Don't insert characters in vim command mode

GlobalKeymap.bindKey can take a selector and a custom function that
maps key events to commands. If it returns false, no command is
triggered but event propagation is halted.

src/atom/binding-set.coffee

@@ -1,3 +1,4 @@
+_ = require 'underscore'
 $ = require 'jquery'
 Specificity = require 'specificity'
 
@@ -11,13 +12,19 @@ class BindingSet
     '=': 187, ';': 186, '\'': 222, '[': 219, ']': 221, '\\': 220
 
   selector: null
-  bindings: null
+  bindingMap: null
+  bindingFunction: null
 
-  constructor: (@selector, @bindings) ->
+  constructor: (@selector, mapOrFunction) ->
+    if _.isFunction(mapOrFunction)
+      @bindingFunction = mapOrFunction
+    else
+      @bindingMap = mapOrFunction
     @specificity = Specificity(@selector)
 
   commandForEvent: (event) ->
-    for pattern, command of @bindings
+    return @bindingFunction(event) if @bindingFunction
+    for pattern, command of @bindingMap
       return command if @eventMatchesPattern(event, pattern)
     null
 

src/atom/global-keymap.coffee

@@ -18,9 +18,12 @@ class GlobalKeymap
       candidateBindingSets = @bindingSets.filter (set) -> currentNode.is(set.selector)
       candidateBindingSets.sort (a, b) -> b.specificity - a.specificity
       for bindingSet in candidateBindingSets
-        if command = bindingSet.commandForEvent(event)
+        command = bindingSet.commandForEvent(event)
+        if command
           @triggerCommandEvent(event, command)
           return false
+        else if command == false
+          return false
       currentNode = currentNode.parent()
     true
 

src/atom/vim-mode.coffee

@@ -9,6 +9,7 @@ class VimMode
 
   constructor: (@editor) ->
     @opStack = []
+    atom.bindKeys '.command-mode', > false
     atom.bindKeys '.command-mode', @commandModeBindings()
     atom.bindKeys '.insert-mode', '<esc>': 'command-mode:activate'