chore: remove *all* extern crate statements (#1738)

Depends on #1737

This branch removes all remaining `extern crate` statements. Most of
these are in old code and were not removed when updating to Rust 2018.
Whoops!

Our MSRV no longer requires `extern crate`, so we don't need these. The
exception is `extern crate` statements for `std` and `alloc`, which are
still the way these libraries are included explicitly when building for
`no_std` platforms.

In some cases, the tests had to explicitly import the `span!` and
`event!` macros at every use, because their names conflict with the
`span` and `event` modules in the test support code. Oh well.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

Author: hawkw

tracing-core/src/callsite.rs

@@ -12,7 +12,7 @@ use crate::{
     subscriber::Interest,
 };
 
-lazy_static! {
+crate::lazy_static! {
     static ref REGISTRY: Mutex<Registry> = Mutex::new(Registry {
         callsites: Vec::new(),
         dispatchers: Vec::new(),

tracing-core/src/lib.rs

@@ -225,14 +225,11 @@ macro_rules! metadata {
     };
 }
 
-// std uses lazy_static from crates.io
+// when `std` is enabled, use the `lazy_static` crate from crates.io
 #[cfg(feature = "std")]
-#[macro_use]
-extern crate lazy_static;
+pub(crate) use lazy_static::lazy_static;
 
-// no_std uses vendored version of lazy_static 1.4.0 (4216696) with spin
-// This can conflict when included in a project already using std lazy_static
-// Remove this module when cargo enables specifying dependencies for no_std
+// Facade module: `no_std` uses spinlocks, `std` uses the mutexes in the standard library
 #[cfg(not(feature = "std"))]
 #[macro_use]
 mod lazy_static;

tracing-core/src/subscriber.rs

@@ -246,8 +246,7 @@ pub trait Subscriber: 'static {
     /// but values for them won't be recorded at this time.
     ///
     /// ```rust,ignore
-    /// #[macro_use]
-    /// extern crate tracing;
+    /// # use tracing::span;
     ///
     /// let mut span = span!("my_span", foo = 3, bar, baz);
     ///

tracing-serde/README.md

@@ -53,10 +53,6 @@ tracing-serde = "0.1"
 Next, add this to your crate:
 
 ```rust
-#[macro_use]
-extern crate tracing;
-extern crate tracing_serde;
-
 use tracing_serde::AsSerde;
 ```
 

tracing/benches/subscriber.rs

@@ -1,6 +1,3 @@
-extern crate criterion;
-extern crate tracing;
-
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 use tracing::Level;
 

tracing/src/level_filters.rs

@@ -65,7 +65,7 @@ pub use tracing_core::{metadata::ParseLevelFilterError, LevelFilter};
 /// [module-level documentation]: ../index.html#compile-time-filters
 pub const STATIC_MAX_LEVEL: LevelFilter = MAX_LEVEL;
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(all(not(debug_assertions), feature = "release_max_level_off"))] {
         const MAX_LEVEL: LevelFilter = LevelFilter::OFF;
     } else if #[cfg(all(not(debug_assertions), feature = "release_max_level_error"))] {

tracing/src/lib.rs

@@ -882,9 +882,6 @@
 #[cfg(not(feature = "std"))]
 extern crate alloc;
 
-#[macro_use]
-extern crate cfg_if;
-
 #[cfg(feature = "log")]
 #[doc(hidden)]
 pub use log;

tracing/test-log-support/src/lib.rs

@@ -1,4 +1,3 @@
-extern crate log;
 use log::{LevelFilter, Log, Metadata, Record};
 use std::sync::{Arc, Mutex};
 

tracing/test-log-support/tests/log_no_trace.rs

@@ -1,9 +1,5 @@
-#[macro_use]
-extern crate tracing;
-extern crate test_log_support;
-
 use test_log_support::Test;
-use tracing::Level;
+use tracing::{error, info, span, trace, warn, Level};
 
 #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test::wasm_bindgen_test)]
 #[test]

tracing/test-log-support/tests/log_with_trace.rs

@@ -1,9 +1,5 @@
-#[macro_use]
-extern crate tracing;
-extern crate test_log_support;
-
 use test_log_support::Test;
-use tracing::Level;
+use tracing::{error, info, span, trace, warn, Level};
 
 pub struct NopSubscriber;