feat(filter): Add a Logger decorator

crates/env_filter/src/directive.rs

@@ -0,0 +1,20 @@
+use log::Level;
+use log::LevelFilter;
+
+#[derive(Debug)]
+pub(crate) struct Directive {
+    pub(crate) name: Option<String>,
+    pub(crate) level: LevelFilter,
+}
+
+// Check whether a level and target are enabled by the set of directives.
+pub(crate) fn enabled(directives: &[Directive], level: Level, target: &str) -> bool {
+    // Search for the longest match, the vector is assumed to be pre-sorted.
+    for directive in directives.iter().rev() {
+        match directive.name {
+            Some(ref name) if !target.starts_with(&**name) => {}
+            Some(..) | None => return level <= directive.level,
+        }
+    }
+    false
+}