compiler/rustc_trait_selection/src/traits/misc.rs

   1 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
   2
   3 use crate::infer::InferCtxtExt as _;
   4 use crate::traits::{self, ObligationCause};
   5
   6 use rustc_hir as hir;
   7 use rustc_infer::infer::TyCtxtInferExt;
   8 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
   9
  10 use crate::traits::error_reporting::InferCtxtExt;
  11
  12 #[derive(Clone)]
  13 pub enum CopyImplementationError<'tcx> {
  14     InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>)>),
  15     NotAnAdt,
  16     HasDestructor,
  17 }
  18
  19 pub fn can_type_implement_copy<'tcx>(
  20     tcx: TyCtxt<'tcx>,
  21     param_env: ty::ParamEnv<'tcx>,
  22     self_type: Ty<'tcx>,
  23     parent_cause: ObligationCause<'tcx>,
  24 ) -> Result<(), CopyImplementationError<'tcx>> {
  25     // FIXME: (@jroesch) float this code up
  26     tcx.infer_ctxt().enter(|infcx| {
  27         let (adt, substs) = match self_type.kind() {
  28             // These types used to have a builtin impl.
  29             // Now libcore provides that impl.
  30             ty::Uint(_)
  31             | ty::Int(_)
  32             | ty::Bool
  33             | ty::Float(_)
  34             | ty::Char
  35             | ty::RawPtr(..)
  36             | ty::Never
  37             | ty::Ref(_, _, hir::Mutability::Not)
  38             | ty::Array(..) => return Ok(()),
  39
  40             ty::Adt(adt, substs) => (adt, substs),
  41
  42             _ => return Err(CopyImplementationError::NotAnAdt),
  43         };
  44
  45         let mut infringing = Vec::new();
  46         for variant in adt.variants() {
  47             for field in &variant.fields {
  48                 let ty = field.ty(tcx, substs);
  49                 if ty.references_error() {
  50                     continue;
  51                 }
  52                 let span = tcx.def_span(field.did);
  53                 // FIXME(compiler-errors): This gives us better spans for bad
  54                 // projection types like in issue-50480.
  55                 // If the ADT has substs, point to the cause we are given.
  56                 // If it does not, then this field probably doesn't normalize
  57                 // to begin with, and point to the bad field's span instead.
  58                 let cause = if field
  59                     .ty(tcx, traits::InternalSubsts::identity_for_item(tcx, adt.did()))
  60                     .has_non_region_param()
  61                 {
  62                     parent_cause.clone()
  63                 } else {
  64                     ObligationCause::dummy_with_span(span)
  65                 };
  66                 match traits::fully_normalize(&infcx, cause, param_env, ty) {
  67                     Ok(ty) => {
  68                         if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
  69                             infringing.push((field, ty));
  70                         }
  71                     }
  72                     Err(errors) => {
  73                         infcx.report_fulfillment_errors(&errors, None, false);
  74                     }
  75                 };
  76             }
  77         }
  78         if !infringing.is_empty() {
  79             return Err(CopyImplementationError::InfrigingFields(infringing));
  80         }
  81         if adt.has_dtor(tcx) {
  82             return Err(CopyImplementationError::HasDestructor);
  83         }
  84
  85         Ok(())
  86     })
  87 }