cuepls: support formatting of CUE files

Add support for the formatting of CUE files.

While we are here, create a cuelang package alongside the existing
golang package.

Lots more formatting required in later CLs, but again this is a good
bootstrap.

For #142

Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: I13ab83c1251714182e69d06bb53ed08f94bac709
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1174174
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@gmail.com>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

cmd/cuepls/internal/test/integration/base/base_test.go

@@ -7,6 +7,7 @@ import (
 
 	"cuelang.org/go/internal/golangorgx/gopls/hooks"
 	. "cuelang.org/go/internal/golangorgx/gopls/test/integration"
+	"cuelang.org/go/internal/golangorgx/gopls/test/integration/fake"
 	"github.com/go-quicktest/qt"
 )
 
@@ -20,14 +21,17 @@ func TestFormatFile(t *testing.T) {
 module mod.com
 
 go 1.12
--- foo.go --
-	package foo
+-- foo.cue --
+package foo
+
+  // this is a test
 `
 	Run(t, files, func(t *testing.T, env *Env) {
-		env.OpenFile("foo.go")
-		env.FormatBuffer("foo.go")
-		got := env.BufferText("foo.go")
-		want := "package foo\n"
+		env.OpenFile("foo.cue")
+		env.EditBuffer("foo.cue", fake.NewEdit(0, 0, 1, 0, "package bar\n"))
+		env.FormatBuffer("foo.cue")
+		got := env.BufferText("foo.cue")
+		want := "package bar\n\n// this is a test\n"
 		qt.Assert(t, qt.Equals(got, want))
 	})
 }

internal/golangorgx/gopls/cuelang/format.go

@@ -0,0 +1,60 @@
+// Copyright 2024 The CUE Authors
+//
+// 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 golang defines the LSP features for navigation, analysis,
+// and refactoring of Go source code.
+package cuelang
+
+import (
+	"bytes"
+	"context"
+
+	cueformat "cuelang.org/go/cue/format"
+
+	"cuelang.org/go/internal/golangorgx/gopls/cache"
+	"cuelang.org/go/internal/golangorgx/gopls/file"
+	"cuelang.org/go/internal/golangorgx/gopls/protocol"
+	"cuelang.org/go/internal/golangorgx/tools/diff"
+	"cuelang.org/go/internal/golangorgx/tools/event"
+)
+
+// FormatCUE formats a CUE file with a given range.
+func FormatCUE(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle) ([]protocol.TextEdit, error) {
+	ctx, done := event.Start(ctx, "source.FormatCUE")
+	defer done()
+
+	// TODO cache the parsed artefacts, which will include the mapper
+
+	src, err := fh.Content()
+	if err != nil {
+		return nil, err
+	}
+	res, err := cueformat.Source(src)
+	if err != nil {
+		// TODO fix up the AST like gopls so we can do more with
+		// partial/incomplete code.
+		//
+		// For now return early because there is nothing we can do.
+		return nil, nil
+	}
+
+	// If the format did nothing, do nothing
+	if bytes.Equal(src, res) {
+		return nil, nil
+	}
+
+	mapper := protocol.NewMapper(fh.URI(), src)
+	edits := diff.Strings(string(src), string(res))
+	return protocol.EditsFromDiffEdits(mapper, edits)
+}

internal/golangorgx/gopls/server/format.go

@@ -7,6 +7,7 @@ package server
 import (
 	"context"
 
+	"cuelang.org/go/internal/golangorgx/gopls/cuelang"
 	"cuelang.org/go/internal/golangorgx/gopls/file"
 	"cuelang.org/go/internal/golangorgx/gopls/golang"
 	"cuelang.org/go/internal/golangorgx/gopls/protocol"
@@ -27,6 +28,11 @@ func (s *server) Formatting(ctx context.Context, params *protocol.DocumentFormat
 	switch snapshot.FileKind(fh) {
 	case file.Go:
 		return golang.Format(ctx, snapshot, fh)
+	case file.CUE:
+		return cuelang.FormatCUE(ctx, snapshot, fh)
+	default:
+		// TODO warn that we did not know how to format that file... why was the
+		// request routed to this LSP?
 	}
 	return nil, nil // empty result
 }