Add WASMTIME_LOG_NO_CONTEXT (#9902)

* Documentation

* Add WASMTIME_LOG_NO_CONTEXT

When using trace logging for compiler debugging, the usual
'context': time, level, target, are just visual noise.

Add an environment variable to disable them.

crates/cli-flags/src/lib.rs

@@ -541,11 +541,19 @@ impl CommonOptions {
         } else {
             use std::io::IsTerminal;
             use tracing_subscriber::{EnvFilter, FmtSubscriber};
-            let b = FmtSubscriber::builder()
+            let builder = FmtSubscriber::builder()
                 .with_writer(std::io::stderr)
                 .with_env_filter(EnvFilter::from_env("WASMTIME_LOG"))
                 .with_ansi(std::io::stderr().is_terminal());
-            b.init();
+            if std::env::var("WASMTIME_LOG_NO_CONTEXT").is_ok_and(|value| value.eq("1")) {
+                builder
+                    .with_level(false)
+                    .with_target(false)
+                    .without_time()
+                    .init()
+            } else {
+                builder.init();
+            }
         }
         #[cfg(not(feature = "logging"))]
         if self.debug.log_to_files == Some(true) || self.debug.logging == Some(true) {

crates/cranelift/src/debug/transform/debug_transform_logging.rs

@@ -123,7 +123,10 @@ impl<'a> fmt::Debug for DieDetailedSummary<'a> {
                 AttributeValue::CallingConvention(value) => write!(f, "{value}"),
                 AttributeValue::Inline(value) => write!(f, "{value}"),
                 AttributeValue::Ordering(value) => write!(f, "{value}"),
-                AttributeValue::UnitRef(offset) => write!(f, "0x{:08x}", offset.0),
+                AttributeValue::UnitRef(offset) => {
+                    let section_offset = offset.to_unit_section_offset(unit);
+                    write!(f, "0x{:08x}", get_offset_value(section_offset))
+                }
                 AttributeValue::DebugInfoRef(offset) => write!(f, "0x{:08x}", offset.0),
                 unexpected_attr => write!(f, "<unexpected attr: {unexpected_attr:?}>"),
             }?;

docs/cli-logging.md

@@ -23,6 +23,9 @@ Wasmtime can also redirect the log messages into log files, with the
 `-D log-to-files` option. It creates one file per thread within Wasmtime, with
 the files named `wasmtime.dbg.*`.
 
+Additional environment variables that work with `WASMTIME_LOG` (__not__ `-D log-to-files`):
+ - `WASMTIME_LOG_NO_CONTEXT`: if set to `1`, removes the time, level and target from output.
+
 [`log`]: https://crates.io/crates/log
 [`tracing-subscriber`]: https://crates.io/crates/tracing-subscriber
 [tracing-subscriber's EnvFilter docs]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#directives