diff options
| -rw-r--r-- | compiler/rustc_hir_typeck/src/fallback.rs | 30 |
1 files changed, 20 insertions, 10 deletions
diff --git a/compiler/rustc_hir_typeck/src/fallback.rs b/compiler/rustc_hir_typeck/src/fallback.rs index ada716addd0..8d8573c65c5 100644 --- a/compiler/rustc_hir_typeck/src/fallback.rs +++ b/compiler/rustc_hir_typeck/src/fallback.rs @@ -565,6 +565,8 @@ impl<'tcx> FnCtxt<'_, 'tcx> { Some(self.root_var(self.shallow_resolve(ty).ty_vid()?)) } + /// Given a set of diverging vids and coercions, walk the HIR to gather a + /// set of suggestions which can be applied to preserve fallback to unit. fn try_to_suggest_annotations( &self, diverging_vids: &[ty::TyVid], @@ -574,26 +576,34 @@ impl<'tcx> FnCtxt<'_, 'tcx> { self.tcx.hir().maybe_body_owned_by(self.body_id).expect("body id must have an owner"); // For each diverging var, look through the HIR for a place to give it // a type annotation. We do this per var because we only really need one - // per var. + // suggestion to influence a var to be `()`. let suggestions = diverging_vids .iter() .copied() .filter_map(|vid| { let reachable_vids = graph::depth_first_search_as_undirected(coercions, vid).collect(); - VidVisitor { reachable_vids, fcx: self }.visit_expr(body.value).break_value() + AnnotateUnitFallbackVisitor { reachable_vids, fcx: self } + .visit_expr(body.value) + .break_value() }) .collect(); errors::SuggestAnnotations { suggestions } } } -/// Try to collect a useful suggestion to preserve fallback to `()`. -struct VidVisitor<'a, 'tcx> { +/// Try to walk the HIR to find a place to insert a useful suggestion +/// to preserve fallback to `()` in 2024. +struct AnnotateUnitFallbackVisitor<'a, 'tcx> { reachable_vids: FxHashSet<ty::TyVid>, fcx: &'a FnCtxt<'a, 'tcx>, } -impl<'tcx> VidVisitor<'_, 'tcx> { +impl<'tcx> AnnotateUnitFallbackVisitor<'_, 'tcx> { + // For a given path segment, if it's missing a turbofish, try to suggest adding + // one so we can constrain an argument to `()`. To keep the suggestion simple, + // we want to simply suggest `_` for all the other args. This (for now) only + // works when there are only type variables (and region variables, since we can + // elide them)... fn suggest_for_segment( &self, arg_segment: &'tcx hir::PathSegment<'tcx>, @@ -627,7 +637,7 @@ impl<'tcx> VidVisitor<'_, 'tcx> { ControlFlow::Continue(()) } } -impl<'tcx> Visitor<'tcx> for VidVisitor<'_, 'tcx> { +impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> { type Result = ControlFlow<errors::SuggestAnnotation>; fn visit_ty(&mut self, hir_ty: &'tcx hir::Ty<'tcx>) -> Self::Result { @@ -657,9 +667,7 @@ impl<'tcx> Visitor<'tcx> for VidVisitor<'_, 'tcx> { return hir::intravisit::walk_qpath(self, qpath, id); } }; - // Alternatively, try to turbofish `::<_, (), _>` (ignoring lifetimes, - // since we don't need to turbofish those; they'll be inferred). - // FIXME: Same logic could work for types... + // Alternatively, try to turbofish `::<_, (), _>`. if let Some(def_id) = self.fcx.typeck_results.borrow().qpath_res(qpath, id).opt_def_id() { self.suggest_for_segment(arg_segment, def_id, id)?; } @@ -668,6 +676,7 @@ impl<'tcx> Visitor<'tcx> for VidVisitor<'_, 'tcx> { fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) -> Self::Result { // Try to suggest adding an explicit qself `()` to a trait method path. + // i.e. changing `Default::default()` to `<() as Default>::default()`. if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind && let Res::Def(DefKind::AssocFn, def_id) = path.res && self.fcx.tcx.trait_of_item(def_id).is_some() @@ -679,7 +688,7 @@ impl<'tcx> Visitor<'tcx> for VidVisitor<'_, 'tcx> { let span = path.span.shrink_to_lo().to(trait_segment.ident.span); return ControlFlow::Break(errors::SuggestAnnotation::Path(span)); } - // Or else turbofishing the method + // Or else, try suggesting turbofishing the method args. if let hir::ExprKind::MethodCall(segment, ..) = expr.kind && let Some(def_id) = self.fcx.typeck_results.borrow().type_dependent_def_id(expr.hir_id) @@ -690,6 +699,7 @@ impl<'tcx> Visitor<'tcx> for VidVisitor<'_, 'tcx> { } fn visit_local(&mut self, local: &'tcx hir::LetStmt<'tcx>) -> Self::Result { + // For a local, try suggest annotating the type if it's missing. if let None = local.ty && let ty = self.fcx.typeck_results.borrow().node_type(local.hir_id) && let Some(vid) = self.fcx.root_vid(ty) |