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::TraitEngine;
7 use rustc_infer::traits::{ObligationCause, WellFormedLoc};
8 use rustc_middle::ty::query::Providers;
9 use rustc_middle::ty::{self, Region, ToPredicate, TyCtxt, TypeFoldable, TypeFolder};
10 use rustc_trait_selection::traits;
12 pub fn provide(providers: &mut Providers) {
13 *providers = Providers { diagnostic_hir_wf_check, ..*providers };
16 // Ideally, this would be in `rustc_trait_selection`, but we
17 // need access to `ItemCtxt`
18 fn diagnostic_hir_wf_check<'tcx>(
20 (predicate, loc): (ty::Predicate<'tcx>, WellFormedLoc),
21 ) -> Option<ObligationCause<'tcx>> {
24 let def_id = match loc {
25 WellFormedLoc::Ty(def_id) => def_id,
26 WellFormedLoc::Param { function, param_idx: _ } => function,
28 let hir_id = hir.local_def_id_to_hir_id(def_id);
30 // HIR wfcheck should only ever happen as part of improving an existing error
32 .delay_span_bug(tcx.def_span(def_id), "Performed HIR wfcheck without an existing error!");
34 let icx = ItemCtxt::new(tcx, def_id.to_def_id());
36 // To perform HIR-based WF checking, we iterate over all HIR types
37 // that occur 'inside' the item we're checking. For example,
38 // given the type `Option<MyStruct<u8>>`, we will check
39 // `Option<MyStruct<u8>>`, `MyStruct<u8>`, and `u8`.
40 // For each type, we perform a well-formed check, and see if we get
41 // an error that matches our expected predicate. We save
42 // the `ObligationCause` corresponding to the *innermost* type,
43 // which is the most specific type that we can point to.
44 // In general, the different components of an `hir::Ty` may have
45 // completely different spans due to macro invocations. Pointing
46 // to the most accurate part of the type can be the difference
47 // between a useless span (e.g. the macro invocation site)
48 // and a useful span (e.g. a user-provided type passed into the macro).
50 // This approach is quite inefficient - we redo a lot of work done
51 // by the normal WF checker. However, this code is run at most once
52 // per reported error - it will have no impact when compilation succeeds,
53 // and should only have an impact if a very large number of errors is
54 // displayed to the user.
55 struct HirWfCheck<'tcx> {
57 predicate: ty::Predicate<'tcx>,
58 cause: Option<ObligationCause<'tcx>>,
62 param_env: ty::ParamEnv<'tcx>,
66 impl<'tcx> Visitor<'tcx> for HirWfCheck<'tcx> {
67 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
68 self.tcx.infer_ctxt().enter(|infcx| {
69 let mut fulfill = traits::FulfillmentContext::new();
71 self.icx.to_ty(ty).fold_with(&mut EraseAllBoundRegions { tcx: self.tcx });
72 let cause = traits::ObligationCause::new(
75 traits::ObligationCauseCode::MiscObligation,
77 fulfill.register_predicate_obligation(
79 traits::Obligation::new(
82 ty::Binder::dummy(ty::PredicateKind::WellFormed(tcx_ty.into()))
83 .to_predicate(self.tcx),
87 let errors = fulfill.select_all_or_error(&infcx);
88 if !errors.is_empty() {
89 tracing::debug!("Wf-check got errors for {:?}: {:?}", ty, errors);
91 if error.obligation.predicate == self.predicate {
92 // Save the cause from the greatest depth - this corresponds
93 // to picking more-specific types (e.g. `MyStruct<u8>`)
94 // over less-specific types (e.g. `Option<MyStruct<u8>>`)
95 if self.depth >= self.cause_depth {
96 self.cause = Some(error.obligation.cause);
97 self.cause_depth = self.depth
104 intravisit::walk_ty(self, ty);
109 let mut visitor = HirWfCheck {
116 param_env: tcx.param_env(def_id.to_def_id()),
120 // Get the starting `hir::Ty` using our `WellFormedLoc`.
121 // We will walk 'into' this type to try to find
122 // a more precise span for our predicate.
124 WellFormedLoc::Ty(_) => match hir.get(hir_id) {
125 hir::Node::ImplItem(item) => match item.kind {
126 hir::ImplItemKind::TyAlias(ty) => Some(ty),
127 hir::ImplItemKind::Const(ty, _) => Some(ty),
128 ref item => bug!("Unexpected ImplItem {:?}", item),
130 hir::Node::TraitItem(item) => match item.kind {
131 hir::TraitItemKind::Type(_, ty) => ty,
132 hir::TraitItemKind::Const(ty, _) => Some(ty),
133 ref item => bug!("Unexpected TraitItem {:?}", item),
135 hir::Node::Item(item) => match item.kind {
136 hir::ItemKind::Static(ty, _, _) | hir::ItemKind::Const(ty, _) => Some(ty),
137 hir::ItemKind::Impl(ref impl_) => {
138 assert!(impl_.of_trait.is_none(), "Unexpected trait impl: {:?}", impl_);
141 ref item => bug!("Unexpected item {:?}", item),
143 hir::Node::Field(field) => Some(field.ty),
144 hir::Node::ForeignItem(ForeignItem {
145 kind: ForeignItemKind::Static(ty, _), ..
147 ref node => bug!("Unexpected node {:?}", node),
149 WellFormedLoc::Param { function: _, param_idx } => {
150 let fn_decl = hir.fn_decl_by_hir_id(hir_id).unwrap();
152 if param_idx as usize == fn_decl.inputs.len() {
153 match fn_decl.output {
154 hir::FnRetTy::Return(ty) => Some(ty),
155 // The unit type `()` is always well-formed
156 hir::FnRetTy::DefaultReturn(_span) => None,
159 Some(&fn_decl.inputs[param_idx as usize])
163 if let Some(ty) = ty {
164 visitor.visit_ty(ty);
169 struct EraseAllBoundRegions<'tcx> {
173 // Higher ranked regions are complicated.
174 // To make matters worse, the HIR WF check can instantiate them
175 // outside of a `Binder`, due to the way we (ab)use
176 // `ItemCtxt::to_ty`. To make things simpler, we just erase all
177 // of them, regardless of depth. At worse, this will give
178 // us an inaccurate span for an error message, but cannot
179 // lead to unsoundness (we call `delay_span_bug` at the start
180 // of `diagnostic_hir_wf_check`).
181 impl<'tcx> TypeFolder<'tcx> for EraseAllBoundRegions<'tcx> {
182 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
185 fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
186 if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }