other: add back local time in debug logs (#1346)

* other: add back local time in debug logs

This still has a UTC fallback.

* cleanup and some warnings

Cargo.lock

@@ -830,6 +830,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "num_threads"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2819ce041d2ee131036f4fc9d6ae7ae125a3a40e97ba64d04fe799ad9dabbb44"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "nvml-wrapper"
 version = "0.9.0"
@@ -1311,6 +1320,8 @@ checksum = "c4a34ab300f2dee6e562c10a046fc05e358b29f9bf92277f30c3c8d82275f6f5"
 dependencies = [
  "deranged",
  "itoa",
+ "libc",
+ "num_threads",
  "powerfmt",
  "serde",
  "time-core",

Cargo.toml

@@ -69,7 +69,7 @@ nvidia = ["nvml-wrapper"]
 zfs = []
 
 # Including logging for debugging purposes.
-logging = ["fern", "log"]
+logging = ["fern", "log", "time/local-offset"]
 
 # The features we use on deploy. Logging is not included as that is primarily (for now) just for debugging locally.
 deploy = ["battery", "gpu", "zfs"]

src/utils/logging.rs

@@ -1,16 +1,37 @@
+#[cfg(feature = "logging")]
+pub static OFFSET: once_cell::sync::Lazy<time::UtcOffset> = once_cell::sync::Lazy::new(|| {
+    use time::util::local_offset::Soundness;
+
+    // SAFETY: We only invoke this once, quickly, and it should be invoked in a single-thread context.
+    // We also should only ever hit this logging at all in a debug context which is generally fine,
+    // release builds should have this logging disabled entirely for now.
+    unsafe {
+        // XXX: If we ever DO add general logging as a release feature, evaluate this again and whether this is
+        // something we want enabled in release builds! What might be safe is falling back to the non-set-soundness
+        // mode when specifically using certain feature flags (e.g. dev-logging feature enables this behaviour).
+
+        time::util::local_offset::set_soundness(Soundness::Unsound);
+        let res = time::UtcOffset::current_local_offset().unwrap_or(time::UtcOffset::UTC);
+        time::util::local_offset::set_soundness(Soundness::Sound);
+
+        res
+    }
+});
+
 #[cfg(feature = "logging")]
 pub fn init_logger(
     min_level: log::LevelFilter, debug_file_name: &std::ffi::OsStr,
 ) -> Result<(), fern::InitError> {
     fern::Dispatch::new()
         .format(|out, message, record| {
-            // Note we aren't using local time since it only works on single-threaded processes.
-            // If that ever does get patched in again, enable the "local-offset" feature.
-            let offset = time::OffsetDateTime::now_utc();
+            let offset_time = {
+                let utc = time::OffsetDateTime::now_utc();
+                utc.checked_to_offset(*OFFSET).unwrap_or(utc)
+            };
 
             out.finish(format_args!(
                 "{}[{}][{}] {}",
-                offset
+                offset_time
                     .format(&time::macros::format_description!(
                         // The weird "[[[" is because we need to escape a bracket ("[[") to show one "[".
                         // See https://time-rs.github.io/book/api/format-description.html