only use discard_impls_shadowed_by_env outside of coherence

Author: lcnr

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -306,9 +306,12 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
 
         self.assemble_param_env_candidates(goal, &mut candidates);
 
-        self.assemble_coherence_unknowable_candidates(goal, &mut candidates);
-
-        self.discard_impls_shadowed_by_env(goal, &mut candidates);
+        match self.solver_mode() {
+            SolverMode::Normal => self.discard_impls_shadowed_by_env(goal, &mut candidates),
+            SolverMode::Coherence => {
+                self.assemble_coherence_unknowable_candidates(goal, &mut candidates)
+            }
+        }
 
         candidates
     }
@@ -795,11 +798,6 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         candidates: &mut Vec<Candidate<'tcx>>,
     ) {
         let tcx = self.tcx();
-        match self.solver_mode() {
-            SolverMode::Normal => return,
-            SolverMode::Coherence => {}
-        };
-
         let result = self.probe_misc_candidate("coherence unknowable").enter(|ecx| {
             let trait_ref = goal.predicate.trait_ref(tcx);
             #[derive(Debug)]