implement version of normalize_erasing_regions that doesn't assume value is normalizable

compiler/rustc_lint/src/types.rs

@@ -1337,7 +1337,9 @@ impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
             let layout = match cx.layout_of(ty) {
                 Ok(layout) => layout,
                 Err(
-                    ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
+                    ty::layout::LayoutError::Unknown(_)
+                    | ty::layout::LayoutError::SizeOverflow(_)
+                    | ty::layout::LayoutError::NormalizationFailure(_, _),
                 ) => return,
             };
             let (variants, tag) = match layout.variants {

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -493,7 +493,7 @@ impl dyn MachineStopType {
 }
 
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-static_assert_size!(InterpError<'_>, 64);
+static_assert_size!(InterpError<'_>, 88);
 
 pub enum InterpError<'tcx> {
     /// The program caused undefined behavior.

compiler/rustc_middle/src/query/mod.rs

@@ -1658,6 +1658,20 @@ rustc_queries! {
         desc { "normalizing `{}`", goal.value }
     }
 
+    /// Do not call this query directly: invoke `try_normalize_erasing_regions` instead.
+    query try_normalize_generic_arg_after_erasing_regions(
+        goal: ParamEnvAnd<'tcx, GenericArg<'tcx>>
+    ) -> Result<GenericArg<'tcx>, NoSolution> {
+        desc { "trying to normalize `{}`", goal.value }
+    }
+
+    /// Do not call this query directly: invoke `try_normalize_erasing_regions` instead.
+    query try_normalize_mir_const_after_erasing_regions(
+        goal: ParamEnvAnd<'tcx, mir::ConstantKind<'tcx>>
+    ) -> Result<mir::ConstantKind<'tcx>, NoSolution> {
+        desc { "trying to normalize `{}`", goal.value }
+    }
+
     query implied_outlives_bounds(
         goal: CanonicalTyGoal<'tcx>
     ) -> Result<

compiler/rustc_middle/src/ty/layout.rs

@@ -1,5 +1,6 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir::{GeneratorLayout, GeneratorSavedLocal};
+use crate::ty::normalize_erasing_regions::NormalizationError;
 use crate::ty::subst::Subst;
 use crate::ty::{self, subst::SubstsRef, ReprOptions, Ty, TyCtxt, TypeFoldable};
 use rustc_ast as ast;
@@ -199,6 +200,7 @@ pub const MAX_SIMD_LANES: u64 = 1 << 0xF;
 pub enum LayoutError<'tcx> {
     Unknown(Ty<'tcx>),
     SizeOverflow(Ty<'tcx>),
+    NormalizationFailure(Ty<'tcx>, NormalizationError<'tcx>),
 }
 
 impl<'tcx> fmt::Display for LayoutError<'tcx> {
@@ -208,16 +210,24 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
             LayoutError::SizeOverflow(ty) => {
                 write!(f, "values of the type `{}` are too big for the current architecture", ty)
             }
+            LayoutError::NormalizationFailure(t, e) => write!(
+                f,
+                "unable to determine layout for `{}` because `{}` cannot be normalized",
+                t,
+                e.get_type_for_failure()
+            ),
         }
     }
 }
 
+#[instrument(skip(tcx, query), level = "debug")]
 fn layout_of<'tcx>(
     tcx: TyCtxt<'tcx>,
     query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
 ) -> Result<TyAndLayout<'tcx>, LayoutError<'tcx>> {
     ty::tls::with_related_context(tcx, move |icx| {
         let (param_env, ty) = query.into_parts();
+        debug!(?ty);
 
         if !tcx.recursion_limit().value_within_limit(icx.layout_depth) {
             tcx.sess.fatal(&format!("overflow representing the type `{}`", ty));
@@ -229,7 +239,14 @@ fn layout_of<'tcx>(
         ty::tls::enter_context(&icx, |_| {
             let param_env = param_env.with_reveal_all_normalized(tcx);
             let unnormalized_ty = ty;
-            let ty = tcx.normalize_erasing_regions(param_env, ty);
+
+            let ty = match tcx.try_normalize_erasing_regions(param_env, ty) {
+                Ok(t) => t,
+                Err(normalization_error) => {
+                    return Err(LayoutError::NormalizationFailure(ty, normalization_error));
+                }
+            };
+
             if ty != unnormalized_ty {
                 // Ensure this layout is also cached for the normalized type.
                 return tcx.layout_of(param_env.and(ty));

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -8,10 +8,28 @@
 //! or constant found within. (This underlying query is what is cached.)
 
 use crate::mir;
+use crate::traits::query::NoSolution;
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{self, Ty, TyCtxt};
 
+#[derive(Debug, Copy, Clone, HashStable, TyEncodable, TyDecodable)]
+pub enum NormalizationError<'tcx> {
+    Type(Ty<'tcx>),
+    Const(ty::Const<'tcx>),
+    ConstantKind(mir::ConstantKind<'tcx>),
+}
+
+impl<'tcx> NormalizationError<'tcx> {
+    pub fn get_type_for_failure(&self) -> String {
+        match self {
+            NormalizationError::Type(t) => format!("{}", t),
+            NormalizationError::Const(c) => format!("{}", c),
+            NormalizationError::ConstantKind(ck) => format!("{}", ck),
+        }
+    }
+}
+
 impl<'tcx> TyCtxt<'tcx> {
     /// Erase the regions in `value` and then fully normalize all the
     /// types found within. The result will also have regions erased.
@@ -32,6 +50,8 @@ impl<'tcx> TyCtxt<'tcx> {
         // Erase first before we do the real query -- this keeps the
         // cache from being too polluted.
         let value = self.erase_regions(value);
+        debug!(?value);
+
         if !value.has_projections() {
             value
         } else {
@@ -41,6 +61,44 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// Tries to erase the regions in `value` and then fully normalize all the
+    /// types found within. The result will also have regions erased.
+    ///
+    /// Contrary to `normalize_erasing_regions` this function does not assume that normalization
+    /// succeeds.
+    pub fn try_normalize_erasing_regions<T>(
+        self,
+        param_env: ty::ParamEnv<'tcx>,
+        value: T,
+    ) -> Result<T, NormalizationError<'tcx>>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        debug!(
+            "try_normalize_erasing_regions::<{}>(value={:?}, param_env={:?})",
+            std::any::type_name::<T>(),
+            value,
+            param_env,
+        );
+
+        // Erase first before we do the real query -- this keeps the
+        // cache from being too polluted.
+        let value = self.erase_regions(value);
+        debug!(?value);
+
+        if !value.has_projections() {
+            Ok(value)
+        } else {
+            let mut folder = TryNormalizeAfterErasingRegionsFolder::new(self, param_env);
+            let result = value.fold_with(&mut folder);
+
+            match folder.found_normalization_error() {
+                Some(e) => Err(e),
+                None => Ok(result),
+            }
+        }
+    }
+
     /// If you have a `Binder<'tcx, T>`, you can do this to strip out the
     /// late-bound regions and then normalize the result, yielding up
     /// a `T` (with regions erased). This is appropriate when the
@@ -91,11 +149,14 @@ struct NormalizeAfterErasingRegionsFolder<'tcx> {
 }
 
 impl<'tcx> NormalizeAfterErasingRegionsFolder<'tcx> {
+    #[instrument(skip(self), level = "debug")]
     fn normalize_generic_arg_after_erasing_regions(
         &self,
         arg: ty::GenericArg<'tcx>,
     ) -> ty::GenericArg<'tcx> {
         let arg = self.param_env.and(arg);
+        debug!(?arg);
+
         self.tcx.normalize_generic_arg_after_erasing_regions(arg)
     }
 }
@@ -126,3 +187,69 @@ impl TypeFolder<'tcx> for NormalizeAfterErasingRegionsFolder<'tcx> {
         Ok(self.tcx.normalize_mir_const_after_erasing_regions(arg))
     }
 }
+
+struct TryNormalizeAfterErasingRegionsFolder<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    normalization_error: Option<NormalizationError<'tcx>>,
+}
+
+impl<'tcx> TryNormalizeAfterErasingRegionsFolder<'tcx> {
+    fn new(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
+        TryNormalizeAfterErasingRegionsFolder { tcx, param_env, normalization_error: None }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn try_normalize_generic_arg_after_erasing_regions(
+        &self,
+        arg: ty::GenericArg<'tcx>,
+    ) -> Result<ty::GenericArg<'tcx>, NoSolution> {
+        let arg = self.param_env.and(arg);
+        debug!(?arg);
+
+        self.tcx.try_normalize_generic_arg_after_erasing_regions(arg)
+    }
+
+    pub fn found_normalization_error(&self) -> Option<NormalizationError<'tcx>> {
+        self.normalization_error
+    }
+}
+
+impl TypeFolder<'tcx> for TryNormalizeAfterErasingRegionsFolder<'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        match self.try_normalize_generic_arg_after_erasing_regions(ty.into()) {
+            Ok(t) => t.expect_ty(),
+            Err(_) => {
+                self.normalization_error = Some(NormalizationError::Type(ty));
+                ty
+            }
+        }
+    }
+
+    fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
+        match self.try_normalize_generic_arg_after_erasing_regions(c.into()) {
+            Ok(t) => t.expect_const(),
+            Err(_) => {
+                self.normalization_error = Some(NormalizationError::Const(*c));
+                c
+            }
+        }
+    }
+
+    #[inline]
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        // FIXME: This *probably* needs canonicalization too!
+        let arg = self.param_env.and(c);
+        match self.tcx.try_normalize_mir_const_after_erasing_regions(arg) {
+            Ok(c) => c,
+            Err(_) => {
+                self.normalization_error = Some(NormalizationError::ConstantKind(c));
+                c
+            }
+        }
+    }
+}

compiler/rustc_traits/src/normalize_erasing_regions.rs

@@ -20,6 +20,14 @@ crate fn provide(p: &mut Providers) {
         normalize_mir_const_after_erasing_regions: |tcx, goal| {
             normalize_after_erasing_regions(tcx, goal)
         },
+        try_normalize_generic_arg_after_erasing_regions: |tcx, goal| {
+            debug!("try_normalize_generic_arg_after_erasing_regions(goal={:#?}", goal);
+
+            try_normalize_after_erasing_regions(tcx, goal)
+        },
+        try_normalize_mir_const_after_erasing_regions: |tcx, goal| {
+            try_normalize_after_erasing_regions(tcx, goal)
+        },
         ..*p
     };
 }
@@ -56,6 +64,38 @@ fn normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Cop
     })
 }
 
+#[instrument(level = "debug", skip(tcx))]
+fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Copy>(
+    tcx: TyCtxt<'tcx>,
+    goal: ParamEnvAnd<'tcx, T>,
+) -> Result<T, NoSolution> {
+    let ParamEnvAnd { param_env, value } = goal;
+    tcx.infer_ctxt().enter(|infcx| {
+        let cause = ObligationCause::dummy();
+        match infcx.at(&cause, param_env).normalize(value) {
+            Ok(Normalized { value: normalized_value, obligations: normalized_obligations }) => {
+                // We don't care about the `obligations`; they are
+                // always only region relations, and we are about to
+                // erase those anyway:
+                debug_assert_eq!(
+                    normalized_obligations.iter().find(|p| not_outlives_predicate(&p.predicate)),
+                    None,
+                );
+
+                let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
+                // It's unclear when `resolve_vars` would have an effect in a
+                // fresh `InferCtxt`. If this assert does trigger, it will give
+                // us a test case.
+                debug_assert_eq!(normalized_value, resolved_value);
+                let erased = infcx.tcx.erase_regions(resolved_value);
+                debug_assert!(!erased.needs_infer(), "{:?}", erased);
+                Ok(erased)
+            }
+            Err(NoSolution) => Err(NoSolution),
+        }
+    })
+}
+
 fn not_outlives_predicate(p: &ty::Predicate<'tcx>) -> bool {
     match p.kind().skip_binder() {
         ty::PredicateKind::RegionOutlives(..) | ty::PredicateKind::TypeOutlives(..) => false,