ipn: generate LoginProfileView and use it instead of *LoginProfile where appropriate

Conventionally, we use views (e.g., ipn.PrefsView, tailcfg.NodeView, etc.) when
dealing with structs that shouldn't be mutated. However, ipn.LoginProfile has been
an exception so far, with a mix of passing and returning LoginProfile by reference
(allowing accidental mutations) and by value (which is wasteful, given its
current size of 192 bytes).

In this PR, we generate an ipn.LoginProfileView and use it instead of passing/returning
LoginProfiles by mutable reference or copying them when passing/returning by value.
Now, LoginProfiles can only be mutated by (*profileManager).setProfilePrefs.

Updates #14823

Signed-off-by: Nick Khyl <nickk@tailscale.com>

ipn/ipn_view.go

@@ -18,7 +18,73 @@ import (
 	"tailscale.com/types/views"
 )
 
-//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=Prefs,ServeConfig,ServiceConfig,TCPPortHandler,HTTPHandler,WebServerConfig
+//go:generate go run tailscale.com/cmd/cloner  -clonefunc=false -type=LoginProfile,Prefs,ServeConfig,ServiceConfig,TCPPortHandler,HTTPHandler,WebServerConfig
+
+// View returns a read-only view of LoginProfile.
+func (p *LoginProfile) View() LoginProfileView {
+	return LoginProfileView{ж: p}
+}
+
+// LoginProfileView provides a read-only view over LoginProfile.
+//
+// Its methods should only be called if `Valid()` returns true.
+type LoginProfileView struct {
+	// ж is the underlying mutable value, named with a hard-to-type
+	// character that looks pointy like a pointer.
+	// It is named distinctively to make you think of how dangerous it is to escape
+	// to callers. You must not let callers be able to mutate it.
+	ж *LoginProfile
+}
+
+// Valid reports whether v's underlying value is non-nil.
+func (v LoginProfileView) Valid() bool { return v.ж != nil }
+
+// AsStruct returns a clone of the underlying value which aliases no memory with
+// the original.
+func (v LoginProfileView) AsStruct() *LoginProfile {
+	if v.ж == nil {
+		return nil
+	}
+	return v.ж.Clone()
+}
+
+func (v LoginProfileView) MarshalJSON() ([]byte, error) { return json.Marshal(v.ж) }
+
+func (v *LoginProfileView) UnmarshalJSON(b []byte) error {
+	if v.ж != nil {
+		return errors.New("already initialized")
+	}
+	if len(b) == 0 {
+		return nil
+	}
+	var x LoginProfile
+	if err := json.Unmarshal(b, &x); err != nil {
+		return err
+	}
+	v.ж = &x
+	return nil
+}
+
+func (v LoginProfileView) ID() ProfileID                    { return v.ж.ID }
+func (v LoginProfileView) Name() string                     { return v.ж.Name }
+func (v LoginProfileView) NetworkProfile() NetworkProfile   { return v.ж.NetworkProfile }
+func (v LoginProfileView) Key() StateKey                    { return v.ж.Key }
+func (v LoginProfileView) UserProfile() tailcfg.UserProfile { return v.ж.UserProfile }
+func (v LoginProfileView) NodeID() tailcfg.StableNodeID     { return v.ж.NodeID }
+func (v LoginProfileView) LocalUserID() WindowsUserID       { return v.ж.LocalUserID }
+func (v LoginProfileView) ControlURL() string               { return v.ж.ControlURL }
+
+// A compilation failure here means this code must be regenerated, with the command at the top of this file.
+var _LoginProfileViewNeedsRegeneration = LoginProfile(struct {
+	ID             ProfileID
+	Name           string
+	NetworkProfile NetworkProfile
+	Key            StateKey
+	UserProfile    tailcfg.UserProfile
+	NodeID         tailcfg.StableNodeID
+	LocalUserID    WindowsUserID
+	ControlURL     string
+}{})
 
 // View returns a read-only view of Prefs.
 func (p *Prefs) View() PrefsView {