make severity of level computations const (#1369)

Author: shaun-cox

opentelemetry-appender-log/src/lib.rs

@@ -18,10 +18,9 @@ where
 {
     fn enabled(&self, _metadata: &Metadata) -> bool {
         #[cfg(feature = "logs_level_enabled")]
-        return self.logger.event_enabled(
-            map_severity_to_otel_severity(_metadata.level()),
-            _metadata.target(),
-        );
+        return self
+            .logger
+            .event_enabled(severity_of_level(_metadata.level()), _metadata.target());
         #[cfg(not(feature = "logs_level_enabled"))]
         true
     }
@@ -30,7 +29,7 @@ where
         if self.enabled(record.metadata()) {
             self.logger.emit(
                 LogRecordBuilder::new()
-                    .with_severity_number(map_severity_to_otel_severity(record.level()))
+                    .with_severity_number(severity_of_level(record.level()))
                     .with_severity_text(record.level().as_str())
                     // Not populating ObservedTimestamp, instead relying on OpenTelemetry
                     // API to populate it with current time.
@@ -61,7 +60,7 @@ where
     }
 }
 
-fn map_severity_to_otel_severity(level: Level) -> Severity {
+const fn severity_of_level(level: Level) -> Severity {
     match level {
         Level::Error => Severity::Error,
         Level::Warn => Severity::Warn,

opentelemetry-appender-tracing/src/layer.rs

@@ -1,5 +1,6 @@
 use opentelemetry::logs::{LogRecord, Logger, LoggerProvider, Severity};
 use std::borrow::Cow;
+use tracing_core::Level;
 use tracing_subscriber::Layer;
 
 const INSTRUMENTATION_LIBRARY_NAME: &str = "opentelemetry-appender-tracing";
@@ -100,7 +101,7 @@ where
     ) {
         let meta = event.metadata();
         let mut log_record: LogRecord = LogRecord::default();
-        log_record.severity_number = Some(map_severity_to_otel_severity(meta.level().as_str()));
+        log_record.severity_number = Some(severity_of_level(meta.level()));
         log_record.severity_text = Some(meta.level().to_string().into());
 
         // add the `name` metadata to attributes
@@ -124,19 +125,18 @@ where
         _event: &tracing_core::Event<'_>,
         _ctx: tracing_subscriber::layer::Context<'_, S>,
     ) -> bool {
-        let severity = map_severity_to_otel_severity(_event.metadata().level().as_str());
+        let severity = severity_of_level(_event.metadata().level());
         self.logger
             .event_enabled(severity, _event.metadata().target())
     }
 }
 
-fn map_severity_to_otel_severity(level: &str) -> Severity {
-    match level {
-        "INFO" => Severity::Info,
-        "DEBUG" => Severity::Debug,
-        "TRACE" => Severity::Trace,
-        "WARN" => Severity::Warn,
-        "ERROR" => Severity::Error,
-        _ => Severity::Info, // won't reach here
+const fn severity_of_level(level: &Level) -> Severity {
+    match *level {
+        Level::TRACE => Severity::Trace,
+        Level::DEBUG => Severity::Debug,
+        Level::INFO => Severity::Info,
+        Level::WARN => Severity::Warn,
+        Level::ERROR => Severity::Error,
     }
 }