build: require Go >= 1.7

We have decided to bump the requirement to Go 1.7 because it enables
subtests and allows dropping backwards-compatibility code. This is in
line with Go's support policy. Go 1.6 and earlier no longer receive
security updates.

.travis.yml

@@ -3,14 +3,6 @@ go_import_path: github.com/ethereum/go-ethereum
 sudo: false
 matrix:
   include:
-    - os: linux
-      dist: trusty
-      go: 1.5.4
-      env:
-        - GO15VENDOREXPERIMENT=1
-    - os: linux
-      dist: trusty
-      go: 1.6.2
     - os: linux
       dist: trusty
       go: 1.7.5

README.md

@@ -16,7 +16,7 @@ For prerequisites and detailed build instructions please read the
 [Installation Instructions](https://github.com/ethereum/go-ethereum/wiki/Building-Ethereum)
 on the wiki.
 
-Building geth requires both a Go and a C compiler.
+Building geth requires both a Go (version 1.7 or later) and a C compiler.
 You can install them using your favourite package manager.
 Once the dependencies are installed, run
 

build/ci.go

@@ -162,9 +162,9 @@ func doInstall(cmdline []string) {
 
 	// Check Go version. People regularly open issues about compilation
 	// failure with outdated Go. This should save them the trouble.
-	if runtime.Version() < "go1.4" && !strings.HasPrefix(runtime.Version(), "devel") {
+	if runtime.Version() < "go1.7" && !strings.HasPrefix(runtime.Version(), "devel") {
 		log.Println("You have Go version", runtime.Version())
-		log.Println("go-ethereum requires at least Go version 1.4 and cannot")
+		log.Println("go-ethereum requires at least Go version 1.7 and cannot")
 		log.Println("be compiled with an earlier version. Please upgrade your Go installation.")
 		os.Exit(1)
 	}
@@ -219,16 +219,9 @@ func buildFlags(env build.Environment) (flags []string) {
 		flags = append(flags, "-tags", "opencl")
 	}
 
-	// Since Go 1.5, the separator char for link time assignments
-	// is '=' and using ' ' prints a warning. However, Go < 1.5 does
-	// not support using '='.
-	sep := " "
-	if runtime.Version() > "go1.5" || strings.Contains(runtime.Version(), "devel") {
-		sep = "="
-	}
 	// Set gitCommit constant via link-time assignment.
 	if env.Commit != "" {
-		flags = append(flags, "-ldflags", "-X main.gitCommit"+sep+env.Commit)
+		flags = append(flags, "-ldflags", "-X main.gitCommit="+env.Commit)
 	}
 	return flags
 }
@@ -249,10 +242,7 @@ func goToolArch(arch string, subcmd string, args ...string) *exec.Cmd {
 			cmd.Args = append(cmd.Args, []string{"-ldflags", "-extldflags -Wl,--allow-multiple-definition"}...)
 		}
 	}
-	cmd.Env = []string{
-		"GO15VENDOREXPERIMENT=1",
-		"GOPATH=" + build.GOPATH(),
-	}
+	cmd.Env = []string{"GOPATH=" + build.GOPATH()}
 	if arch == "" || arch == runtime.GOARCH {
 		cmd.Env = append(cmd.Env, "GOBIN="+GOBIN)
 	} else {

build/env.sh

@@ -20,8 +20,7 @@ fi
 
 # Set up the environment to use the workspace.
 GOPATH="$workspace"
-GO15VENDOREXPERIMENT=1
-export GOPATH GO15VENDOREXPERIMENT
+export GOPATH
 
 # Run the command inside the workspace.
 cd "$ethdir/go-ethereum"