Extract init_env_logger to crate

compiler/rustc_log/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "rustc_log"
+version = "0.0.0"
+edition = "2021"
+
+[lib]
+doctest = false
+
+[dependencies]
+atty = "0.2"
+tracing = "0.1.28"
+tracing-subscriber = { version = "0.3.3", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
+tracing-tree = "0.2.0"
+
+[features]
+max_level_info = ['tracing/max_level_info']

compiler/rustc_log/src/lib.rs

@@ -0,0 +1,78 @@
+//! This crate allows tools to enable rust logging without having to magically
+//! match rustc's tracing crate version.
+
+use std::env::{self, VarError};
+use std::fmt::{self, Display};
+use std::io;
+use tracing_subscriber::filter::{Directive, EnvFilter, LevelFilter};
+use tracing_subscriber::layer::SubscriberExt;
+
+pub fn init_rustc_env_logger() -> Result<(), Error> {
+    init_env_logger("RUSTC_LOG")
+}
+
+/// In contrast to `init_rustc_env_logger` this allows you to choose an env var
+/// other than `RUSTC_LOG`.
+pub fn init_env_logger(env: &str) -> Result<(), Error> {
+    let filter = match env::var(env) {
+        Ok(env) => EnvFilter::new(env),
+        _ => EnvFilter::default().add_directive(Directive::from(LevelFilter::WARN)),
+    };
+
+    let color_logs = match env::var(String::from(env) + "_COLOR") {
+        Ok(value) => match value.as_ref() {
+            "always" => true,
+            "never" => false,
+            "auto" => stderr_isatty(),
+            _ => return Err(Error::InvalidColorValue(value)),
+        },
+        Err(VarError::NotPresent) => stderr_isatty(),
+        Err(VarError::NotUnicode(_value)) => return Err(Error::NonUnicodeColorValue),
+    };
+
+    let layer = tracing_tree::HierarchicalLayer::default()
+        .with_writer(io::stderr)
+        .with_indent_lines(true)
+        .with_ansi(color_logs)
+        .with_targets(true)
+        .with_indent_amount(2);
+    #[cfg(parallel_compiler)]
+    let layer = layer.with_thread_ids(true).with_thread_names(true);
+
+    let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);
+    tracing::subscriber::set_global_default(subscriber).unwrap();
+
+    Ok(())
+}
+
+pub fn stdout_isatty() -> bool {
+    atty::is(atty::Stream::Stdout)
+}
+
+pub fn stderr_isatty() -> bool {
+    atty::is(atty::Stream::Stderr)
+}
+
+#[derive(Debug)]
+pub enum Error {
+    InvalidColorValue(String),
+    NonUnicodeColorValue,
+}
+
+impl std::error::Error for Error {}
+
+impl Display for Error {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Error::InvalidColorValue(value) => write!(
+                formatter,
+                "invalid log color value '{}': expected one of always, never, or auto",
+                value,
+            ),
+            Error::NonUnicodeColorValue => write!(
+                formatter,
+                "non-Unicode log color value: expected one of always, never, or auto",
+            ),
+        }
+    }
+}