2 files changed, 40 insertions, 7 deletions

diff --git a/crates/hir_ty/src/tests.rs b/crates/hir_ty/src/tests.rs
index c953925ec..91c9d38c5 100644
--- a/crates/hir_ty/src/tests.rs
+++ b/crates/hir_ty/src/tests.rs
@@ -8,7 +8,7 @@ mod method_resolution;
 mod macros;
 mod display_source_code;
 
-use std::sync::Arc;
+use std::{env, sync::Arc};
 
 use base_db::{fixture::WithFixture, FileRange, SourceDatabase, SourceDatabaseExt};
 use expect::Expect;
@@ -22,12 +22,14 @@ use hir_def::{
     AssocItemId, DefWithBodyId, LocalModuleId, Lookup, ModuleDefId,
 };
 use hir_expand::{db::AstDatabase, InFile};
-use stdx::format_to;
+use stdx::{format_to, RacyFlag};
 use syntax::{
     algo,
     ast::{self, AstNode},
     SyntaxNode,
 };
+use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};
+use tracing_tree::HierarchicalLayer;
 
 use crate::{
     db::HirDatabase, display::HirDisplay, infer::TypeMismatch, test_db::TestDB, InferenceResult, Ty,
@@ -37,9 +39,12 @@ use crate::{
 // against snapshots of the expected results using expect. Use
 // `env UPDATE_EXPECT=1 cargo test -p hir_ty` to update the snapshots.
 
-fn setup_tracing() -> tracing::subscriber::DefaultGuard {
-    use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};
-    use tracing_tree::HierarchicalLayer;
+fn setup_tracing() -> Option<tracing::subscriber::DefaultGuard> {
+    static ENABLE: RacyFlag = RacyFlag::new();
+    if !ENABLE.get(|| env::var("CHALK_DEBUG").is_ok()) {
+        return None;
+    }
+
     let filter = EnvFilter::from_env("CHALK_DEBUG");
     let layer = HierarchicalLayer::default()
         .with_indent_lines(true)
@@ -47,7 +52,7 @@ fn setup_tracing() -> tracing::subscriber::DefaultGuard {
         .with_indent_amount(2)
         .with_writer(std::io::stderr);
     let subscriber = Registry::default().with(filter).with(layer);
-    tracing::subscriber::set_default(subscriber)
+    Some(tracing::subscriber::set_default(subscriber))
 }
 
 fn check_types(ra_fixture: &str) {
diff --git a/crates/stdx/src/lib.rs b/crates/stdx/src/lib.rs
index 265d19288..5d60f0219 100644
--- a/crates/stdx/src/lib.rs
+++ b/crates/stdx/src/lib.rs
@@ -1,5 +1,8 @@
 //! Missing batteries for standard libraries.
-use std::time::Instant;
+use std::{
+    sync::atomic::{AtomicUsize, Ordering},
+    time::Instant,
+};
 
 mod macros;
 
@@ -134,6 +137,31 @@ where
     left
 }
 
+pub struct RacyFlag(AtomicUsize);
+
+impl RacyFlag {
+    pub const fn new() -> RacyFlag {
+        RacyFlag(AtomicUsize::new(0))
+    }
+
+    pub fn get(&self, init: impl FnMut() -> bool) -> bool {
+        let mut init = Some(init);
+        self.get_impl(&mut || init.take().map_or(false, |mut f| f()))
+    }
+
+    fn get_impl(&self, init: &mut dyn FnMut() -> bool) -> bool {
+        match self.0.load(Ordering::Relaxed) {
+            0 => false,
+            1 => true,
+            _ => {
+                let res = init();
+                self.0.store(if res { 1 } else { 0 }, Ordering::Relaxed);
+                res
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;