diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs index dd3f7289a60..60685119fb9 100644 --- a/compiler/rustc_ast_lowering/src/item.rs +++ b/compiler/rustc_ast_lowering/src/item.rs @@ -496,8 +496,7 @@ fn lower_use_tree( } } - let res = - self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect(); + let res = self.lower_import_res(id, path.span); let path = self.lower_use_path(res, &path, ParamMode::Explicit); hir::ItemKind::Use(path, hir::UseKind::Single) } @@ -533,7 +532,8 @@ fn lower_use_tree( // for that we return the `{}` import (called the // `ListStem`). - let prefix = Path { segments, span: prefix.span.to(path.span), tokens: None }; + let span = prefix.span.to(path.span); + let prefix = Path { segments, span, tokens: None }; // Add all the nested `PathListItem`s to the HIR. for &(ref use_tree, id) in trees { @@ -567,9 +567,16 @@ fn lower_use_tree( }); } - let res = - self.expect_full_res_from_use(id).map(|res| self.lower_res(res)).collect(); - let path = self.lower_use_path(res, &prefix, ParamMode::Explicit); + let path = if trees.is_empty() && !prefix.segments.is_empty() { + // For empty lists we need to lower the prefix so it is checked for things + // like stability later. + let res = self.lower_import_res(id, span); + self.lower_use_path(res, &prefix, ParamMode::Explicit) + } else { + // For non-empty lists we can just drop all the data, the prefix is already + // present in HIR as a part of nested imports. + self.arena.alloc(hir::UsePath { res: smallvec![], segments: &[], span }) + }; hir::ItemKind::Use(path, hir::UseKind::ListStem) } } diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs index 3621844efc8..14a83c7eda6 100644 --- a/compiler/rustc_ast_lowering/src/lib.rs +++ b/compiler/rustc_ast_lowering/src/lib.rs @@ -63,7 +63,7 @@ use rustc_session::parse::{add_feature_diagnostics, feature_err}; use rustc_span::symbol::{kw, sym, Ident, Symbol}; use rustc_span::{DesugaringKind, Span, DUMMY_SP}; -use smallvec::SmallVec; +use smallvec::{smallvec, SmallVec}; use std::collections::hash_map::Entry; use thin_vec::ThinVec; @@ -749,8 +749,14 @@ fn expect_full_res(&mut self, id: NodeId) -> Res { self.resolver.get_partial_res(id).map_or(Res::Err, |pr| pr.expect_full_res()) } - fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator> { - self.resolver.get_import_res(id).present_items() + fn lower_import_res(&mut self, id: NodeId, span: Span) -> SmallVec<[Res; 3]> { + let res = self.resolver.get_import_res(id).present_items(); + let res: SmallVec<_> = res.map(|res| self.lower_res(res)).collect(); + if res.is_empty() { + self.dcx().span_delayed_bug(span, "no resolution for an import"); + return smallvec![Res::Err]; + } + res } fn make_lang_item_qpath(&mut self, lang_item: hir::LangItem, span: Span) -> hir::QPath<'hir> { diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs index c679ee56fcd..4df68f8e929 100644 --- a/compiler/rustc_ast_lowering/src/path.rs +++ b/compiler/rustc_ast_lowering/src/path.rs @@ -156,6 +156,7 @@ pub(crate) fn lower_use_path( p: &Path, param_mode: ParamMode, ) -> &'hir hir::UsePath<'hir> { + assert!((1..=3).contains(&res.len())); self.arena.alloc(hir::UsePath { res, segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {