1 files changed, 68 insertions, 0 deletions
diff --git a/crates/core/logger.rs b/crates/core/logger.rs
new file mode 100644
index 00000000..f12f0b19
--- /dev/null
+++ b/crates/core/logger.rs
@@ -0,0 +1,68 @@
+// This module defines a super simple logger that works with the `log` crate.
+// We don't need anything fancy; just basic log levels and the ability to
+// print to stderr. We therefore avoid bringing in extra dependencies just
+// for this functionality.
+
+use log::{self, Log};
+
+/// The simplest possible logger that logs to stderr.
+///
+/// This logger does no filtering. Instead, it relies on the `log` crates
+/// filtering via its global max_level setting.
+#[derive(Debug)]
+pub struct Logger(());
+
+const LOGGER: &'static Logger = &Logger(());
+
+impl Logger {
+    /// Create a new logger that logs to stderr and initialize it as the
+    /// global logger. If there was a problem setting the logger, then an
+    /// error is returned.
+    pub fn init() -> Result<(), log::SetLoggerError> {
+        log::set_logger(LOGGER)
+    }
+}
+
+impl Log for Logger {
+    fn enabled(&self, _: &log::Metadata) -> bool {
+        // We set the log level via log::set_max_level, so we don't need to
+        // implement filtering here.
+        true
+    }
+
+    fn log(&self, record: &log::Record) {
+        match (record.file(), record.line()) {
+            (Some(file), Some(line)) => {
+                eprintln!(
+                    "{}|{}|{}:{}: {}",
+                    record.level(),
+                    record.target(),
+                    file,
+                    line,
+                    record.args()
+                );
+            }
+            (Some(file), None) => {
+                eprintln!(
+                    "{}|{}|{}: {}",
+                    record.level(),
+                    record.target(),
+                    file,
+                    record.args()
+                );
+            }
+            _ => {
+                eprintln!(
+                    "{}|{}: {}",
+                    record.level(),
+                    record.target(),
+                    record.args()
+                );
+            }
+        }
+    }
+
+    fn flush(&self) {
+        // We use eprintln! which is flushed on every call.
+    }
+}