Add soong_build primary builder

Initial build logic for building android with soong.  It can build
a variety of C and C++ files for arm/arm64 and host.

Change-Id: I10eb37c2c2a50be6af1bb5fd568c0962b9476bf0
diff --git a/config/config.go b/config/config.go
new file mode 100644
index 0000000..6cdc211
--- /dev/null
+++ b/config/config.go
@@ -0,0 +1,152 @@
+// Copyright 2015 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 config
+
+import (
+	"android/soong/common"
+	"encoding/json"
+	"fmt"
+	"os"
+	"runtime"
+)
+
+var _ common.Config = (*Config)(nil)
+
+// The configuration file name
+const ConfigFileName = "soong.config"
+
+// A FileConfigurableOptions contains options which can be configured by the
+// config file. These will be included in the config struct.
+type FileConfigurableOptions struct {
+}
+
+func NewFileConfigurableOptions() FileConfigurableOptions {
+	f := FileConfigurableOptions{}
+	return f
+}
+
+// A Config object represents the entire build configuration for Blue.
+type Config struct {
+	FileConfigurableOptions
+
+	srcDir string // the path of the root source directory
+}
+
+// loads configuration options from a JSON file in the cwd.
+func loadFromConfigFile(config *Config) error {
+	// Make a proxy config
+	var configProxy FileConfigurableOptions
+
+	// Try to open the file
+	configFileReader, err := os.Open(ConfigFileName)
+	defer configFileReader.Close()
+	if os.IsNotExist(err) {
+		// Need to create a file, so that blueprint & ninja don't get in
+		// a dependency tracking loop.
+		// Make a file-configurable-options with defaults, write it out using
+		// a json writer.
+		configProxy = NewFileConfigurableOptions()
+		err = saveToConfigFile(configProxy)
+		if err != nil {
+			return err
+		}
+	} else {
+		// Make a decoder for it
+		jsonDecoder := json.NewDecoder(configFileReader)
+		err = jsonDecoder.Decode(&configProxy)
+		if err != nil {
+			return fmt.Errorf("config file: %s did not parse correctly: "+err.Error(), ConfigFileName)
+		}
+	}
+
+	// Copy the configurable options out of the config_proxy into the config,
+	// and we're done!
+	config.FileConfigurableOptions = configProxy
+
+	// No error
+	return nil
+}
+
+func saveToConfigFile(config FileConfigurableOptions) error {
+	data, err := json.MarshalIndent(&config, "", "    ")
+	if err != nil {
+		return fmt.Errorf("cannot marshal config data: %s", err.Error())
+	}
+
+	configFileWriter, err := os.Create(ConfigFileName)
+	if err != nil {
+		return fmt.Errorf("cannot create empty config file %s: %s\n", ConfigFileName, err.Error())
+	}
+	defer configFileWriter.Close()
+
+	_, err = configFileWriter.Write(data)
+	if err != nil {
+		return fmt.Errorf("default config file: %s could not be written: %s", ConfigFileName, err.Error())
+	}
+
+	return nil
+}
+
+// New creates a new Config object.  The srcDir argument specifies the path to
+// the root source directory. It also loads the config file, if found.
+func New(srcDir string) (*Config, error) {
+	// Make a config with default options
+	config := &Config{srcDir: srcDir}
+
+	// Load any configurable options from the configuration file
+	err := loadFromConfigFile(config)
+	if err != nil {
+		return nil, err
+	}
+
+	return config, nil
+}
+
+func (c *Config) SrcDir() string {
+	return c.srcDir
+}
+
+// HostGoOS returns the OS of the system that the Go toolchain is being run on.
+func (c *Config) HostGoOS() string {
+	return runtime.GOOS
+}
+
+// PrebuiltOS returns the name of the host OS used in prebuilts directories
+func (c *Config) PrebuiltOS() string {
+	switch runtime.GOOS {
+	case "linux":
+		return "linux-x86"
+	case "darwin":
+		return "darwin-x86"
+	default:
+		panic("Unknown GOOS")
+	}
+}
+
+// GoRoot returns the path to the root directory of the Go toolchain.
+func (c *Config) GoRoot() string {
+	return fmt.Sprintf("%s/prebuilts/go/%s", c.srcDir, c.PrebuiltOS())
+}
+
+func (c *Config) CpPreserveSymlinksFlags() string {
+	switch c.HostGoOS() {
+	case "darwin":
+		return "-R"
+	case "linux":
+		return "-d"
+	default:
+		return ""
+	}
+}