1 files changed, 127 insertions, 0 deletions
diff --git a/go/tools/releaser/releaser.go b/go/tools/releaser/releaser.go
new file mode 100644
index 00000000..e8ba95c1
--- /dev/null
+++ b/go/tools/releaser/releaser.go
@@ -0,0 +1,127 @@
+// Copyright 2021 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.
+
+// releaser is a tool for maintaining rules_go and Gazelle. It automates
+// multiple tasks related to preparing releases, like upgrading dependencies,
+// and uploading release artifacts.
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+)
+
+func main() {
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer cancel()
+	if err := run(ctx, os.Stderr, os.Args[1:]); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+type command struct {
+	name, description, help string
+	run                     func(context.Context, io.Writer, []string) error
+}
+
+var commands = []*command{
+	&helpCmd,
+	&prepareCmd,
+	&upgradeDepCmd,
+}
+
+func run(ctx context.Context, stderr io.Writer, args []string) error {
+	if len(args) == 0 {
+		return errors.New("no command specified. For a list of commands, run:\n\treleaser help")
+	}
+	name, args := args[0], args[1:]
+	for _, arg := range args {
+		if arg == "-h" || name == "-help" || name == "--help" {
+			return helpCmd.run(ctx, stderr, args)
+		}
+	}
+	for _, cmd := range commands {
+		if cmd.name == name {
+			return cmd.run(ctx, stderr, args)
+		}
+	}
+	return fmt.Errorf("unknown command %q. For a list of commands, run:\n\treleaser help", name)
+}
+
+var helpCmd = command{
+	name:        "help",
+	description: "prints information on how to use any subcommand",
+	help: `releaser help [subcommand]
+
+The help sub-command prints information on how to use any subcommand. Run help
+without arguments for a list of all subcommands.
+`,
+}
+
+func init() {
+	// break init cycle
+	helpCmd.run = runHelp
+}
+
+func runHelp(ctx context.Context, stderr io.Writer, args []string) error {
+	if len(args) > 1 {
+		return usageErrorf(&helpCmd, "help accepts at most one argument.")
+	}
+
+	if len(args) == 1 {
+		name := args[0]
+		for _, cmd := range commands {
+			if cmd.name == name {
+				fmt.Fprintf(stderr, "%s\n\n%s\n", cmd.description, cmd.help)
+				return nil
+			}
+		}
+		return fmt.Errorf("Unknown command %s. For a list of supported subcommands, run:\n\treleaser help", name)
+	}
+
+	fmt.Fprint(stderr, "releaser supports the following subcommands:\n\n")
+	maxNameLen := 0
+	for _, cmd := range commands {
+		if len(cmd.name) > maxNameLen {
+			maxNameLen = len(cmd.name)
+		}
+	}
+	for _, cmd := range commands {
+		fmt.Fprintf(stderr, "\t%-*s    %s\n", maxNameLen, cmd.name, cmd.description)
+	}
+	fmt.Fprintf(stderr, "\nRun 'releaser help <subcommand>' for more information on any command.\n")
+	return nil
+}
+
+type usageError struct {
+	cmd *command
+	err error
+}
+
+func (e *usageError) Error() string {
+	return fmt.Sprintf("%v. For usage info, run:\n\treleaser help %s", e.err, e.cmd.name)
+}
+
+func (e *usageError) Unwrap() error {
+	return e.err
+}
+
+func usageErrorf(cmd *command, format string, args ...interface{}) error {
+	return &usageError{cmd: cmd, err: fmt.Errorf(format, args...)}
+}