overlook overflows in rustdoc trait solving

src/librustc/traits/query/evaluate_obligation.rs

@@ -20,7 +20,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
     ) -> bool {
-        self.evaluate_obligation(obligation).may_apply()
+        self.evaluate_obligation_no_overflow(obligation).may_apply()
     }
 
     /// Evaluates whether the predicate can be satisfied in the given
@@ -30,28 +30,44 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
     ) -> bool {
-        self.evaluate_obligation(obligation) == EvaluationResult::EvaluatedToOk
+        self.evaluate_obligation_no_overflow(obligation) == EvaluationResult::EvaluatedToOk
     }
 
-    // Helper function that canonicalizes and runs the query, as well as handles
-    // overflow.
-    fn evaluate_obligation(
+    /// Evaluate a given predicate, capturing overflow and propagating it back.
+    pub fn evaluate_obligation(
         &self,
         obligation: &PredicateObligation<'tcx>,
-    ) -> EvaluationResult {
+    ) -> Result<EvaluationResult, OverflowError> {
         let mut _orig_values = SmallVec::new();
         let c_pred = self.canonicalize_query(&obligation.param_env.and(obligation.predicate),
                                              &mut _orig_values);
         // Run canonical query. If overflow occurs, rerun from scratch but this time
         // in standard trait query mode so that overflow is handled appropriately
         // within `SelectionContext`.
-        match self.tcx.global_tcx().evaluate_obligation(c_pred) {
+        self.tcx.global_tcx().evaluate_obligation(c_pred)
+    }
+
+    // Helper function that canonicalizes and runs the query. If an
+    // overflow results, we re-run it in the local context so we can
+    // report a nice error.
+    fn evaluate_obligation_no_overflow(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> EvaluationResult {
+        match self.evaluate_obligation(obligation) {
             Ok(result) => result,
             Err(OverflowError) => {
                 let mut selcx =
                     SelectionContext::with_query_mode(&self, TraitQueryMode::Standard);
                 selcx.evaluate_obligation_recursively(obligation)
-                     .expect("Overflow should be caught earlier in standard query mode")
+                    .unwrap_or_else(|r| {
+                        span_bug!(
+                            obligation.cause.span,
+                            "Overflow should be caught earlier in standard query mode: {:?}, {:?}",
+                            obligation,
+                            r,
+                        )
+                    })
             }
         }
     }

src/librustc/traits/select.rs

@@ -1376,7 +1376,10 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         let tcx = self.tcx();
         let trait_ref = cache_fresh_trait_pred.skip_binder().trait_ref;
         if self.can_use_global_caches(param_env) {
-            if let Some(trait_ref) = tcx.lift_to_global(&trait_ref) {
+            if let Err(Overflow) = candidate {
+                // Don't cache overflow globally; we only produce this
+                // in certain modes.
+            } else if let Some(trait_ref) = tcx.lift_to_global(&trait_ref) {
                 if let Some(candidate) = tcx.lift_to_global(&candidate) {
                     debug!(
                         "insert_candidate_cache(trait_ref={:?}, candidate={:?}) global",

src/librustc/traits/structural_impls.rs

@@ -175,7 +175,7 @@ impl<'a, 'tcx> Lift<'tcx> for traits::SelectionError<'a> {
             super::ConstEvalFailure(ref err) => tcx.lift(&**err).map(|err| super::ConstEvalFailure(
                 err.into(),
             )),
-            super::Overflow => bug!(), // FIXME: ape ConstEvalFailure?
+            super::Overflow => Some(super::Overflow),
         }
     }
 }

src/librustdoc/clean/blanket_impl.rs

@@ -103,11 +103,20 @@ impl<'a, 'tcx, 'rcx, 'cstore> BlanketImplFinder <'a, 'tcx, 'rcx, 'cstore> {
                         // FIXME(eddyb) ignoring `obligations` might cause false positives.
                         drop(obligations);
 
-                        let may_apply = infcx.predicate_may_hold(&traits::Obligation::new(
-                            cause.clone(),
-                            param_env,
-                            trait_ref.to_predicate(),
-                        ));
+                        debug!(
+                            "invoking predicate_may_hold: {:?}",
+                            trait_ref,
+                        );
+                        let may_apply = match infcx.evaluate_obligation(
+                            &traits::Obligation::new(
+                                cause.clone(),
+                                param_env,
+                                trait_ref.to_predicate(),
+                            ),
+                        ) {
+                            Ok(eval_result) => eval_result.may_apply(),
+                            Err(traits::OverflowError) => true, // overflow doesn't mean yes *or* no
+                        };
                         if !may_apply {
                             return
                         }

src/test/rustdoc/issue-52873.rs

@@ -0,0 +1,171 @@
+// Regression test for #52873. We used to ICE due to unexpected
+// overflows when checking for "blanket impl inclusion".
+
+use std::marker::PhantomData;
+use std::cmp::Ordering;
+use std::ops::{Add, Mul};
+
+pub type True = B1;
+pub type False = B0;
+pub type U0 = UTerm;
+pub type U1 = UInt<UTerm, B1>;
+
+pub trait NonZero {}
+
+pub trait Bit {
+}
+
+pub trait Unsigned {
+}
+
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Debug, Default)]
+pub struct B0;
+
+impl B0 {
+    #[inline]
+    pub fn new() -> B0 {
+        B0
+    }
+}
+
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Debug, Default)]
+pub struct B1;
+
+impl B1 {
+    #[inline]
+    pub fn new() -> B1 {
+        B1
+    }
+}
+
+impl Bit for B0 {
+}
+
+impl Bit for B1 {
+}
+
+impl NonZero for B1 {}
+
+pub trait PrivatePow<Y, N> {
+    type Output;
+}
+pub type PrivatePowOut<A, Y, N> = <A as PrivatePow<Y, N>>::Output;
+
+pub type Add1<A> = <A as Add<::B1>>::Output;
+pub type Prod<A, B> = <A as Mul<B>>::Output;
+pub type Square<A> = <A as Mul>::Output;
+pub type Sum<A, B> = <A as Add<B>>::Output;
+
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Debug, Default)]
+pub struct UTerm;
+
+impl UTerm {
+    #[inline]
+    pub fn new() -> UTerm {
+        UTerm
+    }
+}
+
+impl Unsigned for UTerm {
+}
+
+#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Debug, Default)]
+pub struct UInt<U, B> {
+    _marker: PhantomData<(U, B)>,
+}
+
+impl<U: Unsigned, B: Bit> UInt<U, B> {
+    #[inline]
+    pub fn new() -> UInt<U, B> {
+        UInt {
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<U: Unsigned, B: Bit> Unsigned for UInt<U, B> {
+}
+
+impl<U: Unsigned, B: Bit> NonZero for UInt<U, B> {}
+
+impl Add<B0> for UTerm {
+    type Output = UTerm;
+    fn add(self, _: B0) -> Self::Output {
+        UTerm
+    }
+}
+
+impl<U: Unsigned, B: Bit> Add<B0> for UInt<U, B> {
+    type Output = UInt<U, B>;
+    fn add(self, _: B0) -> Self::Output {
+        UInt::new()
+    }
+}
+
+impl<U: Unsigned> Add<U> for UTerm {
+    type Output = U;
+    fn add(self, _: U) -> Self::Output {
+        unsafe { ::std::mem::uninitialized() }
+    }
+}
+
+impl<U: Unsigned, B: Bit> Mul<B0> for UInt<U, B> {
+    type Output = UTerm;
+    fn mul(self, _: B0) -> Self::Output {
+        UTerm
+    }
+}
+
+impl<U: Unsigned, B: Bit> Mul<B1> for UInt<U, B> {
+    type Output = UInt<U, B>;
+    fn mul(self, _: B1) -> Self::Output {
+        UInt::new()
+    }
+}
+
+impl<U: Unsigned> Mul<U> for UTerm {
+    type Output = UTerm;
+    fn mul(self, _: U) -> Self::Output {
+        UTerm
+    }
+}
+
+impl<Ul: Unsigned, B: Bit, Ur: Unsigned> Mul<UInt<Ur, B>> for UInt<Ul, B0>
+where
+    Ul: Mul<UInt<Ur, B>>,
+{
+    type Output = UInt<Prod<Ul, UInt<Ur, B>>, B0>;
+    fn mul(self, _: UInt<Ur, B>) -> Self::Output {
+        unsafe { ::std::mem::uninitialized() }
+    }
+}
+
+pub trait Pow<Exp> {
+    type Output;
+}
+
+impl<X: Unsigned, N: Unsigned> Pow<N> for X
+where
+    X: PrivatePow<U1, N>,
+{
+    type Output = PrivatePowOut<X, U1, N>;
+}
+
+impl<Y: Unsigned, X: Unsigned> PrivatePow<Y, U0> for X {
+    type Output = Y;
+}
+
+impl<Y: Unsigned, X: Unsigned> PrivatePow<Y, U1> for X
+where
+    X: Mul<Y>,
+{
+    type Output = Prod<X, Y>;
+}
+
+impl<Y: Unsigned, U: Unsigned, B: Bit, X: Unsigned> PrivatePow<Y, UInt<UInt<U, B>, B0>> for X
+where
+    X: Mul,
+    Square<X>: PrivatePow<Y, UInt<U, B>>,
+{
+    type Output = PrivatePowOut<Square<X>, Y, UInt<U, B>>;
+}