layout,io/input: move disabling events from layout.Context to input.Source

The fix for #605 moved the disabling of event delivery from Source
to Context to enable disabled Contexts to still react to commands
(invalidate, focus etc.). However, that change in turn caused #641 where
the exported Context.Source field would no longer know not to deliver
events.

This change partially reverts the fix for #605 by moving disabledness
back to Source, fixing #641. Disabled Sources are left capable of
executing commands, thus keeping #605 fixed.

Thanks to Chris et al for keeping the use-cases straight enough for me
to come up with this (hopefully final) fix.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
Fixes: https://todo.sr.ht/~eliasnaur/gio/641
References: https://todo.sr.ht/~eliasnaur/gio/605

io/input/router.go

@@ -62,7 +62,8 @@ type Router struct {
 // Source implements the interface between a Router and user interface widgets.
 // The zero-value Source is disabled.
 type Source struct {
-	r *Router
+	r        *Router
+	disabled bool
 }
 
 // Command represents a request such as moving the focus, or initiating a clipboard read.
@@ -171,30 +172,38 @@ func (q *Router) Source() Source {
 
 // Execute a command.
 func (s Source) Execute(c Command) {
-	if !s.enabled() {
+	if !s.Enabled() {
 		return
 	}
 	s.r.execute(c)
 }
 
-// enabled reports whether the source is enabled. Only enabled
+// Disabled returns a copy of this source that don't deliver any events.
-// Sources deliver events and respond to commands.
+func (s Source) Disabled() Source {
-func (s Source) enabled() bool {
+	s2 := s
-	return s.r != nil
+	s2.disabled = true
+	return s2
+}
+
+// Enabled reports whether the source is enabled. Only enabled
+// Sources deliver events.
+func (s Source) Enabled() bool {
+	return s.r != nil && !s.disabled
 }
 
 // Focused reports whether tag is focused, according to the most recent
 // [key.FocusEvent] delivered.
 func (s Source) Focused(tag event.Tag) bool {
-	if !s.enabled() {
+	if !s.Enabled() {
 		return false
 	}
 	return s.r.state().keyState.focus == tag
 }
 
 // Event returns the next event that matches at least one of filters.
+// If the source is disabled, no events will be reported.
 func (s Source) Event(filters ...event.Filter) (event.Event, bool) {
-	if !s.enabled() {
+	if !s.Enabled() {
 		return nil, false
 	}
 	return s.r.Event(filters...)

layout/context.go

@@ -5,7 +5,6 @@ package layout
 import (
 	"time"
 
-	"gioui.org/io/event"
 	"gioui.org/io/input"
 	"gioui.org/io/system"
 	"gioui.org/op"
@@ -29,7 +28,6 @@ type Context struct {
 	// Interested users must look up and populate these values manually.
 	Locale system.Locale
 
-	disabled bool
 	input.Source
 	*op.Ops
 }
@@ -44,21 +42,8 @@ func (c Context) Sp(v unit.Sp) int {
 	return c.Metric.Sp(v)
 }
 
-func (c Context) Event(filters ...event.Filter) (event.Event, bool) {
-	if c.disabled {
-		return nil, false
-	}
-	return c.Source.Event(filters...)
-}
-
-// Enabled reports whether this context is enabled. Disabled contexts
-// don't report events.
-func (c Context) Enabled() bool {
-	return !c.disabled
-}
-
 // Disabled returns a copy of this context that don't deliver any events.
 func (c Context) Disabled() Context {
-	c.disabled = true
+	c.Source = c.Source.Disabled()
 	return c
 }