isDefault supports scoped settings

spec/config-spec.coffee

@@ -99,6 +99,16 @@ describe "Config", ->
       expect(atom.config.isDefault('foo.same')).toBe false
       expect(atom.config.isDefault('foo.changes')).toBe false
 
+    describe "when scoped settings are used", ->
+      it "returns false when a scoped setting was set by the user", ->
+        expect(atom.config.isDefault('.source.coffee', 'foo.bar.baz')).toBe true
+
+        atom.config.addScopedSettings("default", ".source.coffee", foo: bar: baz: 42)
+        expect(atom.config.isDefault('.source.coffee', 'foo.bar.baz')).toBe true
+
+        atom.config.set('.source.coffee', 'foo.bar.baz', 55)
+        expect(atom.config.isDefault('.source.coffee', 'foo.bar.baz')).toBe false
+
   describe ".toggle(keyPath)", ->
     it "negates the boolean value of the current key path value", ->
       atom.config.set('foo.a', 1)

src/config.coffee

@@ -540,8 +540,16 @@ class Config
   #
   # Returns a {Boolean}, `true` if the current value is the default, `false`
   # otherwise.
-  isDefault: (keyPath) ->
-    not _.valueForKeyPath(@settings, keyPath)?
+  isDefault: (scopeSelector, keyPath) ->
+    if arguments.length == 1
+      keyPath = scopeSelector
+      scopeSelector = null
+
+    if scopeSelector?
+      settings = @scopedSettingsStore.propertiesForSourceAndSelector('user-config', scopeSelector)
+      not _.valueForKeyPath(settings, keyPath)?
+    else
+      not _.valueForKeyPath(@settings, keyPath)?
 
   # Extended: Retrieve the schema for a specific key path. The schema will tell
   # you what type the keyPath expects, and other metadata about the config