Remove rustc_transmute's dependence on rustc_infer.

`TransmuteTypeEnv` only needs a `TyCtxt`, not an `InferCtxt`.

Author: nnethercote

Cargo.lock

@@ -4500,7 +4500,6 @@ dependencies = [
  "rustc_abi",
  "rustc_data_structures",
  "rustc_hir",
- "rustc_infer",
  "rustc_macros",
  "rustc_middle",
  "rustc_span",

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -2544,7 +2544,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             let src = trait_pred.trait_ref.args.type_at(1);
             let err_msg = format!("`{src}` cannot be safely transmuted into `{dst}`");
 
-            match rustc_transmute::TransmuteTypeEnv::new(self.infcx).is_transmutable(
+            match rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx).is_transmutable(
                 obligation.cause,
                 src_and_dst,
                 assume,

compiler/rustc_trait_selection/src/solve/delegate.rs

@@ -236,7 +236,7 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         };
 
         // FIXME(transmutability): This really should be returning nested goals for `Answer::If*`
-        match rustc_transmute::TransmuteTypeEnv::new(&self.0).is_transmutable(
+        match rustc_transmute::TransmuteTypeEnv::new(self.0.tcx).is_transmutable(
             ObligationCause::dummy(),
             rustc_transmute::Types { src, dst },
             assume,

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -424,7 +424,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let src = predicate.trait_ref.args.type_at(1);
 
         debug!(?src, ?dst);
-        let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx);
+        let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx.tcx);
         let maybe_transmutable = transmute_env.is_transmutable(
             obligation.cause.clone(),
             rustc_transmute::Types { dst, src },

compiler/rustc_transmute/Cargo.toml

@@ -8,7 +8,6 @@ edition = "2024"
 rustc_abi = { path = "../rustc_abi", optional = true }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir", optional = true }
-rustc_infer = { path = "../rustc_infer", optional = true }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_middle = { path = "../rustc_middle", optional = true }
 rustc_span = { path = "../rustc_span", optional = true }
@@ -19,7 +18,6 @@ tracing = "0.1"
 rustc = [
     "dep:rustc_abi",
     "dep:rustc_hir",
-    "dep:rustc_infer",
     "dep:rustc_macros",
     "dep:rustc_middle",
     "dep:rustc_span",

compiler/rustc_transmute/src/lib.rs

@@ -81,7 +81,6 @@ pub enum Reason<T> {
 #[cfg(feature = "rustc")]
 mod rustc {
     use rustc_hir::lang_items::LangItem;
-    use rustc_infer::infer::InferCtxt;
     use rustc_macros::TypeVisitable;
     use rustc_middle::traits::ObligationCause;
     use rustc_middle::ty::{Const, ParamEnv, Ty, TyCtxt};
@@ -97,13 +96,13 @@ mod rustc {
         pub dst: Ty<'tcx>,
     }
 
-    pub struct TransmuteTypeEnv<'cx, 'tcx> {
-        infcx: &'cx InferCtxt<'tcx>,
+    pub struct TransmuteTypeEnv<'tcx> {
+        tcx: TyCtxt<'tcx>,
     }
 
-    impl<'cx, 'tcx> TransmuteTypeEnv<'cx, 'tcx> {
-        pub fn new(infcx: &'cx InferCtxt<'tcx>) -> Self {
-            Self { infcx }
+    impl<'tcx> TransmuteTypeEnv<'tcx> {
+        pub fn new(tcx: TyCtxt<'tcx>) -> Self {
+            Self { tcx }
         }
 
         #[allow(unused)]
@@ -117,7 +116,7 @@ mod rustc {
                 types.src,
                 types.dst,
                 assume,
-                self.infcx.tcx,
+                self.tcx,
             )
             .answer()
         }