actions [nfc]: Move open-link logic here, from lib/widgets/content

We'll use when we add a "Learn more"-button param to
showErrorDialog, coming up.

Author: chrisbobbe

lib/widgets/actions.dart

@@ -281,4 +281,30 @@ abstract final class PlatformActions {
         SnackBar(behavior: SnackBarBehavior.floating, content: successContent));
     }
   }
+
+  /// Opens a URL with [ZulipBinding.launchUrl], with an error dialog on failure.
+  // TODO widget tests
+  static Future<void> launchUrl(BuildContext context, Uri url) async {
+    final globalSettings = GlobalStoreWidget.settingsOf(context);
+
+    bool launched = false;
+    String? errorMessage;
+    try {
+      launched = await ZulipBinding.instance.launchUrl(url,
+        mode: globalSettings.getUrlLaunchMode(url));
+    } on PlatformException catch (e) {
+      errorMessage = e.message;
+    }
+    if (!launched) { // TODO(log)
+      if (!context.mounted) return;
+
+      final zulipLocalizations = ZulipLocalizations.of(context);
+      showErrorDialog(context: context,
+        title: zulipLocalizations.errorCouldNotOpenLinkTitle,
+        message: [
+          zulipLocalizations.errorCouldNotOpenLink(url.toString()),
+          if (errorMessage != null) errorMessage,
+        ].join("\n\n"));
+    }
+  }
 }

lib/widgets/content.dart

@@ -4,17 +4,16 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
-import 'package:flutter/services.dart';
 import 'package:html/dom.dart' as dom;
 import 'package:intl/intl.dart';
 
 import '../api/core.dart';
 import '../api/model/model.dart';
 import '../generated/l10n/zulip_localizations.dart';
 import '../model/avatar_url.dart';
-import '../model/binding.dart';
 import '../model/content.dart';
 import '../model/internal_link.dart';
+import 'actions.dart';
 import 'code_block.dart';
 import 'dialog.dart';
 import 'icons.dart';
@@ -1406,26 +1405,7 @@ void _launchUrl(BuildContext context, String urlString) async {
     return;
   }
 
-  final globalSettings = GlobalStoreWidget.settingsOf(context);
-  bool launched = false;
-  String? errorMessage;
-  try {
-    launched = await ZulipBinding.instance.launchUrl(url,
-      mode: globalSettings.getUrlLaunchMode(url));
-  } on PlatformException catch (e) {
-    errorMessage = e.message;
-  }
-  if (!launched) { // TODO(log)
-    if (!context.mounted) return;
-
-    final zulipLocalizations = ZulipLocalizations.of(context);
-    showErrorDialog(context: context,
-      title: zulipLocalizations.errorCouldNotOpenLinkTitle,
-      message: [
-        zulipLocalizations.errorCouldNotOpenLink(url.toString()),
-        if (errorMessage != null) errorMessage,
-      ].join("\n\n"));
-  }
+  await PlatformActions.launchUrl(context, url);
 }
 
 /// Like [Image.network], but includes [authHeader] if [src] is on-realm.

lib/widgets/login.dart

@@ -343,6 +343,9 @@ class _LoginPageState extends State<LoginPage> {
       // Could set [_inProgress]… but we'd need to unset it if the web-auth
       // attempt is aborted (by the user closing the browser, for example),
       // and I don't think we can reliably know when that happens.
+
+      // Not using [PlatformActions.launchUrl] because web auth needs special
+      // error handling.
       await ZulipBinding.instance.launchUrl(url, mode: LaunchMode.inAppBrowserView);
     } catch (e) {
       assert(debugLog(e.toString()));