After bazel execution, symlink results in out/

This ensures that USE_BAZEL=1 mode has the same directory structure
under out/ as it does without USE_BAZEL=1.

Test: Manually verified building USE_BAZEL=1 aosp_flame with droid and
libc

Change-Id: I27e810772d1bf04bd7930ea122217b93d2fd48b4

ui/build/bazel.go

@@ -15,6 +15,8 @@
 package build
 
 import (
+	"io/ioutil"
+	"os"
 	"path/filepath"
 	"strings"
 )
@@ -51,4 +53,57 @@ func runBazel(ctx Context, config Config) {
 	cmd.Dir = filepath.Join(config.OutDir(), "..")
 	ctx.Status.Status("Starting Bazel..")
 	cmd.RunAndStreamOrFatal()
+
+	// Obtain the Bazel output directory for ninja_build.
+	infoArgs := []string{
+		"info",
+		"output_path",
+	}
+
+	infoCmd := Command(ctx, config, "bazel", bazelExecutable, infoArgs...)
+
+	infoCmd.Environment.Set("DIST_DIR", config.DistDir())
+	infoCmd.Environment.Set("SHELL", "/bin/bash")
+	infoCmd.Dir = filepath.Join(config.OutDir(), "..")
+	ctx.Status.Status("Getting Bazel Info..")
+	outputBasePath := string(infoCmd.OutputOrFatal())
+	// TODO: Don't hardcode out/ as the bazel output directory. This is
+	// currently hardcoded as ninja_build.output_root.
+	bazelNinjaBuildOutputRoot := filepath.Join(outputBasePath, "..", "out")
+
+	symlinkOutdir(ctx, config, bazelNinjaBuildOutputRoot, ".")
+}
+
+// For all files F recursively under rootPath/relativePath, creates symlinks
+// such that OutDir/F resolves to rootPath/F via symlinks.
+func symlinkOutdir(ctx Context, config Config, rootPath string, relativePath string) {
+	destDir := filepath.Join(rootPath, relativePath)
+	os.MkdirAll(destDir, 0755)
+	files, err := ioutil.ReadDir(destDir)
+	if err != nil {
+		ctx.Fatal(err)
+	}
+	for _, f := range files {
+		destPath := filepath.Join(destDir, f.Name())
+		srcPath := filepath.Join(config.OutDir(), relativePath, f.Name())
+		if statResult, err := os.Stat(srcPath); err == nil {
+			if statResult.Mode().IsDir() && f.IsDir() {
+				// Directory under OutDir already exists, so recurse on its contents.
+				symlinkOutdir(ctx, config, rootPath, filepath.Join(relativePath, f.Name()))
+			} else if !statResult.Mode().IsDir() && !f.IsDir() {
+				// File exists both in source and destination, and it's not a directory
+				// in either location. Do nothing.
+				// This can arise for files which are generated under OutDir outside of
+				// soong_build, such as .bootstrap files.
+			} else {
+				// File is a directory in one location but not the other. Raise an error.
+				ctx.Fatalf("Could not link %s to %s due to conflict", srcPath, destPath)
+			}
+		} else if os.IsNotExist(err) {
+			// Create symlink srcPath -> fullDestPath.
+			os.Symlink(destPath, srcPath)
+		} else {
+			ctx.Fatalf("Unable to stat %s: %s", srcPath, err)
+		}
+	}
 }