Allow microfactory to be used as a package

In addition to running with `go run` and creating a microfactory binary,
allow microfactory to be used as a package from other go tools as well.

To allow other packages to use this, it needs to be in a non-main
package, but `go run` requires a main package. So microfactory.bash runs
a sed script before running microfactory with `go run`.

This could also be solved by using a relative import, but neither
blueprint nor microfactory currently support that.

Change-Id: I084163b14720102b3fb93a3c9d44b5d0225ff2c8

Blueprints

@@ -176,6 +176,13 @@ bootstrap_go_binary{
 
 blueprint_go_binary {
     name: "microfactory",
+    deps: ["blueprint-microfactory"],
+    srcs: ["microfactory/main/main.go"],
+}
+
+bootstrap_go_package {
+    name: "blueprint-microfactory",
+    pkgPath: "github.com/google/blueprint/microfactory",
     srcs: ["microfactory/microfactory.go"],
     testSrcs: ["microfactory/microfactory_test.go"],
 }

microfactory/main/main.go

@@ -0,0 +1,23 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"github.com/google/blueprint/microfactory"
+)
+
+func main() {
+	microfactory.Main()
+}

microfactory/microfactory.bash

@@ -47,7 +47,12 @@ function build_go
 
     local mf_cmd
     if [ $from_src -eq 1 ]; then
-        mf_cmd="${GOROOT}/bin/go run ${mf_src}/microfactory.go"
+        # `go run` requires a single main package, so create one
+        local gen_src_dir="${BUILDDIR}/.microfactory_$(uname)_intermediates/src"
+        mkdir -p "${gen_src_dir}"
+        sed "s/^package microfactory/package main/" "${mf_src}/microfactory.go" >"${gen_src_dir}/microfactory.go"
+
+        mf_cmd="${GOROOT}/bin/go run ${gen_src_dir}/microfactory.go"
     else
         mf_cmd="${mf_bin}"
     fi

microfactory/microfactory.go

@@ -39,7 +39,7 @@
 // Combined with a shell script like microfactory.bash that uses `go run` to
 // run Microfactory for the first time, go programs can be quickly bootstrapped
 // entirely from source (and a standard go distribution).
-package main
+package microfactory
 
 import (
 	"bytes"
@@ -430,7 +430,7 @@ func (p *GoPackage) Link(out string) error {
 // and if does, it will launch a new copy and return true. Otherwise it will return
 // false to continue executing.
 func rebuildMicrofactory(mybin string, pkgMap *pkgPathMapping) bool {
-	mysrc, ok, err := pkgMap.Path("github.com/google/blueprint/microfactory")
+	mysrc, ok, err := pkgMap.Path("github.com/google/blueprint/microfactory/main")
 	if err != nil {
 		fmt.Println(os.Stderr, "Error finding microfactory source:", err)
 		os.Exit(1)
@@ -501,7 +501,9 @@ func un(f func()) {
 	f()
 }
 
-func main() {
+// microfactory.bash will make a copy of this file renamed into the main package for use with `go run`
+func main() { Main() }
+func Main() {
 	var output, mybin, trimPath string
 	var pkgMap pkgPathMapping
 

microfactory/microfactory_test.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package main
+package microfactory
 
 import (
 	"flag"