Initialize UI components only when they're needed.

HUD: Initialize only when the frame receives the focus and Vimium is enabled.
Vomnibar: Initialize in the top frame when Vimium is enabled in *any* frame.

Warning:  There may be a race condition here.  Specifically, if Vimium
is disabled in the main/top frame (T) but enabled in another frame (A), then the
initialisation could happen in frame A before frame T is listening, so
frame T would miss the initialization message (which is only sent once).

Message listeners are installed early (and probably installed first in
the main/top frame), and the `isEnabledForUrl` messaging takes some
time, so perhaps it's OK.  But it *is* a race condition.

Fixes #1838.

4 files changed, 20 insertions, 5 deletions

diff --git a/content_scripts/hud.coffee b/content_scripts/hud.coffee
index e56644df..aa8a6bbd 100644
--- a/content_scripts/hud.coffee
+++ b/content_scripts/hud.coffee
@@ -86,7 +86,7 @@ HUD =
   isReady: do ->
     ready = false
     DomUtils.documentReady -> ready = true
-    -> ready and document.body != null
+    -> ready and document.body != null and @hudUI?
 
   enabled: -> true
 
diff --git a/content_scripts/vimium_frontend.coffee b/content_scripts/vimium_frontend.coffee
index 2e57ee1a..5acabcfc 100644
--- a/content_scripts/vimium_frontend.coffee
+++ b/content_scripts/vimium_frontend.coffee
@@ -149,6 +149,7 @@ initializePreDomReady = ->
     # A frame has received the focus.  We don't care here (the Vomnibar/UI-component handles this).
     frameFocused: ->
     checkEnabledAfterURLChange: checkEnabledAfterURLChange
+    initializeTopFrame: initializeTopFrame
     runInTopFrame: ({sourceFrameId, registryEntry}) ->
       Utils.invokeCommandString registryEntry.command, [sourceFrameId, registryEntry] if DomUtils.isTopFrame()
 
@@ -218,9 +219,6 @@ initializeOnDomReady = ->
     isEnabledForUrl = false
     chrome.runtime.sendMessage = ->
     window.removeEventListener "focus", onFocus
-  # We only initialize the vomnibar in the tab's main frame, because it's only ever opened there.
-  Vomnibar.init() if DomUtils.isTopFrame()
-  HUD.init()
 
 registerFrame = ->
   # Don't register frameset containers; focusing them is no use.
@@ -436,6 +434,17 @@ extend window,
               indicator: false
 
 
+initializeTopFrame = (request = null) ->
+  initializeTopFrame = -> # Only do this initialization once.
+  # We only initialize the vomnibar in the tab's top/main frame, because it's only ever opened there.
+  if DomUtils.isTopFrame()
+    Vomnibar.init()
+  else
+    # Ignore requests from other frames (if we're not the top frame).
+    unless request?
+      # Tell the top frame to initialize the Vomnibar.
+      chrome.runtime.sendMessage handler: "sendMessageToFrames", message: name: "initializeTopFrame"
+
 # Checks if Vimium should be enabled or not in this frame.  As a side effect, it also informs the background
 # page whether this frame has the focus, allowing the background page to track the active frame's URL.
 checkIfEnabledForUrl = (frameIsFocused = windowIsFocused()) ->
@@ -443,7 +452,11 @@ checkIfEnabledForUrl = (frameIsFocused = windowIsFocused()) ->
   chrome.runtime.sendMessage { handler: "isEnabledForUrl", url: url, frameIsFocused: frameIsFocused }, (response) ->
     { isEnabledForUrl, passKeys } = response
     installListeners() # But only if they have not been installed already.
-    if HUD.isReady() and not isEnabledForUrl
+    # Initialize UI components. We only initialize these once we know that Vimium is enabled; see #1838.
+    if isEnabledForUrl
+      initializeTopFrame()
+      HUD.init() if frameIsFocused
+    else if HUD.isReady()
       # Quickly hide any HUD we might already be showing, e.g. if we entered insert mode on page load.
       HUD.hide()
     normalMode?.setPassKeys passKeys
diff --git a/tests/dom_tests/dom_tests.coffee b/tests/dom_tests/dom_tests.coffee
index 0745e5b2..3797a37b 100644
--- a/tests/dom_tests/dom_tests.coffee
+++ b/tests/dom_tests/dom_tests.coffee
@@ -1,6 +1,7 @@
 
 # Install frontend event handlers.
 installListeners()
+HUD.init()
 
 installListener = (element, event, callback) ->
   element.addEventListener event, (-> callback.apply(this, arguments)), true
diff --git a/tests/dom_tests/vomnibar_test.coffee b/tests/dom_tests/vomnibar_test.coffee
index 3eda6234..0898e33a 100644
--- a/tests/dom_tests/vomnibar_test.coffee
+++ b/tests/dom_tests/vomnibar_test.coffee
@@ -1,5 +1,6 @@
 vomnibarFrame = null
 SearchEngines.refresh ""
+Vomnibar.init()
 
 context "Keep selection within bounds",