1 use crate::collect::ItemCtxt;
3 use rustc_hir::intravisit::{self, Visitor};
4 use rustc_hir::{ForeignItem, ForeignItemKind, HirId};
5 use rustc_infer::infer::TyCtxtInferExt;
6 use rustc_infer::traits::{ObligationCause, WellFormedLoc};
7 use rustc_middle::ty::query::Providers;
8 use rustc_middle::ty::{self, Region, TyCtxt, TypeFoldable, TypeFolder};
9 use rustc_trait_selection::traits;
11 pub fn provide(providers: &mut Providers) {
12 *providers = Providers { diagnostic_hir_wf_check, ..*providers };
15 // Ideally, this would be in `rustc_trait_selection`, but we
16 // need access to `ItemCtxt`
17 fn diagnostic_hir_wf_check<'tcx>(
19 (predicate, loc): (ty::Predicate<'tcx>, WellFormedLoc),
20 ) -> Option<ObligationCause<'tcx>> {
23 let def_id = match loc {
24 WellFormedLoc::Ty(def_id) => def_id,
25 WellFormedLoc::Param { function, param_idx: _ } => function,
27 let hir_id = hir.local_def_id_to_hir_id(def_id);
29 // HIR wfcheck should only ever happen as part of improving an existing error
31 .delay_span_bug(tcx.def_span(def_id), "Performed HIR wfcheck without an existing error!");
33 let icx = ItemCtxt::new(tcx, def_id.to_def_id());
35 // To perform HIR-based WF checking, we iterate over all HIR types
36 // that occur 'inside' the item we're checking. For example,
37 // given the type `Option<MyStruct<u8>>`, we will check
38 // `Option<MyStruct<u8>>`, `MyStruct<u8>`, and `u8`.
39 // For each type, we perform a well-formed check, and see if we get
40 // an error that matches our expected predicate. We save
41 // the `ObligationCause` corresponding to the *innermost* type,
42 // which is the most specific type that we can point to.
43 // In general, the different components of an `hir::Ty` may have
44 // completely different spans due to macro invocations. Pointing
45 // to the most accurate part of the type can be the difference
46 // between a useless span (e.g. the macro invocation site)
47 // and a useful span (e.g. a user-provided type passed into the macro).
49 // This approach is quite inefficient - we redo a lot of work done
50 // by the normal WF checker. However, this code is run at most once
51 // per reported error - it will have no impact when compilation succeeds,
52 // and should only have an impact if a very large number of errors is
53 // displayed to the user.
54 struct HirWfCheck<'tcx> {
56 predicate: ty::Predicate<'tcx>,
57 cause: Option<ObligationCause<'tcx>>,
61 param_env: ty::ParamEnv<'tcx>,
65 impl<'tcx> Visitor<'tcx> for HirWfCheck<'tcx> {
66 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
67 let infcx = self.tcx.infer_ctxt().build();
68 let tcx_ty = self.icx.to_ty(ty).fold_with(&mut EraseAllBoundRegions { tcx: self.tcx });
69 let cause = traits::ObligationCause::new(
72 traits::ObligationCauseCode::WellFormed(None),
74 let errors = traits::fully_solve_obligation(
76 traits::Obligation::new(
80 ty::Binder::dummy(ty::PredicateKind::WellFormed(tcx_ty.into())),
83 if !errors.is_empty() {
84 debug!("Wf-check got errors for {:?}: {:?}", ty, errors);
86 if error.obligation.predicate == self.predicate {
87 // Save the cause from the greatest depth - this corresponds
88 // to picking more-specific types (e.g. `MyStruct<u8>`)
89 // over less-specific types (e.g. `Option<MyStruct<u8>>`)
90 if self.depth >= self.cause_depth {
91 self.cause = Some(error.obligation.cause);
92 self.cause_depth = self.depth
98 intravisit::walk_ty(self, ty);
103 let mut visitor = HirWfCheck {
110 param_env: tcx.param_env(def_id.to_def_id()),
114 // Get the starting `hir::Ty` using our `WellFormedLoc`.
115 // We will walk 'into' this type to try to find
116 // a more precise span for our predicate.
117 let tys = match loc {
118 WellFormedLoc::Ty(_) => match hir.get(hir_id) {
119 hir::Node::ImplItem(item) => match item.kind {
120 hir::ImplItemKind::Type(ty) => vec![ty],
121 hir::ImplItemKind::Const(ty, _) => vec![ty],
122 ref item => bug!("Unexpected ImplItem {:?}", item),
124 hir::Node::TraitItem(item) => match item.kind {
125 hir::TraitItemKind::Type(_, ty) => ty.into_iter().collect(),
126 hir::TraitItemKind::Const(ty, _) => vec![ty],
127 ref item => bug!("Unexpected TraitItem {:?}", item),
129 hir::Node::Item(item) => match item.kind {
130 hir::ItemKind::Static(ty, _, _) | hir::ItemKind::Const(ty, _) => vec![ty],
131 hir::ItemKind::Impl(ref impl_) => match &impl_.of_trait {
137 .flat_map(|seg| seg.args().args)
139 if let hir::GenericArg::Type(ty) = arg { Some(*ty) } else { None }
141 .chain([impl_.self_ty])
147 ref item => bug!("Unexpected item {:?}", item),
149 hir::Node::Field(field) => vec![field.ty],
150 hir::Node::ForeignItem(ForeignItem {
151 kind: ForeignItemKind::Static(ty, _), ..
153 hir::Node::GenericParam(hir::GenericParam {
154 kind: hir::GenericParamKind::Type { default: Some(ty), .. },
157 ref node => bug!("Unexpected node {:?}", node),
159 WellFormedLoc::Param { function: _, param_idx } => {
160 let fn_decl = hir.fn_decl_by_hir_id(hir_id).unwrap();
162 if param_idx as usize == fn_decl.inputs.len() {
163 match fn_decl.output {
164 hir::FnRetTy::Return(ty) => vec![ty],
165 // The unit type `()` is always well-formed
166 hir::FnRetTy::DefaultReturn(_span) => vec![],
169 vec![&fn_decl.inputs[param_idx as usize]]
174 visitor.visit_ty(ty);
179 struct EraseAllBoundRegions<'tcx> {
183 // Higher ranked regions are complicated.
184 // To make matters worse, the HIR WF check can instantiate them
185 // outside of a `Binder`, due to the way we (ab)use
186 // `ItemCtxt::to_ty`. To make things simpler, we just erase all
187 // of them, regardless of depth. At worse, this will give
188 // us an inaccurate span for an error message, but cannot
189 // lead to unsoundness (we call `delay_span_bug` at the start
190 // of `diagnostic_hir_wf_check`).
191 impl<'tcx> TypeFolder<'tcx> for EraseAllBoundRegions<'tcx> {
192 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
195 fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
196 if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }