feat(level): add off, debug, and trace options for default Level

add example for changing the default, and mention in the docs

examples/default_level.rs

@@ -0,0 +1,33 @@
+use clap::Parser;
+use clap_verbosity_flag::{InfoLevel, Verbosity};
+
+/// Foo
+#[derive(Debug, Parser)]
+struct DefaultCli {
+    #[command(flatten)]
+    verbose: Verbosity,
+}
+
+/// Bar
+#[derive(Debug, Parser)]
+struct InfoCli {
+    #[command(flatten)]
+    verbose: Verbosity<InfoLevel>,
+}
+
+fn main() {
+    let error_cli = DefaultCli::parse();
+
+    dbg!(&error_cli.verbose);
+
+    assert_eq!(
+        error_cli.verbose.log_level_filter(),
+        log::LevelFilter::Error
+    );
+
+    let info_cli = InfoCli::parse();
+
+    dbg!(&info_cli.verbose);
+
+    assert_eq!(info_cli.verbose.log_level_filter(), log::LevelFilter::Info);
+}

src/lib.rs

@@ -40,7 +40,7 @@
 //! - `-vvv` show debug
 //! - `-vvvv` show trace
 //!
-//! You can also customize the default logging level:
+//! You can also customize the default logging level with the `Verbosity<T>` generic:
 //! ```rust,no_run
 //! # use clap::Parser;
 //! use clap_verbosity_flag::{Verbosity, InfoLevel};
@@ -52,6 +52,7 @@
 //!     verbose: Verbosity<InfoLevel>,
 //! }
 //! ```
+//! See `default_level` in examples.
 //!
 //! Or implement our [`LogLevel`] trait to customize the default log level and help output.
 
@@ -210,6 +211,36 @@ impl LogLevel for InfoLevel {
     }
 }
 
+/// Default to [`log::Level::Debug`]
+#[derive(Copy, Clone, Debug, Default)]
+pub struct DebugLevel;
+
+impl LogLevel for DebugLevel {
+    fn default() -> Option<log::Level> {
+        Some(log::Level::Debug)
+    }
+}
+
+/// Default to [`log::Level::Trace`]
+#[derive(Copy, Clone, Debug, Default)]
+pub struct TraceLevel;
+
+impl LogLevel for TraceLevel {
+    fn default() -> Option<log::Level> {
+        Some(log::Level::Trace)
+    }
+}
+
+/// Default to [`None`]
+#[derive(Copy, Clone, Debug, Default)]
+pub struct OffLevel;
+
+impl LogLevel for OffLevel {
+    fn default() -> Option<log::Level> {
+        None
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;