Experimental approach to cancelling unnecessary promises

If a view or other resources are destroyed while a promise is being
resolved, subsequent code can fail. This is generally harmless, but it
results in unnecessary errors being logged to the console.

To address this, promises can use a new function,
Zotero.Promise.check(), to test whether a value is truthy or 0 and
automatically throw a specific error that's ignored by the unhandled
rejection handler if not.

Example usage:

getAsync().tap(() => Zotero.Promise.check(this.win));

If this.win is cleaned up while getAsync() is being resolved, subsequent
lines won't be run, and nothing will be logged to the console.

chrome/content/zotero/bindings/attachmentbox.xml

@@ -142,7 +142,8 @@
 					Zotero.spawn(function* () {
 						Zotero.debug('Refreshing attachment box');
 						
-						yield Zotero.Promise.all([this.item.loadItemData(), this.item.loadNote()]);
+						yield Zotero.Promise.all([this.item.loadItemData(), this.item.loadNote()])
+							.tap(() => Zotero.Promise.check(this.item));
 						
 						var attachmentBox = document.getAnonymousNodes(this)[0];
 						var title = this._id('title');
@@ -254,7 +255,8 @@
 						
 						// Page count
 						if (this.displayPages) {
-							var pages = yield Zotero.Fulltext.getPages(this.item.id);
+							var pages = yield Zotero.Fulltext.getPages(this.item.id)
+								.tap(() => Zotero.Promise.check(this.item));
 							var pages = pages ? pages.total : null;
 							if (pages) {
 								this._id("pages-label").value = Zotero.getString('itemFields.pages')
@@ -273,7 +275,8 @@
 						if (this.displayDateModified) {
 							this._id("dateModified-label").value = Zotero.getString('itemFields.dateModified')
 								+ Zotero.getString('punctuation.colon');
-							var mtime = yield this.item.attachmentModificationTime;
+							var mtime = yield this.item.attachmentModificationTime
+								.tap(() => Zotero.Promise.check(this.item));
 							if (mtime) {
 								this._id("dateModified").value = new Date(mtime).toLocaleString();
 							}
@@ -292,7 +295,8 @@
 						
 						// Full-text index information
 						if (this.displayIndexed) {
-							yield this.updateItemIndexedState();
+							yield this.updateItemIndexedState()
+								.tap(() => Zotero.Promise.check(this.item));
 							indexStatusRow.hidden = false;
 						}
 						else {
@@ -471,7 +475,8 @@
 						var indexStatus = this._id('index-status');
 						var reindexButton = this._id('reindex');
 						
-						var status = yield Zotero.Fulltext.getIndexedState(this.item);
+						var status = yield Zotero.Fulltext.getIndexedState(this.item)
+							.tap(() => Zotero.Promise.check(this.item));
 						var str = 'fulltext.indexState.';
 						switch (status) {
 							case Zotero.Fulltext.INDEX_STATE_UNAVAILABLE:
@@ -495,7 +500,13 @@
 						var str = Zotero.getString('pane.items.menu.reindexItem');
 						reindexButton.setAttribute('tooltiptext', str);
 						
-						if (this.editable && (yield Zotero.Fulltext.canReindex(this.item))) {
+						var show = false;
+						if (this.editable) {
+							show = yield Zotero.Fulltext.canReindex(this.item)
+								.tap(() => Zotero.Promise.check(this.item));
+						}
+						
+						if (show) {
 							reindexButton.setAttribute('hidden', false);
 						}
 						else {

chrome/content/zotero/xpcom/zotero.js

@@ -165,6 +165,25 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 		this.initializationPromise = this.initializationDeferred.promise;
 		this.locked = true;
 		
+		// Add a function to Zotero.Promise to check whether a value is still defined, and if not
+		// to throw a specific error that's ignored by the unhandled rejection handler in
+		// bluebird.js. This allows for easily cancelling promises when they're no longer
+		// needed, for example after a view is destroyed.
+		//
+		// Example usage:
+		//
+		// getAsync.tap(() => Zotero.Promise.check(this.win))
+		//
+		// If this.win is cleaned up while getAsync() is being resolved, subsequent lines won't
+		// be run, and nothing will be logged to the console.
+		this.Promise.check = function (val) {
+			if (!val && val !== 0) {
+				let e = new Error;
+				e.name = "ZoteroPromiseInterrupt";
+				throw e;
+			}
+		};
+		
 		// Load in the preferences branch for the extension
 		Zotero.Prefs.init();
 		Zotero.Debug.init(options && options.forceDebugLog);

resource/bluebird.js

@@ -91,12 +91,16 @@
     Promise = e();
     // TEMP: Only turn on if debug logging enabled?
     Promise.longStackTraces();
-    Promise.onPossiblyUnhandledRejection(function(error) {
+    Promise.onPossiblyUnhandledRejection(function (e, promise) {
+		if (e.name == 'ZoteroPromiseInterrupt') {
+			return;
+		}
+    	
 		// Ignore some errors during tests
-		if (error.message && error.message.indexOf(' -- ignore') != -1) return;
+		if (e.message && e.message.indexOf(' -- ignore') != -1) return;
 		
-        self.debug('Unhandled rejection:\n\n' + error.stack);
+        self.debug('Unhandled rejection:\n\n' + e.stack);
-        throw error;
+        throw e;
     });
     return;