Make output modes configurable

Added "fix" and "diff" modes

go/tools/gazel/gazel/BUILD

@@ -1,10 +1,27 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_binary")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_binary", "go_test")
 
-go_binary(
-    name = "gazel",
-    srcs = ["main.go"],
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "diff.go",
+        "fix.go",
+        "main.go",
+        "print.go",
+    ],
     deps = [
         "@io_bazel_buildifier//core:go_default_library",
+        "@io_bazel_buildifier//differ:go_default_library",
         "//go/tools/gazel/generator:go_default_library",
     ],
 )
+
+go_binary(
+    name = "gazel",
+    library = ":go_default_library",
+)
+
+go_test(
+    name = "gazel_test",
+    srcs = ["fix_test.go"],
+    library = ":go_default_library",
+)

go/tools/gazel/gazel/diff.go

@@ -0,0 +1,52 @@
+/* Copyright 2016 The Bazel Authors. 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 main
+
+import (
+	"io/ioutil"
+	"os"
+
+	bzl "github.com/bazelbuild/buildifier/core"
+	"github.com/bazelbuild/buildifier/differ"
+)
+
+func diffFile(file *bzl.File) (err error) {
+	f, err := ioutil.TempFile("", "BUILD")
+	if err != nil {
+		return err
+	}
+	defer func() {
+		merr := os.Remove(f.Name())
+		if err == nil {
+			err = merr
+		}
+	}()
+	defer f.Close()
+	if _, err = f.Write(bzl.Format(file)); err != nil {
+		return err
+	}
+	if err := f.Sync(); err != nil {
+		return err
+	}
+
+	diff := differ.Find()
+	if _, err := os.Stat(file.Path); os.IsNotExist(err) {
+		diff.Show(os.DevNull, f.Name())
+		return nil
+	}
+	diff.Show(file.Path, f.Name())
+	return nil
+}

go/tools/gazel/gazel/fix.go

@@ -0,0 +1,27 @@
+/* Copyright 2016 The Bazel Authors. 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 main
+
+import (
+	"io/ioutil"
+
+	bzl "github.com/bazelbuild/buildifier/core"
+)
+
+func fixFile(file *bzl.File) error {
+	// TODO(yugui): Respect exisiting manual configurations as well as possible
+	return ioutil.WriteFile(file.Path, bzl.Format(file), 0644)
+}

go/tools/gazel/gazel/fix_test.go

@@ -0,0 +1,64 @@
+/* Copyright 2016 The Bazel Authors. 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 main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	bzl "github.com/bazelbuild/buildifier/core"
+)
+
+func TestFixFile(t *testing.T) {
+	tmpdir := os.Getenv("TEST_TMPDIR")
+	dir, err := ioutil.TempDir(tmpdir, "")
+	if err != nil {
+		t.Fatalf("ioutil.TempDir(%q, %q) failed with %v; want success", tmpdir, "", err)
+	}
+	defer os.RemoveAll(dir)
+
+	stubFile := &bzl.File{
+		Path: filepath.Join(dir, "BUILD"),
+		Stmt: []bzl.Expr{
+			&bzl.CallExpr{
+				X: &bzl.LiteralExpr{Token: "foo_rule"},
+				List: []bzl.Expr{
+					&bzl.BinaryExpr{
+						X:  &bzl.LiteralExpr{Token: "name"},
+						Op: "=",
+						Y:  &bzl.StringExpr{Value: "bar"},
+					},
+				},
+			},
+		},
+	}
+
+	if err := fixFile(stubFile); err != nil {
+		t.Errorf("fixFile(%#v) failed with %v; want success", stubFile, err)
+		return
+	}
+
+	buf, err := ioutil.ReadFile(stubFile.Path)
+	if err != nil {
+		t.Errorf("ioutil.ReadFile(%q) failed with %v; want success", stubFile.Path, err)
+		return
+	}
+	if got, want := string(buf), bzl.FormatString(stubFile); got != want {
+		t.Errorf("buf = %q; want %q", got, want)
+	}
+}

go/tools/gazel/gazel/main.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"path/filepath"
 
 	bzl "github.com/bazelbuild/buildifier/core"
 	"github.com/bazelbuild/rules_go/go/tools/gazel/generator"
@@ -31,9 +32,16 @@ var (
 	rulesGoRepo = flag.String("rules_go_repo", generator.DefaultRulesGoRepo, "repository name of rules_go")
 	goPrefix    = flag.String("go_prefix", "", "go_prefix of the target workspace")
 	repoRoot    = flag.String("repo_root", "", "path to a directory which corresponds to go_prefix")
+	mode        = flag.String("mode", "print", "print, fix or diff")
 )
 
-func run(dirs []string) error {
+var modeFromName = map[string]func(*bzl.File) error{
+	"print": printFile,
+	"fix":   fixFile,
+	"diff":  diffFile,
+}
+
+func run(dirs []string, emit func(*bzl.File) error) error {
 	g, err := generator.New(*repoRoot, *goPrefix)
 	if err != nil {
 		return err
@@ -46,7 +54,8 @@ func run(dirs []string) error {
 			return err
 		}
 		for _, f := range files {
-			if _, err := os.Stdout.Write(bzl.Format(f)); err != nil {
+			f.Path = filepath.Join(*repoRoot, f.Path)
+			if err := emit(f); err != nil {
 				return err
 			}
 		}
@@ -68,6 +77,11 @@ It takes a list of paths to Go package directories.
 It recursively traverses its subpackages.
 All the directories must be under the directory specified in -repo_root.
 
+There are several modes of gazel.
+In print mode, gazel prints reconciled BUILD files to stdout.
+In fix mode, gazel creates BUILD files or updates existing ones.
+In diff mode, gazel shows diff.
+
 FLAGS:
 `)
 	flag.PrintDefaults()
@@ -89,7 +103,13 @@ func main() {
 		// TODO(yugui): Guess repoRoot at the same time as goPrefix
 		*repoRoot = flag.Arg(0)
 	}
-	if err := run(flag.Args()); err != nil {
+
+	emit := modeFromName[*mode]
+	if emit == nil {
+		log.Fatalf("unrecognized mode %s", *mode)
+	}
+
+	if err := run(flag.Args(), emit); err != nil {
 		log.Fatal(err)
 	}
 }

go/tools/gazel/gazel/print.go

@@ -0,0 +1,27 @@
+/* Copyright 2016 The Bazel Authors. 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 main
+
+import (
+	"os"
+
+	bzl "github.com/bazelbuild/buildifier/core"
+)
+
+func printFile(f *bzl.File) (err error) {
+	_, err = os.Stdout.Write(bzl.Format(f))
+	return err
+}