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`.

1 files changed, 99 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 7fda0662a34..d6f7ee748bb 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -103,7 +103,7 @@ use crate::error::{OpaqueHiddenTypeMismatch, TypeMismatchReason};
 use crate::metadata::ModChild;
 use crate::middle::privacy::EffectiveVisibilities;
 use crate::mir::{Body, CoroutineLayout};
-use crate::query::Providers;
+use crate::query::{IntoQueryParam, Providers};
 use crate::traits::{self, Reveal};
 use crate::ty;
 pub use crate::ty::diagnostics::*;
@@ -1122,6 +1122,104 @@ impl<'tcx, T> ParamEnvAnd<'tcx, T> {
     }
 }
 
+/// The environment in which to do trait solving.
+///
+/// Most of the time you only need to care about the `ParamEnv`
+/// as the `TypingMode` is simply stored in the `InferCtxt`.
+///
+/// However, there are some places which rely on trait solving
+/// without using an `InferCtxt` themselves. For these to be
+/// able to use the trait system they have to be able to initialize
+/// such an `InferCtxt` with the right `typing_mode`, so they need
+/// to track both.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
+#[derive(TypeVisitable, TypeFoldable)]
+pub struct TypingEnv<'tcx> {
+    pub typing_mode: TypingMode<'tcx>,
+    pub param_env: ParamEnv<'tcx>,
+}
+
+impl<'tcx> TypingEnv<'tcx> {
+    // FIXME(#132279): This method should be removed but simplifies the
+    // transition.
+    pub fn from_param_env(param_env: ParamEnv<'tcx>) -> TypingEnv<'tcx> {
+        TypingEnv { typing_mode: TypingMode::from_param_env(param_env), param_env }
+    }
+
+    /// Create a typing environment with no where-clauses in scope
+    /// where all opaque types and default associated items are revealed.
+    ///
+    /// This is only suitable for monomorphized, post-typeck environments.
+    /// Do not use this for MIR optimizations, as even though they also
+    /// use `TypingMode::PostAnalysis`, they may still have where-clauses
+    /// in scope.
+    pub fn fully_monomorphized() -> TypingEnv<'tcx> {
+        TypingEnv { typing_mode: TypingMode::PostAnalysis, param_env: ParamEnv::reveal_all() }
+    }
+
+    /// Create a typing environment for use during analysis outside of a body.
+    ///
+    /// Using a typing environment inside of bodies is not supported as the body
+    /// may define opaque types. In this case the used functions have to be
+    /// converted to use proper canonical inputs instead.
+    pub fn non_body_analysis(
+        tcx: TyCtxt<'tcx>,
+        def_id: impl IntoQueryParam<DefId>,
+    ) -> TypingEnv<'tcx> {
+        TypingEnv { typing_mode: TypingMode::non_body_analysis(), param_env: tcx.param_env(def_id) }
+    }
+
+    pub fn post_analysis(tcx: TyCtxt<'tcx>, def_id: impl IntoQueryParam<DefId>) -> TypingEnv<'tcx> {
+        TypingEnv {
+            typing_mode: TypingMode::PostAnalysis,
+            param_env: tcx.param_env_reveal_all_normalized(def_id),
+        }
+    }
+
+    /// Modify the `typing_mode` to `PostAnalysis` and eagerly reveal all
+    /// opaque types in the `param_env`.
+    pub fn with_reveal_all_normalized(self, tcx: TyCtxt<'tcx>) -> TypingEnv<'tcx> {
+        let TypingEnv { typing_mode: _, param_env } = self;
+        let param_env = param_env.with_reveal_all_normalized(tcx);
+        TypingEnv { typing_mode: TypingMode::PostAnalysis, param_env }
+    }
+
+    /// Combine this typing environment with the given `value` to be used by
+    /// not (yet) canonicalized queries. This only works if the value does not
+    /// contain anything local to some `InferCtxt`, i.e. inference variables or
+    /// placeholders.
+    pub fn as_query_input<T>(self, value: T) -> PseudoCanonicalInput<'tcx, T>
+    where
+        T: TypeVisitable<TyCtxt<'tcx>>,
+    {
+        debug_assert!(!value.has_infer());
+        // FIXME(#132279): We should assert that the value does not contain any placeholders
+        // as these placeholders are also local to the current inference context. However, we
+        // currently use pseudo-canonical queries in the trait solver which replaces params with
+        // placeholders. We should also simply not use pseudo-canonical queries in the trait
+        // solver, at which point we can readd this assert.
+        //
+        // debug_assert!(!value.has_placeholders());
+        PseudoCanonicalInput { typing_env: self, value }
+    }
+}
+
+/// Similar to `CanonicalInput`, this carries the `typing_mode` and the environment
+/// necessary to do any kind of trait solving inside of nested queries.
+///
+/// Unlike proper canonicalization, this requires the `param_env` and the `value` to not
+/// contain anything local to the `infcx` of the caller, so we don't actually canonicalize
+/// anything.
+///
+/// This should be created by using `infcx.pseudo_canonicalize_query(param_env, value)`
+/// or by using `typing_env.as_query_input(value)`.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(HashStable)]
+pub struct PseudoCanonicalInput<'tcx, T> {
+    pub typing_env: TypingEnv<'tcx>,
+    pub value: T,
+}
+
 #[derive(Copy, Clone, Debug, HashStable, Encodable, Decodable)]
 pub struct Destructor {
     /// The `DefId` of the destructor method