set_logger wants to panic

README.md

@@ -72,7 +72,7 @@ extern crate log;
 extern crate env_logger;
 
 fn main() {
-    env_logger::init().unwrap();
+    env_logger::init();
 
     info!("starting up");
 
@@ -185,5 +185,5 @@ builder.target(Target::Stdout);
 if env::var("RUST_LOG").is_ok() {
     builder.parse(&env::var("RUST_LOG").unwrap());
 }
-builder.init().unwrap();
+builder.init();
 ```

env/src/lib.rs

@@ -20,7 +20,7 @@
 //! use log::Level;
 //!
 //! fn main() {
-//!     env_logger::init().unwrap();
+//!     env_logger::init();
 //!
 //!     debug!("this is a debug {}", "message");
 //!     error!("this is printed by default");
@@ -194,7 +194,7 @@ pub struct Logger {
 ///        builder.parse(&env::var("RUST_LOG").unwrap());
 ///     }
 ///
-///     builder.init().unwrap();
+///     builder.init();
 ///
 ///     error!("error message");
 ///     info!("info message");
@@ -273,15 +273,27 @@ impl Builder {
     ///
     /// This should be called early in the execution of a Rust program, and the
     /// global logger may only be initialized once. Future initialization
-    /// attempts will return an error.
-    pub fn init(&mut self) -> Result<(), SetLoggerError> {
-        log::set_logger(|max_level| {
+    /// attempts will return error.
+    pub fn try_init(&mut self) -> Result<(), SetLoggerError> {
+        log::try_set_logger(|max_level| {
             let logger = self.build();
             max_level.set(logger.filter());
             Box::new(logger)
         })
     }
 
+    /// Initializes the global logger with an env logger.
+    ///
+    /// This should be called early in the execution of a Rust program, and the
+    /// global logger may only be initialized once. Future initialization
+    /// attempts will panic.
+    pub fn init(&mut self) {
+        let logger = self.build();
+        let filter = logger.filter();
+        let logger = Box::new(logger);
+        log::set_logger(logger, filter);
+    }
+
     /// Build an env logger.
     pub fn build(&mut self) -> Logger {
         if self.directives.is_empty() {
@@ -375,7 +387,22 @@ struct Directive {
 /// This should be called early in the execution of a Rust program, and the
 /// global logger may only be initialized once. Future initialization attempts
 /// will return an error.
-pub fn init() -> Result<(), SetLoggerError> {
+pub fn try_init() -> Result<(), SetLoggerError> {
+    let mut builder = Builder::new();
+
+    if let Ok(s) = env::var("RUST_LOG") {
+        builder.parse(&s);
+    }
+
+    builder.try_init()
+}
+
+/// Initializes the global logger with an env logger.
+///
+/// This should be called early in the execution of a Rust program, and the
+/// global logger may only be initialized once. Future initialization attempts
+/// will panic.
+pub fn init() {
     let mut builder = Builder::new();
 
     if let Ok(s) = env::var("RUST_LOG") {

env/tests/regexp_filter.rs

@@ -14,7 +14,7 @@ fn main() {
 }
 
 fn child_main() {
-    env_logger::init().unwrap();
+    env_logger::init();
     info!("XYZ Message");
 }
 

src/lib.rs

@@ -83,7 +83,7 @@
 //! fn main() {
 //!     // Select env_logger, one possible logger implementation
 //!     // (see https://doc.rust-lang.org/log/env_logger/index.html)
-//!     env_logger::init().unwrap();
+//!     env_logger::init();
 //!
 //!     info!("starting up");
 //!     error!("error: {}", 404);
@@ -141,11 +141,10 @@
 //! # }
 //! # fn main() {}
 //! # #[cfg(feature = "use_std")]
-//! pub fn init() -> Result<(), SetLoggerError> {
-//!     log::set_logger(|max_level| {
-//!         max_level.set(LevelFilter::Info);
-//!         Box::new(SimpleLogger)
-//!     })
+//! pub fn init() {
+//!     let filter = LevelFilter::Info;
+//!     let logger = Box::new(SimpleLogger);
+//!     log::set_logger(logger, filter);
 //! }
 //! ```
 //!
@@ -171,7 +170,7 @@
 //! #   fn flush(&self) {}
 //! # }
 //! # fn main() {}
-//! pub fn init() -> Result<(), SetLoggerError> {
+//! pub fn try_init() -> Result<(), SetLoggerError> {
 //!     unsafe {
 //!         log::set_logger_raw(|max_level| {
 //!             static LOGGER: SimpleLogger = SimpleLogger;
@@ -825,21 +824,46 @@ pub fn max_level() -> LevelFilter {
 /// highest log level that the logger will not ignore.
 ///
 /// This function may only be called once in the lifetime of a program. Any log
-/// events that occur before the call to `set_logger` completes will be
+/// events that occur before the call to `try_set_logger` completes will be
 /// ignored.
 ///
 /// This function does not typically need to be called manually. Logger
 /// implementations should provide an initialization method that calls
-/// `set_logger` internally.
+/// `try_set_logger` internally.
 ///
 /// Requires the `use_std` feature (enabled by default).
 #[cfg(feature = "use_std")]
-pub fn set_logger<M>(make_logger: M) -> Result<(), SetLoggerError>
+pub fn try_set_logger<M>(make_logger: M) -> Result<(), SetLoggerError>
     where M: FnOnce(MaxLevelFilter) -> Box<Log>
 {
     unsafe { set_logger_raw(|max_level| mem::transmute(make_logger(max_level))) }
 }
 
+/// Sets the global logger.
+///
+/// This function may only be called once in the lifetime of a program. Any log
+/// events that occur before the call to `set_logger` completes will be
+/// ignored.
+///
+/// This function will panic on future initialization attempts.
+///
+/// This function does not typically need to be called manually. Logger
+/// implementations should provide an initialization method that calls
+/// `set_logger` internally.
+///
+/// Requires the `use_std` feature (enabled by default).
+///
+/// # Panics
+///
+/// The function will panic if it is called more than once.
+#[cfg(feature = "use_std")]
+pub fn set_logger(logger: Box<Log>, filter: LevelFilter) {
+    match try_set_logger(|max| { max.set(filter); logger }) {
+        Ok(()) => {}
+        Err(_) => panic!("global logger is already initialized"),
+    }
+}
+
 /// Sets the global logger from a raw pointer.
 ///
 /// This function is similar to `set_logger` except that it is usable in

tests/filters.rs

@@ -6,9 +6,9 @@ use log::{Level, LevelFilter, Log, Record, Metadata};
 use log::MaxLevelFilter;
 
 #[cfg(feature = "use_std")]
-use log::set_logger;
+use log::try_set_logger;
 #[cfg(not(feature = "use_std"))]
-fn set_logger<M>(make_logger: M) -> Result<(), log::SetLoggerError>
+fn try_set_logger<M>(make_logger: M) -> Result<(), log::SetLoggerError>
     where M: FnOnce(MaxLevelFilter) -> Box<Log>
 {
     unsafe { log::set_logger_raw(|x| std::mem::transmute(make_logger(x))) }
@@ -33,15 +33,14 @@ impl Log for Logger {
 
 fn main() {
     let mut a = None;
-    set_logger(|max| {
-                   let me = Arc::new(State {
-                                         last_log: Mutex::new(None),
-                                         filter: max,
-                                     });
-                   a = Some(me.clone());
-                   Box::new(Logger(me))
-               })
-            .unwrap();
+    try_set_logger(|max| {
+       let me = Arc::new(State {
+                            last_log: Mutex::new(None),
+                            filter: max,
+                         });
+       a = Some(me.clone());
+       Box::new(Logger(me))
+    }).unwrap();
     let a = a.unwrap();
 
     test(&a, LevelFilter::Off);

tests/max_level_features/main.rs

@@ -1,13 +1,14 @@
-#[macro_use] extern crate log;
+#[macro_use]
+extern crate log;
 
 use std::sync::{Arc, Mutex};
 use log::{Level, LevelFilter, Log, Record, Metadata};
 use log::MaxLevelFilter;
 
 #[cfg(feature = "use_std")]
-use log::set_logger;
+use log::try_set_logger;
 #[cfg(not(feature = "use_std"))]
-fn set_logger<M>(make_logger: M) -> Result<(), log::SetLoggerError>
+fn try_set_logger<M>(make_logger: M) -> Result<(), log::SetLoggerError>
     where M: FnOnce(MaxLevelFilter) -> Box<Log> {
     unsafe {
         log::set_logger_raw(|x| std::mem::transmute(make_logger(x)))
@@ -33,7 +34,7 @@ impl Log for Logger {
 
 fn main() {
     let mut a = None;
-    set_logger(|max| {
+    try_set_logger(|max| {
         let me = Arc::new(State {
             last_log: Mutex::new(None),
             filter: max,