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| author | Michael Goulet <michael@errs.io> | 2022-11-14 23:25:41 +0000 |
|---|---|---|
| committer | Michael Goulet <michael@errs.io> | 2022-11-29 19:02:40 +0000 |
| commit | 9512446a00dd203196dc0e716bd34d107299bc1d (patch) | |
| tree | eaa332e6ce2ce1e1aafac38f6da8f922299feb14 | |
| parent | e0098a5cc3a87d857e597af824d0ce1ed1ad85e0 (diff) | |
| download | rust-9512446a00dd203196dc0e716bd34d107299bc1d.tar.gz rust-9512446a00dd203196dc0e716bd34d107299bc1d.zip | |
Explain why rematch_impl fails to be infallible
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/select/mod.rs | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index a2d2d44fbc2..a3c182d4bec 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -2140,6 +2140,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { match self.match_impl(impl_def_id, impl_trait_ref, obligation) { Ok(substs) => substs, Err(()) => { + // FIXME: A rematch may fail when a candidate cache hit occurs + // on thefreshened form of the trait predicate, but the match + // fails for some reason that is not captured in the freshened + // cache key. For example, equating an impl trait ref against + // the placeholder trait ref may fail due the Generalizer relation + // raising a CyclicalTy error due to a sub_root_var relation + // for a variable being generalized... self.infcx.tcx.sess.delay_span_bug( obligation.cause.span, &format!( |