1 files changed, 122 insertions, 0 deletions
diff --git a/compiler/rustc_log/src/lib.rs b/compiler/rustc_log/src/lib.rs
new file mode 100644
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+++ b/compiler/rustc_log/src/lib.rs
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+//! This crate allows tools to enable rust logging without having to magically
+//! match rustc's tracing crate version.
+//!
+//! For example if someone is working on rustc_ast and wants to write some
+//! minimal code against it to run in a debugger, with access to the `debug!`
+//! logs emitted by rustc_ast, that can be done by writing:
+//!
+//! ```toml
+//! [dependencies]
+//! rustc_ast = { path = "../rust/compiler/rustc_ast" }
+//! rustc_log = { path = "../rust/compiler/rustc_log" }
+//! rustc_span = { path = "../rust/compiler/rustc_span" }
+//! ```
+//!
+//! ```
+//! fn main() {
+//!     rustc_log::init_rustc_env_logger().unwrap();
+//!
+//!     let edition = rustc_span::edition::Edition::Edition2021;
+//!     rustc_span::create_session_globals_then(edition, || {
+//!         /* ... */
+//!     });
+//! }
+//! ```
+//!
+//! Now `RUSTC_LOG=debug cargo run` will run your minimal main.rs and show
+//! rustc's debug logging. In a workflow like this, one might also add
+//! `std::env::set_var("RUSTC_LOG", "debug")` to the top of main so that `cargo
+//! run` by itself is sufficient to get logs.
+//!
+//! The reason rustc_log is a tiny separate crate, as opposed to exposing the
+//! same things in rustc_driver only, is to enable the above workflow. If you
+//! had to depend on rustc_driver in order to turn on rustc's debug logs, that's
+//! an enormously bigger dependency tree; every change you make to rustc_ast (or
+//! whichever piece of the compiler you are interested in) would involve
+//! rebuilding all the rest of rustc up to rustc_driver in order to run your
+//! main.rs. Whereas by depending only on rustc_log and the few crates you are
+//! debugging, you can make changes inside those crates and quickly run main.rs
+//! to read the debug logs.
+
+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 verbose_entry_exit = match env::var_os(String::from(env) + "_ENTRY_EXIT") {
+        None => false,
+        Some(v) => &v != "0",
+    };
+
+    let layer = tracing_tree::HierarchicalLayer::default()
+        .with_writer(io::stderr)
+        .with_indent_lines(true)
+        .with_ansi(color_logs)
+        .with_targets(true)
+        .with_verbose_exit(verbose_entry_exit)
+        .with_verbose_entry(verbose_entry_exit)
+        .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",
+            ),
+        }
+    }
+}