gopls/internal/golang: add skeleton for move type codeaction

This is the first CL for implementing move type refactoring,
which will allow users to move a type declaration to a different
package. The code action producer for move type is off.

Change-Id: I10bface65ab6e1cb94180433360c923e8fa78c59
Reviewed-on: https://go-review.googlesource.com/c/tools/+/724020
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: madelinekalil

gopls/internal/golang/codeaction.go

@@ -255,6 +255,7 @@ var codeActionProducers = [...]codeActionProducer{
 	{kind: settings.RefactorExtractVariableAll, fn: refactorExtractVariableAll, needPkg: true},
 	{kind: settings.RefactorInlineCall, fn: refactorInlineCall, needPkg: true},
 	{kind: settings.RefactorInlineVariable, fn: refactorInlineVariable, needPkg: true},
+	// {kind: settings.RefactorMoveType, fn: refactorMoveType, needPkg: true},
 	{kind: settings.RefactorRewriteChangeQuote, fn: refactorRewriteChangeQuote},
 	{kind: settings.RefactorRewriteFillStruct, fn: refactorRewriteFillStruct, needPkg: true},
 	{kind: settings.RefactorRewriteFillSwitch, fn: refactorRewriteFillSwitch, needPkg: true},
@@ -1132,3 +1133,12 @@ func toggleCompilerOptDetails(ctx context.Context, req *codeActionsRequest) erro
 	}
 	return nil
 }
+
+func refactorMoveType(ctx context.Context, req *codeActionsRequest) error {
+	curSel, _ := req.pgf.Cursor.FindByPos(req.start, req.end)
+	if _, _, _, typeName, ok := selectionContainsType(curSel); ok {
+		cmd := command.NewMoveTypeCommand(fmt.Sprintf("Move type %s", typeName), command.MoveTypeArgs{Location: req.loc})
+		req.addCommandAction(cmd, false)
+	}
+	return nil
+}

gopls/internal/golang/movetype.go

@@ -0,0 +1,45 @@
+// Copyright 2025 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 golang
+
+import (
+	"context"
+	"fmt"
+	"go/ast"
+	"go/token"
+
+	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/gopls/internal/cache"
+	"golang.org/x/tools/gopls/internal/file"
+	"golang.org/x/tools/gopls/internal/protocol"
+	"golang.org/x/tools/internal/moreiters"
+)
+
+// MoveType moves the selected type declaration into a new package and updates all references.
+func MoveType(ctx context.Context, fh file.Handle, snapshot *cache.Snapshot, loc protocol.Location, newPkgDir string) ([]protocol.DocumentChange, error) {
+	return nil, fmt.Errorf("MoveType: not yet supported")
+}
+
+// selectionContainsType returns the Cursor, GenDecl and TypeSpec of the type
+// declaration that encloses cursor if one exists. Otherwise it returns false.
+func selectionContainsType(cursor inspector.Cursor) (inspector.Cursor, *ast.GenDecl, *ast.TypeSpec, string, bool) {
+	declCur, ok := moreiters.First(cursor.Enclosing((*ast.GenDecl)(nil)))
+	if !ok {
+		return inspector.Cursor{}, &ast.GenDecl{}, &ast.TypeSpec{}, "", false
+	}
+
+	// Verify that we have a type declaration (e.g. not an import declaration).
+	declNode := declCur.Node().(*ast.GenDecl)
+	if declNode.Tok != token.TYPE {
+		return inspector.Cursor{}, &ast.GenDecl{}, &ast.TypeSpec{}, "", false
+	}
+
+	typSpec, ok := declNode.Specs[0].(*ast.TypeSpec)
+	if !ok {
+		return inspector.Cursor{}, &ast.GenDecl{}, &ast.TypeSpec{}, "", false
+	}
+
+	return declCur, declNode, declNode.Specs[0].(*ast.TypeSpec), typSpec.Name.Name, true
+}

gopls/internal/protocol/command/command_gen.go

@@ -322,6 +322,9 @@ type Interface interface {
 
 	// ModifyTags: Add or remove struct tags on a given node.
 	ModifyTags(context.Context, ModifyTagsArgs) error
+
+	// MoveType: Move a type declaration to a different package.
+	MoveType(context.Context, MoveTypeArgs) error
 }
 
 type RunTestsArgs struct {
@@ -876,3 +879,11 @@ type LSPArgs struct {
 	Method string          `json:"method"`
 	Param  json.RawMessage `json:"param"`
 }
+
+// MoveTypeArgs specifies a "move type" refactoring to perform.
+type MoveTypeArgs struct {
+	// The location of the type to move.
+	Location protocol.Location
+	// TODO(mkalil): Determine format of the parameter that specifies where to
+	// move the type to.
+}

gopls/internal/protocol/command/interface.go

@@ -1892,3 +1892,16 @@ func parseTransform(input string) (modifytags.Transform, error) {
 		return modifytags.SnakeCase, fmt.Errorf("invalid Transform value")
 	}
 }
+
+func (c *commandHandler) MoveType(ctx context.Context, args command.MoveTypeArgs) error {
+	err := c.run(ctx, commandConfig{
+		forURI: args.Location.URI,
+	}, func(ctx context.Context, deps commandDeps) error {
+		changes, err := golang.MoveType(ctx, deps.fh, deps.snapshot, args.Location, "newpkg/new.go")
+		if err != nil {
+			return err
+		}
+		return applyChanges(ctx, c.s.client, changes)
+	})
+	return err
+}

gopls/internal/server/command.go

@@ -114,6 +114,9 @@ const (
 	RefactorExtractVariableAll protocol.CodeActionKind = "refactor.extract.variable-all"
 	RefactorExtractToNewFile   protocol.CodeActionKind = "refactor.extract.toNewFile"
 
+	// refactor.move
+	RefactorMoveType protocol.CodeActionKind = "refactor.move.moveType"
+
 	// Note: add new kinds to:
 	// - the SupportedCodeActions map in default.go
 	// - the codeActionProducers table in ../golang/codeaction.go

gopls/internal/settings/codeactionkind.go

@@ -71,6 +71,7 @@ func DefaultOptions(overrides ...func(*Options)) *Options {
 						RefactorExtractVariable:          true,
 						RefactorExtractVariableAll:       true,
 						RefactorExtractToNewFile:         true,
+						RefactorMoveType:                 true, // off while implementation unfinished
 						// Not GoTest: it must be explicit in CodeActionParams.Context.Only
 					},
 					file.Mod: {