add unit tests, docs related to available log level names

README.md

@@ -39,14 +39,44 @@ fn main() {
 }
 ```
 
-Then when running the executable, specify a value for the `RUST_LOG`
+Then when running the executable, specify a value for the **`RUST_LOG`**
 environment variable that corresponds with the log messages you want to show.
 
 ```bash
 $ RUST_LOG=info ./main
 [2018-11-03T06:09:06Z INFO  default] starting up
 ```
 
+The letter case is not significant for the logging level names; e.g., `debug`,
+`DEBUG`, and `dEbuG` all represent the same logging level. Therefore, the
+previous example could also have been written this way, specifying the log
+level as `INFO` rather than as `info`:
+
+```bash
+$ RUST_LOG=INFO ./main
+[2018-11-03T06:09:06Z INFO  default] starting up
+```
+
+So which form should you use? For consistency, our convention is to use lower
+case names. Where our docs do use other forms, they do so in the context of
+specific examples, so you won't be surprised if you see similar usage in the
+wild.
+
+The log levels that may be specified correspond to the [`log::Level`][level-enum]
+enum from the `log` crate. They are:
+
+   * `error`
+   * `warn`
+   * `info`
+   * `debug`
+   * `trace`
+
+[level-enum]:  https://docs.rs/log/latest/log/enum.Level.html  "log::Level (docs.rs)"
+
+There is also a pseudo logging level, `off`, which may be specified to disable
+all logging for a given module or for the entire application. As with the
+logging levels, the letter case is not significant.
+
 `env_logger` can be configured in other ways besides an environment variable. See [the examples](https://github.com/env-logger-rs/env_logger/tree/master/examples) for more approaches.
 
 ### In tests

src/filter/mod.rs

@@ -395,13 +395,193 @@ mod tests {
         assert!(!enabled(&logger.directives, Level::Debug, "crate2"));
     }
 
+    // Some of our tests are only correct or complete when they cover the full
+    // universe of variants for log::Level. In the unlikely event that a new
+    // variant is added in the future, this test will detect the scenario and
+    // alert us to the need to review and update the tests. In such a
+    // situation, this test will fail to compile, and the error message will
+    // look something like this:
+    //
+    //     error[E0004]: non-exhaustive patterns: `NewVariant` not covered
+    //        --> src/filter/mod.rs:413:15
+    //         |
+    //     413 |         match level_universe {
+    //         |               ^^^^^^^^^^^^^^ pattern `NewVariant` not covered
+    #[test]
+    fn ensure_tests_cover_level_universe() {
+        let level_universe: Level = Level::Trace; // use of trace variant is arbitrary
+        match level_universe {
+            Level::Error | Level::Warn | Level::Info | Level::Debug | Level::Trace => (),
+        }
+    }
+
     #[test]
     fn parse_default() {
         let logger = Builder::new().parse("info,crate1::mod1=warn").build();
         assert!(enabled(&logger.directives, Level::Warn, "crate1::mod1"));
         assert!(enabled(&logger.directives, Level::Info, "crate2::mod2"));
     }
 
+    #[test]
+    fn parse_default_bare_level_off_lc() {
+        let logger = Builder::new().parse("off").build();
+        assert!(!enabled(&logger.directives, Level::Error, ""));
+        assert!(!enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_off_uc() {
+        let logger = Builder::new().parse("OFF").build();
+        assert!(!enabled(&logger.directives, Level::Error, ""));
+        assert!(!enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_error_lc() {
+        let logger = Builder::new().parse("error").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(!enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_error_uc() {
+        let logger = Builder::new().parse("ERROR").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(!enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_warn_lc() {
+        let logger = Builder::new().parse("warn").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_warn_uc() {
+        let logger = Builder::new().parse("WARN").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(!enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_info_lc() {
+        let logger = Builder::new().parse("info").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_info_uc() {
+        let logger = Builder::new().parse("INFO").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(!enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_debug_lc() {
+        let logger = Builder::new().parse("debug").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_debug_uc() {
+        let logger = Builder::new().parse("DEBUG").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(enabled(&logger.directives, Level::Debug, ""));
+        assert!(!enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_trace_lc() {
+        let logger = Builder::new().parse("trace").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(enabled(&logger.directives, Level::Debug, ""));
+        assert!(enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    #[test]
+    fn parse_default_bare_level_trace_uc() {
+        let logger = Builder::new().parse("TRACE").build();
+        assert!(enabled(&logger.directives, Level::Error, ""));
+        assert!(enabled(&logger.directives, Level::Warn, ""));
+        assert!(enabled(&logger.directives, Level::Info, ""));
+        assert!(enabled(&logger.directives, Level::Debug, ""));
+        assert!(enabled(&logger.directives, Level::Trace, ""));
+    }
+
+    // In practice, the desired log level is typically specified by a token
+    // that is either all lowercase (e.g., 'trace') or all uppercase (.e.g,
+    // 'TRACE'), but this tests serves as a reminder that
+    // log::Level::from_str() ignores all case variants.
+    #[test]
+    fn parse_default_bare_level_debug_mixed() {
+        {
+            let logger = Builder::new().parse("Debug").build();
+            assert!(enabled(&logger.directives, Level::Error, ""));
+            assert!(enabled(&logger.directives, Level::Warn, ""));
+            assert!(enabled(&logger.directives, Level::Info, ""));
+            assert!(enabled(&logger.directives, Level::Debug, ""));
+            assert!(!enabled(&logger.directives, Level::Trace, ""));
+        }
+        {
+            let logger = Builder::new().parse("debuG").build();
+            assert!(enabled(&logger.directives, Level::Error, ""));
+            assert!(enabled(&logger.directives, Level::Warn, ""));
+            assert!(enabled(&logger.directives, Level::Info, ""));
+            assert!(enabled(&logger.directives, Level::Debug, ""));
+            assert!(!enabled(&logger.directives, Level::Trace, ""));
+        }
+        {
+            let logger = Builder::new().parse("deBug").build();
+            assert!(enabled(&logger.directives, Level::Error, ""));
+            assert!(enabled(&logger.directives, Level::Warn, ""));
+            assert!(enabled(&logger.directives, Level::Info, ""));
+            assert!(enabled(&logger.directives, Level::Debug, ""));
+            assert!(!enabled(&logger.directives, Level::Trace, ""));
+        }
+        {
+            let logger = Builder::new().parse("DeBuG").build(); // LaTeX flavor!
+            assert!(enabled(&logger.directives, Level::Error, ""));
+            assert!(enabled(&logger.directives, Level::Warn, ""));
+            assert!(enabled(&logger.directives, Level::Info, ""));
+            assert!(enabled(&logger.directives, Level::Debug, ""));
+            assert!(!enabled(&logger.directives, Level::Trace, ""));
+        }
+    }
+
     #[test]
     fn match_full_path() {
         let logger = make_logger_filter(vec![
@@ -569,6 +749,36 @@ mod tests {
         assert!(filter.is_none());
     }
 
+    #[test]
+    fn parse_spec_global_bare_warn_lc() {
+        // test parse_spec with no crate, in isolation, all lowercase
+        let (dirs, filter) = parse_spec("warn");
+        assert_eq!(dirs.len(), 1);
+        assert_eq!(dirs[0].name, None);
+        assert_eq!(dirs[0].level, LevelFilter::Warn);
+        assert!(filter.is_none());
+    }
+
+    #[test]
+    fn parse_spec_global_bare_warn_uc() {
+        // test parse_spec with no crate, in isolation, all uppercase
+        let (dirs, filter) = parse_spec("WARN");
+        assert_eq!(dirs.len(), 1);
+        assert_eq!(dirs[0].name, None);
+        assert_eq!(dirs[0].level, LevelFilter::Warn);
+        assert!(filter.is_none());
+    }
+
+    #[test]
+    fn parse_spec_global_bare_warn_mixed() {
+        // test parse_spec with no crate, in isolation, mixed case
+        let (dirs, filter) = parse_spec("wArN");
+        assert_eq!(dirs.len(), 1);
+        assert_eq!(dirs[0].name, None);
+        assert_eq!(dirs[0].level, LevelFilter::Warn);
+        assert!(filter.is_none());
+    }
+
     #[test]
     fn parse_spec_valid_filter() {
         let (dirs, filter) = parse_spec("crate1::mod1=error,crate1::mod2,crate2=debug/abc");

src/lib.rs

@@ -8,9 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! A simple logger configured via environment variables which writes
-//! to stdout or stderr, for use with the logging facade exposed by the
-//! [`log` crate][log-crate-url].
+//! A simple logger that can be configured via environment variables, for use
+//! with the logging facade exposed by the [`log` crate][log-crate-url].
+//!
+//! Despite having "env" in its name, **`env_logger`** can also be configured by
+//! other means besides environment variables. See [the examples][gh-repo-examples]
+//! in the source repository for more approaches.
+//!
+//! By default, `env_logger` writes logs to `stderr`, but can be configured to
+//! instead write them to `stdout`.
 //!
 //! ## Example
 //!
@@ -83,11 +89,12 @@
 //!
 //! ## Enabling logging
 //!
-//! Log levels are controlled on a per-module basis, and by default all logging
-//! is disabled except for `error!`. Logging is controlled via the `RUST_LOG`
-//! environment variable. The value of this environment variable is a
-//! comma-separated list of logging directives. A logging directive is of the
-//! form:
+//! Log levels are controlled on a per-module basis, and **by default all
+//! logging is disabled except for the `error` level**.
+//!
+//! Logging is controlled via the **`RUST_LOG`** environment variable. The
+//! value of this environment variable is a comma-separated list of *logging
+//! directives*. A logging directive is of the form:
 //!
 //! ```text
 //! path::to::module=level
@@ -99,21 +106,51 @@
 //! Furthermore, this path is a prefix-search, so all modules nested in the
 //! specified module will also have logging enabled.
 //!
-//! The actual `level` is optional to specify. If omitted, all logging will
-//! be enabled. If specified, it must be one of the strings `debug`, `error`,
-//! `info`, `warn`, or `trace`.
+//! When providing the crate name or a module path, explicitly specifying the
+//! log level is optional. If omitted, all logging for the item (and its
+//! children) will be enabled.
+//!
+//! The names of the log levels that may be specified correspond to the
+//! variations of the [`log::Level`][level-enum] enum from the `log`
+//! crate. They are:
+//!
+//!    * `error`
+//!    * `warn`
+//!    * `info`
+//!    * `debug`
+//!    * `trace`
+//!
+//! There is also a pseudo logging level, `off`, which may be specified to
+//! disable all logging for a given module or for the entire application. As
+//! with the logging levels, the letter case is not significant[^fn-off].
+//!
+//! [^fn-off]: Similar to the universe of log level names, the `off` pseudo
+//!    log level feature is also provided by the underlying `log` crate.
+//!
+//! The letter case is not significant for the logging level names; e.g.,
+//! `debug`, `DEBUG`, and `dEbuG` all represent the same logging level. For
+//! consistency, our convention is to use the lower case names. Where our docs
+//! do use other forms, they do so in the context of specific examples, so you
+//! won't be surprised if you see similar usage in the wild.
 //!
 //! As the log level for a module is optional, the module to enable logging for
-//! is also optional. If only a `level` is provided, then the global log
-//! level for all modules is set to this value.
+//! is also optional. **If only a level is provided, then the global log
+//! level for all modules is set to this value.**
 //!
 //! Some examples of valid values of `RUST_LOG` are:
 //!
 //! * `hello` turns on all logging for the 'hello' module
+//! * `trace` turns on all logging for the application, regardless of its name
+//! * `TRACE` turns on all logging for the application, regardless of its name (same as previous)
 //! * `info` turns on all info logging
+//! * `INFO` turns on all info logging (same as previous)
 //! * `hello=debug` turns on debug logging for 'hello'
+//! * `hello=DEBUG` turns on debug logging for 'hello' (same as previous)
 //! * `hello,std::option` turns on hello, and std's option logging
 //! * `error,hello=warn` turn on global error logging and also warn for hello
+//! * `error,hello=off`` turn on global error logging, but turn off logging for hello
+//! * `off` turns off all logging for the application
+//! * `OFF` turns off all logging for the application (same as previous)
 //!
 //! ## Filtering results
 //!
@@ -223,6 +260,8 @@
 //! env_logger::Builder::from_env(Env::default().default_filter_or("warn")).init();
 //! ```
 //!
+//! [gh-repo-examples]: https://github.com/env-logger-rs/env_logger/tree/master/examples
+//! [level-enum]: https://docs.rs/log/latest/log/enum.Level.html
 //! [log-crate-url]: https://docs.rs/log/
 //! [`Builder`]: struct.Builder.html
 //! [`Builder::is_test`]: struct.Builder.html#method.is_test