find bazel-related files and add them to bazel.list and ninja deps

This retriggers soong_build whenever a new bzl, WORKSPACE, or
BUILD.bazel file is changed or added.

Test: Manually verified on bionic/libc genrules with manual changes to
related BUILD/bzl/WORKSPACE files -- these all retrigger builds.
Test: Updated finder_test.go

Change-Id: I634384f88781a6b6db32f5d6bf9c07e179e14c39

ui/build/finder.go

@@ -63,10 +63,13 @@ func NewSourceFinder(ctx Context, config Config) (f *finder.Finder) {
 			"AndroidProducts.mk",
 			"Android.bp",
 			"Blueprints",
+			"BUILD.bazel",
 			"CleanSpec.mk",
 			"OWNERS",
 			"TEST_MAPPING",
+			"WORKSPACE",
 		},
+		IncludeSuffixes: []string{".bzl"},
 	}
 	dumpDir := config.FileListDir()
 	f, err = finder.New(cacheParams, filesystem, logger.New(ioutil.Discard),
@@ -77,6 +80,16 @@ func NewSourceFinder(ctx Context, config Config) (f *finder.Finder) {
 	return f
 }
 
+func findBazelFiles(entries finder.DirEntries) (dirNames []string, fileNames []string) {
+	matches := []string{}
+	for _, foundName := range entries.FileNames {
+		if foundName == "BUILD.bazel" || foundName == "WORKSPACE" || strings.HasSuffix(foundName, ".bzl") {
+			matches = append(matches, foundName)
+		}
+	}
+	return entries.DirNames, matches
+}
+
 // FindSources searches for source files known to <f> and writes them to the filesystem for
 // use later.
 func FindSources(ctx Context, config Config, f *finder.Finder) {
@@ -99,6 +112,12 @@ func FindSources(ctx Context, config Config, f *finder.Finder) {
 		ctx.Fatalf("Could not export product list: %v", err)
 	}
 
+	bazelFiles := f.FindMatching(".", findBazelFiles)
+	err = dumpListToFile(ctx, config, bazelFiles, filepath.Join(dumpDir, "bazel.list"))
+	if err != nil {
+		ctx.Fatalf("Could not export bazel BUILD list: %v", err)
+	}
+
 	cleanSpecs := f.FindFirstNamedAt(".", "CleanSpec.mk")
 	err = dumpListToFile(ctx, config, cleanSpecs, filepath.Join(dumpDir, "CleanSpec.mk.list"))
 	if err != nil {