Auto merge of #117814 - RalfJung:rustc-logger-without-set-var, r=TaKO8Ki

rustc_log: provide a way to init logging based on the values, not names, of the env vars

Miri wants to affect how rustc does logging. So far this required setting environment variables before calling `rustc_driver::init_rustc_env_logger`. However, `set_var` is a function one should really [avoid calling](https://github.com/rust-lang/rust/issues/90308), so this adds the necessary APIs to rustc such that Miri can just pass it the *values* of all the log-relevant environment variables, rather than having to change the global environment.

2 files changed, 41 insertions, 30 deletions

diff --git a/src/tools/error_index_generator/main.rs b/src/tools/error_index_generator/main.rs
index 62a58576da5..3a23ff7fe6a 100644
--- a/src/tools/error_index_generator/main.rs
+++ b/src/tools/error_index_generator/main.rs
@@ -1,6 +1,7 @@
 #![feature(rustc_private)]
 
 extern crate rustc_driver;
+extern crate rustc_log;
 extern crate rustc_session;
 
 use std::env;
@@ -173,7 +174,7 @@ fn parse_args() -> (OutputFormat, PathBuf) {
 fn main() {
     let handler =
         rustc_session::EarlyErrorHandler::new(rustc_session::config::ErrorOutputType::default());
-    rustc_driver::init_env_logger(&handler, "RUST_LOG");
+    rustc_driver::init_logger(&handler, rustc_log::LoggerConfig::from_env("RUST_LOG"));
     let (format, dst) = parse_args();
     let result = main_with_result(format, &dst);
     if let Err(e) = result {
diff --git a/src/tools/miri/src/bin/miri.rs b/src/tools/miri/src/bin/miri.rs
index cd628444fed..7f777cd4727 100644
--- a/src/tools/miri/src/bin/miri.rs
+++ b/src/tools/miri/src/bin/miri.rs
@@ -9,11 +9,12 @@ extern crate rustc_data_structures;
 extern crate rustc_driver;
 extern crate rustc_hir;
 extern crate rustc_interface;
+extern crate rustc_log;
 extern crate rustc_metadata;
 extern crate rustc_middle;
 extern crate rustc_session;
 
-use std::env;
+use std::env::{self, VarError};
 use std::num::NonZeroU64;
 use std::path::PathBuf;
 use std::str::FromStr;
@@ -183,45 +184,54 @@ macro_rules! show_error {
     ($($tt:tt)*) => { show_error(&format_args!($($tt)*)) };
 }
 
-fn init_early_loggers(handler: &EarlyErrorHandler) {
-    // Note that our `extern crate log` is *not* the same as rustc's; as a result, we have to
-    // initialize them both, and we always initialize `miri`'s first.
-    let env = env_logger::Env::new().filter("MIRI_LOG").write_style("MIRI_LOG_STYLE");
-    env_logger::init_from_env(env);
-    // Enable verbose entry/exit logging by default if MIRI_LOG is set.
-    if env::var_os("MIRI_LOG").is_some() && env::var_os("RUSTC_LOG_ENTRY_EXIT").is_none() {
-        env::set_var("RUSTC_LOG_ENTRY_EXIT", "1");
-    }
-    // We only initialize `rustc` if the env var is set (so the user asked for it).
-    // If it is not set, we avoid initializing now so that we can initialize
-    // later with our custom settings, and *not* log anything for what happens before
-    // `miri` gets started.
-    if env::var_os("RUSTC_LOG").is_some() {
-        rustc_driver::init_rustc_env_logger(handler);
-    }
-}
+fn rustc_logger_config() -> rustc_log::LoggerConfig {
+    // Start with the usual env vars.
+    let mut cfg = rustc_log::LoggerConfig::from_env("RUSTC_LOG");
 
-fn init_late_loggers(handler: &EarlyErrorHandler, tcx: TyCtxt<'_>) {
-    // We initialize loggers right before we start evaluation. We overwrite the `RUSTC_LOG`
-    // env var if it is not set, control it based on `MIRI_LOG`.
-    // (FIXME: use `var_os`, but then we need to manually concatenate instead of `format!`.)
+    // Overwrite if MIRI_LOG is set.
     if let Ok(var) = env::var("MIRI_LOG") {
-        if env::var_os("RUSTC_LOG").is_none() {
+        // MIRI_LOG serves as default for RUSTC_LOG, if that is not set.
+        if matches!(cfg.filter, Err(VarError::NotPresent)) {
             // We try to be a bit clever here: if `MIRI_LOG` is just a single level
             // used for everything, we only apply it to the parts of rustc that are
             // CTFE-related. Otherwise, we use it verbatim for `RUSTC_LOG`.
             // This way, if you set `MIRI_LOG=trace`, you get only the right parts of
             // rustc traced, but you can also do `MIRI_LOG=miri=trace,rustc_const_eval::interpret=debug`.
             if log::Level::from_str(&var).is_ok() {
-                env::set_var(
-                    "RUSTC_LOG",
-                    format!("rustc_middle::mir::interpret={var},rustc_const_eval::interpret={var}"),
-                );
+                cfg.filter = Ok(format!(
+                    "rustc_middle::mir::interpret={var},rustc_const_eval::interpret={var}"
+                ));
             } else {
-                env::set_var("RUSTC_LOG", &var);
+                cfg.filter = Ok(var);
             }
-            rustc_driver::init_rustc_env_logger(handler);
         }
+        // Enable verbose entry/exit logging by default if MIRI_LOG is set.
+        if matches!(cfg.verbose_entry_exit, Err(VarError::NotPresent)) {
+            cfg.verbose_entry_exit = Ok(format!("1"));
+        }
+    }
+
+    cfg
+}
+
+fn init_early_loggers(handler: &EarlyErrorHandler) {
+    // Note that our `extern crate log` is *not* the same as rustc's; as a result, we have to
+    // initialize them both, and we always initialize `miri`'s first.
+    let env = env_logger::Env::new().filter("MIRI_LOG").write_style("MIRI_LOG_STYLE");
+    env_logger::init_from_env(env);
+    // Now for rustc. We only initialize `rustc` if the env var is set (so the user asked for it).
+    // If it is not set, we avoid initializing now so that we can initialize later with our custom
+    // settings, and *not* log anything for what happens before `miri` gets started.
+    if env::var_os("RUSTC_LOG").is_some() {
+        rustc_driver::init_logger(handler, rustc_logger_config());
+    }
+}
+
+fn init_late_loggers(handler: &EarlyErrorHandler, tcx: TyCtxt<'_>) {
+    // If `RUSTC_LOG` is not set, then `init_early_loggers` did not call
+    // `rustc_driver::init_logger`, so we have to do this now.
+    if env::var_os("RUSTC_LOG").is_none() {
+        rustc_driver::init_logger(handler, rustc_logger_config());
     }
 
     // If `MIRI_BACKTRACE` is set and `RUSTC_CTFE_BACKTRACE` is not, set `RUSTC_CTFE_BACKTRACE`.