commit 946ac296b56906a2134e41dfeb70dd8deb70a098
parent 5a0d2702c25946b391432d3d82bb082ee323091c
Author: Ben Dean-Kawamura <bdk@mozilla.com>
Date: Thu, 23 Oct 2025 14:19:48 +0000
Bug 1995771 - Document Rust component logging on Android/iOS, r=markh
The new parts are copied these from
https://github.com/mozilla/application-services/blob/main/docs/logging.md
Other than that I just updated the markdown header levels.
Differential Revision: https://phabricator.services.mozilla.com/D269622
Diffstat:
1 file changed, 37 insertions(+), 3 deletions(-)
diff --git a/docs/rust-components/developing-rust-components/logging.md b/docs/rust-components/developing-rust-components/logging.md
@@ -5,7 +5,9 @@
Make sure to use the logging macros from the `tracing_support` crate (`tracing_support::debug!`, `tracing_support::info!`, etc).
`error_support` also contains a copy of the same macros, which can be a more convenient import for components that already depend on `error_support`.
-## Forwarding logs to the browser console
+## Logs on Desktop
+
+### Forwarding logs to the browser console
Rust logs can be forwarded to the JavaScript browser console using the `toolkit.rust-components.logging.crates` pref.
This pref stores a comma-separated list of items, where each item is a logging target and an optional logging level.
@@ -27,12 +29,12 @@ For example, `logins,autofill:warn,error,suggest` would forward:
- Suggest logs at the debug level
- All other logs at the error level.
-## Error reporting
+### Error reporting
Errors from the error reporter have level `error` so they will be forwarded to the browser console by default.
Add the `app-services-error-reporter` target to get breadcrumbs forwarded as well.
-## setupLoggerForTarget
+### setupLoggerForTarget
An alternative logging mechanism is `setupLoggerForTarget`.
This allows you to connect tracing events to the `Log.sys.mjs` logger.
@@ -47,3 +49,35 @@ ChromeUtils.defineESModuleGetters(lazy, {
// In your initialization code
lazy.setupLoggerForTarget("tabs", "Sync.Engine.Tabs");
```
+
+## Logs on Android
+
+On android, logs currently go to logcat.
+Android Studio can be used to view the logcat logs; connect the device over USB
+and view the Logcat tab at the bottom of Android Studio. Check to make sure you
+have the right device selected at the top left of the Logcat pane, and the
+correct process to the right of that. One trick to avoid having to select the
+correct process (as there are main and content processes) is to choose "No
+Filters" from the menu on the top right of the Logcat pane. Then, use the search
+box to search for the log messages you are trying to find.
+
+There are also many other utilities, command line and graphical, that can be
+used to view logcat logs from a connected android device in a more flexible
+manner.
+
+### Changing the loglevel in Android
+
+If you need more verbose logging, after the call to `RustLog.enable()` in
+`FenixApplication`, you may call `RustLog.setMaxLevel(Log.Priority.DEBUG,
+true)`.
+
+## Logs on iOS
+
+If you're using `Xcode`, then you can view the logs in the debugger.
+
+If you're not using `Xcode`, then:
+
+* Navigate to the settings page
+* tap the version number 5 times to get to the secret menu
+* Select "copy log files to container"
+* Find the logs on your files folder
