1 files changed, 52 insertions, 0 deletions
diff --git a/gopls/internal/lsp/cache/keys.go b/gopls/internal/lsp/cache/keys.go
new file mode 100644
index 000000000..449daba3a
--- /dev/null
+++ b/gopls/internal/lsp/cache/keys.go
@@ -0,0 +1,52 @@
+// Copyright 2020 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 cache
+
+import (
+	"io"
+
+	"golang.org/x/tools/internal/event/label"
+)
+
+var (
+	KeyCreateSession   = NewSessionKey("create_session", "A new session was added")
+	KeyUpdateSession   = NewSessionKey("update_session", "Updated information about a session")
+	KeyShutdownSession = NewSessionKey("shutdown_session", "A session was shut down")
+)
+
+// SessionKey represents an event label key that has a *Session value.
+type SessionKey struct {
+	name        string
+	description string
+}
+
+// NewSessionKey creates a new Key for *Session values.
+func NewSessionKey(name, description string) *SessionKey {
+	return &SessionKey{name: name, description: description}
+}
+
+func (k *SessionKey) Name() string        { return k.name }
+func (k *SessionKey) Description() string { return k.description }
+
+func (k *SessionKey) Format(w io.Writer, buf []byte, l label.Label) {
+	io.WriteString(w, k.From(l).ID())
+}
+
+// Of creates a new Label with this key and the supplied session.
+func (k *SessionKey) Of(v *Session) label.Label { return label.OfValue(k, v) }
+
+// Get can be used to get the session for the key from a label.Map.
+func (k *SessionKey) Get(lm label.Map) *Session {
+	if t := lm.Find(k); t.Valid() {
+		return k.From(t)
+	}
+	return nil
+}
+
+// From can be used to get the session value from a Label.
+func (k *SessionKey) From(t label.Label) *Session {
+	err, _ := t.UnpackValue().(*Session)
+	return err
+}