1 files changed, 59 insertions, 0 deletions
diff --git a/gopls/internal/lsp/cmd/subcommands.go b/gopls/internal/lsp/cmd/subcommands.go
new file mode 100644
index 000000000..e30c42b85
--- /dev/null
+++ b/gopls/internal/lsp/cmd/subcommands.go
@@ -0,0 +1,59 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cmd
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"text/tabwriter"
+
+	"golang.org/x/tools/internal/tool"
+)
+
+// subcommands is a helper that may be embedded for commands that delegate to
+// subcommands.
+type subcommands []tool.Application
+
+func (s subcommands) DetailedHelp(f *flag.FlagSet) {
+	w := tabwriter.NewWriter(f.Output(), 0, 0, 2, ' ', 0)
+	defer w.Flush()
+	fmt.Fprint(w, "\nSubcommand:\n")
+	for _, c := range s {
+		fmt.Fprintf(w, "  %s\t%s\n", c.Name(), c.ShortHelp())
+	}
+	printFlagDefaults(f)
+}
+
+func (s subcommands) Usage() string { return "<subcommand> [arg]..." }
+
+func (s subcommands) Run(ctx context.Context, args ...string) error {
+	if len(args) == 0 {
+		return tool.CommandLineErrorf("must provide subcommand")
+	}
+	command, args := args[0], args[1:]
+	for _, c := range s {
+		if c.Name() == command {
+			s := flag.NewFlagSet(c.Name(), flag.ExitOnError)
+			return tool.Run(ctx, s, c, args)
+		}
+	}
+	return tool.CommandLineErrorf("unknown subcommand %v", command)
+}
+
+func (s subcommands) Commands() []tool.Application { return s }
+
+// getSubcommands returns the subcommands of a given Application.
+func getSubcommands(a tool.Application) []tool.Application {
+	// This interface is satisfied both by tool.Applications
+	// that embed subcommands, and by *cmd.Application.
+	type hasCommands interface {
+		Commands() []tool.Application
+	}
+	if sub, ok := a.(hasCommands); ok {
+		return sub.Commands()
+	}
+	return nil
+}