fix: hasAccess() silently loses error context when no token is available

dist/OAuth2.gs

@@ -570,7 +570,14 @@ Service_.prototype.hasAccess = function() {
   if (token && !this.isExpired_(token)) return true; // Token still has access.
   var canGetToken = (token && this.canRefresh_(token)) ||
       this.privateKey_ || this.grantType_;
-  if (!canGetToken) return false;
+  if (!canGetToken) {
+    this.lastError_ = new Error('No token found and no way to generate one. ' +
+        'The user needs to be redirected to the authorization URL returned ' +
+        'by getAuthorizationUrl(), or the service needs to be configured ' +
+        'with setPrivateKey() or setGrantType() for a token to be ' +
+        'generated automatically.');
+    return false;
+  }
 
   return this.lockable_(function() {
     // Get the token again, bypassing the local memory cache.

src/Service.js

@@ -477,7 +477,14 @@ Service_.prototype.hasAccess = function() {
   if (token && !this.isExpired_(token)) return true; // Token still has access.
   var canGetToken = (token && this.canRefresh_(token)) ||
       this.privateKey_ || this.grantType_;
-  if (!canGetToken) return false;
+  if (!canGetToken) {
+    this.lastError_ = new Error('No token found and no way to generate one. ' +
+        'The user needs to be redirected to the authorization URL returned ' +
+        'by getAuthorizationUrl(), or the service needs to be configured ' +
+        'with setPrivateKey() or setGrantType() for a token to be ' +
+        'generated automatically.');
+    return false;
+  }
 
   return this.lockable_(function() {
     // Get the token again, bypassing the local memory cache.

test/test.js

@@ -359,6 +359,23 @@ describe('Service', () => {
       service.hasAccess();
       assert.equal(lock.counter, 0);
     });
+
+    it('should set lastError_ when there is no token and no way to get one',
+        () => {
+          var properties = new MockProperties();
+          var service = OAuth2.createService('test')
+              .setClientId('abc')
+              .setClientSecret('def')
+              .setTokenUrl('http://www.example.com')
+              .setAuthorizationBaseUrl('http://www.example.com')
+              .setPropertyStore(properties);
+
+          var result = service.hasAccess();
+
+          assert.isFalse(result);
+          assert.exists(service.getLastError());
+          assert.match(service.getLastError().message, /no way to generate/);
+        });
   });
 
   describe('#refresh()', () => {