Use web-time on Wasm

tracing-subscriber/Cargo.toml

@@ -32,6 +32,7 @@ fmt = ["registry", "std"]
 ansi = ["fmt", "nu-ansi-term"]
 registry = ["sharded-slab", "thread_local", "std"]
 json = ["tracing-serde", "serde", "serde_json"]
+wasm-bindgen = ["web-time"]
 
 # Enables support for local time when using the `time` crate timestamp
 # formatters.
@@ -65,6 +66,9 @@ chrono = { version = "0.4.26", default-features = false, features = ["clock", "s
 sharded-slab = { version = "0.1.4", optional = true }
 thread_local = { version = "1.1.4", optional = true }
 
+[target.'cfg(all(target_family = "wasm", not(any(target_os = "emscripten", target_os = "wasi"))))'.dependencies]
+web-time = { version = "0.2", optional = true }
+
 [dev-dependencies]
 tracing = { path = "../tracing", version = "0.2" }
 tracing-mock = { path = "../tracing-mock", features = ["tracing-subscriber"] }

tracing-subscriber/src/fmt/fmt_subscriber.rs

@@ -5,9 +5,20 @@ use crate::{
     subscribe::{self, Context},
 };
 use format::{FmtSpan, TimingDisplay};
+#[cfg(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+))]
+use web_time::Instant;
+#[cfg(not(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+)))]
+use std::time::Instant;
 use std::{
     any::TypeId, cell::RefCell, env, fmt, io, marker::PhantomData, ops::Deref, ptr::NonNull,
-    time::Instant,
 };
 use tracing_core::{
     field,

tracing-subscriber/src/fmt/time/datetime.rs

@@ -193,7 +193,19 @@
 // obstacle to adoption, that text has been removed.
 
 
+#[cfg(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+))]
+use web_time as time;
 use std::fmt;
+#[cfg(not(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+)))]
+use std::time;
 
 /// A date/time type which exists primarily to convert `SystemTime` timestamps into an ISO 8601
 /// formatted string.
@@ -243,9 +255,9 @@ impl fmt::Display for DateTime {
     }
 }
 
-impl From<std::time::SystemTime> for DateTime {
-    fn from(timestamp: std::time::SystemTime) -> DateTime {
-        let (t, nanos) = match timestamp.duration_since(std::time::UNIX_EPOCH) {
+impl From<time::SystemTime> for DateTime {
+    fn from(timestamp: time::SystemTime) -> DateTime {
+        let (t, nanos) = match timestamp.duration_since(time::UNIX_EPOCH) {
             Ok(duration) => {
                 debug_assert!(duration.as_secs() <= std::i64::MAX as u64);
                 (duration.as_secs() as i64, duration.subsec_nanos())
@@ -333,7 +345,7 @@ impl From<std::time::SystemTime> for DateTime {
 #[cfg(test)]
 mod tests {
     use std::i32;
-    use std::time::{Duration, UNIX_EPOCH};
+    use super::time::{Duration, UNIX_EPOCH};
 
     use super::*;
 

tracing-subscriber/src/fmt/time/mod.rs

@@ -1,7 +1,18 @@
 //! Formatters for event timestamps.
 use crate::fmt::format::Writer;
 use std::fmt;
-use std::time::Instant;
+#[cfg(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+))]
+use web_time as time;
+#[cfg(not(all(
+    target_family = "wasm",
+    not(any(target_os = "emscripten", target_os = "wasi")),
+    feature = "wasm-bindgen"
+)))]
+use std::time as time;
 
 mod datetime;
 
@@ -112,19 +123,19 @@ pub struct SystemTime;
 /// The `Default` implementation for `Uptime` makes the epoch the current time.
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
 pub struct Uptime {
-    epoch: Instant,
+    epoch: time::Instant,
 }
 
 impl Default for Uptime {
     fn default() -> Self {
         Uptime {
-            epoch: Instant::now(),
+            epoch: time::Instant::now(),
         }
     }
 }
 
-impl From<Instant> for Uptime {
-    fn from(epoch: Instant) -> Self {
+impl From<time::Instant> for Uptime {
+    fn from(epoch: time::Instant) -> Self {
         Uptime { epoch }
     }
 }
@@ -134,7 +145,7 @@ impl FormatTime for SystemTime {
         write!(
             w,
             "{}",
-            datetime::DateTime::from(std::time::SystemTime::now())
+            datetime::DateTime::from(time::SystemTime::now())
         )
     }
 }

tracing-subscriber/src/lib.rs

@@ -74,6 +74,8 @@
 //!   than `Vec`) as a performance optimization. Enabled by default.
 //! - [`parking_lot`]: Use the `parking_lot` crate's `RwLock` implementation
 //!   rather than the Rust standard library's implementation.
+//! - `wasm-bindgen`: Uses the [`web-time`] crate to allow `Uptime` and `SystemTime` to
+//!   be used in browsers.
 //!
 //! ### `no_std` Support
 //!
@@ -129,6 +131,7 @@
 //! [`time` crate]: https://crates.io/crates/time
 //! [`liballoc`]: https://doc.rust-lang.org/alloc/index.html
 //! [`libstd`]: https://doc.rust-lang.org/std/index.html
+//! [`web-time`]: https://crates.io/crates/web-time
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png",
     html_favicon_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/favicon.ico",