[ty] Add comment explaining why HasTrackedScope is implemented for Identifier and why it works (#21057)

crates/ty_python_semantic/src/semantic_model.rs

@@ -505,8 +505,10 @@ impl HasTrackedScope for ast::Expr {}
 impl HasTrackedScope for ast::ExprRef<'_> {}
 impl HasTrackedScope for &ast::ExprRef<'_> {}
 
-// See https://github.com/astral-sh/ty/issues/572 why this implementation exists
-// even when we never register identifiers during semantic index building.
+// We never explicitly register the scope of an `Identifier`.
+// However, `ExpressionsScopeMap` stores the text ranges of each scope.
+// That allows us to look up the identifier's scope for as long as it's
+// inside an expression (because the ranges overlap).
 impl HasTrackedScope for ast::Identifier {}
 
 #[cfg(test)]