blob: b5d3beb4f8a9b70331639b0d3e9ec8aa7ce2645f [file] [log] [blame]
//! Lowers the AST to the HIR.
//!
//! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
//! much like a fold. Where lowering involves a bit more work things get more
//! interesting and there are some invariants you should know about. These mostly
//! concern spans and IDs.
//!
//! Spans are assigned to AST nodes during parsing and then are modified during
//! expansion to indicate the origin of a node and the process it went through
//! being expanded. IDs are assigned to AST nodes just before lowering.
//!
//! For the simpler lowering steps, IDs and spans should be preserved. Unlike
//! expansion we do not preserve the process of lowering in the spans, so spans
//! should not be modified here. When creating a new node (as opposed to
//! 'folding' an existing one), then you create a new ID using `next_id()`.
//!
//! You must ensure that IDs are unique. That means that you should only use the
//! ID from an AST node in a single HIR node (you can assume that AST node-IDs
//! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
//! If you do, you must then set the new node's ID to a fresh one.
//!
//! Spans are used for error messages and for tools to map semantics back to
//! source code. It is therefore not as important with spans as IDs to be strict
//! about use (you can't break the compiler by screwing up a span). Obviously, a
//! HIR node can only have a single span. But multiple nodes can have the same
//! span and spans don't need to be kept in order, etc. Where code is preserved
//! by lowering, it should have the same span as in the AST. Where HIR nodes are
//! new it is probably best to give a span for the whole AST node being lowered.
//! All nodes should have real spans, don't use dummy spans. Tools are likely to
//! get confused if the spans from leaf AST nodes occur in multiple places
//! in the HIR, especially for multiple identifiers.
#![feature(array_value_iter)]
#![feature(crate_visibility_modifier)]
#![feature(or_patterns)]
#![recursion_limit = "256"]
use rustc_ast::ast;
use rustc_ast::ast::*;
use rustc_ast::attr;
use rustc_ast::node_id::NodeMap;
use rustc_ast::token::{self, DelimToken, Nonterminal, Token};
use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
use rustc_ast::visit::{self, AssocCtxt, Visitor};
use rustc_ast::walk_list;
use rustc_ast_pretty::pprust;
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::sync::Lrc;
use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX};
use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
use rustc_hir::intravisit;
use rustc_hir::{ConstArg, GenericArg, ParamName};
use rustc_index::vec::{Idx, IndexVec};
use rustc_session::config::nightly_options;
use rustc_session::lint::{builtin::BARE_TRAIT_OBJECTS, BuiltinLintDiagnostics, LintBuffer};
use rustc_session::parse::ParseSess;
use rustc_session::Session;
use rustc_span::hygiene::ExpnId;
use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::Span;
use log::{debug, trace};
use smallvec::{smallvec, SmallVec};
use std::collections::BTreeMap;
use std::mem;
macro_rules! arena_vec {
($this:expr; $($x:expr),*) => ({
let a = [$($x),*];
$this.arena.alloc_from_iter(std::array::IntoIter::new(a))
});
}
mod expr;
mod item;
mod pat;
mod path;
const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx);
struct LoweringContext<'a, 'hir: 'a> {
crate_root: Option<Symbol>,
/// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
sess: &'a Session,
resolver: &'a mut dyn ResolverAstLowering,
/// HACK(Centril): there is a cyclic dependency between the parser and lowering
/// if we don't have this function pointer. To avoid that dependency so that
/// librustc_middle is independent of the parser, we use dynamic dispatch here.
nt_to_tokenstream: NtToTokenstream,
/// Used to allocate HIR nodes
arena: &'hir Arena<'hir>,
/// The items being lowered are collected here.
items: BTreeMap<hir::HirId, hir::Item<'hir>>,
trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
exported_macros: Vec<hir::MacroDef<'hir>>,
non_exported_macro_attrs: Vec<ast::Attribute>,
trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
modules: BTreeMap<hir::HirId, hir::ModuleItems>,
generator_kind: Option<hir::GeneratorKind>,
/// When inside an `async` context, this is the `HirId` of the
/// `task_context` local bound to the resume argument of the generator.
task_context: Option<hir::HirId>,
/// Used to get the current `fn`'s def span to point to when using `await`
/// outside of an `async fn`.
current_item: Option<Span>,
catch_scopes: Vec<NodeId>,
loop_scopes: Vec<NodeId>,
is_in_loop_condition: bool,
is_in_trait_impl: bool,
is_in_dyn_type: bool,
/// What to do when we encounter either an "anonymous lifetime
/// reference". The term "anonymous" is meant to encompass both
/// `'_` lifetimes as well as fully elided cases where nothing is
/// written at all (e.g., `&T` or `std::cell::Ref<T>`).
anonymous_lifetime_mode: AnonymousLifetimeMode,
/// Used to create lifetime definitions from in-band lifetime usages.
/// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
/// When a named lifetime is encountered in a function or impl header and
/// has not been defined
/// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
/// to this list. The results of this list are then added to the list of
/// lifetime definitions in the corresponding impl or function generics.
lifetimes_to_define: Vec<(Span, ParamName)>,
/// `true` if in-band lifetimes are being collected. This is used to
/// indicate whether or not we're in a place where new lifetimes will result
/// in in-band lifetime definitions, such a function or an impl header,
/// including implicit lifetimes from `impl_header_lifetime_elision`.
is_collecting_in_band_lifetimes: bool,
/// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
/// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
/// against this list to see if it is already in-scope, or if a definition
/// needs to be created for it.
///
/// We always store a `normalize_to_macros_2_0()` version of the param-name in this
/// vector.
in_scope_lifetimes: Vec<ParamName>,
current_module: hir::HirId,
type_def_lifetime_params: DefIdMap<usize>,
current_hir_id_owner: Vec<(LocalDefId, u32)>,
item_local_id_counters: NodeMap<u32>,
node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
allow_try_trait: Option<Lrc<[Symbol]>>,
allow_gen_future: Option<Lrc<[Symbol]>>,
}
pub trait ResolverAstLowering {
fn def_key(&mut self, id: DefId) -> DefKey;
fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
/// Obtains resolution for a `NodeId` with a single resolution.
fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
/// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
/// Obtains resolution for a label with the given `NodeId`.
fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
/// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
/// This should only return `None` during testing.
fn definitions(&mut self) -> &mut Definitions;
/// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
/// resolves it based on `is_value`.
fn resolve_str_path(
&mut self,
span: Span,
crate_root: Option<Symbol>,
components: &[Symbol],
ns: Namespace,
) -> (ast::Path, Res<NodeId>);
fn lint_buffer(&mut self) -> &mut LintBuffer;
fn next_node_id(&mut self) -> NodeId;
fn trait_map(&self) -> &NodeMap<Vec<hir::TraitCandidate>>;
fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
fn local_def_id(&self, node: NodeId) -> LocalDefId;
fn create_def(
&mut self,
parent: LocalDefId,
node_id: ast::NodeId,
data: DefPathData,
expn_id: ExpnId,
span: Span,
) -> LocalDefId;
}
type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
/// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
/// and if so, what meaning it has.
#[derive(Debug)]
enum ImplTraitContext<'b, 'a> {
/// Treat `impl Trait` as shorthand for a new universal generic parameter.
/// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
/// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
///
/// Newly generated parameters should be inserted into the given `Vec`.
Universal(&'b mut Vec<hir::GenericParam<'a>>),
/// Treat `impl Trait` as shorthand for a new opaque type.
/// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
/// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
///
ReturnPositionOpaqueTy {
/// `DefId` for the parent function, used to look up necessary
/// information later.
fn_def_id: DefId,
/// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin,
},
/// Impl trait in type aliases, consts and statics.
OtherOpaqueTy {
/// Set of lifetimes that this opaque type can capture, if it uses
/// them. This includes lifetimes bound since we entered this context.
/// For example, in
///
/// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
///
/// the inner opaque type captures `'a` because it uses it. It doesn't
/// need to capture `'b` because it already inherits the lifetime
/// parameter from `A`.
// FIXME(impl_trait): but `required_region_bounds` will ICE later
// anyway.
capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
/// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding,
origin: hir::OpaqueTyOrigin,
},
/// `impl Trait` is not accepted in this position.
Disallowed(ImplTraitPosition),
}
/// Position in which `impl Trait` is disallowed.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
enum ImplTraitPosition {
/// Disallowed in `let` / `const` / `static` bindings.
Binding,
/// All other posiitons.
Other,
}
impl<'a> ImplTraitContext<'_, 'a> {
#[inline]
fn disallowed() -> Self {
ImplTraitContext::Disallowed(ImplTraitPosition::Other)
}
fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
use self::ImplTraitContext::*;
match self {
Universal(params) => Universal(params),
ReturnPositionOpaqueTy { fn_def_id, origin } => {
ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
}
OtherOpaqueTy { capturable_lifetimes, origin } => {
OtherOpaqueTy { capturable_lifetimes, origin: *origin }
}
Disallowed(pos) => Disallowed(*pos),
}
}
}
pub fn lower_crate<'a, 'hir>(
sess: &'a Session,
krate: &'a Crate,
resolver: &'a mut dyn ResolverAstLowering,
nt_to_tokenstream: NtToTokenstream,
arena: &'hir Arena<'hir>,
) -> hir::Crate<'hir> {
let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
LoweringContext {
crate_root: sess.parse_sess.injected_crate_name.get().copied(),
sess,
resolver,
nt_to_tokenstream,
arena,
items: BTreeMap::new(),
trait_items: BTreeMap::new(),
impl_items: BTreeMap::new(),
bodies: BTreeMap::new(),
trait_impls: BTreeMap::new(),
modules: BTreeMap::new(),
exported_macros: Vec::new(),
non_exported_macro_attrs: Vec::new(),
catch_scopes: Vec::new(),
loop_scopes: Vec::new(),
is_in_loop_condition: false,
is_in_trait_impl: false,
is_in_dyn_type: false,
anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
type_def_lifetime_params: Default::default(),
current_module: hir::CRATE_HIR_ID,
current_hir_id_owner: vec![(LocalDefId { local_def_index: CRATE_DEF_INDEX }, 0)],
item_local_id_counters: Default::default(),
node_id_to_hir_id: IndexVec::new(),
generator_kind: None,
task_context: None,
current_item: None,
lifetimes_to_define: Vec::new(),
is_collecting_in_band_lifetimes: false,
in_scope_lifetimes: Vec::new(),
allow_try_trait: Some([sym::try_trait][..].into()),
allow_gen_future: Some([sym::gen_future][..].into()),
}
.lower_crate(krate)
}
#[derive(Copy, Clone, PartialEq)]
enum ParamMode {
/// Any path in a type context.
Explicit,
/// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
ExplicitNamed,
/// The `module::Type` in `module::Type::method` in an expression.
Optional,
}
enum ParenthesizedGenericArgs {
Ok,
Err,
}
/// What to do when we encounter an **anonymous** lifetime
/// reference. Anonymous lifetime references come in two flavors. You
/// have implicit, or fully elided, references to lifetimes, like the
/// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
/// or `Ref<'_, T>`. These often behave the same, but not always:
///
/// - certain usages of implicit references are deprecated, like
/// `Ref<T>`, and we sometimes just give hard errors in those cases
/// as well.
/// - for object bounds there is a difference: `Box<dyn Foo>` is not
/// the same as `Box<dyn Foo + '_>`.
///
/// We describe the effects of the various modes in terms of three cases:
///
/// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
/// of a `&` (e.g., the missing lifetime in something like `&T`)
/// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
/// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
/// elided bounds follow special rules. Note that this only covers
/// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
/// '_>` is a case of "modern" elision.
/// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
/// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
/// non-deprecated equivalent.
///
/// Currently, the handling of lifetime elision is somewhat spread out
/// between HIR lowering and -- as described below -- the
/// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
/// an "elided" or "underscore" lifetime name. In the future, we probably want to move
/// everything into HIR lowering.
#[derive(Copy, Clone, Debug)]
enum AnonymousLifetimeMode {
/// For **Modern** cases, create a new anonymous region parameter
/// and reference that.
///
/// For **Dyn Bound** cases, pass responsibility to
/// `resolve_lifetime` code.
///
/// For **Deprecated** cases, report an error.
CreateParameter,
/// Give a hard error when either `&` or `'_` is written. Used to
/// rule out things like `where T: Foo<'_>`. Does not imply an
/// error on default object bounds (e.g., `Box<dyn Foo>`).
ReportError,
/// Pass responsibility to `resolve_lifetime` code for all cases.
PassThrough,
}
struct ImplTraitTypeIdVisitor<'a> {
ids: &'a mut SmallVec<[NodeId; 1]>,
}
impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
fn visit_ty(&mut self, ty: &Ty) {
match ty.kind {
TyKind::Typeof(_) | TyKind::BareFn(_) => return,
TyKind::ImplTrait(id, _) => self.ids.push(id),
_ => {}
}
visit::walk_ty(self, ty);
}
fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
if let Some(ref p) = path_segment.args {
if let GenericArgs::Parenthesized(_) = **p {
return;
}
}
visit::walk_path_segment(self, path_span, path_segment)
}
}
impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
/// Full-crate AST visitor that inserts into a fresh
/// `LoweringContext` any information that may be
/// needed from arbitrary locations in the crate,
/// e.g., the number of lifetime generic parameters
/// declared for every type and trait definition.
struct MiscCollector<'tcx, 'lowering, 'hir> {
lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
hir_id_owner: Option<NodeId>,
}
impl MiscCollector<'_, '_, '_> {
fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: LocalDefId) {
match tree.kind {
UseTreeKind::Simple(_, id1, id2) => {
for &id in &[id1, id2] {
self.lctx.resolver.create_def(
owner,
id,
DefPathData::Misc,
ExpnId::root(),
tree.prefix.span,
);
self.lctx.allocate_hir_id_counter(id);
}
}
UseTreeKind::Glob => (),
UseTreeKind::Nested(ref trees) => {
for &(ref use_tree, id) in trees {
let hir_id = self.lctx.allocate_hir_id_counter(id);
self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
}
}
}
}
fn with_hir_id_owner<T>(
&mut self,
owner: Option<NodeId>,
f: impl FnOnce(&mut Self) -> T,
) -> T {
let old = mem::replace(&mut self.hir_id_owner, owner);
let r = f(self);
self.hir_id_owner = old;
r
}
}
impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
fn visit_pat(&mut self, p: &'tcx Pat) {
if let PatKind::Paren(..) | PatKind::Rest = p.kind {
// Doesn't generate a HIR node
} else if let Some(owner) = self.hir_id_owner {
self.lctx.lower_node_id_with_owner(p.id, owner);
}
visit::walk_pat(self, p)
}
fn visit_item(&mut self, item: &'tcx Item) {
let hir_id = self.lctx.allocate_hir_id_counter(item.id);
match item.kind {
ItemKind::Struct(_, ref generics)
| ItemKind::Union(_, ref generics)
| ItemKind::Enum(_, ref generics)
| ItemKind::TyAlias(_, ref generics, ..)
| ItemKind::Trait(_, _, ref generics, ..) => {
let def_id = self.lctx.resolver.local_def_id(item.id);
let count = generics
.params
.iter()
.filter(|param| match param.kind {
ast::GenericParamKind::Lifetime { .. } => true,
_ => false,
})
.count();
self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
}
ItemKind::Use(ref use_tree) => {
self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
}
_ => {}
}
self.with_hir_id_owner(Some(item.id), |this| {
visit::walk_item(this, item);
});
}
fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
self.lctx.allocate_hir_id_counter(item.id);
let owner = match (&item.kind, ctxt) {
// Ignore patterns in trait methods without bodies.
(AssocItemKind::Fn(_, _, _, None), AssocCtxt::Trait) => None,
_ => Some(item.id),
};
self.with_hir_id_owner(owner, |this| visit::walk_assoc_item(this, item, ctxt));
}
fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
// Ignore patterns in foreign items
self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
}
fn visit_ty(&mut self, t: &'tcx Ty) {
match t.kind {
// Mirrors the case in visit::walk_ty
TyKind::BareFn(ref f) => {
walk_list!(self, visit_generic_param, &f.generic_params);
// Mirrors visit::walk_fn_decl
for parameter in &f.decl.inputs {
// We don't lower the ids of argument patterns
self.with_hir_id_owner(None, |this| {
this.visit_pat(&parameter.pat);
});
self.visit_ty(&parameter.ty)
}
self.visit_fn_ret_ty(&f.decl.output)
}
_ => visit::walk_ty(self, t),
}
}
}
self.lower_node_id(CRATE_NODE_ID);
debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
let module = self.lower_mod(&c.module);
let attrs = self.lower_attrs(&c.attrs);
let body_ids = body_ids(&self.bodies);
let proc_macros =
c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
let trait_map = self
.resolver
.trait_map()
.iter()
.map(|(&k, v)| (self.node_id_to_hir_id[k].unwrap(), v.clone()))
.collect();
let mut def_id_to_hir_id = IndexVec::default();
for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
if def_id_to_hir_id.len() <= def_id.index() {
def_id_to_hir_id.resize(def_id.index() + 1, None);
}
def_id_to_hir_id[def_id] = hir_id;
}
}
self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
hir::Crate {
item: hir::CrateItem { module, attrs, span: c.span },
exported_macros: self.arena.alloc_from_iter(self.exported_macros),
non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
items: self.items,
trait_items: self.trait_items,
impl_items: self.impl_items,
bodies: self.bodies,
body_ids,
trait_impls: self.trait_impls,
modules: self.modules,
proc_macros,
trait_map,
}
}
fn insert_item(&mut self, item: hir::Item<'hir>) {
let id = item.hir_id;
// FIXME: Use `debug_asset-rt`.
assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
self.items.insert(id, item);
self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
}
fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
// Set up the counter if needed.
self.item_local_id_counters.entry(owner).or_insert(0);
// Always allocate the first `HirId` for the owner itself.
let lowered = self.lower_node_id_with_owner(owner, owner);
debug_assert_eq!(lowered.local_id.as_u32(), 0);
lowered
}
fn lower_node_id_generic(
&mut self,
ast_node_id: NodeId,
alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
) -> hir::HirId {
assert_ne!(ast_node_id, DUMMY_NODE_ID);
let min_size = ast_node_id.as_usize() + 1;
if min_size > self.node_id_to_hir_id.len() {
self.node_id_to_hir_id.resize(min_size, None);
}
if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
existing_hir_id
} else {
// Generate a new `HirId`.
let hir_id = alloc_hir_id(self);
self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
hir_id
}
}
fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
let counter = self
.item_local_id_counters
.insert(owner, HIR_ID_COUNTER_LOCKED)
.unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
let def_id = self.resolver.local_def_id(owner);
self.current_hir_id_owner.push((def_id, counter));
let ret = f(self);
let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap();
debug_assert!(def_id == new_def_id);
debug_assert!(new_counter >= counter);
let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
ret
}
/// This method allocates a new `HirId` for the given `NodeId` and stores it in
/// the `LoweringContext`'s `NodeId => HirId` map.
/// Take care not to call this method if the resulting `HirId` is then not
/// actually used in the HIR, as that would trigger an assertion in the
/// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
/// properly. Calling the method twice with the same `NodeId` is fine though.
fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
self.lower_node_id_generic(ast_node_id, |this| {
let &mut (owner, ref mut local_id_counter) =
this.current_hir_id_owner.last_mut().unwrap();
let local_id = *local_id_counter;
*local_id_counter += 1;
hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
})
}
fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
self.lower_node_id_generic(ast_node_id, |this| {
let local_id_counter = this
.item_local_id_counters
.get_mut(&owner)
.expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
let local_id = *local_id_counter;
// We want to be sure not to modify the counter in the map while it
// is also on the stack. Otherwise we'll get lost updates when writing
// back from the stack to the map.
debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
*local_id_counter += 1;
let owner = this.resolver.opt_local_def_id(owner).expect(
"you forgot to call `create_def` or are lowering node-IDs \
that do not belong to the current owner",
);
hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
})
}
fn next_id(&mut self) -> hir::HirId {
let node_id = self.resolver.next_node_id();
self.lower_node_id(node_id)
}
fn lower_res(&mut self, res: Res<NodeId>) -> Res {
res.map_id(|id| {
self.lower_node_id_generic(id, |_| {
panic!("expected `NodeId` to be lowered already for res {:#?}", res);
})
})
}
fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
if pr.unresolved_segments() != 0 {
panic!("path not fully resolved: {:?}", pr);
}
pr.base_res()
})
}
fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
self.resolver.get_import_res(id).present_items()
}
fn diagnostic(&self) -> &rustc_errors::Handler {
self.sess.diagnostic()
}
/// Reuses the span but adds information like the kind of the desugaring and features that are
/// allowed inside this span.
fn mark_span_with_reason(
&self,
reason: DesugaringKind,
span: Span,
allow_internal_unstable: Option<Lrc<[Symbol]>>,
) -> Span {
span.fresh_expansion(ExpnData {
allow_internal_unstable,
..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition(), None)
})
}
fn with_anonymous_lifetime_mode<R>(
&mut self,
anonymous_lifetime_mode: AnonymousLifetimeMode,
op: impl FnOnce(&mut Self) -> R,
) -> R {
debug!(
"with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
anonymous_lifetime_mode,
);
let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
self.anonymous_lifetime_mode = anonymous_lifetime_mode;
let result = op(self);
self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
debug!(
"with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
old_anonymous_lifetime_mode
);
result
}
/// Creates a new `hir::GenericParam` for every new lifetime and
/// type parameter encountered while evaluating `f`. Definitions
/// are created with the parent provided. If no `parent_id` is
/// provided, no definitions will be returned.
///
/// Presuming that in-band lifetimes are enabled, then
/// `self.anonymous_lifetime_mode` will be updated to match the
/// parameter while `f` is running (and restored afterwards).
fn collect_in_band_defs<T>(
&mut self,
parent_def_id: LocalDefId,
anonymous_lifetime_mode: AnonymousLifetimeMode,
f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
) -> (Vec<hir::GenericParam<'hir>>, T) {
assert!(!self.is_collecting_in_band_lifetimes);
assert!(self.lifetimes_to_define.is_empty());
let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
self.anonymous_lifetime_mode = anonymous_lifetime_mode;
self.is_collecting_in_band_lifetimes = true;
let (in_band_ty_params, res) = f(self);
self.is_collecting_in_band_lifetimes = false;
self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
let params = lifetimes_to_define
.into_iter()
.map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
.chain(in_band_ty_params.into_iter())
.collect();
(params, res)
}
/// Converts a lifetime into a new generic parameter.
fn lifetime_to_generic_param(
&mut self,
span: Span,
hir_name: ParamName,
parent_def_id: LocalDefId,
) -> hir::GenericParam<'hir> {
let node_id = self.resolver.next_node_id();
// Get the name we'll use to make the def-path. Note
// that collisions are ok here and this shouldn't
// really show up for end-user.
let (str_name, kind) = match hir_name {
ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
};
// Add a definition for the in-band lifetime def.
self.resolver.create_def(
parent_def_id,
node_id,
DefPathData::LifetimeNs(str_name),
ExpnId::root(),
span,
);
hir::GenericParam {
hir_id: self.lower_node_id(node_id),
name: hir_name,
attrs: &[],
bounds: &[],
span,
pure_wrt_drop: false,
kind: hir::GenericParamKind::Lifetime { kind },
}
}
/// When there is a reference to some lifetime `'a`, and in-band
/// lifetimes are enabled, then we want to push that lifetime into
/// the vector of names to define later. In that case, it will get
/// added to the appropriate generics.
fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
if !self.is_collecting_in_band_lifetimes {
return;
}
if !self.sess.features_untracked().in_band_lifetimes {
return;
}
if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
return;
}
let hir_name = ParamName::Plain(ident);
if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
}) {
return;
}
self.lifetimes_to_define.push((ident.span, hir_name));
}
/// When we have either an elided or `'_` lifetime in an impl
/// header, we convert it to an in-band lifetime.
fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
assert!(self.is_collecting_in_band_lifetimes);
let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
let hir_name = ParamName::Fresh(index);
self.lifetimes_to_define.push((span, hir_name));
hir_name
}
// Evaluates `f` with the lifetimes in `params` in-scope.
// This is used to track which lifetimes have already been defined, and
// which are new in-band lifetimes that need to have a definition created
// for them.
fn with_in_scope_lifetime_defs<T>(
&mut self,
params: &[GenericParam],
f: impl FnOnce(&mut Self) -> T,
) -> T {
let old_len = self.in_scope_lifetimes.len();
let lt_def_names = params.iter().filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
}
_ => None,
});
self.in_scope_lifetimes.extend(lt_def_names);
let res = f(self);
self.in_scope_lifetimes.truncate(old_len);
res
}
/// Appends in-band lifetime defs and argument-position `impl
/// Trait` defs to the existing set of generics.
///
/// Presuming that in-band lifetimes are enabled, then
/// `self.anonymous_lifetime_mode` will be updated to match the
/// parameter while `f` is running (and restored afterwards).
fn add_in_band_defs<T>(
&mut self,
generics: &Generics,
parent_def_id: LocalDefId,
anonymous_lifetime_mode: AnonymousLifetimeMode,
f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
) -> (hir::Generics<'hir>, T) {
let (in_band_defs, (mut lowered_generics, res)) =
self.with_in_scope_lifetime_defs(&generics.params, |this| {
this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
let mut params = Vec::new();
// Note: it is necessary to lower generics *before* calling `f`.
// When lowering `async fn`, there's a final step when lowering
// the return type that assumes that all in-scope lifetimes have
// already been added to either `in_scope_lifetimes` or
// `lifetimes_to_define`. If we swapped the order of these two,
// in-band-lifetimes introduced by generics or where-clauses
// wouldn't have been added yet.
let generics =
this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
let res = f(this, &mut params);
(params, (generics, res))
})
});
let mut lowered_params: Vec<_> =
lowered_generics.params.into_iter().chain(in_band_defs).collect();
// FIXME(const_generics): the compiler doesn't always cope with
// unsorted generic parameters at the moment, so we make sure
// that they're ordered correctly here for now. (When we chain
// the `in_band_defs`, we might make the order unsorted.)
lowered_params.sort_by_key(|param| match param.kind {
hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
});
lowered_generics.params = lowered_params.into();
let lowered_generics = lowered_generics.into_generics(self.arena);
(lowered_generics, res)
}
fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
let was_in_dyn_type = self.is_in_dyn_type;
self.is_in_dyn_type = in_scope;
let result = f(self);
self.is_in_dyn_type = was_in_dyn_type;
result
}
fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
let was_in_loop_condition = self.is_in_loop_condition;
self.is_in_loop_condition = false;
let catch_scopes = mem::take(&mut self.catch_scopes);
let loop_scopes = mem::take(&mut self.loop_scopes);
let ret = f(self);
self.catch_scopes = catch_scopes;
self.loop_scopes = loop_scopes;
self.is_in_loop_condition = was_in_loop_condition;
ret
}
fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
}
fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
// Note that we explicitly do not walk the path. Since we don't really
// lower attributes (we use the AST version) there is nowhere to keep
// the `HirId`s. We don't actually need HIR version of attributes anyway.
let kind = match attr.kind {
AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
path: item.path.clone(),
args: self.lower_mac_args(&item.args),
}),
AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
};
Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
}
fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
match *args {
MacArgs::Empty => MacArgs::Empty,
MacArgs::Delimited(dspan, delim, ref tokens) => {
MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
}
MacArgs::Eq(eq_span, ref tokens) => {
MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
}
}
}
fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
}
fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
match tree {
TokenTree::Token(token) => self.lower_token(token),
TokenTree::Delimited(span, delim, tts) => {
TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
}
}
}
fn lower_token(&mut self, token: Token) -> TokenStream {
match token.kind {
token::Interpolated(nt) => {
let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
TokenTree::Delimited(
DelimSpan::from_single(token.span),
DelimToken::NoDelim,
self.lower_token_stream(tts),
)
.into()
}
_ => TokenTree::Token(token).into(),
}
}
/// Given an associated type constraint like one of these:
///
/// ```
/// T: Iterator<Item: Debug>
/// ^^^^^^^^^^^
/// T: Iterator<Item = Debug>
/// ^^^^^^^^^^^^
/// ```
///
/// returns a `hir::TypeBinding` representing `Item`.
fn lower_assoc_ty_constraint(
&mut self,
constraint: &AssocTyConstraint,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::TypeBinding<'hir> {
debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
let kind = match constraint.kind {
AssocTyConstraintKind::Equality { ref ty } => {
hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
}
AssocTyConstraintKind::Bound { ref bounds } => {
let mut capturable_lifetimes;
// Piggy-back on the `impl Trait` context to figure out the correct behavior.
let (desugar_to_impl_trait, itctx) = match itctx {
// We are in the return position:
//
// fn foo() -> impl Iterator<Item: Debug>
//
// so desugar to
//
// fn foo() -> impl Iterator<Item = impl Debug>
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
// We are in the argument position, but within a dyn type:
//
// fn foo(x: dyn Iterator<Item: Debug>)
//
// so desugar to
//
// fn foo(x: dyn Iterator<Item = impl Debug>)
ImplTraitContext::Universal(..) if self.is_in_dyn_type => (true, itctx),
// In `type Foo = dyn Iterator<Item: Debug>` we desugar to
// `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
// "impl trait context" to permit `impl Debug` in this position (it desugars
// then to an opaque type).
//
// FIXME: this is only needed until `impl Trait` is allowed in type aliases.
ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
capturable_lifetimes = FxHashSet::default();
(
true,
ImplTraitContext::OtherOpaqueTy {
capturable_lifetimes: &mut capturable_lifetimes,
origin: hir::OpaqueTyOrigin::Misc,
},
)
}
// We are in the parameter position, but not within a dyn type:
//
// fn foo(x: impl Iterator<Item: Debug>)
//
// so we leave it as is and this gets expanded in astconv to a bound like
// `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
// `impl Iterator`.
_ => (false, itctx),
};
if desugar_to_impl_trait {
// Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
// constructing the HIR for `impl bounds...` and then lowering that.
let impl_trait_node_id = self.resolver.next_node_id();
let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
self.resolver.create_def(
parent_def_id,
impl_trait_node_id,
DefPathData::ImplTrait,
ExpnId::root(),
constraint.span,
);
self.with_dyn_type_scope(false, |this| {
let node_id = this.resolver.next_node_id();
let ty = this.lower_ty(
&Ty {
id: node_id,
kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
span: constraint.span,
},
itctx,
);
hir::TypeBindingKind::Equality { ty }
})
} else {
// Desugar `AssocTy: Bounds` into a type binding where the
// later desugars into a trait predicate.
let bounds = self.lower_param_bounds(bounds, itctx);
hir::TypeBindingKind::Constraint { bounds }
}
}
};
hir::TypeBinding {
hir_id: self.lower_node_id(constraint.id),
ident: constraint.ident,
kind,
span: constraint.span,
}
}
fn lower_generic_arg(
&mut self,
arg: &ast::GenericArg,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericArg<'hir> {
match arg {
ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(&lt)),
ast::GenericArg::Type(ty) => {
// We parse const arguments as path types as we cannot distinguish them during
// parsing. We try to resolve that ambiguity by attempting resolution in both the
// type and value namespaces. If we resolved the path in the value namespace, we
// transform it into a generic const argument.
if let TyKind::Path(ref qself, ref path) = ty.kind {
if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
let res = partial_res.base_res();
if !res.matches_ns(Namespace::TypeNS) {
debug!(
"lower_generic_arg: Lowering type argument as const argument: {:?}",
ty,
);
// Construct a AnonConst where the expr is the "ty"'s path.
let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
let node_id = self.resolver.next_node_id();
// Add a definition for the in-band const def.
self.resolver.create_def(
parent_def_id,
node_id,
DefPathData::AnonConst,
ExpnId::root(),
ty.span,
);
let path_expr = Expr {
id: ty.id,
kind: ExprKind::Path(qself.clone(), path.clone()),
span: ty.span,
attrs: AttrVec::new(),
tokens: None,
};
let ct = self.with_new_scopes(|this| hir::AnonConst {
hir_id: this.lower_node_id(node_id),
body: this.lower_const_body(path_expr.span, Some(&path_expr)),
});
return GenericArg::Const(ConstArg { value: ct, span: ty.span });
}
}
}
GenericArg::Type(self.lower_ty_direct(&ty, itctx))
}
ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
value: self.lower_anon_const(&ct),
span: ct.value.span,
}),
}
}
fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
self.arena.alloc(self.lower_ty_direct(t, itctx))
}
fn lower_path_ty(
&mut self,
t: &Ty,
qself: &Option<QSelf>,
path: &Path,
param_mode: ParamMode,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::Ty<'hir> {
let id = self.lower_node_id(t.id);
let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
let ty = self.ty_path(id, t.span, qpath);
if let hir::TyKind::TraitObject(..) = ty.kind {
self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
}
ty
}
fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
hir::Ty { hir_id: self.next_id(), kind, span }
}
fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
self.ty(span, hir::TyKind::Tup(tys))
}
fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
let kind = match t.kind {
TyKind::Infer => hir::TyKind::Infer,
TyKind::Err => hir::TyKind::Err,
TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
TyKind::Rptr(ref region, ref mt) => {
let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
let lifetime = match *region {
Some(ref lt) => self.lower_lifetime(lt),
None => self.elided_ref_lifetime(span),
};
hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
}
TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
generic_params: this.lower_generic_params(
&f.generic_params,
&NodeMap::default(),
ImplTraitContext::disallowed(),
),
unsafety: this.lower_unsafety(f.unsafety),
abi: this.lower_extern(f.ext),
decl: this.lower_fn_decl(&f.decl, None, false, None),
param_names: this.lower_fn_params_to_names(&f.decl),
}))
})
}),
TyKind::Never => hir::TyKind::Never,
TyKind::Tup(ref tys) => {
hir::TyKind::Tup(self.arena.alloc_from_iter(
tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
))
}
TyKind::Paren(ref ty) => {
return self.lower_ty_direct(ty, itctx);
}
TyKind::Path(ref qself, ref path) => {
return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
}
TyKind::ImplicitSelf => {
let res = self.expect_full_res(t.id);
let res = self.lower_res(res);
hir::TyKind::Path(hir::QPath::Resolved(
None,
self.arena.alloc(hir::Path {
res,
segments: arena_vec![self; hir::PathSegment::from_ident(
Ident::with_dummy_span(kw::SelfUpper)
)],
span: t.span,
}),
))
}
TyKind::Array(ref ty, ref length) => {
hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
}
TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
TyKind::TraitObject(ref bounds, kind) => {
let mut lifetime_bound = None;
let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
let bounds =
this.arena.alloc_from_iter(bounds.iter().filter_map(
|bound| match *bound {
GenericBound::Trait(
ref ty,
TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
// `?const ?Bound` will cause an error during AST validation
// anyways, so treat it like `?Bound` as compilation proceeds.
GenericBound::Trait(
_,
TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
) => None,
GenericBound::Outlives(ref lifetime) => {
if lifetime_bound.is_none() {
lifetime_bound = Some(this.lower_lifetime(lifetime));
}
None
}
},
));
let lifetime_bound =
lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
(bounds, lifetime_bound)
});
if kind != TraitObjectSyntax::Dyn {
self.maybe_lint_bare_trait(t.span, t.id, false);
}
hir::TyKind::TraitObject(bounds, lifetime_bound)
}
TyKind::ImplTrait(def_node_id, ref bounds) => {
let span = t.span;
match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
.lower_opaque_impl_trait(
span,
Some(fn_def_id),
origin,
def_node_id,
None,
|this| this.lower_param_bounds(bounds, itctx),
),
ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => {
// Reset capturable lifetimes, any nested impl trait
// types will inherit lifetimes from this opaque type,
// so don't need to capture them again.
let nested_itctx = ImplTraitContext::OtherOpaqueTy {
capturable_lifetimes: &mut FxHashSet::default(),
origin,
};
self.lower_opaque_impl_trait(
span,
None,
origin,
def_node_id,
Some(capturable_lifetimes),
|this| this.lower_param_bounds(bounds, nested_itctx),
)
}
ImplTraitContext::Universal(in_band_ty_params) => {
// Add a definition for the in-band `Param`.
let def_id = self.resolver.local_def_id(def_node_id);
let hir_bounds = self.lower_param_bounds(
bounds,
ImplTraitContext::Universal(in_band_ty_params),
);
// Set the name to `impl Bound1 + Bound2`.
let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
in_band_ty_params.push(hir::GenericParam {
hir_id: self.lower_node_id(def_node_id),
name: ParamName::Plain(ident),
pure_wrt_drop: false,
attrs: &[],
bounds: hir_bounds,
span,
kind: hir::GenericParamKind::Type {
default: None,
synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
},
});
hir::TyKind::Path(hir::QPath::Resolved(
None,
self.arena.alloc(hir::Path {
span,
res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
}),
))
}
ImplTraitContext::Disallowed(pos) => {
let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
"bindings or function and inherent method return types"
} else {
"function and inherent method return types"
};
let mut err = struct_span_err!(
self.sess,
t.span,
E0562,
"`impl Trait` not allowed outside of {}",
allowed_in,
);
if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
{
err.help(
"add `#![feature(impl_trait_in_bindings)]` to the crate \
attributes to enable",
);
}
err.emit();
hir::TyKind::Err
}
}
}
TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
TyKind::CVarArgs => {
self.sess.delay_span_bug(
t.span,
"`TyKind::CVarArgs` should have been handled elsewhere",
);
hir::TyKind::Err
}
};
hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
}
fn lower_opaque_impl_trait(
&mut self,
span: Span,
fn_def_id: Option<DefId>,
origin: hir::OpaqueTyOrigin,
opaque_ty_node_id: NodeId,
capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
) -> hir::TyKind<'hir> {
debug!(
"lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
fn_def_id, opaque_ty_node_id, span,
);
// Make sure we know that some funky desugaring has been going on here.
// This is a first: there is code in other places like for loop
// desugaring that explicitly states that we don't want to track that.
// Not tracking it makes lints in rustc and clippy very fragile, as
// frequently opened issues show.
let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
self.allocate_hir_id_counter(opaque_ty_node_id);
let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
opaque_ty_node_id,
opaque_ty_def_id,
&hir_bounds,
capturable_lifetimes,
);
debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
let opaque_ty_item = hir::OpaqueTy {
generics: hir::Generics {
params: lifetime_defs,
where_clause: hir::WhereClause { predicates: &[], span },
span,
},
bounds: hir_bounds,
impl_trait_fn: fn_def_id,
origin,
};
trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
let opaque_ty_id =
lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
// `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, lifetimes)
})
}
/// Registers a new opaque type with the proper `NodeId`s and
/// returns the lowered node-ID for the opaque type.
fn generate_opaque_type(
&mut self,
opaque_ty_node_id: NodeId,
opaque_ty_item: hir::OpaqueTy<'hir>,
span: Span,
opaque_ty_span: Span,
) -> hir::HirId {
let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
// Generate an `type Foo = impl Trait;` declaration.
trace!("registering opaque type with id {:#?}", opaque_ty_id);
let opaque_ty_item = hir::Item {
hir_id: opaque_ty_id,
ident: Ident::invalid(),
attrs: Default::default(),
kind: opaque_ty_item_kind,
vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
span: opaque_ty_span,
};
// Insert the item into the global item list. This usually happens
// automatically for all AST items. But this opaque type item
// does not actually exist in the AST.
self.insert_item(opaque_ty_item);
opaque_ty_id
}
fn lifetimes_from_impl_trait_bounds(
&mut self,
opaque_ty_id: NodeId,
parent_def_id: LocalDefId,
bounds: hir::GenericBounds<'hir>,
lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
debug!(
"lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
parent_def_id={:?}, \
bounds={:#?})",
opaque_ty_id, parent_def_id, bounds,
);
// This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
// appear in the bounds, excluding lifetimes that are created within the bounds.
// E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
context: &'r mut LoweringContext<'a, 'hir>,
parent: LocalDefId,
opaque_ty_id: NodeId,
collect_elided_lifetimes: bool,
currently_bound_lifetimes: Vec<hir::LifetimeName>,
already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
output_lifetimes: Vec<hir::GenericArg<'hir>>,
output_lifetime_params: Vec<hir::GenericParam<'hir>>,
lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
}
impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
type Map = intravisit::ErasedMap<'v>;
fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
intravisit::NestedVisitorMap::None
}
fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
// Don't collect elided lifetimes used inside of `Fn()` syntax.
if parameters.parenthesized {
let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
self.collect_elided_lifetimes = false;
intravisit::walk_generic_args(self, span, parameters);
self.collect_elided_lifetimes = old_collect_elided_lifetimes;
} else {
intravisit::walk_generic_args(self, span, parameters);
}
}
fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
// Don't collect elided lifetimes used inside of `fn()` syntax.
if let hir::TyKind::BareFn(_) = t.kind {
let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
self.collect_elided_lifetimes = false;
// Record the "stack height" of `for<'a>` lifetime bindings
// to be able to later fully undo their introduction.
let old_len = self.currently_bound_lifetimes.len();
intravisit::walk_ty(self, t);
self.currently_bound_lifetimes.truncate(old_len);
self.collect_elided_lifetimes = old_collect_elided_lifetimes;
} else {
intravisit::walk_ty(self, t)
}
}
fn visit_poly_trait_ref(
&mut self,
trait_ref: &'v hir::PolyTraitRef<'v>,
modifier: hir::TraitBoundModifier,
) {
// Record the "stack height" of `for<'a>` lifetime bindings
// to be able to later fully undo their introduction.
let old_len = self.currently_bound_lifetimes.len();
intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
self.currently_bound_lifetimes.truncate(old_len);
}
fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
// Record the introduction of 'a in `for<'a> ...`.
if let hir::GenericParamKind::Lifetime { .. } = param.kind {
// Introduce lifetimes one at a time so that we can handle
// cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
let lt_name = hir::LifetimeName::Param(param.name);
self.currently_bound_lifetimes.push(lt_name);
}
intravisit::walk_generic_param(self, param);
}
fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
let name = match lifetime.name {
hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
if self.collect_elided_lifetimes {
// Use `'_` for both implicit and underscore lifetimes in
// `type Foo<'_> = impl SomeTrait<'_>;`.
hir::LifetimeName::Underscore
} else {
return;
}
}
hir::LifetimeName::Param(_) => lifetime.name,
// Refers to some other lifetime that is "in
// scope" within the type.
hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
hir::LifetimeName::Error | hir::LifetimeName::Static => return,
};
if !self.currently_bound_lifetimes.contains(&name)
&& !self.already_defined_lifetimes.contains(&name)
&& self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
{
self.already_defined_lifetimes.insert(name);
self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
hir_id: self.context.next_id(),
span: lifetime.span,
name,
}));
let def_node_id = self.context.resolver.next_node_id();
let hir_id =
self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
self.context.resolver.create_def(
self.parent,
def_node_id,
DefPathData::LifetimeNs(name.ident().name),
ExpnId::root(),
lifetime.span,
);
let (name, kind) = match name {
hir::LifetimeName::Underscore => (
hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
hir::LifetimeParamKind::Elided,
),
hir::LifetimeName::Param(param_name) => {
(param_name, hir::LifetimeParamKind::Explicit)
}
_ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
};
self.output_lifetime_params.push(hir::GenericParam {
hir_id,
name,
span: lifetime.span,
pure_wrt_drop: false,
attrs: &[],
bounds: &[],
kind: hir::GenericParamKind::Lifetime { kind },
});
}
}
}
let mut lifetime_collector = ImplTraitLifetimeCollector {
context: self,
parent: parent_def_id,
opaque_ty_id,
collect_elided_lifetimes: true,
currently_bound_lifetimes: Vec::new(),
already_defined_lifetimes: FxHashSet::default(),
output_lifetimes: Vec::new(),
output_lifetime_params: Vec::new(),
lifetimes_to_include,
};
for bound in bounds {
intravisit::walk_param_bound(&mut lifetime_collector, &bound);
}
let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
lifetime_collector;
(
self.arena.alloc_from_iter(output_lifetimes),
self.arena.alloc_from_iter(output_lifetime_params),
)
}
fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
let mut ids = SmallVec::<[NodeId; 1]>::new();
if self.sess.features_untracked().impl_trait_in_bindings {
if let Some(ref ty) = l.ty {
let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
visitor.visit_ty(ty);
}
}
let ty = l.ty.as_ref().map(|t| {
let mut capturable_lifetimes;
self.lower_ty(
t,
if self.sess.features_untracked().impl_trait_in_bindings {
capturable_lifetimes = FxHashSet::default();
ImplTraitContext::OtherOpaqueTy {
capturable_lifetimes: &mut capturable_lifetimes,
origin: hir::OpaqueTyOrigin::Binding,
}
} else {
ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
},
)
});
let init = l.init.as_ref().map(|e| self.lower_expr(e));
(
hir::Local {
hir_id: self.lower_node_id(l.id),
ty,
pat: self.lower_pat(&l.pat),
init,
span: l.span,
attrs: l.attrs.clone(),
source: hir::LocalSource::Normal,
},
ids,
)
}
fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
// Skip the `...` (`CVarArgs`) trailing arguments from the AST,
// as they are not explicit in HIR/Ty function signatures.
// (instead, the `c_variadic` flag is set to `true`)
let mut inputs = &decl.inputs[..];
if decl.c_variadic() {
inputs = &inputs[..inputs.len() - 1];
}
self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
PatKind::Ident(_, ident, _) => ident,
_ => Ident::new(kw::Invalid, param.pat.span),
}))
}
// Lowers a function declaration.
//
// `decl`: the unlowered (AST) function declaration.
// `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
// given DefId, otherwise impl Trait is disallowed. Must be `Some` if
// `make_ret_async` is also `Some`.
// `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
// This guards against trait declarations and implementations where `impl Trait` is
// disallowed.
// `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
// return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
// return type `impl Trait` item.
fn lower_fn_decl(
&mut self,
decl: &FnDecl,
mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
impl_trait_return_allow: bool,
make_ret_async: Option<NodeId>,
) -> &'hir hir::FnDecl<'hir> {
debug!(
"lower_fn_decl(\
fn_decl: {:?}, \
in_band_ty_params: {:?}, \
impl_trait_return_allow: {}, \
make_ret_async: {:?})",
decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
);
let lt_mode = if make_ret_async.is_some() {
// In `async fn`, argument-position elided lifetimes
// must be transformed into fresh generic parameters so that
// they can be applied to the opaque `impl Trait` return type.
AnonymousLifetimeMode::CreateParameter
} else {
self.anonymous_lifetime_mode
};
let c_variadic = decl.c_variadic();
// Remember how many lifetimes were already around so that we can
// only look at the lifetime parameters introduced by the arguments.
let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
// Skip the `...` (`CVarArgs`) trailing arguments from the AST,
// as they are not explicit in HIR/Ty function signatures.
// (instead, the `c_variadic` flag is set to `true`)
let mut inputs = &decl.inputs[..];
if c_variadic {
inputs = &inputs[..inputs.len() - 1];
}
this.arena.alloc_from_iter(inputs.iter().map(|param| {
if let Some((_, ibty)) = &mut in_band_ty_params {
this.lower_ty_direct(&param.ty, ImplTraitContext::Universal(ibty))
} else {
this.lower_ty_direct(&param.ty, ImplTraitContext::disallowed())
}
}))
});
let output = if let Some(ret_id) = make_ret_async {
self.lower_async_fn_ret_ty(
&decl.output,
in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
ret_id,
)
} else {
match decl.output {
FnRetTy::Ty(ref ty) => {
let context = match in_band_ty_params {
Some((def_id, _)) if impl_trait_return_allow => {
ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id: def_id,
origin: hir::OpaqueTyOrigin::FnReturn,
}
}
_ => ImplTraitContext::disallowed(),
};
hir::FnRetTy::Return(self.lower_ty(ty, context))
}
FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
}
};
self.arena.alloc(hir::FnDecl {
inputs,
output,
c_variadic,
implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
let is_mutable_pat = match arg.pat.kind {
PatKind::Ident(BindingMode::ByValue(mt) | BindingMode::ByRef(mt), _, _) => {
mt == Mutability::Mut
}
_ => false,
};
match arg.ty.kind {
TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
// Given we are only considering `ImplicitSelf` types, we needn't consider
// the case where we have a mutable pattern to a reference as that would
// no longer be an `ImplicitSelf`.
TyKind::Rptr(_, ref mt)
if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
{
hir::ImplicitSelfKind::MutRef
}
TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
hir::ImplicitSelfKind::ImmRef
}
_ => hir::ImplicitSelfKind::None,
}
}),
})
}
// Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
// combined with the following definition of `OpaqueTy`:
//
// type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
//
// `inputs`: lowered types of parameters to the function (used to collect lifetimes)
// `output`: unlowered output type (`T` in `-> T`)
// `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
// `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
// `elided_lt_replacement`: replacement for elided lifetimes in the return type
fn lower_async_fn_ret_ty(
&mut self,
output: &FnRetTy,
fn_def_id: DefId,
opaque_ty_node_id: NodeId,
) -> hir::FnRetTy<'hir> {
debug!(
"lower_async_fn_ret_ty(\
output={:?}, \
fn_def_id={:?}, \
opaque_ty_node_id={:?})",
output, fn_def_id, opaque_ty_node_id,
);
let span = output.span();
let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
self.allocate_hir_id_counter(opaque_ty_node_id);
// When we create the opaque type for this async fn, it is going to have
// to capture all the lifetimes involved in the signature (including in the
// return type). This is done by introducing lifetime parameters for:
//
// - all the explicitly declared lifetimes from the impl and function itself;
// - all the elided lifetimes in the fn arguments;
// - all the elided lifetimes in the return type.
//
// So for example in this snippet:
//
// ```rust
// impl<'a> Foo<'a> {
// async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
// // ^ '0 ^ '1 ^ '2
// // elided lifetimes used below
// }
// }
// ```
//
// we would create an opaque type like:
//
// ```
// type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
// ```
//
// and we would then desugar `bar` to the equivalent of:
//
// ```rust
// impl<'a> Foo<'a> {
// fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
// }
// ```
//
// Note that the final parameter to `Bar` is `'_`, not `'2` --
// this is because the elided lifetimes from the return type
// should be figured out using the ordinary elision rules, and
// this desugaring achieves that.
//
// The variable `input_lifetimes_count` tracks the number of
// lifetime parameters to the opaque type *not counting* those
// lifetimes elided in the return type. This includes those
// that are explicitly declared (`in_scope_lifetimes`) and
// those elided lifetimes we found in the arguments (current
// content of `lifetimes_to_define`). Next, we will process
// the return type, which will cause `lifetimes_to_define` to
// grow.
let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
// We have to be careful to get elision right here. The
// idea is that we create a lifetime parameter for each
// lifetime in the return type. So, given a return type
// like `async fn foo(..) -> &[&u32]`, we lower to `impl
// Future<Output = &'1 [ &'2 u32 ]>`.
//
// Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
// hence the elision takes place at the fn site.
let future_bound = this
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
});
debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
// Calculate all the lifetimes that should be captured
// by the opaque type. This should include all in-scope
// lifetime parameters, including those defined in-band.
//
// Note: this must be done after lowering the output type,
// as the output type may introduce new in-band lifetimes.
let lifetime_params: Vec<(Span, ParamName)> = this
.in_scope_lifetimes
.iter()
.cloned()
.map(|name| (name.ident().span, name))
.chain(this.lifetimes_to_define.iter().cloned())
.collect();
debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
let generic_params =
this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
}));
let opaque_ty_item = hir::OpaqueTy {
generics: hir::Generics {
params: generic_params,
where_clause: hir::WhereClause { predicates: &[], span },
span,
},
bounds: arena_vec![this; future_bound],
impl_trait_fn: Some(fn_def_id),
origin: hir::OpaqueTyOrigin::AsyncFn,
};
trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
let opaque_ty_id =
this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
(opaque_ty_id, lifetime_params)
});
// As documented above on the variable
// `input_lifetimes_count`, we need to create the lifetime
// arguments to our opaque type. Continuing with our example,
// we're creating the type arguments for the return type:
//
// ```
// Bar<'a, 'b, '0, '1, '_>
// ```
//
// For the "input" lifetime parameters, we wish to create
// references to the parameters themselves, including the
// "implicit" ones created from parameter types (`'a`, `'b`,
// '`0`, `'1`).
//
// For the "output" lifetime parameters, we just want to
// generate `'_`.
let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
.iter()
.map(|&(span, hir_name)| {
// Input lifetime like `'a` or `'1`:
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span,
name: hir::LifetimeName::Param(hir_name),
})
})
.collect();
generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
// Output lifetime like `'_`.
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span,
name: hir::LifetimeName::Implicit,
})));
let generic_args = self.arena.alloc_from_iter(generic_args);
// Create the `Foo<...>` reference itself. Note that the `type
// Foo = impl Trait` is, internally, created as a child of the
// async fn, so the *type parameters* are inherited. It's
// only the lifetime parameters that we must supply.
let opaque_ty_ref = hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, generic_args);
let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
}
/// Transforms `-> T` into `Future<Output = T>`
fn lower_async_fn_output_type_to_future_bound(
&mut self,
output: &FnRetTy,
fn_def_id: DefId,
span: Span,
) -> hir::GenericBound<'hir> {
// Compute the `T` in `Future<Output = T>` from the return type.
let output_ty = match output {
FnRetTy::Ty(ty) => {
// Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
// `impl Future` opaque type that `async fn` implicitly
// generates.
let context = ImplTraitContext::ReturnPositionOpaqueTy {
fn_def_id,
origin: hir::OpaqueTyOrigin::FnReturn,
};
self.lower_ty(ty, context)
}
FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
};
// "<Output = T>"
let future_params = self.arena.alloc(hir::GenericArgs {
args: &[],
bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
parenthesized: false,
});
// ::std::future::Future<future_params>
let future_path =
self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
hir::GenericBound::Trait(
hir::PolyTraitRef {
trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
bound_generic_params: &[],
span,
},
hir::TraitBoundModifier::None,
)
}
fn lower_param_bound(
&mut self,
tpb: &GenericBound,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericBound<'hir> {
match *tpb {
GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
self.lower_poly_trait_ref(ty, itctx),
self.lower_trait_bound_modifier(modifier),
),
GenericBound::Outlives(ref lifetime) => {
hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
}
}
}
fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
let span = l.ident.span;
match l.ident {
ident if ident.name == kw::StaticLifetime => {
self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
}
ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
AnonymousLifetimeMode::CreateParameter => {
let fresh_name = self.collect_fresh_in_band_lifetime(span);
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
}
AnonymousLifetimeMode::PassThrough => {
self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
}
AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
},
ident => {
self.maybe_collect_in_band_lifetime(ident);
let param_name = ParamName::Plain(ident);
self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
}
}
}
fn new_named_lifetime(
&mut self,
id: NodeId,
span: Span,
name: hir::LifetimeName,
) -> hir::Lifetime {
hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
}
fn lower_generic_params_mut<'s>(
&'s mut self,
params: &'s [GenericParam],
add_bounds: &'s NodeMap<Vec<GenericBound>>,
mut itctx: ImplTraitContext<'s, 'hir>,
) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
params
.iter()
.map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
}
fn lower_generic_params(
&mut self,
params: &[GenericParam],
add_bounds: &NodeMap<Vec<GenericBound>>,
itctx: ImplTraitContext<'_, 'hir>,
) -> &'hir [hir::GenericParam<'hir>] {
self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
}
fn lower_generic_param(
&mut self,
param: &GenericParam,
add_bounds: &NodeMap<Vec<GenericBound>>,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericParam<'hir> {
let mut bounds: Vec<_> = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_param_bounds_mut(&param.bounds, itctx.reborrow()).collect()
});
let (name, kind) = match param.kind {
GenericParamKind::Lifetime => {
let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
self.is_collecting_in_band_lifetimes = false;
let lt = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
});
let param_name = match lt.name {
hir::LifetimeName::Param(param_name) => param_name,
hir::LifetimeName::Implicit
| hir::LifetimeName::Underscore
| hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
hir::LifetimeName::ImplicitObjectLifetimeDefault => {
self.sess.diagnostic().span_bug(
param.ident.span,
"object-lifetime-default should not occur here",
);
}
hir::LifetimeName::Error => ParamName::Error,
};
let kind =
hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
self.is_collecting_in_band_lifetimes = was_collecting_in_band;
(param_name, kind)
}
GenericParamKind::Type { ref default, .. } => {
let add_bounds = add_bounds.get(&param.id).map_or(&[][..], |x| &x);
if !add_bounds.is_empty() {
let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
bounds.extend(params);
}
let kind = hir::GenericParamKind::Type {
default: default.as_ref().map(|x| {
self.lower_ty(
x,
ImplTraitContext::OtherOpaqueTy {
capturable_lifetimes: &mut FxHashSet::default(),
origin: hir::OpaqueTyOrigin::Misc,
},
)
}),
synthetic: param
.attrs
.iter()
.filter(|attr| attr.check_name(sym::rustc_synthetic))
.map(|_| hir::SyntheticTyParamKind::ImplTrait)
.next(),
};
(hir::ParamName::Plain(param.ident), kind)
}
GenericParamKind::Const { ref ty, kw_span: _ } => {
let ty = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
this.lower_ty(&ty, ImplTraitContext::disallowed())
});
(hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty })
}
};
hir::GenericParam {
hir_id: self.lower_node_id(param.id),
name,
span: param.ident.span,
pure_wrt_drop: attr::contains_name(&param.attrs, sym::may_dangle),
attrs: self.lower_attrs(&param.attrs),
bounds: self.arena.alloc_from_iter(bounds),
kind,
}
}
fn lower_trait_ref(
&mut self,
p: &TraitRef,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::TraitRef<'hir> {
let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
hir::QPath::Resolved(None, path) => path,
qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
};
hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
}
fn lower_poly_trait_ref(
&mut self,
p: &PolyTraitRef,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::PolyTraitRef<'hir> {
let bound_generic_params = self.lower_generic_params(
&p.bound_generic_params,
&NodeMap::default(),
itctx.reborrow(),
);
let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
// Any impl Trait types defined within this scope can capture
// lifetimes bound on this predicate.
let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
ParamName::Plain(param.ident.normalize_to_macros_2_0()),
)),
_ => None,
});
if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
capturable_lifetimes.extend(lt_def_names.clone());
}
let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
for param in lt_def_names {
capturable_lifetimes.remove(&param);
}
}
res
});
hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
}
fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
}
fn lower_param_bounds(
&mut self,
bounds: &[GenericBound],
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericBounds<'hir> {
self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
}
fn lower_param_bounds_mut<'s>(
&'s mut self,
bounds: &'s [GenericBound],
mut itctx: ImplTraitContext<'s, 'hir>,
) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
}
fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
}
fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
let mut stmts = vec![];
let mut expr: Option<&'hir _> = None;
for (index, stmt) in b.stmts.iter().enumerate() {
if index == b.stmts.len() - 1 {
if let StmtKind::Expr(ref e) = stmt.kind {
expr = Some(self.lower_expr(e));
} else {
stmts.extend(self.lower_stmt(stmt));
}
} else {
stmts.extend(self.lower_stmt(stmt));
}
}
hir::Block {
hir_id: self.lower_node_id(b.id),
stmts: self.arena.alloc_from_iter(stmts),
expr,
rules: self.lower_block_check_mode(&b.rules),
span: b.span,
targeted_by_break,
}
}
/// Lowers a block directly to an expression, presuming that it
/// has no attributes and is not targeted by a `break`.
fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
let block = self.lower_block(b, false);
self.expr_block(block, AttrVec::new())
}
fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
self.with_new_scopes(|this| hir::AnonConst {
hir_id: this.lower_node_id(c.id),
body: this.lower_const_body(c.value.span, Some(&c.value)),
})
}
fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
let kind = match s.kind {
StmtKind::Local(ref l) => {
let (l, item_ids) = self.lower_local(l);
let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
.into_iter()
.map(|item_id| {
let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
self.stmt(s.span, hir::StmtKind::Item(item_id))
})
.collect();
ids.push({
hir::Stmt {
hir_id: self.lower_node_id(s.id),
kind: hir::StmtKind::Local(self.arena.alloc(l)),
span: s.span,
}
});
return ids;
}
StmtKind::Item(ref it) => {
// Can only use the ID once.
let mut id = Some(s.id);
return self
.lower_item_id(it)
.into_iter()
.map(|item_id| {
let hir_id = id
.take()
.map(|id| self.lower_node_id(id))
.unwrap_or_else(|| self.next_id());
hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
})
.collect();
}
StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
StmtKind::Empty => return smallvec![],
StmtKind::MacCall(..) => panic!("shouldn't exist here"),
};
smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
}
fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
match *b {
BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
BlockCheckMode::Unsafe(u) => {
hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
}
}
}
fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
match u {
CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
UserProvided => hir::UnsafeSource::UserProvided,
}
}
fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
match f {
TraitBoundModifier::None => hir::TraitBoundModifier::None,
TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
// `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
// placeholder for compilation to proceed.
TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
hir::TraitBoundModifier::Maybe
}
}
}
// Helper methods for building HIR.
fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
hir::Stmt { span, kind, hir_id: self.next_id() }
}
fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
}
fn stmt_let_pat(
&mut self,
attrs: AttrVec,
span: