Support dependencies on environment variables

Ninja can't depend on environment variables, so modifying build
behavior based on environment variables requires coordinating
between the soong script that invokes ninja and the soong_build
manifest generator.

Allow any module to call Config.Getenv to get the contents of an
environment variable while registering a dependency on it.
After all modules have been processed write out the state of
all used environment variables to a JSON file called
.soong.environment.  During the next build the soong script
will use the soong_env tool to compare the contents of
.soong.environment to the current environment, and force a
build manifest regeneration by deleting the .soong.environment
file if any variables have changed.

Change-Id: Id0d81933a857bc2fc1cd7a393a3c6cec73dc4824

2 files changed, 56 insertions, 0 deletions

diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index b84b804c..cb579e9c 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -64,6 +64,7 @@ func main() {
 
 	// Singletons
 	ctx.RegisterSingletonType("checkbuild", common.CheckbuildSingleton)
+	ctx.RegisterSingletonType("env", common.EnvSingleton)
 
 	configuration, err := config.New(srcDir)
 	if err != nil {
diff --git a/cmd/soong_env/soong_env.go b/cmd/soong_env/soong_env.go
new file mode 100644
index 00000000..933e525a
--- /dev/null
+++ b/cmd/soong_env/soong_env.go
@@ -0,0 +1,55 @@
+// 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.
+
+// soong_glob is the command line tool that checks if the list of files matching a glob has
+// changed, and only updates the output file list if it has changed.  It is used to optimize
+// out build.ninja regenerations when non-matching files are added.  See
+// android/soong/common/glob.go for a longer description.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"android/soong/env"
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "usage: soong_env env_file\n")
+	fmt.Fprintf(os.Stderr, "exits with success if the environment varibles in env_file match\n")
+	fmt.Fprintf(os.Stderr, "the current environment\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func main() {
+	flag.Parse()
+
+	if flag.NArg() != 1 {
+		usage()
+	}
+
+	stale, err := env.StaleEnvFile(flag.Arg(0))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %s\n", err.Error())
+		os.Exit(1)
+	}
+
+	if stale {
+		os.Exit(1)
+	}
+
+	os.Exit(0)
+}