastructure. "go build" lets us pass explicitly the
destination path of the binary to be generated.

There's just one complexity with how to decide on the name of the
binary that should be produced, and we have two cases:

 - <pkg>_BUILD_TARGETS is the default, i.e ".". In this case we assume
   a single binary is produced by "go build", and we name if after the
   lower case package name. We allow this to be overridden thanks to
   <pkg>_BIN_NAME.

 - <pkg>_BUILD_TARGETS is non-default, and typically contains
   something like "foo bar" or "cmd/foo cmd/bar". In this case, we
   assume the binaries to be produced are "foo" and "bar", i.e we take
   the non-directory part of the build target to name the binaries.

Because we're using this -o option, we no longer need to explicitly
create the binary directory, it is done by "go build".

Fixes:

  http://autobuild.buildroot.net/results/1f9cd7c48e8c8f41326632a9c0de83915d72c45b/

[Peter: use $(or instead of $(if as suggested by Arnout]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-golang.txt

@@ -86,7 +86,18 @@ therefore only use a few of them, or none.
 
 * +FOO_BUILD_TARGETS+ can be used to pass the list of targets that
   should be built. If +FOO_BUILD_TARGETS+ is not specified, it
-  defaults to +.+.
+  defaults to +.+. We then have two cases:
+
+** +FOO_BUILD_TARGETS+ is +.+. In this case, we assume only one binary
+   will be produced, and that by default we name it after the package
+   name. If that is not appropriate, the name of the produced binary
+   can be overridden using +FOO_BIN_NAME+.
+
+** +FOO_BUILD_TARGETS+ is not +.+. In this case, we iterate over the
+   values to build each target, and for each produced a binary that is
+   the non-directory component of the target. For example if
+   +FOO_BUILD_TARGETS = cmd/docker cmd/dockerd+ the binaries produced
+   are +docker+ and +dockerd+.
 
 * +FOO_INSTALL_BINS+ can be used to pass the list of binaries that
   should be installed in +/usr/bin+ on the target. If

package/pkg-golang.mk

@@ -62,12 +62,16 @@ $(2)_DEPENDENCIES += host-go
 
 $(2)_BUILD_TARGETS ?= .
 
-$(2)_INSTALL_BINS ?= $(1)
+# If the build target is just ".", then we assume the binary to be
+# produced is named after the package. If however, a build target has
+# been specified, we assume that the binaries to be produced are named
+# after each build target building them (below in <pkg>_BUILD_CMDS).
+ifeq ($$($(2)_BUILD_TARGETS),.)
+$(2)_BIN_NAME ?= $(1)
+endif
 
-# The go build/install command installs the binaries inside
-# gopath/bin/linux_GOARCH/ when cross compilation is enabled. We set this
-# variable here to be used by packages if needed.
-$(2)_BINDIR = $$($(2)_WORKSPACE)/bin/linux_$$(GO_GOARCH)
+$(2)_BINDIR = bin
+$(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
@@ -84,17 +88,13 @@ $(2)_SRC_PATH = $$(@D)/$$($(2)_WORKSPACE)/src/$$($(2)_SRC_SUBDIR)
 # file.
 ifndef $(2)_CONFIGURE_CMDS
 define $(2)_CONFIGURE_CMDS
-	mkdir -p $$(@D)/$$($(2)_WORKSPACE)/bin
 	mkdir -p $$(dir $$($(2)_SRC_PATH))
 	ln -sf $$(@D) $$($(2)_SRC_PATH)
 endef
 endif
 
-# Build step. Only define it if not already defined by the package .mk file. We
-# use the install command instead of build command here because the install
-# command just moves the package binaries into <workspace>/bin/linux_GOARCH/.
-# This leverages the go build infrastructure for building and installing
-# multiple binaries.
+# Build step. Only define it if not already defined by the package .mk
+# file.
 ifndef $(2)_BUILD_CMDS
 define $(2)_BUILD_CMDS
 	$$(foreach d,$$($(2)_BUILD_TARGETS),\
@@ -102,7 +102,9 @@ define $(2)_BUILD_CMDS
 		$$(GO_TARGET_ENV) \
 			GOPATH="$$(@D)/$$($(2)_WORKSPACE)" \
 			$$($(2)_GO_ENV) \
-			$$(GO_BIN) install -v $$($(2)_BUILD_OPTS) ./$$(d)
+			$$(GO_BIN) build -v $$($(2)_BUILD_OPTS) \
+			-o $$(@D)/$$($(2)_BINDIR)/$$(or $$($(2)_BIN_NAME),$$(notdir $$(d))) \
+			./$$(d)
 	)
 endef
 endif