Fix global LogTracer installation by using InitError enum instead of Boxed errors (#406)

## Motivation

I thought the boxing errors solution implemented in #400 was equivalent
to the enum solution in
emschwartz@f22bae5,
but the current master doesn't actually work to install the global
`LogTracer`.

I can't figure out why the current cargo features don't end up turning
on [this line][1], but I confirmed with the log example in
4511325
that it's not currently working.

[1]: https://github.com/tokio-rs/tracing/blob/master/tracing-subscriber/src/fmt/mod.rs#L452-L453

* subscriber: use InitError enum instead of Box

the Boxing solution while using the feature tracing-log/std didn't actually seem to work

* examples: log compatibility

* fix dependencies

Signed-off-by: Eliza Weisman <[email protected]>

* fix boxed errors

Signed-off-by: Eliza Weisman <[email protected]>

* cargo fmt

Signed-off-by: Eliza Weisman <[email protected]>

Author: emschwartz

examples/examples/log.rs

@@ -0,0 +1,8 @@
+fn main() {
+    tracing_subscriber::fmt::Subscriber::builder()
+        .with_max_level(tracing::Level::TRACE)
+        .init();
+
+    log::debug!("this is a log line");
+    tracing::debug!("this is a tracing line");
+}

tracing-log/Cargo.toml

@@ -18,13 +18,13 @@ readme = "README.md"
 
 [features]
 default = ["log-tracer", "trace-logger", "std"]
+std = ["log/std"]
 log-tracer = []
 trace-logger = []
-std = ["log/std"]
 
 [dependencies]
 tracing-core = "0.1.2"
-log = { version = "0.4", features = ["std"] }
+log = { version = "0.4" }
 lazy_static = "1.3.0"
 env_logger = { version = "0.6", optional = true }
 

tracing-log/src/log_tracer.rs

@@ -28,6 +28,7 @@
 //! [ignore]: struct.Builder.html#method.ignore_crate
 use crate::{format_trace, AsTrace};
 use log;
+pub use log::SetLoggerError;
 use tracing_core::dispatcher;
 
 /// A simple "logger" that converts all log records into `tracing` `Event`s.
@@ -110,7 +111,8 @@ impl LogTracer {
     /// initializing it.
     ///
     /// [`builder`]: #method.builder
-    pub fn init_with_filter(level: log::LevelFilter) -> Result<(), log::SetLoggerError> {
+    #[cfg(feature = "std")]
+    pub fn init_with_filter(level: log::LevelFilter) -> Result<(), SetLoggerError> {
         Self::builder().with_max_level(level).init()
     }
 
@@ -143,7 +145,8 @@ impl LogTracer {
     ///
     /// [`init_with_filter`]: #method.init_with_filter
     /// [`builder`]: #method.builder
-    pub fn init() -> Result<(), log::SetLoggerError> {
+    #[cfg(feature = "std")]
+    pub fn init() -> Result<(), SetLoggerError> {
         Self::builder().init()
     }
 }
@@ -237,7 +240,8 @@ impl Builder {
     /// as the default logger.
     ///
     /// Setting a global logger can only be done once.
-    pub fn init(self) -> Result<(), log::SetLoggerError> {
+    #[cfg(feature = "std")]
+    pub fn init(self) -> Result<(), SetLoggerError> {
         let ignore_crates = self.ignore_crates.into_boxed_slice();
         let logger = Box::new(LogTracer { ignore_crates });
         log::set_boxed_logger(logger)?;

tracing-subscriber/Cargo.toml

@@ -39,7 +39,7 @@ smallvec = { optional = true, version = "0.6.10"}
 lazy_static = { optional = true, version = "1" }
 
 # fmt
-tracing-log = { path = "../tracing-log", version = "0.1", optional = true, default-features = false, features = ["std", "log-tracer"] }
+tracing-log = { path = "../tracing-log", version = "0.1", optional = true, default-features = false, features = ["log-tracer", "std"] }
 ansi_term = { version = "0.11", optional = true }
 owning_ref = { version = "0.4.0", optional = true }
 chrono = { version = "0.4", optional = true }

tracing-subscriber/src/fmt/mod.rs

@@ -448,14 +448,14 @@ where
     /// Returns an Error if the initialization was unsuccessful, likely
     /// because a global subscriber was already installed by another
     /// call to `try_init`.
-    pub fn try_init(self) -> Result<(), impl Error + Send + Sync + 'static> {
-        #[cfg(feature = "tracing-log/std")]
-        tracing_log::LogTracer::init().map_err(Box::new)?;
+    pub fn try_init(self) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        #[cfg(feature = "tracing-log")]
+        tracing_log::LogTracer::init()?;
 
         tracing_core::dispatcher::set_global_default(tracing_core::dispatcher::Dispatch::new(
             self.finish(),
         ))
-        .map_err(Box::new)
+        .map_err(Into::into)
     }
 
     /// Install this Subscriber as the global default.
@@ -859,7 +859,7 @@ impl Default for Settings {
 ///     https://docs.rs/tracing-log/0.1.0/tracing_log/struct.LogTracer.html
 /// [`RUST_LOG` environment variable]:
 ///     ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV
-pub fn try_init() -> Result<(), impl Error + Send + Sync + 'static> {
+pub fn try_init() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
     Subscriber::builder()
         .with_env_filter(crate::EnvFilter::from_default_env())
         .try_init()