composer: show error bubble on file upload error

components/app.js

@@ -220,6 +220,7 @@ export default class App extends Component {
 		this.handleAddNetworkClick = this.handleAddNetworkClick.bind(this);
 		this.handleNetworkSubmit = this.handleNetworkSubmit.bind(this);
 		this.handleNetworkRemove = this.handleNetworkRemove.bind(this);
+		this.showError = this.showError.bind(this);
 		this.handleDismissError = this.handleDismissError.bind(this);
 		this.handleAuthSubmit = this.handleAuthSubmit.bind(this);
 		this.handleRegisterSubmit = this.handleRegisterSubmit.bind(this);
@@ -2292,6 +2293,7 @@ export default class App extends Component {
 				client=${activeClient}
 				readOnly=${composerReadOnly}
 				onSubmit=${this.handleComposerSubmit}
+				onError=${this.showError}
 				autocomplete=${this.autocomplete}
 				commandOnly=${commandOnly}
 				maxLen=${privmsgMaxLen}

components/composer.js

@@ -185,7 +185,13 @@ export default class Composer extends Component {
 			promises.push(this.uploadFile(file));
 		}
 
-		let urls = await Promise.all(promises);
+		let urls;
+		try {
+			urls = await Promise.all(promises);
+		} catch (err) {
+			this.props.onError(new Error("Failed to upload files", { cause: err }));
+			return;
+		}
 
 		this.setState((state) => {
 			if (state.text) {