From 0ad7701b04f03602ef1cd86ebbae09d4a0f5a2b1 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 5 Jan 2026 16:34:41 +1100
Subject: [PATCH] Remove `variables` arg from
 `Canonicalizer::canonicalize_response`.

It's an empty `Vec` at both call sites, and so is unnecessary.
---
 .../rustc_next_trait_solver/src/canonical/canonicalizer.rs | 4 ++--
 compiler/rustc_next_trait_solver/src/canonical/mod.rs      | 7 ++-----
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_next_trait_solver/src/canonical/canonicalizer.rs b/compiler/rustc_next_trait_solver/src/canonical/canonicalizer.rs
index 6c114d601157..c2a7414911ff 100644
--- a/compiler/rustc_next_trait_solver/src/canonical/canonicalizer.rs
+++ b/compiler/rustc_next_trait_solver/src/canonical/canonicalizer.rs
@@ -84,14 +84,14 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
     pub(super) fn canonicalize_response<T: TypeFoldable<I>>(
         delegate: &'a D,
         max_input_universe: ty::UniverseIndex,
-        variables: &'a mut Vec<I::GenericArg>,
         value: T,
     ) -> ty::Canonical<I, T> {
+        let mut variables = Vec::new();
         let mut canonicalizer = Canonicalizer {
             delegate,
             canonicalize_mode: CanonicalizeMode::Response { max_input_universe },
 
-            variables,
+            variables: &mut variables,
             variable_lookup_table: Default::default(),
             sub_root_lookup_table: Default::default(),
             var_kinds: Vec::new(),
diff --git a/compiler/rustc_next_trait_solver/src/canonical/mod.rs b/compiler/rustc_next_trait_solver/src/canonical/mod.rs
index b4cea8701d82..d562b8fac4c4 100644
--- a/compiler/rustc_next_trait_solver/src/canonical/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/canonical/mod.rs
@@ -82,10 +82,7 @@ where
     I: Interner,
     T: TypeFoldable<I>,
 {
-    let mut orig_values = Default::default();
-    let canonical =
-        Canonicalizer::canonicalize_response(delegate, max_input_universe, &mut orig_values, value);
-    canonical
+    Canonicalizer::canonicalize_response(delegate, max_input_universe, value)
 }
 
 /// After calling a canonical query, we apply the constraints returned
@@ -308,7 +305,7 @@ where
     let var_values = CanonicalVarValues { var_values: delegate.cx().mk_args(var_values) };
     let state = inspect::State { var_values, data };
     let state = eager_resolve_vars(delegate, state);
-    Canonicalizer::canonicalize_response(delegate, max_input_universe, &mut vec![], state)
+    Canonicalizer::canonicalize_response(delegate, max_input_universe, state)
 }
 
 // FIXME: needs to be pub to be accessed by downstream