feat: add try_start() and try_with_level()

src/lib.rs

@@ -9,6 +9,8 @@
 //! log::info!("Listening on port 8080");
 //! ```
 
+use log::SetLoggerError;
+
 pub use log::LevelFilter;
 
 #[cfg(not(target_arch = "wasm32"))]
@@ -22,42 +24,101 @@ mod wasm;
 
 /// Starts logging depending on current environment.
 ///
-/// # Log output
+/// ## Log output
 ///
 /// - when compiling with `--release` uses ndjson.
 /// - pretty-prints otherwise.
 /// - works in WASM out of the box.
 ///
-/// # Examples
+/// ## Examples
 ///
 /// ```
 /// femme::start();
 /// log::warn!("Unauthorized access attempt on /login");
 /// log::info!("Listening on port 8080");
 /// ```
+///
+/// ## Panics
+///
+/// This function will panic if it is called more than once, or if another library has already initialized a global logger.
+///
 pub fn start() {
-    with_level(LevelFilter::Info);
+    with_level(LevelFilter::Info)
+}
+
+/// Starts logging depending on current environment.
+///
+/// ## Log output
+///
+/// - when compiling with `--release` uses ndjson.
+/// - pretty-prints otherwise.
+/// - works in WASM out of the box.
+///
+/// ## Examples
+///
+/// ```
+/// femme::try_start().ok(); // Handle Result or ignore
+/// log::warn!("Unauthorized access attempt on /login");
+/// log::info!("Listening on port 8080");
+/// ```
+///
+/// ## Errors
+///
+/// This function will fail if it is called more than once, or if another library has already initialized a global logger.
+///
+pub fn try_start() -> Result<(), SetLoggerError> {
+    try_with_level(LevelFilter::Info)
 }
 
 /// Start logging with a log level.
 ///
 /// All messages under the specified log level will statically be filtered out.
 ///
-/// # Examples
+/// ## Examples
+///
 /// ```
-/// femme::with_level(log::LevelFilter::Trace);
+/// femme::with_level(log::LevelFilter::Warn);
+/// log::warn!("Unauthorized access attempt on /login");
+/// log::info!("Listening on port 8080"); // Will be hidden
 /// ```
+///
+/// ## Panics
+///
+/// This function will panic if it is called more than once, or if another library has already initialized a global logger.
+///
 pub fn with_level(level: log::LevelFilter) {
+    try_with_level(level).expect("Could not start logging")
+}
+
+/// Start logging with a log level.
+///
+/// All messages under the specified log level will statically be filtered out.
+///
+/// ## Examples
+///
+/// ```
+/// femme::try_with_level(log::LevelFilter::Warn).ok(); // Handle Result or ignore
+/// log::warn!("Unauthorized access attempt on /login");
+/// log::info!("Listening on port 8080"); // Will be hidden
+/// ```
+///
+/// ## Errors
+///
+/// This function will fail if it is called more than once, or if another library has already initialized a global logger.
+///
+pub fn try_with_level(level: log::LevelFilter) -> Result<(), SetLoggerError> {
     #[cfg(target_arch = "wasm32")]
-    wasm::start(level);
+    wasm::start(level)?;
 
     #[cfg(not(target_arch = "wasm32"))]
     {
         // Use ndjson in release mode, pretty logging while debugging.
         if cfg!(debug_assertions) {
-            pretty::start(level);
+            pretty::start(level)?;
         } else {
-            ndjson::start(level);
+            ndjson::start(level)?;
         }
     }
+
+    Ok(())
 }

src/ndjson.rs

@@ -1,14 +1,15 @@
 //! Print logs as ndjson.
 
-use log::{kv, LevelFilter, Log, Metadata, Record};
+use log::{kv, LevelFilter, Log, Metadata, Record, SetLoggerError};
 use std::io::{self, StdoutLock, Write};
 use std::time;
 
 /// Start logging.
-pub(crate) fn start(level: LevelFilter) {
+pub(crate) fn start(level: LevelFilter) -> Result<(), SetLoggerError> {
     let logger = Box::new(Logger {});
-    log::set_boxed_logger(logger).expect("Could not start logging");
+    log::set_boxed_logger(logger)?;
     log::set_max_level(level);
+    Ok(())
 }
 
 #[derive(Debug)]

src/pretty.rs

@@ -1,6 +1,6 @@
 //! Pretty print logs.
 
-use log::{kv, Level, LevelFilter, Log, Metadata, Record};
+use log::{kv, Level, LevelFilter, Log, Metadata, Record, SetLoggerError};
 use std::io::{self, StdoutLock, Write};
 
 // ANSI term codes.
@@ -11,10 +11,11 @@ const GREEN: &'static str = "\x1b[32m";
 const YELLOW: &'static str = "\x1b[33m";
 
 /// Start logging.
-pub(crate) fn start(level: LevelFilter) {
+pub(crate) fn start(level: LevelFilter) -> Result<(), SetLoggerError> {
     let logger = Box::new(Logger {});
-    log::set_boxed_logger(logger).expect("Could not start logging");
+    log::set_boxed_logger(logger)?;
     log::set_max_level(level);
+    Ok(())
 }
 
 #[derive(Debug)]

src/wasm.rs

@@ -1,16 +1,17 @@
 //! Print logs as ndjson.
 
 use js_sys::Object;
-use log::{kv, Level, LevelFilter, Log, Metadata, Record};
+use log::{kv, Level, LevelFilter, Log, Metadata, Record, SetLoggerError};
 use wasm_bindgen::prelude::*;
 
 use std::collections::HashMap;
 
 /// Start logging.
-pub(crate) fn start(level: LevelFilter) {
+pub(crate) fn start(level: LevelFilter) -> Result<(), SetLoggerError> {
     let logger = Box::new(Logger {});
-    log::set_boxed_logger(logger).expect("Could not start logging");
+    log::set_boxed_logger(logger)?;
     log::set_max_level(level);
+    Ok(())
 }
 
 #[derive(Debug)]