Document check_region_obligations_and_report_errors, simplify a call …

…to resolve_regions

compiler/rustc_infer/src/infer/mod.rs

@@ -1324,6 +1324,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
+    ///
+    /// Make sure to call [`InferCtxt::process_registered_region_obligations`]
+    /// first, or preferrably use [`InferCtxt::check_region_obligations_and_report_errors`]
+    /// to do both of these operations together.
     pub fn resolve_regions_and_report_errors(
         &self,
         generic_param_scope: LocalDefId,

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -111,6 +111,9 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
+    /// NOTE: Prefer using [`InferCtxt::check_region_obligations_and_report_errors`]
+    /// instead of calling this directly.
+    ///
     /// Process the region obligations that must be proven (during
     /// `regionck`) for the given `body_id`, given information about
     /// the region bounds in scope and so forth. This function must be
@@ -162,6 +165,9 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         }
     }
 
+    /// Processes registered region obliations and resolves regions, reporting
+    /// any errors if any were raised. Prefer using this function over manually
+    /// calling `resolve_regions_and_report_errors`.
     pub fn check_region_obligations_and_report_errors(
         &self,
         generic_param_scope: LocalDefId,

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -398,13 +398,7 @@ fn resolve_negative_obligation<'cx, 'tcx>(
     let outlives_env = OutlivesEnvironment::new(param_env);
     infcx.process_registered_region_obligations(outlives_env.region_bound_pairs(), param_env);
 
-    let errors = infcx.resolve_regions(&outlives_env);
-
-    if !errors.is_empty() {
-        return false;
-    }
-
-    true
+    infcx.resolve_regions(&outlives_env).is_empty()
 }
 
 pub fn trait_ref_is_knowable<'tcx>(