1 files changed, 80 insertions, 0 deletions
diff --git a/gopls/internal/lsp/cmd/prepare_rename.go b/gopls/internal/lsp/cmd/prepare_rename.go
new file mode 100644
index 000000000..5e9d732fb
--- /dev/null
+++ b/gopls/internal/lsp/cmd/prepare_rename.go
@@ -0,0 +1,80 @@
+// Copyright 2019 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"
+	"errors"
+	"flag"
+	"fmt"
+
+	"golang.org/x/tools/gopls/internal/lsp/protocol"
+	"golang.org/x/tools/gopls/internal/span"
+	"golang.org/x/tools/internal/tool"
+)
+
+// prepareRename implements the prepare_rename verb for gopls.
+type prepareRename struct {
+	app *Application
+}
+
+func (r *prepareRename) Name() string      { return "prepare_rename" }
+func (r *prepareRename) Parent() string    { return r.app.Name() }
+func (r *prepareRename) Usage() string     { return "<position>" }
+func (r *prepareRename) ShortHelp() string { return "test validity of a rename operation at location" }
+func (r *prepareRename) DetailedHelp(f *flag.FlagSet) {
+	fmt.Fprint(f.Output(), `
+Example:
+
+	$ # 1-indexed location (:line:column or :#offset) of the target identifier
+	$ gopls prepare_rename helper/helper.go:8:6
+	$ gopls prepare_rename helper/helper.go:#53
+`)
+	printFlagDefaults(f)
+}
+
+// ErrInvalidRenamePosition is returned when prepareRename is run at a position that
+// is not a candidate for renaming.
+var ErrInvalidRenamePosition = errors.New("request is not valid at the given position")
+
+func (r *prepareRename) Run(ctx context.Context, args ...string) error {
+	if len(args) != 1 {
+		return tool.CommandLineErrorf("prepare_rename expects 1 argument (file)")
+	}
+
+	conn, err := r.app.connect(ctx)
+	if err != nil {
+		return err
+	}
+	defer conn.terminate(ctx)
+
+	from := span.Parse(args[0])
+	file := conn.openFile(ctx, from.URI())
+	if file.err != nil {
+		return file.err
+	}
+	loc, err := file.mapper.SpanLocation(from)
+	if err != nil {
+		return err
+	}
+	p := protocol.PrepareRenameParams{
+		TextDocumentPositionParams: protocol.LocationTextDocumentPositionParams(loc),
+	}
+	result, err := conn.PrepareRename(ctx, &p)
+	if err != nil {
+		return fmt.Errorf("prepare_rename failed: %w", err)
+	}
+	if result == nil {
+		return ErrInvalidRenamePosition
+	}
+
+	s, err := file.mapper.RangeSpan(result.Range)
+	if err != nil {
+		return err
+	}
+
+	fmt.Println(s)
+	return nil
+}