gopls/internal/protocol: customize InsertReplaceEdit JSON unmarshal

InsertReplaceEdit is used instead of TextEdit in CompletionItem
in editors that support it. These two types are alike in appearance
but can be differentiated by the presence or absence of
certain properties. UnmarshalJSON of the sum type tries to
unmarshal as TextEdit only if unmarshal as InsertReplaceEdit fails.
Due to this similarity, unmarshal with the different type never fails.

Add a custom JSON unmarshaller for InsertReplaceEdit,
so it fails when the required fields are missing. That makes
Or_CompletionItem_textEdit decode TextEdit type correctly.

For golang/go#40871
For golang/go#61215

Change-Id: I62471fa973fa376cad5eb3934522ff21c14e3647
Reviewed-on: https://go-review.googlesource.com/c/tools/+/587135
Reviewed-by: Peter Weinberger <pjw@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: hyangah

gopls/internal/protocol/tsinsertreplaceedit.go

@@ -0,0 +1,40 @@
+// Copyright 2024 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 protocol
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// InsertReplaceEdit is used instead of TextEdit in CompletionItem
+// in editors that support it. These two types are alike in appearance
+// but can be differentiated by the presence or absence of
+// certain properties. UnmarshalJSON of the sum type tries to
+// unmarshal as TextEdit only if unmarshal as InsertReplaceEdit fails.
+// However, due to this similarity, unmarshal with the other type
+// never fails. This file has a custom JSON unmarshaller for
+// InsertReplaceEdit, that fails if the required fields are missing.
+
+// UnmarshalJSON unmarshals InsertReplaceEdit with extra
+// checks on the presence of "insert" and "replace" properties.
+func (e *InsertReplaceEdit) UnmarshalJSON(data []byte) error {
+	var required struct {
+		NewText string
+		Insert  *Range `json:"insert,omitempty"`
+		Replace *Range `json:"replace,omitempty"`
+	}
+
+	if err := json.Unmarshal(data, &required); err != nil {
+		return err
+	}
+	if required.Insert == nil && required.Replace == nil {
+		return fmt.Errorf("not InsertReplaceEdit")
+	}
+	e.NewText = required.NewText
+	e.Insert = *required.Insert
+	e.Replace = *required.Replace
+	return nil
+}

gopls/internal/protocol/tsinsertreplaceedit_test.go

@@ -0,0 +1,44 @@
+// Copyright 2024 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 protocol
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestInsertReplaceEdit_UnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		in      any
+		wantErr bool
+	}{
+		{
+			name: "TextEdit",
+			in:   TextEdit{NewText: "new text", Range: Range{Start: Position{Line: 1}}},
+		},
+		{
+			name: "InsertReplaceEdit",
+			in:   InsertReplaceEdit{NewText: "new text", Insert: Range{Start: Position{Line: 100}}, Replace: Range{End: Position{Line: 200}}},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			data, err := json.MarshalIndent(Or_CompletionItem_textEdit{Value: tt.in}, "", " ")
+			if err != nil {
+				t.Fatalf("failed to marshal: %v", err)
+			}
+			var decoded Or_CompletionItem_textEdit
+			if err := json.Unmarshal(data, &decoded); err != nil {
+				t.Fatalf("failed to unmarshal: %v", err)
+			}
+			if diff := cmp.Diff(tt.in, decoded.Value); diff != "" {
+				t.Errorf("unmarshal returns unexpected result: (-want +got):\n%s", diff)
+			}
+		})
+	}
+}