diff options
| -rw-r--r-- | src/librustc/ty/util.rs | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs index 871aeb78af5..635845a65c2 100644 --- a/src/librustc/ty/util.rs +++ b/src/librustc/ty/util.rs @@ -270,6 +270,10 @@ impl<'tcx> TyCtxt<'tcx> { /// Returns the deeply last field of nested structures, or the same type if /// not a structure at all. Corresponds to the only possible unsized field, /// and its type can be used to determine unsizing strategy. + /// + /// Should only be called if `ty` has no inference variables and does not + /// need its lifetimes preserved (e.g. as part of codegen); otherwise + /// normalization attempt may cause compiler bugs. pub fn struct_tail_erasing_lifetimes(self, ty: Ty<'tcx>, param_env: ty::ParamEnv<'tcx>) @@ -287,8 +291,8 @@ impl<'tcx> TyCtxt<'tcx> { /// handle `<T as Trait>::Assoc` and `impl Trait`); pass the identity /// function to indicate no normalization should take place. /// - /// See also `struct_tail_erasing_lifetimes`, which is what callers running - /// after type checking should use. + /// See also `struct_tail_erasing_lifetimes`, which is suitable for use + /// during codegen. pub fn struct_tail_with_normalize(self, mut ty: Ty<'tcx>, normalize: impl Fn(Ty<'tcx>) -> Ty<'tcx>) @@ -337,7 +341,8 @@ impl<'tcx> TyCtxt<'tcx> { /// For `(Foo<Foo<T>>, Foo<dyn Trait>)`, the result will be `(Foo<T>, Trait)`, /// whereas struct_tail produces `T`, and `Trait`, respectively. /// - /// Must only be called after type-checking is complete; otherwise + /// Should only be called if the types have no inference variables and do + /// not need their lifetimes preserved (e.g. as part of codegen); otherwise /// normalization attempt may cause compiler bugs. pub fn struct_lockstep_tails_erasing_lifetimes(self, source: Ty<'tcx>, @@ -356,8 +361,8 @@ impl<'tcx> TyCtxt<'tcx> { /// For `(Foo<Foo<T>>, Foo<dyn Trait>)`, the result will be `(Foo<T>, Trait)`, /// whereas struct_tail produces `T`, and `Trait`, respectively. /// - /// See also struct_lockstep_tails_erasing_lifetimes, which - /// is what callers running after type checking should use. + /// See also `struct_lockstep_tails_erasing_lifetimes`, which is suitable for use + /// during codegen. pub fn struct_lockstep_tails_with_normalize(self, source: Ty<'tcx>, target: Ty<'tcx>, |