//! Miscellaneous type-system utilities that are too small to deserve their own modules.

use crate::infer::InferCtxtExt as _;
use crate::traits::{self, ObligationCause};

use rustc_hir as hir;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};

use crate::traits::error_reporting::TypeErrCtxtExt;

#[derive(Clone)]
pub enum CopyImplementationError<'tcx> {
    InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>)>),
    NotAnAdt,
    HasDestructor,
}

pub fn can_type_implement_copy<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    self_type: Ty<'tcx>,
    parent_cause: ObligationCause<'tcx>,
) -> Result<(), CopyImplementationError<'tcx>> {
    // FIXME: (@jroesch) float this code up
    let infcx = tcx.infer_ctxt().build();
    let (adt, substs) = match self_type.kind() {
        // These types used to have a builtin impl.
        // Now libcore provides that impl.
        ty::Uint(_)
        | ty::Int(_)
        | ty::Bool
        | ty::Float(_)
        | ty::Char
        | ty::RawPtr(..)
        | ty::Never
        | ty::Ref(_, _, hir::Mutability::Not)
        | ty::Array(..) => return Ok(()),

        ty::Adt(adt, substs) => (adt, substs),

        _ => return Err(CopyImplementationError::NotAnAdt),
    };

    let mut infringing = Vec::new();
    for variant in adt.variants() {
        for field in &variant.fields {
            let ty = field.ty(tcx, substs);
            if ty.references_error() {
                continue;
            }
            let span = tcx.def_span(field.did);
            // FIXME(compiler-errors): This gives us better spans for bad
            // projection types like in issue-50480.
            // If the ADT has substs, point to the cause we are given.
            // If it does not, then this field probably doesn't normalize
            // to begin with, and point to the bad field's span instead.
            let cause = if field
                .ty(tcx, traits::InternalSubsts::identity_for_item(tcx, adt.did()))
                .has_non_region_param()
            {
                parent_cause.clone()
            } else {
                ObligationCause::dummy_with_span(span)
            };
            match traits::fully_normalize(&infcx, cause, param_env, ty) {
                Ok(ty) => {
                    if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
                        infringing.push((field, ty));
                    }
                }
                Err(errors) => {
                    infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
                }
            };
        }
    }
    if !infringing.is_empty() {
        return Err(CopyImplementationError::InfrigingFields(infringing));
    }
    if adt.has_dtor(tcx) {
        return Err(CopyImplementationError::HasDestructor);
    }

    Ok(())
}