1 files changed, 62 insertions, 0 deletions
diff --git a/third_party/rust/env_logger/examples/custom_logger.rs b/third_party/rust/env_logger/examples/custom_logger.rs
new file mode 100644
index 0000000000..ca3a4a9012
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+++ b/third_party/rust/env_logger/examples/custom_logger.rs
@@ -0,0 +1,62 @@
+/*!
+Using `env_logger` to drive a custom logger.
+
+Before running this example, try setting the `MY_LOG_LEVEL` environment variable to `info`:
+
+```no_run,shell
+$ export MY_LOG_LEVEL='info'
+```
+
+If you only want to change the way logs are formatted, look at the `custom_format` example.
+*/
+
+#[macro_use]
+extern crate log;
+
+use env_logger::filter::{Builder, Filter};
+
+use log::{Log, Metadata, Record, SetLoggerError};
+
+const FILTER_ENV: &str = "MY_LOG_LEVEL";
+
+struct MyLogger {
+    inner: Filter,
+}
+
+impl MyLogger {
+    fn new() -> MyLogger {
+        let mut builder = Builder::from_env(FILTER_ENV);
+
+        MyLogger {
+            inner: builder.build(),
+        }
+    }
+
+    fn init() -> Result<(), SetLoggerError> {
+        let logger = Self::new();
+
+        log::set_max_level(logger.inner.filter());
+        log::set_boxed_logger(Box::new(logger))
+    }
+}
+
+impl Log for MyLogger {
+    fn enabled(&self, metadata: &Metadata) -> bool {
+        self.inner.enabled(metadata)
+    }
+
+    fn log(&self, record: &Record) {
+        // Check if the record is matched by the logger before logging
+        if self.inner.matches(record) {
+            println!("{} - {}", record.level(), record.args());
+        }
+    }
+
+    fn flush(&self) {}
+}
+
+fn main() {
+    MyLogger::init().unwrap();
+
+    info!("a log from `MyLogger`");
+}