From 36d4b02fa97a7b19572f524980b7f0fbd6d5d8aa Mon Sep 17 00:00:00 2001
From: Shunsuke Shibayama <45118249+mtshiba@users.noreply.github.com>
Date: Sun, 19 Oct 2025 19:13:10 +0900
Subject: [PATCH] [ty] fix non-deterministic overload function inference
 (#20966)

---
 crates/ty_python_semantic/src/types/infer/builder.rs | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/crates/ty_python_semantic/src/types/infer/builder.rs b/crates/ty_python_semantic/src/types/infer/builder.rs
index 44ed5841f8..9c6826e71e 100644
--- a/crates/ty_python_semantic/src/types/infer/builder.rs
+++ b/crates/ty_python_semantic/src/types/infer/builder.rs
@@ -106,7 +106,7 @@ use crate::types::{
 };
 use crate::types::{ClassBase, add_inferred_python_version_hint_to_diagnostic};
 use crate::unpack::{EvaluationMode, UnpackPosition};
-use crate::{Db, FxOrderSet, Program};
+use crate::{Db, FxIndexSet, FxOrderSet, Program};
 
 mod annotation_expression;
 mod type_expression;
@@ -257,8 +257,10 @@ pub(super) struct TypeInferenceBuilder<'db, 'ast> {
     ///     return x
     /// ```
     ///
+    /// To keep the calculation deterministic, we use an `FxIndexSet` whose order is determined by the sequence of insertion calls.
+    ///
     /// [`check_overloaded_functions`]: TypeInferenceBuilder::check_overloaded_functions
-    called_functions: FxHashSet<FunctionType<'db>>,
+    called_functions: FxIndexSet<FunctionType<'db>>,
 
     /// Whether we are in a context that binds unbound typevars.
     typevar_binding_context: Option<Definition<'db>>,
@@ -312,7 +314,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             region,
             scope,
             return_types_and_ranges: vec![],
-            called_functions: FxHashSet::default(),
+            called_functions: FxIndexSet::default(),
             deferred_state: DeferredExpressionState::None,
             multi_inference_state: MultiInferenceState::Panic,
             expressions: FxHashMap::default(),
@@ -949,7 +951,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         // Collect all the unique overloaded function places in this scope. This requires a set
         // because an overloaded function uses the same place for each of the overloads and the
         // implementation.
-        let overloaded_function_places: FxHashSet<_> = self
+        let overloaded_function_places: FxIndexSet<_> = self
             .declarations
             .iter()
             .filter_map(|(definition, ty)| {
@@ -971,7 +973,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             .index
             .use_def_map(self.scope().file_scope_id(self.db()));
 
-        let mut public_functions = FxHashSet::default();
+        let mut public_functions = FxIndexSet::default();
 
         for place in overloaded_function_places {
             if let Place::Defined(Type::FunctionLiteral(function), _, Definedness::AlwaysDefined) =