ExternalLinkHandler actor: Open some links internally, incl. styles (#4505)

chrome/content/zotero/actors/ExternalLinkHandlerChild.jsm

@@ -7,18 +7,62 @@ class ExternalLinkHandlerChild extends JSWindowActorChild {
 			case "click": {
 				let { button, target } = event;
 				if (button !== 0) {
-					break;
+					return;
 				}
-				if ((target.localName === 'a' || target.localName === 'area') && target.href
-						|| target.localName === 'label' && target.classList.contains('text-link')) {
-					event.stopPropagation();
-					event.preventDefault();
-					await this._sendLaunchURL(target.href || target.getAttribute('href'));
+				
+				let href;
+				if (target.localName === 'a' || target.localName === 'area') {
+					href = target.href;
 				}
+				else if (target.localName === 'label' && target.classList.contains('text-link')) {
+					href = target.getAttribute('href');
+				}
+				
+				if (!href || this._shouldOpenInternally(href)) {
+					return;
+				}
+				
+				event.stopPropagation();
+				event.preventDefault();
+				await this._sendLaunchURL(href);
 				break;
 			}
 		}
 	}
+
+	_shouldOpenInternally(href) {
+		let hrefURL;
+		try {
+			hrefURL = new URL(href);
+		}
+		catch (e) {
+			// Not a valid URL: open externally
+			return false;
+		}
+		let currentURL = this.contentWindow.location;
+		
+		// eslint-disable-next-line no-script-url
+		if (hrefURL.protocol === 'javascript:') {
+			// Link executes a script: open internally
+			return true;
+		}
+		
+		if (hrefURL.origin + hrefURL.pathname + hrefURL.search === currentURL.origin + currentURL.pathname + currentURL.search
+				&& hrefURL.hash) {
+			// Link points to the same page with a hash: open internally
+			return true;
+		}
+
+		if (hrefURL.origin === 'https://www.zotero.org' && /^\/styles\/[^/?#]+$/.test(hrefURL.pathname)) {
+			// Links points directly to CSL in the repo: open internally
+			return true;
+		}
+		
+		// Everything else: open externally
+		// This might include links that Zotero.launchURL() is just going to reject,
+		// like chrome:// URLs, but we'll just let it print that error
+		return false;
+	}
 	
 	async _sendLaunchURL(url) {
 		await this.sendAsyncMessage("launchURL", url);