utils: Add a log_debug() helper

ref #793
And add a log at trace level unconditionally.

Signed-off-by: Colin Walters <[email protected]>

lib/src/blockdev.rs

@@ -98,6 +98,7 @@ pub(crate) fn list_dev(dev: &Utf8Path) -> Result<Device> {
     let mut devs: DevicesOutput = Command::new("lsblk")
         .args(["-J", "-b", "-O"])
         .arg(dev)
+        .log_debug()
         .run_and_parse_json()?;
     for dev in devs.blockdevices.iter_mut() {
         dev.backfill_missing()?;

utils/src/command.rs

@@ -7,6 +7,7 @@ use anyhow::{Context, Result};
 
 /// Helpers intended for [`std::process::Command`].
 pub trait CommandRunExt {
+    fn log_debug(&mut self) -> &mut Self;
     fn run(&mut self) -> Result<()>;
     /// Execute the child process, parsing its stdout as JSON.
     fn run_and_parse_json<T: serde::de::DeserializeOwned>(&mut self) -> Result<T>;
@@ -68,9 +69,20 @@ impl CommandRunExt for Command {
     fn run(&mut self) -> Result<()> {
         let stderr = tempfile::tempfile()?;
         self.stderr(stderr.try_clone()?);
+        tracing::trace!("exec: {self:?}");
         self.status()?.check_status(stderr)
     }
 
+    /// Output a debug-level log message with this command.
+    fn log_debug(&mut self) -> &mut Self {
+        // We unconditionally log at trace level, so avoid double logging
+        if !tracing::enabled!(tracing::Level::TRACE) {
+            tracing::debug!("exec: {self:?}");
+        }
+        self
+    }
+
+    /// Synchronously execute the child, and parse its stdout as JSON.
     fn run_and_parse_json<T: serde::de::DeserializeOwned>(&mut self) -> Result<T> {
         let mut stdout = tempfile::tempfile()?;
         self.stdout(stdout.try_clone()?);