Add updateDecorationForMarker()

src/display-buffer.coffee

@@ -795,6 +795,21 @@ class DisplayBuffer extends Model
     @decorationsByMarkerId[marker.id].push(decoration)
     @emit 'decoration-added', marker, decoration
 
+  updateDecorationForMarker: (marker, decorationPattern, newDecoration) ->
+    unless marker?
+      console.warn 'A null marker cannot be decorated'
+      return
+
+    marker = @getMarker(marker.id)
+    return unless decorations = @decorationsByMarkerId[marker.id]
+
+    for decoration, i in decorations
+      if @decorationMatchesPattern(decoration, decorationPattern) and not _.isEqual(decoration, newDecoration)
+        decorations[i] = newDecoration
+        @emit 'decoration-updated', marker, decoration, newDecoration
+
+    return
+
   removeDecorationForMarker: (marker, decorationPattern) ->
     unless marker?
       console.warn 'A decoration cannot be removed from a null marker'

src/editor.coffee

@@ -218,6 +218,7 @@ class Editor extends Model
     @subscribe @displayBuffer, "decoration-added", (args...) => @emit 'decoration-added', args...
     @subscribe @displayBuffer, "decoration-removed", (args...) => @emit 'decoration-removed', args...
     @subscribe @displayBuffer, "decoration-changed", (args...) => @emit 'decoration-changed', args...
+    @subscribe @displayBuffer, "decoration-updated", (args...) => @emit 'decoration-updated', args...
     @subscribe @displayBuffer, "character-widths-changed", (changeCount) => @emit 'character-widths-changed', changeCount
 
   getViewClass: ->
@@ -1111,6 +1112,10 @@ class Editor extends Model
   addDecorationForMarker: (marker, decoration) ->
     @displayBuffer.addDecorationForMarker(marker, decoration)
 
+  #
+  updateDecorationForMarker: (marker, decorationPattern, newDecoration) ->
+    @displayBuffer.updateDecorationForMarker(marker, decorationPattern, newDecoration)
+
   # Public: Removes all decorations associated with a {Marker} that match a
   # `decorationPattern` and stop tracking the {Marker}.
   #