Add comment regarding performance

crates/red_knot_python_semantic/src/semantic_index/use_def/symbol_state.rs

@@ -155,7 +155,7 @@ impl SymbolDeclarations {
             .push(ScopedVisibilityConstraintId::ALWAYS_TRUE);
     }
 
-    /// Add given visibility constraint to all live bindings.
+    /// Add given visibility constraint to all live declarations.
     pub(super) fn record_visibility_constraint(
         &mut self,
         visibility_constraints: &mut VisibilityConstraints,

crates/red_knot_python_semantic/src/visibility_constraints.rs

@@ -154,6 +154,12 @@ use crate::semantic_index::{
 use crate::types::{infer_expression_types, Truthiness};
 use crate::Db;
 
+/// The maximum depth of recursion when evaluating visibility constraints.
+///
+/// This is a performance optimization that prevents us from descending deeply in case of
+/// pathological cases. The actual limit here has been derived from performance testing on
+/// the `black` codebase. When increasing the limit beyond 32, we see a 5x runtime increase
+/// resulting from a few files with a lot of boolean expressions and `if`-statements.
 const MAX_RECURSION_DEPTH: usize = 24;
 
 #[derive(Clone, Debug, PartialEq, Eq)]