use TypingEnv when no infcx is available

the behavior of the type system not only depends on the current
assumptions, but also the currentnphase of the compiler. This is
mostly necessary as we need to decide whether and how to reveal
opaque types. We track this via the `TypingMode`.

compiler/rustc_infer/src/infer/mod.rs

@@ -38,7 +38,8 @@ use rustc_middle::ty::fold::{
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{
     self, ConstVid, FloatVid, GenericArg, GenericArgKind, GenericArgs, GenericArgsRef,
-    GenericParamDefKind, InferConst, IntVid, Ty, TyCtxt, TyVid, TypingMode,
+    GenericParamDefKind, InferConst, IntVid, PseudoCanonicalInput, Ty, TyCtxt, TyVid,
+    TypeVisitable, TypingEnv, TypingMode,
 };
 use rustc_span::Span;
 use rustc_span::symbol::Symbol;
@@ -565,6 +566,13 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
         (infcx, value, args)
     }
 
+    pub fn build_with_typing_env(
+        mut self,
+        TypingEnv { typing_mode, param_env }: TypingEnv<'tcx>,
+    ) -> (InferCtxt<'tcx>, ty::ParamEnv<'tcx>) {
+        (self.build(typing_mode), param_env)
+    }
+
     pub fn build(&mut self, typing_mode: TypingMode<'tcx>) -> InferCtxt<'tcx> {
         let InferCtxtBuilder { tcx, considering_regions, skip_leak_check, next_trait_solver } =
             *self;
@@ -1278,6 +1286,42 @@ impl<'tcx> InferCtxt<'tcx> {
         u
     }
 
+    /// Extract [ty::TypingMode] of this inference context to get a `TypingEnv`
+    /// which contains the necessary information to use the trait system without
+    /// using canonicalization or carrying this inference context around.
+    pub fn typing_env(&self, param_env: ty::ParamEnv<'tcx>) -> ty::TypingEnv<'tcx> {
+        let typing_mode = match self.typing_mode(param_env) {
+            ty::TypingMode::Coherence => ty::TypingMode::Coherence,
+            // FIXME(#132279): This erases the `defining_opaque_types` as it isn't possible
+            // to handle them without proper canonicalization. This means we may cause cycle
+            // errors and fail to reveal opaques while inside of bodies. We should rename this
+            // function and require explicit comments on all use-sites in the future.
+            ty::TypingMode::Analysis { defining_opaque_types: _ } => {
+                TypingMode::non_body_analysis()
+            }
+            ty::TypingMode::PostAnalysis => ty::TypingMode::PostAnalysis,
+        };
+        ty::TypingEnv { typing_mode, param_env }
+    }
+
+    /// Similar to [Self::canonicalize_query], except that it returns
+    /// a [PseudoCanonicalInput] and requires both the `value` and the
+    /// `param_env` to not contain any inference variables or placeholders.
+    pub fn pseudo_canonicalize_query<V>(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        value: V,
+    ) -> PseudoCanonicalInput<'tcx, V>
+    where
+        V: TypeVisitable<TyCtxt<'tcx>>,
+    {
+        debug_assert!(!value.has_infer());
+        debug_assert!(!value.has_placeholders());
+        debug_assert!(!param_env.has_infer());
+        debug_assert!(!param_env.has_placeholders());
+        self.typing_env(param_env).as_query_input(value)
+    }
+
     /// The returned function is used in a fast path. If it returns `true` the variable is
     /// unchanged, `false` indicates that the status is unknown.
     #[inline]