Make rustdoc share the logger initialization routine with rustc.

src/librustc_driver/lib.rs

@@ -1224,11 +1224,18 @@ pub fn install_ice_hook() {
 }
 
 /// This allows tools to enable rust logging without having to magically match rustc's
-/// log crate version
+/// log crate version.
 pub fn init_rustc_env_logger() {
+    init_env_logger("RUSTC_LOG")
+}
+
+/// This allows tools to enable rust logging without having to magically match rustc's
+/// log crate version. In contrast to `init_rustc_env_logger` it allows you to choose an env var
+/// other than `RUSTC_LOG`.
+pub fn init_env_logger(env: &str) {
     let builder = tracing_subscriber::FmtSubscriber::builder();
 
-    let builder = builder.with_env_filter(tracing_subscriber::EnvFilter::from_env("RUSTC_LOG"));
+    let builder = builder.with_env_filter(tracing_subscriber::EnvFilter::from_env(env));
 
     builder.init()
 }

src/librustdoc/lib.rs

@@ -14,7 +14,6 @@
 #![feature(never_type)]
 #![recursion_limit = "256"]
 
-extern crate env_logger;
 #[macro_use]
 extern crate lazy_static;
 extern crate rustc_ast;
@@ -90,7 +89,8 @@ pub fn main() {
     };
     rustc_driver::set_sigpipe_handler();
     rustc_driver::install_ice_hook();
-    env_logger::init_from_env("RUSTDOC_LOG");
+    rustc_driver::init_env_logger("RUSTDOC_LOG");
+
     let res = std::thread::Builder::new()
         .stack_size(thread_stack_size)
         .spawn(move || get_args().map(|args| main_args(&args)).unwrap_or(1))