diff options
| -rw-r--r-- | compiler/rustc_trait_selection/src/solve/mod.rs | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs index 26ace28f5fd..b328c1a6dce 100644 --- a/compiler/rustc_trait_selection/src/solve/mod.rs +++ b/compiler/rustc_trait_selection/src/solve/mod.rs @@ -265,10 +265,18 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> { if let Some(merged) = self.try_merge_responses(&candidates) { Ok(merged) - } else if let Ok(subst_relate_response) = subst_relate_response { - Ok(subst_relate_response) } else { - self.flounder(&candidates) + // When relating two aliases and we have ambiguity, we prefer + // relating the generic arguments of the aliases over normalizing + // them. This is necessary for inference during typeck. + // + // As this is incomplete, we must not do so during coherence. + match (self.solver_mode(), subst_relate_response) { + (SolverMode::Normal, Ok(response)) => Ok(response), + (SolverMode::Normal, Err(NoSolution)) | (SolverMode::Coherence, _) => { + self.flounder(&candidates) + } + } } } } |