feat: allow using specific formatters for tracing

Author: ctron

README.md

@@ -145,6 +145,10 @@ Valid events are `new`, `enter`, `exit`, `close`, `active`, and `full`.
 See the [`tracing_subscriber` docs][tracing-events-docs-rs] for details
 on what the events mean.
 
+It is also possible to use different tracing formatters using the
+`RUST_TRACING_FORMAT` variable. Supported values are: `full` (default),
+`compact`, and `pretty`.
+
 #### MSRV Policy
 This crate adheres to Cargo's [semantic versioning rules][cargo-semver].
 At a minimum, it builds with the most recent Rust stable release minus

macros/src/lib.rs

@@ -271,11 +271,26 @@ fn expand_tracing_init(attribute_args: &AttributeArgs) -> Tokens {
         }
       };
 
-      let _ = ::test_log::tracing_subscriber::FmtSubscriber::builder()
+      let builder = ::test_log::tracing_subscriber::FmtSubscriber::builder()
         .with_env_filter(#env_filter)
         .with_span_events(__internal_event_filter)
-        .with_test_writer()
-        .try_init();
+        .with_test_writer();
+
+      let _ = match ::std::env::var_os("RUST_TRACING_FORMAT").as_deref().and_then(std::ffi::OsStr::to_str) {
+        None | Some("full") => {
+            builder.try_init()
+        }
+        Some("compact") => {
+            builder.compact().try_init()
+        },
+        #[cfg(feature = "color")]
+        Some("pretty") => {
+            builder.pretty().try_init()
+        },
+        Some(other) => {
+            panic!("test-log: RUST_TRACING_FORMAT has an unsupported value of '{other}'. Supported are: full, compact, pretty.");
+        }
+      };
     }
   }
 }