Merge pull request #4678 from ipfs/fix/gopath-default

build: match Go's GOPATH defaults behaviour

bin/check_go_path

@@ -7,11 +7,6 @@ if [ -z "$PWD" ]; then
 	exit 1
 fi
 
-if [ -z "$GOPATH" ]; then
-	echo "GOPATH not set, you must have go configured properly to install ipfs"
-	exit 1
-fi
-
 while [ ${#} -gt 1 ]; do
 	if [ "$PWD" = "$2" ]; then
 		exit 0
@@ -20,5 +15,5 @@ while [ ${#} -gt 1 ]; do
 done
 
 echo "go-ipfs must be built from within your \$GOPATH directory."
-echo "expected within '$GOPATH' but got '$PWD'"
+echo "expected within '$(go env GOPATH)' but got '$PWD'"
 exit 1

mk/golang.mk

 # golang utilities
 GO_MIN_VERSION = 1.9
 
+
 # pre-definitions
 GOCC ?= go
 GOTAGS ?=
 GOFLAGS ?=
 GOTFLAGS ?=
 
+# match Go's default GOPATH behaviour
+export GOPATH ?= $(shell $(GOCC) env GOPATH)
+
 DEPS_GO :=
 TEST_GO :=
 TEST_GO_BUILD :=