Allow clients to provide a custom logger instance

[mbarta]

Summary

This branch replaces Hotwire Native's built-in, Logcat-only logging with a pluggable logging system. Previously the library logged directly to Android's Logcat and only offered a single on/off switch (debugLoggingEnabled) to control debug output. Apps had no way to capture library logs, route them to their own logging/crash-reporting stack, or control verbosity.

Now the library logs through a HotwireLogger interface. Apps can either keep the built-in default (which prints to Logcat), adjust the log level, or supply their own implementation to handle log messages however they like.

What changed

• Introduced a HotwireLogger interface plus a HotwireLogLevel enum for filtering by severity.
• Added a DefaultHotwireLogger that prints to Logcat, used automatically unless an app opts out.
• All internal core and navigation logging now flows through the configured logger, including the OkHttp HTTP logging interceptor.
• The HTTP logging interceptor is now always installed and simply defers to the logger to decide what (if anything) to emit, rather than being toggled on and off.
• The demo app now demonstrates setting the log level based on the build type.

Public API changes

Removed

• Hotwire.config.debugLoggingEnabled — the boolean flag no longer exists. Behavior is now controlled through the logger and its log level instead.

Added

• Hotwire.config.logger: HotwireLogger — set this to provide a custom logger. Defaults to DefaultHotwireLogger.
• HotwireLogger interface (public, implementable by apps).
• HotwireLogLevel enum: VERBOSE, DEBUG, INFO, WARN, ERROR, NONE.
• DefaultHotwireLogger — the built-in Logcat implementation.

Migration: replace Hotwire.config.debugLoggingEnabled = BuildConfig.DEBUG with a log-level assignment, e.g.:

Hotwire.config.logger.logLevel = if (BuildConfig.DEBUG) HotwireLogLevel.DEBUG else HotwireLogLevel.NONE

The HotwireLogger interface

Apps can implement this interface to receive every log message the library produces and handle it however they want — forward to their own logger, send to a crash reporter, filter, or drop entirely.

interface HotwireLogger {
    var logLevel: HotwireLogLevel
    fun v(tag: String, msg: () -> String)
    fun d(tag: String, msg: () -> String)
    fun i(tag: String, msg: () -> String)
    fun w(tag: String, msg: () -> String)
    fun e(tag: String, throwable: Throwable?, msg: () -> String)
}

Notes on the design:

• Level-based filtering. logLevel lets consumers set a minimum severity. Setting it to NONE silences all output. The default logger uses this to decide what reaches Logcat, and custom loggers are expected to honor it too.
• Lazy message providers. Messages are passed as lambdas (() -> String) so that potentially expensive log strings are only built when the message will actually be emitted.
• Standard severity methods mirror Android's conventions: verbose, debug, info, warn, and error. The error method accepts an optional Throwable so exceptions can be logged with full context.

To use a custom logger:

Hotwire.config.logger = MyCustomLogger()

[jhutarek]

Thanks! I'd consider a couple of tweaks. 🙏

[zoejessica]

I started a draft PR to update the website here: hotwired/hotwire-native-site#91

[jayohms]

@mbarta @jhutarek Please take a look at the latest changes. By introducing a HotwireLogLevel into the HotwireLogger interface, we no longer need to make assumptions about what to log. We don't log anything by default. The consumer can explicitly set the Hotwire.config.logger.logLevel in their application without having to write a custom HotwireLogger implementation.

[mbarta]

Happy with the latest changes @jayohms! It's closer to a standard logger implementation where you can set the desired log level for the default logger while still being able to provide your own if more customisation is needed 👍 Thanks!