Experimental: read and write build files in alternate directories (#286)

* The flags -experimental_{read,write}_build_files_dir may now be used
  to read and write build files to alternate directories, which may be
  outside of the repository root.
* When a build file is read from an alternate directory, the build
  file in the source directory is ignored.
* When a build file is written to an alternate directory, any existing
  build file in that directory is replaced. The build file in the
  source directory is not updated.

cmd/gazelle/diff.go

@@ -20,21 +20,18 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
-
-	"github.com/bazelbuild/bazel-gazelle/internal/config"
-	bzl "github.com/bazelbuild/buildtools/build"
+	"path/filepath"
 )
 
-func diffFile(c *config.Config, file *bzl.File, path string) error {
-	oldContents, err := ioutil.ReadFile(file.Path)
+func diffFile(path string, newContents []byte) error {
+	oldContents, err := ioutil.ReadFile(path)
 	if err != nil {
 		oldContents = nil
 	}
-	newContents := bzl.Format(file)
 	if bytes.Equal(oldContents, newContents) {
 		return nil
 	}
-	f, err := ioutil.TempFile("", c.DefaultBuildFileName())
+	f, err := ioutil.TempFile("", filepath.Base(path))
 	if err != nil {
 		return err
 	}

cmd/gazelle/fix-update.go

@@ -18,6 +18,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -31,19 +32,17 @@ import (
 	"github.com/bazelbuild/bazel-gazelle/internal/resolve"
 	"github.com/bazelbuild/bazel-gazelle/internal/rule"
 	"github.com/bazelbuild/bazel-gazelle/internal/walk"
-	bzl "github.com/bazelbuild/buildtools/build"
 )
 
 // updateConfig holds configuration information needed to run the fix and
 // update commands. This includes everything in config.Config, but it also
 // includes some additional fields that aren't relevant to other packages.
 type updateConfig struct {
-	emit              emitFunc
-	outDir, outSuffix string
-	repos             []repos.Repo
+	emit  emitFunc
+	repos []repos.Repo
 }
 
-type emitFunc func(*config.Config, *bzl.File, string) error
+type emitFunc func(path string, data []byte) error
 
 var modeFromName = map[string]emitFunc{
 	"print": printFile,
@@ -68,8 +67,6 @@ func (ucr *updateConfigurer) RegisterFlags(fs *flag.FlagSet, cmd string, c *conf
 	c.ShouldFix = cmd == "fix"
 
 	fs.StringVar(&ucr.mode, "mode", "fix", "print: prints all of the updated BUILD files\n\tfix: rewrites all of the BUILD files in place\n\tdiff: computes the rewrite but then just does a diff")
-	fs.StringVar(&uc.outDir, "experimental_out_dir", "", "write build files to an alternate directory tree")
-	fs.StringVar(&uc.outSuffix, "experimental_out_suffix", "", "extra suffix appended to build file names. Only used if -experimental_out_dir is also set.")
 }
 
 func (ucr *updateConfigurer) CheckFlags(fs *flag.FlagSet, c *config.Config) error {
@@ -198,7 +195,7 @@ func runFixUpdate(cmd command, args []string) error {
 
 		// Insert or merge rules into the build file.
 		if f == nil {
-			f = rule.EmptyFile(filepath.Join(dir, c.DefaultBuildFileName()))
+			f = rule.EmptyFile(filepath.Join(dir, c.DefaultBuildFileName()), rel)
 			for _, r := range gen {
 				r.Insert(f)
 			}
@@ -236,15 +233,9 @@ func runFixUpdate(cmd command, args []string) error {
 	// Emit merged files.
 	for _, v := range visits {
 		merger.FixLoads(v.file, loads)
-		v.file.Sync()
-		bzl.Rewrite(v.file.File, nil) // have buildifier 'format' our rules.
-
-		path := v.file.Path
-		if uc.outDir != "" {
-			stem := filepath.Base(v.file.Path) + uc.outSuffix
-			path = filepath.Join(uc.outDir, v.pkgRel, stem)
-		}
-		if err := uc.emit(c, v.file.File, path); err != nil {
+		content := v.file.Format()
+		outputPath := findOutputPath(c, v.file)
+		if err := uc.emit(outputPath, content); err != nil {
 			log.Print(err)
 		}
 	}
@@ -269,7 +260,7 @@ func newFixUpdateConfiguration(cmd command, args []string, cexts []config.Config
 	if err := fs.Parse(args); err != nil {
 		if err == flag.ErrHelp {
 			fixUpdateUsage(fs)
-			os.Exit(0)
+			return nil, err
 		}
 		// flag already prints the error; don't print it again.
 		log.Fatal("Try -help for more information.")
@@ -283,7 +274,7 @@ func newFixUpdateConfiguration(cmd command, args []string, cexts []config.Config
 
 	uc := getUpdateConfig(c)
 	workspacePath := filepath.Join(c.RepoRoot, "WORKSPACE")
-	if workspace, err := rule.LoadFile(workspacePath); err != nil {
+	if workspace, err := rule.LoadFile(workspacePath, ""); err != nil {
 		if !os.IsNotExist(err) {
 			return nil, err
 		}
@@ -361,8 +352,7 @@ func fixWorkspace(c *config.Config, workspace *rule.File, loads []rule.LoadInfo)
 	if err := merger.CheckGazelleLoaded(workspace); err != nil {
 		return err
 	}
-	workspace.Sync()
-	return uc.emit(c, workspace.File, workspace.Path)
+	return uc.emit(workspace.Path, workspace.Format())
 }
 
 func findWorkspaceName(f *rule.File) string {
@@ -384,3 +374,25 @@ func isDescendingDir(dir, root string) bool {
 	}
 	return !strings.HasPrefix(rel, "..")
 }
+
+func findOutputPath(c *config.Config, f *rule.File) string {
+	if c.ReadBuildFilesDir == "" && c.WriteBuildFilesDir == "" {
+		return f.Path
+	}
+	baseDir := c.WriteBuildFilesDir
+	if c.WriteBuildFilesDir == "" {
+		baseDir = c.RepoRoot
+	}
+	outputDir := filepath.Join(baseDir, filepath.FromSlash(f.Pkg))
+	defaultOutputPath := filepath.Join(outputDir, c.DefaultBuildFileName())
+	files, err := ioutil.ReadDir(outputDir)
+	if err != nil {
+		// Ignore error. Directory probably doesn't exist.
+		return defaultOutputPath
+	}
+	outputPath := rule.MatchBuildFileName(outputDir, c.ValidBuildFileNames, files)
+	if outputPath == "" {
+		return defaultOutputPath
+	}
+	return outputPath
+}

cmd/gazelle/fix.go

@@ -19,17 +19,11 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
-
-	"github.com/bazelbuild/bazel-gazelle/internal/config"
-	bzl "github.com/bazelbuild/buildtools/build"
 )
 
-func fixFile(c *config.Config, file *bzl.File, path string) error {
+func fixFile(path string, data []byte) error {
 	if err := os.MkdirAll(filepath.Dir(path), 0777); err != nil {
 		return err
 	}
-	if err := ioutil.WriteFile(path, bzl.Format(file), 0666); err != nil {
-		return err
-	}
-	return nil
+	return ioutil.WriteFile(path, data, 0666)
 }

cmd/gazelle/fix_test.go

@@ -20,9 +20,9 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
-	"github.com/bazelbuild/bazel-gazelle/internal/config"
 	bzl "github.com/bazelbuild/buildtools/build"
 )
 
@@ -63,9 +63,7 @@ func TestFixFile(t *testing.T) {
 			},
 		},
 	}
-	c := &config.Config{}
-
-	if err := fixFile(c, stubFile, stubFile.Path); err != nil {
+	if err := fixFile(stubFile.Path, bzl.Format(stubFile)); err != nil {
 		t.Errorf("fixFile(%#v) failed with %v; want success", stubFile, err)
 		return
 	}
@@ -134,3 +132,157 @@ func TestUpdateFile(t *testing.T) {
 		t.Errorf("BUILD.bazel should not exist")
 	}
 }
+
+func TestReadWriteDir(t *testing.T) {
+	buildInFile := fileSpec{
+		path: "in/BUILD.in",
+		content: `
+go_binary(
+    name = "hello",
+    pure = "on",
+)
+`,
+	}
+	buildSrcFile := fileSpec{
+		path:    "src/BUILD.bazel",
+		content: `# src build file`,
+	}
+	oldFiles := []fileSpec{
+		buildInFile,
+		buildSrcFile,
+		{
+			path: "src/hello.go",
+			content: `
+package main
+
+func main() {}
+`,
+		}, {
+			path:    "out/BUILD",
+			content: `this should get replaced`,
+		},
+	}
+
+	for _, tc := range []struct {
+		desc string
+		args []string
+		want []fileSpec
+	}{
+		{
+			desc: "read",
+			args: []string{
+				"-repo_root={{dir}}/src",
+				"-experimental_read_build_files_dir={{dir}}/in",
+				"-build_file_name=BUILD.bazel,BUILD,BUILD.in",
+				"-go_prefix=example.com/repo",
+				"{{dir}}/src",
+			},
+			want: []fileSpec{
+				buildInFile,
+				{
+					path: "src/BUILD.bazel",
+					content: `
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_binary(
+    name = "hello",
+    embed = [":go_default_library"],
+    pure = "on",
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = ["hello.go"],
+    importpath = "example.com/repo",
+    visibility = ["//visibility:private"],
+)
+`,
+				},
+			},
+		}, {
+			desc: "write",
+			args: []string{
+				"-repo_root={{dir}}/src",
+				"-experimental_write_build_files_dir={{dir}}/out",
+				"-build_file_name=BUILD.bazel,BUILD,BUILD.in",
+				"-go_prefix=example.com/repo",
+				"{{dir}}/src",
+			},
+			want: []fileSpec{
+				buildInFile,
+				buildSrcFile,
+				{
+					path: "out/BUILD",
+					content: `
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+# src build file
+
+go_library(
+    name = "go_default_library",
+    srcs = ["hello.go"],
+    importpath = "example.com/repo",
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "repo",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)
+`,
+				},
+			},
+		}, {
+			desc: "read_and_write",
+			args: []string{
+				"-repo_root={{dir}}/src",
+				"-experimental_read_build_files_dir={{dir}}/in",
+				"-experimental_write_build_files_dir={{dir}}/out",
+				"-build_file_name=BUILD.bazel,BUILD,BUILD.in",
+				"-go_prefix=example.com/repo",
+				"{{dir}}/src",
+			},
+			want: []fileSpec{
+				buildInFile,
+				{
+					path: "out/BUILD",
+					content: `
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_binary(
+    name = "hello",
+    embed = [":go_default_library"],
+    pure = "on",
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = ["hello.go"],
+    importpath = "example.com/repo",
+    visibility = ["//visibility:private"],
+)
+`,
+				},
+			},
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			dir, err := createFiles(oldFiles)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer os.RemoveAll(dir)
+			replacer := strings.NewReplacer("{{dir}}", dir, "/", string(os.PathSeparator))
+			for i := range tc.args {
+				tc.args[i] = replacer.Replace(tc.args[i])
+			}
+			if err := run(tc.args); err != nil {
+				t.Error(err)
+			}
+			checkFiles(t, dir, tc.want)
+		})
+	}
+}

cmd/gazelle/gazelle.go

@@ -18,6 +18,7 @@ limitations under the License.
 package main
 
 import (
+	"flag"
 	"fmt"
 	"log"
 	"os"
@@ -76,7 +77,7 @@ func run(args []string) error {
 	case fixCmd, updateCmd:
 		return runFixUpdate(cmd, args)
 	case helpCmd:
-		help()
+		return help()
 	case updateReposCmd:
 		return updateRepos(args)
 	default:
@@ -85,7 +86,7 @@ func run(args []string) error {
 	return nil
 }
 
-func help() {
+func help() error {
 	fmt.Fprint(os.Stderr, `usage: gazelle <command> [args...]
 
 Gazelle is a BUILD file generator for Go projects. It can create new BUILD files
@@ -115,4 +116,5 @@ Gazelle is under active delevopment, and its interface may change
 without notice.
 
 `)
+	return flag.ErrHelp
 }