1 files changed, 118 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
new file mode 100644
index 000000000..32669e23d
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
@@ -0,0 +1,118 @@
+use rustc_middle::ty;
+
+use crate::infer::canonical::OriginalQueryValues;
+use crate::infer::InferCtxt;
+use crate::traits::{
+    EvaluationResult, OverflowError, PredicateObligation, SelectionContext, TraitQueryMode,
+};
+
+pub trait InferCtxtExt<'tcx> {
+    fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool;
+
+    fn predicate_must_hold_considering_regions(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> bool;
+
+    fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool;
+
+    fn evaluate_obligation(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> Result<EvaluationResult, OverflowError>;
+
+    // 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.
+    /*crate*/
+    fn evaluate_obligation_no_overflow(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> EvaluationResult;
+}
+
+impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
+    /// Evaluates whether the predicate can be satisfied (by any means)
+    /// in the given `ParamEnv`.
+    fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool {
+        self.evaluate_obligation_no_overflow(obligation).may_apply()
+    }
+
+    /// Evaluates whether the predicate can be satisfied in the given
+    /// `ParamEnv`, and returns `false` if not certain. However, this is
+    /// not entirely accurate if inference variables are involved.
+    ///
+    /// This version may conservatively fail when outlives obligations
+    /// are required.
+    fn predicate_must_hold_considering_regions(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> bool {
+        self.evaluate_obligation_no_overflow(obligation).must_apply_considering_regions()
+    }
+
+    /// Evaluates whether the predicate can be satisfied in the given
+    /// `ParamEnv`, and returns `false` if not certain. However, this is
+    /// not entirely accurate if inference variables are involved.
+    ///
+    /// This version ignores all outlives constraints.
+    fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool {
+        self.evaluate_obligation_no_overflow(obligation).must_apply_modulo_regions()
+    }
+
+    /// Evaluate a given predicate, capturing overflow and propagating it back.
+    fn evaluate_obligation(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+    ) -> Result<EvaluationResult, OverflowError> {
+        let mut _orig_values = OriginalQueryValues::default();
+
+        let param_env = match obligation.predicate.kind().skip_binder() {
+            ty::PredicateKind::Trait(pred) => {
+                // we ignore the value set to it.
+                let mut _constness = pred.constness;
+                obligation
+                    .param_env
+                    .with_constness(_constness.and(obligation.param_env.constness()))
+            }
+            // constness has no effect on the given predicate.
+            _ => obligation.param_env.without_const(),
+        };
+
+        let c_pred = self
+            .canonicalize_query_keep_static(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`.
+        self.tcx.at(obligation.cause.span()).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::Canonical) => {
+                let mut selcx = SelectionContext::with_query_mode(&self, TraitQueryMode::Standard);
+                selcx.evaluate_root_obligation(obligation).unwrap_or_else(|r| match r {
+                    OverflowError::Canonical => {
+                        span_bug!(
+                            obligation.cause.span,
+                            "Overflow should be caught earlier in standard query mode: {:?}, {:?}",
+                            obligation,
+                            r,
+                        )
+                    }
+                    OverflowError::ErrorReporting => EvaluationResult::EvaluatedToErr,
+                    OverflowError::Error(_) => EvaluationResult::EvaluatedToErr,
+                })
+            }
+            Err(OverflowError::ErrorReporting) => EvaluationResult::EvaluatedToErr,
+            Err(OverflowError::Error(_)) => EvaluationResult::EvaluatedToErr,
+        }
+    }
+}