Add feature flag to minimize RecordLocation unknowns

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "slog-stdlog"
-version = "4.1.0"
+version = "4.2.0"
 authors = ["Dawid Ciężarkiewicz <dpc@dpc.pw>"]
 description = "`log` crate adapter for slog-rs"
 keywords = ["slog", "logging", "json", "log"]
@@ -17,6 +17,7 @@ path = "lib.rs"
 [features]
 default = []
 kv_unstable = ["log/kv_unstable_std", "slog/dynamic-keys"]
+record_location_unstable = []
 
 [dependencies]
 slog = "2.4"

lib.rs

@@ -53,8 +53,8 @@ extern crate log;
 #[cfg(feature = "kv_unstable")]
 mod kv;
 
+use slog::{b, Level, KV};
 use std::{fmt, io};
-use slog::{Level, KV, b};
 
 struct Logger;
 
@@ -69,7 +69,21 @@ fn log_to_slog_level(level: log::Level) -> Level {
 }
 
 fn record_as_location(r: &log::Record) -> slog::RecordLocation {
+    // Warning: expands Record module and file names for non-static strings by leaking strings
+    #[cfg(feature = "record_location_unstable")]
+    let module = r.module_path_static().unwrap_or(match r.module_path() {
+        Some(s) => Box::leak(s.to_string().into_boxed_str()),
+        None => "unknown",
+    });
+    #[cfg(feature = "record_location_unstable")]
+    let file = r.file_static().unwrap_or(match r.file() {
+        Some(s) => Box::leak(s.to_string().into_boxed_str()),
+        None => "unknown",
+    });
+
+    #[cfg(not(feature = "record_location_unstable"))]
     let module = r.module_path_static().unwrap_or("<unknown>");
+    #[cfg(not(feature = "record_location_unstable"))]
     let file = r.file_static().unwrap_or("<unknown>");
     let line = r.line().unwrap_or_default();