Always return Disposable from maintain{Config,Grammar}

spec/text-editor-registry-spec.js

@@ -125,6 +125,25 @@ describe('TextEditorRegistry', function () {
       expect(editor.getGrammar().name).toBe('Null Grammar')
       expect(retainedEditorCount(registry)).toBe(0)
     })
+
+    describe('when called twice with a given editor', function () {
+      it('does nothing the second time', async function () {
+        await atom.packages.activatePackage('language-javascript')
+        const disposable1 = registry.maintainGrammar(editor)
+        const disposable2 = registry.maintainGrammar(editor)
+
+        editor.getBuffer().setPath('test.js')
+        expect(editor.getGrammar().name).toBe('JavaScript')
+
+        disposable2.dispose()
+        editor.getBuffer().setPath('test.txt')
+        expect(editor.getGrammar().name).toBe('Null Grammar')
+
+        disposable1.dispose()
+        editor.getBuffer().setPath('test.js')
+        expect(editor.getGrammar().name).toBe('Null Grammar')
+      })
+    })
   })
 
   describe('.setGrammarOverride', function () {
@@ -625,6 +644,27 @@ describe('TextEditorRegistry', function () {
       expect(delegate.getNonWordCharacters(['e.f', 'g.h'])).toBe('(){}[]')
       expect(delegate.getNonWordCharacters(['i.j'])).toBe('()')
     })
+
+    describe('when called twice with a given editor', function () {
+      it('does nothing the second time', async function () {
+        editor.update({scrollSensitivity: 50})
+
+        const disposable1 = registry.maintainConfig(editor)
+        const disposable2 = registry.maintainConfig(editor)
+        await initialPackageActivation
+
+        atom.config.set('editor.scrollSensitivity', 60)
+        expect(editor.getScrollSensitivity()).toBe(60)
+
+        disposable2.dispose()
+        atom.config.set('editor.scrollSensitivity', 70)
+        expect(editor.getScrollSensitivity()).toBe(70)
+
+        disposable1.dispose()
+        atom.config.set('editor.scrollSensitivity', 80)
+        expect(editor.getScrollSensitivity()).toBe(70)
+      })
+    })
   })
 
   describe('serialization', function () {

src/text-editor-registry.js

@@ -157,7 +157,7 @@ export default class TextEditorRegistry {
   // configuration.
   maintainConfig (editor) {
     if (this.editorsWithMaintainedConfig.has(editor)) {
-      return
+      return new Disposable(noop)
     }
     this.editorsWithMaintainedConfig.add(editor)
 
@@ -202,7 +202,7 @@ export default class TextEditorRegistry {
   // grammar.
   maintainGrammar (editor) {
     if (this.editorsWithMaintainedGrammar.has(editor)) {
-      return
+      return new Disposable(noop)
     }
 
     this.editorsWithMaintainedGrammar.add(editor)
@@ -391,6 +391,8 @@ function shouldEditorUseSoftTabs (editor, tabType, softTabs) {
   }
 }
 
+function noop () {}
+
 class ScopedSettingsDelegate {
   constructor (config) {
     this.config = config