src/librustc_trait_selection/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::ty::{self, Ty, TyCtxt, TypeFoldable};
   7 use rustc_hir as hir;
   8 use rustc_infer::infer::TyCtxtInferExt;
   9
  10 use crate::traits::error_reporting::InferCtxtExt;
  11
  12 #[derive(Clone)]
  13 pub enum CopyImplementationError<'tcx> {
  14     InfrigingFields(Vec<&'tcx ty::FieldDef>),
  15     NotAnAdt,
  16     HasDestructor,
  17 }
  18
  19 pub fn can_type_implement_copy(
  20     tcx: TyCtxt<'tcx>,
  21     param_env: ty::ParamEnv<'tcx>,
  22     self_type: Ty<'tcx>,
  23 ) -> Result<(), CopyImplementationError<'tcx>> {
  24     // FIXME: (@jroesch) float this code up
  25     tcx.infer_ctxt().enter(|infcx| {
  26         let (adt, substs) = match self_type.kind {
  27             // These types used to have a builtin impl.
  28             // Now libcore provides that impl.
  29             ty::Uint(_)
  30             | ty::Int(_)
  31             | ty::Bool
  32             | ty::Float(_)
  33             | ty::Char
  34             | ty::RawPtr(..)
  35             | ty::Never
  36             | ty::Ref(_, _, hir::Mutability::Not) => return Ok(()),
  37
  38             ty::Adt(adt, substs) => (adt, substs),
  39
  40             _ => return Err(CopyImplementationError::NotAnAdt),
  41         };
  42
  43         let mut infringing = Vec::new();
  44         for variant in &adt.variants {
  45             for field in &variant.fields {
  46                 let ty = field.ty(tcx, substs);
  47                 if ty.references_error() {
  48                     continue;
  49                 }
  50                 let span = tcx.def_span(field.did);
  51                 let cause = ObligationCause { span, ..ObligationCause::dummy() };
  52                 let ctx = traits::FulfillmentContext::new();
  53                 match traits::fully_normalize(&infcx, ctx, cause, param_env, &ty) {
  54                     Ok(ty) => {
  55                         if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
  56                             infringing.push(field);
  57                         }
  58                     }
  59                     Err(errors) => {
  60                         infcx.report_fulfillment_errors(&errors, None, false);
  61                     }
  62                 };
  63             }
  64         }
  65         if !infringing.is_empty() {
  66             return Err(CopyImplementationError::InfrigingFields(infringing));
  67         }
  68         if adt.has_dtor(tcx) {
  69             return Err(CopyImplementationError::HasDestructor);
  70         }
  71
  72         Ok(())
  73     })
  74 }