Rollup merge of rust-lang#92545 - dtolnay:rustlog, r=petrochenkov

Extract init_env_logger to crate

I've been doing some work on rustc_ast_pretty using an out-of-tree main.rs and Cargo.toml with the following:

```toml
[dependencies]
rustc_ast = { path = "../rust/compiler/rustc_ast" }
rustc_ast_pretty = { path = "../rust/compiler/rustc_ast_pretty" }
rustc_span = { path = "../rust/compiler/rustc_span" }
```

Rustc_ast_pretty helpfully uses `tracing::debug!` but I found that in order to enable the debug output, my test crate must depend on rustc_driver which is an enormously bigger dependency than what I have been using so far, and slows down iteration time because an enormous dependency tree between rustc_ast and rustc_driver must now be rebuilt after every ast change.

I pulled out the tracing initialization to a new minimal rustc_log crate so that projects depending on the other rustc crates, like rustc_ast_pretty, can access the `debug!` messages in them without building all the rest of rustc.

Author: matthiaskrgr

Cargo.lock

@@ -3808,7 +3808,6 @@ dependencies = [
 name = "rustc_driver"
 version = "0.0.0"
 dependencies = [
- "atty",
  "libc",
  "rustc_ast",
  "rustc_ast_pretty",
@@ -3822,6 +3821,7 @@ dependencies = [
  "rustc_hir_pretty",
  "rustc_interface",
  "rustc_lint",
+ "rustc_log",
  "rustc_metadata",
  "rustc_middle",
  "rustc_parse",
@@ -3833,8 +3833,6 @@ dependencies = [
  "rustc_target",
  "rustc_typeck",
  "tracing",
- "tracing-subscriber",
- "tracing-tree",
  "winapi",
 ]
 
@@ -4077,6 +4075,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "rustc_log"
+version = "0.0.0"
+dependencies = [
+ "atty",
+ "rustc_span",
+ "tracing",
+ "tracing-subscriber",
+ "tracing-tree",
+]
+
 [[package]]
 name = "rustc_macros"
 version = "0.1.0"

compiler/rustc_driver/Cargo.toml

@@ -8,10 +8,8 @@ crate-type = ["dylib"]
 
 [dependencies]
 libc = "0.2"
-atty = "0.2"
 tracing = { version = "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"
+rustc_log = { path = "../rustc_log" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_target = { path = "../rustc_target" }
@@ -40,4 +38,4 @@ winapi = { version = "0.3", features = ["consoleapi", "debugapi", "processenv"]
 
 [features]
 llvm = ['rustc_interface/llvm']
-max_level_info = ['tracing/max_level_info']
+max_level_info = ['rustc_log/max_level_info']

compiler/rustc_driver/src/lib.rs

@@ -24,6 +24,7 @@ use rustc_feature::find_gated_cfg;
 use rustc_interface::util::{self, collect_crate_types, get_codegen_backend};
 use rustc_interface::{interface, Queries};
 use rustc_lint::LintStore;
+use rustc_log::stdout_isatty;
 use rustc_metadata::locator;
 use rustc_save_analysis as save;
 use rustc_save_analysis::DumpHandler;
@@ -514,14 +515,6 @@ impl Compilation {
 #[derive(Copy, Clone)]
 pub struct RustcDefaultCalls;
 
-fn stdout_isatty() -> bool {
-    atty::is(atty::Stream::Stdout)
-}
-
-fn stderr_isatty() -> bool {
-    atty::is(atty::Stream::Stderr)
-}
-
 fn handle_explain(registry: Registry, code: &str, output: ErrorOutputType) {
     let upper_cased_code = code.to_ascii_uppercase();
     let normalised = if upper_cased_code.starts_with('E') {
@@ -1254,54 +1247,18 @@ pub fn install_ice_hook() {
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing crate version.
 pub fn init_rustc_env_logger() {
-    init_env_logger("RUSTC_LOG")
+    if let Err(error) = rustc_log::init_rustc_env_logger() {
+        early_error(ErrorOutputType::default(), &error.to_string());
+    }
 }
 
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing 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) {
-    use tracing_subscriber::{
-        filter::{self, EnvFilter, LevelFilter},
-        layer::SubscriberExt,
-    };
-
-    let filter = match std::env::var(env) {
-        Ok(env) => EnvFilter::new(env),
-        _ => EnvFilter::default().add_directive(filter::Directive::from(LevelFilter::WARN)),
-    };
-
-    let color_logs = match std::env::var(String::from(env) + "_COLOR") {
-        Ok(value) => match value.as_ref() {
-            "always" => true,
-            "never" => false,
-            "auto" => stderr_isatty(),
-            _ => early_error(
-                ErrorOutputType::default(),
-                &format!(
-                    "invalid log color value '{}': expected one of always, never, or auto",
-                    value
-                ),
-            ),
-        },
-        Err(std::env::VarError::NotPresent) => stderr_isatty(),
-        Err(std::env::VarError::NotUnicode(_value)) => early_error(
-            ErrorOutputType::default(),
-            "non-Unicode log color value: expected one of always, never, or auto",
-        ),
-    };
-
-    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();
+    if let Err(error) = rustc_log::init_env_logger(env) {
+        early_error(ErrorOutputType::default(), &error.to_string());
+    }
 }
 
 #[cfg(all(unix, any(target_env = "gnu", target_os = "macos")))]

compiler/rustc_log/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "rustc_log"
+version = "0.0.0"
+edition = "2021"
+
+[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"
+
+[dev-dependencies]
+rustc_span = { path = "../rustc_span" }
+
+[features]
+max_level_info = ['tracing/max_level_info']

compiler/rustc_log/src/lib.rs

@@ -0,0 +1,115 @@
+//! 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 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",
+            ),
+        }
+    }
+}