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rust/compiler/rustc_ast_lowering/src/lib.rs
Camille GILLOT 6857a8d14e Create a specific struct for lifetime capture.
2022-04-27 22:03:12 +02:00

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//! 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), 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(crate_visibility_modifier)]
#![feature(box_patterns)]
#![feature(let_chains)]
#![feature(let_else)]
#![feature(never_type)]
#![recursion_limit = "256"]
#![allow(rustc::potential_query_instability)]
use rustc_ast::token::{self, Token};
use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
use rustc_ast::visit;
use rustc_ast::{self as ast, *};
use rustc_ast_pretty::pprust;
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
use rustc_data_structures::sorted_map::SortedMap;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
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, DefPathHash, LocalDefId, CRATE_DEF_ID};
use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
use rustc_index::vec::{Idx, IndexVec};
use rustc_query_system::ich::StableHashingContext;
use rustc_session::parse::feature_err;
use rustc_session::utils::{FlattenNonterminals, NtToTokenstream};
use rustc_session::Session;
use rustc_span::hygiene::{ExpnId, MacroKind};
use rustc_span::source_map::{respan, DesugaringKind};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use smallvec::SmallVec;
use std::collections::hash_map::Entry;
use tracing::{debug, trace};
macro_rules! arena_vec {
($this:expr; $($x:expr),*) => (
$this.arena.alloc_from_iter([$($x),*])
);
}
mod asm;
mod block;
mod expr;
mod index;
mod item;
mod pat;
mod path;
rustc_hir::arena_types!(rustc_arena::declare_arena);
struct LoweringContext<'a, 'hir: 'a> {
/// 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
/// `rustc_middle` is independent of the parser, we use dynamic dispatch here.
nt_to_tokenstream: NtToTokenstream,
/// Used to allocate HIR nodes.
arena: &'hir Arena<'hir>,
/// Bodies inside the owner being lowered.
bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
/// Attributes inside the owner being lowered.
attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
/// Collect items that were created by lowering the current owner.
children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
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_scope: Option<NodeId>,
loop_scope: Option<NodeId>,
is_in_loop_condition: bool,
is_in_trait_impl: bool,
is_in_dyn_type: bool,
/// Used to create lifetime definitions for anonymous lifetimes.
/// When an anonymous lifetime is encountered in a function or impl header and
/// requires to create a fresh lifetime parameter, 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: FxIndexMap<NodeId, Span>,
/// If anonymous lifetimes are being collected, this field holds the parent
/// `LocalDefId` to create the fresh lifetime parameters' `LocalDefId`.
is_collecting_anonymous_lifetimes: Option<LocalDefId>,
/// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
in_scope_lifetimes: Vec<(ParamName, LocalDefId)>,
/// Used to handle lifetimes appearing in impl-traits.
captured_lifetimes: Option<LifetimeCaptureContext>,
current_hir_id_owner: LocalDefId,
item_local_id_counter: hir::ItemLocalId,
local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
/// NodeIds that are lowered inside the current HIR owner.
node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
allow_try_trait: Option<Lrc<[Symbol]>>,
allow_gen_future: Option<Lrc<[Symbol]>>,
allow_into_future: Option<Lrc<[Symbol]>>,
}
/// Resolution for a lifetime appearing in a type.
#[derive(Copy, Clone, Debug)]
pub enum LifetimeRes {
/// Successfully linked the lifetime to a generic parameter.
Param {
/// Id of the generic parameter that introduced it.
param: LocalDefId,
/// Id of the introducing place. That can be:
/// - an item's id, for the item's generic parameters;
/// - a TraitRef's ref_id, identifying the `for<...>` binder;
/// - a BareFn type's id;
/// - a Path's id when this path has parenthesized generic args.
///
/// This information is used for impl-trait lifetime captures, to know when to or not to
/// capture any given lifetime.
binder: NodeId,
},
/// Created a generic parameter for an anonymous lifetime.
Fresh {
/// Id of the generic parameter that introduced it.
param: LocalDefId,
/// Id to create the HirId.
introducer: Option<NodeId>,
/// Id of the introducing place. See `Param`.
binder: NodeId,
},
/// This variant is used for anonymous lifetimes that we did not resolve during
/// late resolution. Shifting the work to the HIR lifetime resolver.
Anonymous {
/// Id of the introducing place. See `Param`.
binder: NodeId,
/// Whether this lifetime was spelled or elided.
elided: bool,
},
/// Explicit `'static` lifetime.
Static,
/// Resolution failure.
Error,
/// HACK: This is used to recover the NodeId of an elided lifetime.
ElidedAnchor { start: NodeId, end: NodeId },
}
/// When we lower a lifetime, it is inserted in `captures`, and the resolution is modified so
/// to point to the lifetime parameter impl-trait will generate.
/// When traversing `for<...>` binders, they are inserted in `binders_to_ignore` so we know *not*
/// to rebind the introduced lifetimes.
#[derive(Debug)]
struct LifetimeCaptureContext {
/// parent def_id for new definitions
parent_def_id: LocalDefId,
/// Set of lifetimes to rebind.
captures: FxHashMap<
LocalDefId, // original parameter id
(
Span, // Span
NodeId, // synthetized parameter id
ParamName, // parameter name
LifetimeRes, // original resolution
),
>,
/// Traversed binders. The ids in this set should *not* be rebound.
binders_to_ignore: FxHashSet<NodeId>,
}
pub trait ResolverAstLowering {
fn def_key(&self, id: DefId) -> DefKey;
fn def_span(&self, id: LocalDefId) -> Span;
fn item_generics_num_lifetimes(&self, def: DefId) -> usize;
fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>>;
/// Obtains resolution for a `NodeId` with a single resolution.
fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
/// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
/// Obtains resolution for a label with the given `NodeId`.
fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
/// Obtains resolution for a lifetime with the given `NodeId`.
fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
fn create_stable_hashing_context(&self) -> StableHashingContext<'_>;
fn definitions(&self) -> &Definitions;
fn next_node_id(&mut self) -> NodeId;
fn take_trait_map(&mut self, node: NodeId) -> Option<Vec<hir::TraitCandidate>>;
fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
fn local_def_id(&self, node: NodeId) -> LocalDefId;
fn def_path_hash(&self, def_id: DefId) -> DefPathHash;
fn create_def(
&mut self,
parent: LocalDefId,
node_id: ast::NodeId,
data: DefPathData,
expn_id: ExpnId,
span: Span,
) -> LocalDefId;
fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
}
/// 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>>, LocalDefId),
/// 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 {
/// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
origin: hir::OpaqueTyOrigin,
},
/// Impl trait in type aliases.
TypeAliasesOpaqueTy,
/// `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 {
Path,
Variable,
Type,
Trait,
AsyncBlock,
Bound,
Generic,
ExternFnParam,
ClosureParam,
PointerParam,
FnTraitParam,
TraitParam,
ImplParam,
ExternFnReturn,
ClosureReturn,
PointerReturn,
FnTraitReturn,
TraitReturn,
ImplReturn,
}
impl<'a> ImplTraitContext<'_, 'a> {
fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
use self::ImplTraitContext::*;
match self {
Universal(params, parent) => Universal(params, *parent),
ReturnPositionOpaqueTy { origin } => ReturnPositionOpaqueTy { origin: *origin },
TypeAliasesOpaqueTy => TypeAliasesOpaqueTy,
Disallowed(pos) => Disallowed(*pos),
}
}
}
impl std::fmt::Display for ImplTraitPosition {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let name = match self {
ImplTraitPosition::Path => "path",
ImplTraitPosition::Variable => "variable binding",
ImplTraitPosition::Type => "type",
ImplTraitPosition::Trait => "trait",
ImplTraitPosition::AsyncBlock => "async block",
ImplTraitPosition::Bound => "bound",
ImplTraitPosition::Generic => "generic",
ImplTraitPosition::ExternFnParam => "`extern fn` param",
ImplTraitPosition::ClosureParam => "closure param",
ImplTraitPosition::PointerParam => "`fn` pointer param",
ImplTraitPosition::FnTraitParam => "`Fn` trait param",
ImplTraitPosition::TraitParam => "trait method param",
ImplTraitPosition::ImplParam => "`impl` method param",
ImplTraitPosition::ExternFnReturn => "`extern fn` return",
ImplTraitPosition::ClosureReturn => "closure return",
ImplTraitPosition::PointerReturn => "`fn` pointer return",
ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
ImplTraitPosition::TraitReturn => "trait method return",
ImplTraitPosition::ImplReturn => "`impl` method return",
};
write!(f, "{}", name)
}
}
#[derive(Debug)]
enum FnDeclKind {
Fn,
Inherent,
ExternFn,
Closure,
Pointer,
Trait,
Impl,
}
impl FnDeclKind {
fn impl_trait_return_allowed(&self) -> bool {
match self {
FnDeclKind::Fn | FnDeclKind::Inherent => true,
_ => false,
}
}
}
#[derive(Copy, Clone)]
enum AstOwner<'a> {
NonOwner,
Crate(&'a ast::Crate),
Item(&'a ast::Item),
AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
ForeignItem(&'a ast::ForeignItem),
}
fn index_crate<'a>(
resolver: &dyn ResolverAstLowering,
krate: &'a Crate,
) -> IndexVec<LocalDefId, AstOwner<'a>> {
let mut indexer = Indexer { resolver, index: IndexVec::new() };
indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
visit::walk_crate(&mut indexer, krate);
return indexer.index;
struct Indexer<'s, 'a> {
resolver: &'s dyn ResolverAstLowering,
index: IndexVec<LocalDefId, AstOwner<'a>>,
}
impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
fn visit_attribute(&mut self, _: &'a Attribute) {
// We do not want to lower expressions that appear in attributes,
// as they are not accessible to the rest of the HIR.
}
fn visit_item(&mut self, item: &'a ast::Item) {
let def_id = self.resolver.local_def_id(item.id);
self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
self.index[def_id] = AstOwner::Item(item);
visit::walk_item(self, item)
}
fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
let def_id = self.resolver.local_def_id(item.id);
self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
self.index[def_id] = AstOwner::AssocItem(item, ctxt);
visit::walk_assoc_item(self, item, ctxt);
}
fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
let def_id = self.resolver.local_def_id(item.id);
self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
self.index[def_id] = AstOwner::ForeignItem(item);
visit::walk_foreign_item(self, item);
}
}
}
/// Compute the hash for the HIR of the full crate.
/// This hash will then be part of the crate_hash which is stored in the metadata.
fn compute_hir_hash(
resolver: &mut dyn ResolverAstLowering,
owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
) -> Fingerprint {
let mut hir_body_nodes: Vec<_> = owners
.iter_enumerated()
.filter_map(|(def_id, info)| {
let info = info.as_owner()?;
let def_path_hash = resolver.definitions().def_path_hash(def_id);
Some((def_path_hash, info))
})
.collect();
hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
let mut stable_hasher = StableHasher::new();
let mut hcx = resolver.create_stable_hashing_context();
hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
stable_hasher.finish()
}
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 hir::Crate<'hir> {
let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
let ast_index = index_crate(resolver, krate);
let mut owners =
IndexVec::from_fn_n(|_| hir::MaybeOwner::Phantom, resolver.definitions().def_index_count());
for def_id in ast_index.indices() {
item::ItemLowerer {
sess,
resolver,
nt_to_tokenstream,
arena,
ast_index: &ast_index,
owners: &mut owners,
}
.lower_node(def_id);
}
let hir_hash = compute_hir_hash(resolver, &owners);
let krate = hir::Crate { owners, hir_hash };
arena.alloc(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,
}
impl<'a, 'hir> LoweringContext<'a, 'hir> {
fn with_hir_id_owner(
&mut self,
owner: NodeId,
f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
) {
let def_id = self.resolver.local_def_id(owner);
let current_attrs = std::mem::take(&mut self.attrs);
let current_bodies = std::mem::take(&mut self.bodies);
let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
let current_trait_map = std::mem::take(&mut self.trait_map);
let current_owner = std::mem::replace(&mut self.current_hir_id_owner, def_id);
let current_local_counter =
std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
// Always allocate the first `HirId` for the owner itself.
let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
debug_assert_eq!(_old, None);
let item = f(self);
debug_assert_eq!(def_id, item.def_id());
let info = self.make_owner_info(item);
self.attrs = current_attrs;
self.bodies = current_bodies;
self.node_id_to_local_id = current_node_ids;
self.local_id_to_def_id = current_id_to_def_id;
self.trait_map = current_trait_map;
self.current_hir_id_owner = current_owner;
self.item_local_id_counter = current_local_counter;
let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
debug_assert!(_old.is_none())
}
fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
let attrs = std::mem::take(&mut self.attrs);
let mut bodies = std::mem::take(&mut self.bodies);
let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
let trait_map = std::mem::take(&mut self.trait_map);
#[cfg(debug_assertions)]
for (id, attrs) in attrs.iter() {
// Verify that we do not store empty slices in the map.
if attrs.is_empty() {
panic!("Stored empty attributes for {:?}", id);
}
}
bodies.sort_by_key(|(k, _)| *k);
let bodies = SortedMap::from_presorted_elements(bodies);
let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
let (nodes, parenting) =
index::index_hir(self.sess, self.resolver.definitions(), node, &bodies);
let nodes = hir::OwnerNodes {
hash_including_bodies,
hash_without_bodies,
nodes,
bodies,
local_id_to_def_id,
};
let attrs = {
let mut hcx = self.resolver.create_stable_hashing_context();
let mut stable_hasher = StableHasher::new();
attrs.hash_stable(&mut hcx, &mut stable_hasher);
let hash = stable_hasher.finish();
hir::AttributeMap { map: attrs, hash }
};
self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
}
/// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
/// queries which depend on the full HIR tree and those which only depend on the item signature.
fn hash_owner(
&mut self,
node: hir::OwnerNode<'hir>,
bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
) -> (Fingerprint, Fingerprint) {
let mut hcx = self.resolver.create_stable_hashing_context();
let mut stable_hasher = StableHasher::new();
hcx.with_hir_bodies(true, node.def_id(), bodies, |hcx| {
node.hash_stable(hcx, &mut stable_hasher)
});
let hash_including_bodies = stable_hasher.finish();
let mut stable_hasher = StableHasher::new();
hcx.with_hir_bodies(false, node.def_id(), bodies, |hcx| {
node.hash_stable(hcx, &mut stable_hasher)
});
let hash_without_bodies = stable_hasher.finish();
(hash_including_bodies, hash_without_bodies)
}
/// 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 {
assert_ne!(ast_node_id, DUMMY_NODE_ID);
match self.node_id_to_local_id.entry(ast_node_id) {
Entry::Occupied(o) => {
hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
}
Entry::Vacant(v) => {
// Generate a new `HirId`.
let owner = self.current_hir_id_owner;
let local_id = self.item_local_id_counter;
let hir_id = hir::HirId { owner, local_id };
v.insert(local_id);
self.item_local_id_counter.increment_by(1);
assert_ne!(local_id, hir::ItemLocalId::new(0));
if let Some(def_id) = self.resolver.opt_local_def_id(ast_node_id) {
// Do not override a `MaybeOwner::Owner` that may already here.
self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
self.local_id_to_def_id.insert(local_id, def_id);
}
if let Some(traits) = self.resolver.take_trait_map(ast_node_id) {
self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
}
hir_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 {
let res: Result<Res, ()> = res.apply_id(|id| {
let owner = self.current_hir_id_owner;
let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
Ok(hir::HirId { owner, local_id })
});
// We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
// This can happen when trying to lower the return type `x` in erroneous code like
// async fn foo(x: u8) -> x {}
// In that case, `x` is lowered as a function parameter, and the return type is lowered as
// an opaque type as a synthesized HIR owner.
res.unwrap_or(Res::Err)
}
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.mark_with_reason(
allow_internal_unstable,
reason,
self.sess.edition(),
self.resolver.create_stable_hashing_context(),
)
}
/// Intercept all spans entering HIR.
/// Mark a span as relative to the current owning item.
fn lower_span(&self, span: Span) -> Span {
if self.sess.opts.debugging_opts.incremental_relative_spans {
span.with_parent(Some(self.current_hir_id_owner))
} else {
// Do not make spans relative when not using incremental compilation.
span
}
}
fn lower_ident(&self, ident: Ident) -> Ident {
Ident::new(ident.name, self.lower_span(ident.span))
}
/// 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.
fn collect_in_band_defs<T>(
&mut self,
parent_def_id: LocalDefId,
f: impl FnOnce(&mut Self) -> T,
) -> (FxIndexMap<NodeId, Span>, T) {
let lifetime_stash = std::mem::take(&mut self.lifetimes_to_define);
let was_collecting =
std::mem::replace(&mut self.is_collecting_anonymous_lifetimes, Some(parent_def_id));
let res = f(self);
self.is_collecting_anonymous_lifetimes = was_collecting;
let lifetimes_to_define = std::mem::replace(&mut self.lifetimes_to_define, lifetime_stash);
(lifetimes_to_define, res)
}
/// Converts a lifetime into a new generic parameter.
fn fresh_lifetime_to_generic_param(
&mut self,
span: Span,
node_id: NodeId,
) -> hir::GenericParam<'hir> {
let hir_id = self.lower_node_id(node_id);
let def_id = self.resolver.local_def_id(node_id);
hir::GenericParam {
hir_id,
name: hir::ParamName::Fresh(def_id),
bounds: &[],
span: self.lower_span(span),
pure_wrt_drop: false,
kind: hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Elided },
}
}
/// 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 { .. } => {
let def_id = self.resolver.local_def_id(param.id);
let name = ParamName::Plain(param.ident);
Some((name, def_id))
}
_ => 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.
fn add_in_band_defs<T>(
&mut self,
generics: &Generics,
parent_def_id: LocalDefId,
f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
) -> (hir::Generics<'hir>, T) {
let (lifetimes_to_define, (mut lowered_generics, impl_trait_defs, res)) = self
.collect_in_band_defs(parent_def_id, |this| {
this.with_in_scope_lifetime_defs(&generics.params, |this| {
let mut impl_trait_defs = 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 impl_trait_defs,
this.current_hir_id_owner,
),
);
let res = f(this, &mut impl_trait_defs);
(generics, impl_trait_defs, res)
})
});
lowered_generics.params.extend(
lifetimes_to_define
.into_iter()
.map(|(node_id, span)| self.fresh_lifetime_to_generic_param(span, node_id))
.chain(impl_trait_defs),
);
let lowered_generics = lowered_generics.into_generics(self.arena);
(lowered_generics, res)
}
/// Setup lifetime capture for and impl-trait.
/// The captures will be added to `captures`.
fn while_capturing_lifetimes<T>(
&mut self,
parent_def_id: LocalDefId,
captures: &mut FxHashMap<LocalDefId, (Span, NodeId, ParamName, LifetimeRes)>,
f: impl FnOnce(&mut Self) -> T,
) -> T {
let lifetime_stash = std::mem::replace(
&mut self.captured_lifetimes,
Some(LifetimeCaptureContext {
parent_def_id,
captures: std::mem::take(captures),
binders_to_ignore: Default::default(),
}),
);
let ret = f(self);
let ctxt = std::mem::replace(&mut self.captured_lifetimes, lifetime_stash).unwrap();
*captures = ctxt.captures;
ret
}
/// Register a binder to be ignored for lifetime capture.
#[tracing::instrument(level = "debug", skip(self, f))]
#[inline]
fn with_lifetime_binder<T>(&mut self, binder: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
if let Some(ctxt) = &mut self.captured_lifetimes {
ctxt.binders_to_ignore.insert(binder);
}
let ret = f(self);
if let Some(ctxt) = &mut self.captured_lifetimes {
ctxt.binders_to_ignore.remove(&binder);
}
ret
}
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_scope = self.catch_scope.take();
let loop_scope = self.loop_scope.take();
let ret = f(self);
self.catch_scope = catch_scope;
self.loop_scope = loop_scope;
self.is_in_loop_condition = was_in_loop_condition;
ret
}
fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
if attrs.is_empty() {
None
} else {
debug_assert_eq!(id.owner, self.current_hir_id_owner);
let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
debug_assert!(!ret.is_empty());
self.attrs.insert(id.local_id, ret);
Some(ret)
}
}
fn lower_attr(&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.
// Tokens are also not needed after macro expansion and parsing.
let kind = match attr.kind {
AttrKind::Normal(ref item, _) => AttrKind::Normal(
AttrItem {
path: item.path.clone(),
args: self.lower_mac_args(&item.args),
tokens: None,
},
None,
),
AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
};
Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
}
fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
debug_assert_eq!(id.owner, self.current_hir_id_owner);
debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
if let Some(&a) = self.attrs.get(&target_id.local_id) {
debug_assert!(!a.is_empty());
self.attrs.insert(id.local_id, a);
}
}
fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
match *args {
MacArgs::Empty => MacArgs::Empty,
MacArgs::Delimited(dspan, delim, ref tokens) => {
// This is either a non-key-value attribute, or a `macro_rules!` body.
// We either not have any nonterminals present (in the case of an attribute),
// or have tokens available for all nonterminals in the case of a nested
// `macro_rules`: e.g:
//
// ```rust
// macro_rules! outer {
// ($e:expr) => {
// macro_rules! inner {
// () => { $e }
// }
// }
// }
// ```
//
// In both cases, we don't want to synthesize any tokens
MacArgs::Delimited(
dspan,
delim,
self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
)
}
// This is an inert key-value attribute - it will never be visible to macros
// after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
// spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
MacArgs::Eq(eq_span, ref token) => {
// In valid code the value is always representable as a single literal token.
fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
if tokens.len() != 1 {
sess.diagnostic()
.delay_span_bug(span, "multiple tokens in key-value attribute's value");
}
match tokens.into_trees().next() {
Some(TokenTree::Token(token)) => token,
Some(TokenTree::Delimited(_, delim, tokens)) => {
if delim != token::NoDelim {
sess.diagnostic().delay_span_bug(
span,
"unexpected delimiter in key-value attribute's value",
);
}
unwrap_single_token(sess, tokens, span)
}
None => Token::dummy(),
}
}
let tokens = FlattenNonterminals {
parse_sess: &self.sess.parse_sess,
synthesize_tokens: CanSynthesizeMissingTokens::Yes,
nt_to_tokenstream: self.nt_to_tokenstream,
}
.process_token(token.clone());
MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
}
}
}
fn lower_token_stream(
&self,
tokens: TokenStream,
synthesize_tokens: CanSynthesizeMissingTokens,
) -> TokenStream {
FlattenNonterminals {
parse_sess: &self.sess.parse_sess,
synthesize_tokens,
nt_to_tokenstream: self.nt_to_tokenstream,
}
.process_token_stream(tokens)
}
/// 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: &AssocConstraint,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::TypeBinding<'hir> {
debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
// lower generic arguments of identifier in constraint
let gen_args = if let Some(ref gen_args) = constraint.gen_args {
let gen_args_ctor = match gen_args {
GenericArgs::AngleBracketed(ref data) => {
self.lower_angle_bracketed_parameter_data(
data,
ParamMode::Explicit,
itctx.reborrow(),
)
.0
}
GenericArgs::Parenthesized(ref data) => {
let mut err = self.sess.struct_span_err(
gen_args.span(),
"parenthesized generic arguments cannot be used in associated type constraints"
);
// FIXME: try to write a suggestion here
err.emit();
self.lower_angle_bracketed_parameter_data(
&data.as_angle_bracketed_args(),
ParamMode::Explicit,
itctx.reborrow(),
)
.0
}
};
gen_args_ctor.into_generic_args(self)
} else {
self.arena.alloc(hir::GenericArgs::none())
};
let kind = match constraint.kind {
AssocConstraintKind::Equality { ref term } => {
let term = match term {
Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
Term::Const(ref c) => self.lower_anon_const(c).into(),
};
hir::TypeBindingKind::Equality { term }
}
AssocConstraintKind::Bound { ref bounds } => {
let mut parent_def_id = self.current_hir_id_owner;
// 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::TypeAliasesOpaqueTy { .. } => (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(_, parent) if self.is_in_dyn_type => {
parent_def_id = parent;
(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 => {
(true, ImplTraitContext::TypeAliasesOpaqueTy)
}
// 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();
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: this.lower_span(constraint.span),
tokens: None,
},
itctx,
);
hir::TypeBindingKind::Equality { term: ty.into() }
})
} 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: self.lower_ident(constraint.ident),
gen_args,
kind,
span: self.lower_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) => {
match ty.kind {
TyKind::Infer if self.sess.features_untracked().generic_arg_infer => {
return GenericArg::Infer(hir::InferArg {
hir_id: self.lower_node_id(ty.id),
span: self.lower_span(ty.span),
});
}
// 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.
TyKind::Path(ref qself, ref path) => {
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 an AnonConst where the expr is the "ty"'s path.
let parent_def_id = self.current_hir_id_owner;
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 span = self.lower_span(ty.span);
let path_expr = Expr {
id: ty.id,
kind: ExprKind::Path(qself.clone(), path.clone()),
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 });
}
}
}
_ => {}
}
GenericArg::Type(self.lower_ty_direct(&ty, itctx))
}
ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
value: self.lower_anon_const(&ct),
span: self.lower_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);
self.ty_path(id, t.span, qpath)
}
fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(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 region = region.unwrap_or_else(|| {
let Some(LifetimeRes::ElidedAnchor { start, end }) = self.resolver.get_lifetime_res(t.id) else {
panic!()
};
debug_assert_eq!(start.plus(1), end);
let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
Lifetime {
ident: Ident::new(kw::UnderscoreLifetime, span),
id: start,
}
});
let lifetime = self.lower_lifetime(&region);
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_lifetime_binder(t.id, |this| {
hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
generic_params: this.lower_generic_params(
&f.generic_params,
ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
),
unsafety: this.lower_unsafety(f.unsafety),
abi: this.lower_extern(f.ext),
decl: this.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, 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: self.lower_span(t.span),
}),
))
}
TyKind::Array(ref ty, ref length) => {
hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(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)
});
hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
}
TyKind::ImplTrait(def_node_id, ref bounds) => {
let span = t.span;
match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { origin } => self
.lower_opaque_impl_trait(span, origin, def_node_id, |this| {
this.lower_param_bounds(bounds, itctx)
}),
ImplTraitContext::TypeAliasesOpaqueTy => {
let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
self.lower_opaque_impl_trait(
span,
hir::OpaqueTyOrigin::TyAlias,
def_node_id,
|this| this.lower_param_bounds(bounds, nested_itctx),
)
}
ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
// 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, parent_def_id),
);
// 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(self.lower_ident(ident)),
pure_wrt_drop: false,
bounds: hir_bounds,
span: self.lower_span(span),
kind: hir::GenericParamKind::Type { default: None, synthetic: true },
});
hir::TyKind::Path(hir::QPath::Resolved(
None,
self.arena.alloc(hir::Path {
span: self.lower_span(span),
res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
}),
))
}
ImplTraitContext::Disallowed(position) => {
let mut err = struct_span_err!(
self.sess,
t.span,
E0562,
"`impl Trait` only allowed in function and inherent method return types, not in {}",
position
);
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: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
}
#[tracing::instrument(level = "debug", skip(self, lower_bounds))]
fn lower_opaque_impl_trait(
&mut self,
span: Span,
origin: hir::OpaqueTyOrigin,
opaque_ty_node_id: NodeId,
lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
) -> hir::TyKind<'hir> {
// 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);
let mut collected_lifetimes = FxHashMap::default();
self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
let hir_bounds = if origin == hir::OpaqueTyOrigin::TyAlias {
lower_bounds(lctx)
} else {
lctx.while_capturing_lifetimes(
opaque_ty_def_id,
&mut collected_lifetimes,
lower_bounds,
)
};
debug!(?collected_lifetimes);
let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
|(_, &(span, p_id, p_name, _))| {
let hir_id = lctx.lower_node_id(p_id);
debug_assert_ne!(lctx.resolver.opt_local_def_id(p_id), None);
let kind = if p_name.ident().name == kw::UnderscoreLifetime {
hir::LifetimeParamKind::Elided
} else {
hir::LifetimeParamKind::Explicit
};
hir::GenericParam {
hir_id,
name: p_name,
span,
pure_wrt_drop: false,
bounds: &[],
kind: hir::GenericParamKind::Lifetime { kind },
}
},
));
debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
let opaque_ty_item = hir::OpaqueTy {
generics: hir::Generics {
params: lifetime_defs,
where_clause: hir::WhereClause { predicates: &[], span: lctx.lower_span(span) },
span: lctx.lower_span(span),
},
bounds: hir_bounds,
origin,
};
trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
});
let lifetimes = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
|(_, (span, _, p_name, res))| {
let id = self.resolver.next_node_id();
let ident = Ident::new(p_name.ident().name, span);
let l = self.new_named_lifetime_with_res(id, span, ident, res);
hir::GenericArg::Lifetime(l)
},
));
debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
// `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_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_id: LocalDefId,
opaque_ty_item: hir::OpaqueTy<'hir>,
span: Span,
opaque_ty_span: Span,
) -> hir::OwnerNode<'hir> {
let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
// Generate an `type Foo = impl Trait;` declaration.
trace!("registering opaque type with id {:#?}", opaque_ty_id);
let opaque_ty_item = hir::Item {
def_id: opaque_ty_id,
ident: Ident::empty(),
kind: opaque_ty_item_kind,
vis: respan(self.lower_span(span.shrink_to_lo()), hir::VisibilityKind::Inherited),
span: self.lower_span(opaque_ty_span),
};
hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
}
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, _) => self.lower_ident(ident),
_ => Ident::new(kw::Empty, self.lower_span(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<(NodeId, &mut Vec<hir::GenericParam<'hir>>)>,
kind: FnDeclKind,
make_ret_async: Option<NodeId>,
) -> &'hir hir::FnDecl<'hir> {
debug!(
"lower_fn_decl(\
fn_decl: {:?}, \
in_band_ty_params: {:?}, \
kind: {:?}, \
make_ret_async: {:?})",
decl, in_band_ty_params, kind, make_ret_async,
);
let c_variadic = decl.c_variadic();
// 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];
}
let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
if let Some((_, ibty)) = &mut in_band_ty_params {
self.lower_ty_direct(
&param.ty,
ImplTraitContext::Universal(ibty, self.current_hir_id_owner),
)
} else {
self.lower_ty_direct(
&param.ty,
ImplTraitContext::Disallowed(match kind {
FnDeclKind::Fn | FnDeclKind::Inherent => {
unreachable!("fn should allow in-band lifetimes")
}
FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
FnDeclKind::Trait => ImplTraitPosition::TraitParam,
FnDeclKind::Impl => ImplTraitPosition::ImplParam,
}),
)
}
}));
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((node_id, _)) if kind.impl_trait_return_allowed() => {
let fn_def_id = self.resolver.local_def_id(node_id);
ImplTraitContext::ReturnPositionOpaqueTy {
origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
}
}
_ => ImplTraitContext::Disallowed(match kind {
FnDeclKind::Fn | FnDeclKind::Inherent => {
unreachable!("fn should allow in-band lifetimes")
}
FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
}),
};
hir::FnRetTy::Return(self.lower_ty(ty, context))
}
FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
}
};
self.arena.alloc(hir::FnDecl {
inputs,
output,
c_variadic,
implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
use BindingMode::{ByRef, ByValue};
let is_mutable_pat = matches!(
arg.pat.kind,
PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
);
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
#[tracing::instrument(level = "debug", skip(self))]
fn lower_async_fn_ret_ty(
&mut self,
output: &FnRetTy,
fn_node_id: NodeId,
opaque_ty_node_id: NodeId,
) -> hir::FnRetTy<'hir> {
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);
let fn_def_id = self.resolver.local_def_id(fn_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.
debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", self.in_scope_lifetimes);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", self.lifetimes_to_define);
// 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.
//
// Input lifetime like `'a`:
let mut captures = FxHashMap::default();
for &(p_name, def_id) in &self.in_scope_lifetimes {
let Ident { name, span } = p_name.ident();
let node_id = self.resolver.next_node_id();
// Add a definition for the in-band lifetime def.
self.resolver.create_def(
opaque_ty_def_id,
node_id,
DefPathData::LifetimeNs(name),
ExpnId::root(),
span.with_parent(None),
);
let res = match p_name {
hir::ParamName::Plain(_) => {
LifetimeRes::Param { param: def_id, binder: fn_node_id }
}
hir::ParamName::Fresh(_) => {
LifetimeRes::Fresh { param: def_id, introducer: None, binder: fn_node_id }
}
hir::ParamName::Error => LifetimeRes::Error,
};
captures.insert(def_id, (span, node_id, p_name, res));
}
// Input lifetime like `'1`:
for (&node_id, &span) in &self.lifetimes_to_define {
let def_id = self.resolver.local_def_id(node_id);
let new_node_id = self.resolver.next_node_id();
// Add a definition for the in-band lifetime def.
let new_def_id = self.resolver.create_def(
opaque_ty_def_id,
new_node_id,
DefPathData::LifetimeNs(kw::UnderscoreLifetime),
ExpnId::root(),
span.with_parent(None),
);
captures.insert(
def_id,
(
span,
new_node_id,
hir::ParamName::Fresh(new_def_id),
LifetimeRes::Fresh { param: def_id, introducer: None, binder: fn_node_id },
),
);
}
debug!(?captures);
self.with_hir_id_owner(opaque_ty_node_id, |this| {
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
let future_bound =
this.while_capturing_lifetimes(opaque_ty_def_id, &mut captures, |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.
this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
});
debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
debug!("lower_async_fn_ret_ty: captures={:#?}", captures);
let generic_params =
this.arena.alloc_from_iter(captures.iter().map(|(_, &(span, p_id, p_name, _))| {
let hir_id = this.lower_node_id(p_id);
debug_assert_ne!(this.resolver.opt_local_def_id(p_id), None);
let kind = if p_name.ident().name == kw::UnderscoreLifetime {
hir::LifetimeParamKind::Elided
} else {
hir::LifetimeParamKind::Explicit
};
hir::GenericParam {
hir_id,
name: p_name,
span,
pure_wrt_drop: false,
bounds: &[],
kind: hir::GenericParamKind::Lifetime { kind },
}
}));
debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
let opaque_ty_item = hir::OpaqueTy {
generics: hir::Generics {
params: generic_params,
where_clause: hir::WhereClause { predicates: &[], span: this.lower_span(span) },
span: this.lower_span(span),
},
bounds: arena_vec![this; future_bound],
origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
};
trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
});
// As documented above, 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 generic_args =
self.arena.alloc_from_iter(captures.into_iter().map(|(_, (span, _, p_name, res))| {
let id = self.resolver.next_node_id();
let ident = Ident::new(p_name.ident().name, span);
let l = self.new_named_lifetime_with_res(id, span, ident, res);
hir::GenericArg::Lifetime(l)
}));
// 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 { def_id: opaque_ty_def_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: LocalDefId,
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 {
origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
};
self.lower_ty(ty, context)
}
FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
};
// "<Output = T>"
let future_args = self.arena.alloc(hir::GenericArgs {
args: &[],
bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
parenthesized: false,
span_ext: DUMMY_SP,
});
hir::GenericBound::LangItemTrait(
// ::std::future::Future<future_params>
hir::LangItem::Future,
self.lower_span(span),
self.next_id(),
future_args,
)
}
fn lower_param_bound(
&mut self,
tpb: &GenericBound,
itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericBound<'hir> {
match tpb {
GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
self.lower_poly_trait_ref(p, itctx),
self.lower_trait_bound_modifier(*modifier),
),
GenericBound::Outlives(lifetime) => {
hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
}
}
}
fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
let span = self.lower_span(l.ident.span);
let ident = self.lower_ident(l.ident);
let res = self
.resolver
.get_lifetime_res(l.id)
.unwrap_or_else(|| panic!("Missing resolution for lifetime {:?} at {:?}", l, span));
self.new_named_lifetime_with_res(l.id, span, ident, res)
}
#[tracing::instrument(level = "debug", skip(self))]
fn new_named_lifetime_with_res(
&mut self,
id: NodeId,
span: Span,
ident: Ident,
res: LifetimeRes,
) -> hir::Lifetime {
debug!(?self.captured_lifetimes);
let name = match res {
LifetimeRes::Param { param, binder } => {
debug_assert_ne!(ident.name, kw::UnderscoreLifetime);
let p_name = ParamName::Plain(ident);
if let Some(LifetimeCaptureContext { parent_def_id, captures, binders_to_ignore }) =
&mut self.captured_lifetimes
&& !binders_to_ignore.contains(&binder)
{
match captures.entry(param) {
Entry::Occupied(_) => {}
Entry::Vacant(v) => {
let p_id = self.resolver.next_node_id();
self.resolver.create_def(
*parent_def_id,
p_id,
DefPathData::LifetimeNs(p_name.ident().name),
ExpnId::root(),
span.with_parent(None),
);
v.insert((span, p_id, p_name, res));
}
}
}
hir::LifetimeName::Param(p_name)
}
LifetimeRes::Fresh { mut param, introducer, binder } => {
debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
// Only items are allowed to introduce fresh lifetimes,
// so we know `binder` has a `LocalDefId`.
let binder_def_id = self.resolver.local_def_id(binder);
if let Some(LifetimeCaptureContext { parent_def_id, captures, binders_to_ignore }) =
&mut self.captured_lifetimes
&& !binders_to_ignore.contains(&binder)
{
match captures.entry(param) {
Entry::Occupied(o) => param = self.resolver.local_def_id(o.get().1),
Entry::Vacant(v) => {
let p_id = self.resolver.next_node_id();
let p_def_id = self.resolver.create_def(
*parent_def_id,
p_id,
DefPathData::LifetimeNs(kw::UnderscoreLifetime),
ExpnId::root(),
span.with_parent(None),
);
let p_name = ParamName::Fresh(param);
v.insert((span, p_id, p_name, res));
param = p_def_id;
}
}
} else if let Some(introducer) = introducer {
if self.is_collecting_anonymous_lifetimes == Some(binder_def_id)
&& self.resolver.opt_local_def_id(introducer) == Some(param)
{
debug!(
"lifetime_to_define += id={:?} span={:?} res={:?}",
introducer, span, res
);
self.lifetimes_to_define.insert(introducer, span);
}
}
let p_name = ParamName::Fresh(param);
hir::LifetimeName::Param(p_name)
}
LifetimeRes::Anonymous { binder, elided } => {
let l_name = if elided {
hir::LifetimeName::Implicit
} else {
hir::LifetimeName::Underscore
};
if let Some(LifetimeCaptureContext { parent_def_id, captures, binders_to_ignore }) =
&mut self.captured_lifetimes
&& !binders_to_ignore.contains(&binder)
{
let p_id = self.resolver.next_node_id();
let p_def_id = self.resolver.create_def(
*parent_def_id,
p_id,
DefPathData::LifetimeNs(kw::UnderscoreLifetime),
ExpnId::root(),
span.with_parent(None),
);
let p_name = ParamName::Fresh(p_def_id);
captures.insert(p_def_id, (span, p_id, p_name, res));
hir::LifetimeName::Param(p_name)
} else {
l_name
}
}
LifetimeRes::Static => hir::LifetimeName::Static,
LifetimeRes::Error => hir::LifetimeName::Error,
res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
};
debug!(?self.captured_lifetimes);
hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
}
fn lower_generic_params_mut<'s>(
&'s mut self,
params: &'s [GenericParam],
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, itctx.reborrow()))
}
fn lower_generic_params(
&mut self,
params: &[GenericParam],
itctx: ImplTraitContext<'_, 'hir>,
) -> &'hir [hir::GenericParam<'hir>] {
self.arena.alloc_from_iter(self.lower_generic_params_mut(params, itctx))
}
fn lower_generic_param(
&mut self,
param: &GenericParam,
mut itctx: ImplTraitContext<'_, 'hir>,
) -> hir::GenericParam<'hir> {
let bounds: Vec<_> = self.lower_param_bounds_mut(&param.bounds, itctx.reborrow()).collect();
let (name, kind) = match param.kind {
GenericParamKind::Lifetime => {
let param_name = if param.ident.name == kw::StaticLifetime
|| param.ident.name == kw::UnderscoreLifetime
{
ParamName::Error
} else {
let ident = self.lower_ident(param.ident);
ParamName::Plain(ident)
};
let kind =
hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
(param_name, kind)
}
GenericParamKind::Type { ref default, .. } => {
let kind = hir::GenericParamKind::Type {
default: default.as_ref().map(|x| {
self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Type))
}),
synthetic: false,
};
(hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
}
GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
let ty = self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type));
let default = default.as_ref().map(|def| self.lower_anon_const(def));
(
hir::ParamName::Plain(self.lower_ident(param.ident)),
hir::GenericParamKind::Const { ty, default },
)
}
};
let name = match name {
hir::ParamName::Plain(ident) => hir::ParamName::Plain(self.lower_ident(ident)),
name => name,
};
let hir_id = self.lower_node_id(param.id);
self.lower_attrs(hir_id, &param.attrs);
hir::GenericParam {
hir_id,
name,
span: self.lower_span(param.span()),
pure_wrt_drop: self.sess.contains_name(&param.attrs, sym::may_dangle),
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) }
}
#[tracing::instrument(level = "debug", skip(self))]
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, itctx.reborrow());
let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
this.with_lifetime_binder(p.trait_ref.ref_id, |this| {
this.lower_trait_ref(&p.trait_ref, itctx.reborrow())
})
});
hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_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()))
}
/// 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_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
match c.value.kind {
ExprKind::Underscore => {
if self.sess.features_untracked().generic_arg_infer {
hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
} else {
feature_err(
&self.sess.parse_sess,
sym::generic_arg_infer,
c.value.span,
"using `_` for array lengths is unstable",
)
.emit();
hir::ArrayLen::Body(self.lower_anon_const(c))
}
}
_ => hir::ArrayLen::Body(self.lower_anon_const(c)),
}
}
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_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: self.lower_span(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: Option<&'hir [Attribute]>,
span: Span,
init: Option<&'hir hir::Expr<'hir>>,
pat: &'hir hir::Pat<'hir>,
source: hir::LocalSource,
) -> hir::Stmt<'hir> {
let hir_id = self.next_id();
if let Some(a) = attrs {
debug_assert!(!a.is_empty());
self.attrs.insert(hir_id.local_id, a);
}
let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
}
fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
self.block_all(expr.span, &[], Some(expr))
}
fn block_all(
&mut self,
span: Span,
stmts: &'hir [hir::Stmt<'hir>],
expr: Option<&'hir hir::Expr<'hir>>,
) -> &'hir hir::Block<'hir> {
let blk = hir::Block {
stmts,
expr,
hir_id: self.next_id(),
rules: hir::BlockCheckMode::DefaultBlock,
span: self.lower_span(span),
targeted_by_break: false,
};
self.arena.alloc(blk)
}
fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
let field = self.single_pat_field(span, pat);
self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
}
fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
let field = self.single_pat_field(span, pat);
self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
}
fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
let field = self.single_pat_field(span, pat);
self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
}
fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
}
fn single_pat_field(
&mut self,
span: Span,
pat: &'hir hir::Pat<'hir>,
) -> &'hir [hir::PatField<'hir>] {
let field = hir::PatField {
hir_id: self.next_id(),
ident: Ident::new(sym::integer(0), self.lower_span(span)),
is_shorthand: false,
pat,
span: self.lower_span(span),
};
arena_vec![self; field]
}
fn pat_lang_item_variant(
&mut self,
span: Span,
lang_item: hir::LangItem,
fields: &'hir [hir::PatField<'hir>],
hir_id: Option<hir::HirId>,
) -> &'hir hir::Pat<'hir> {
let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
self.pat(span, hir::PatKind::Struct(qpath, fields, false))
}
fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
}
fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::Unannotated)
}
fn pat_ident_binding_mode(
&mut self,
span: Span,
ident: Ident,
bm: hir::BindingAnnotation,
) -> (&'hir hir::Pat<'hir>, hir::HirId) {
let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
(self.arena.alloc(pat), hir_id)
}
fn pat_ident_binding_mode_mut(
&mut self,
span: Span,
ident: Ident,
bm: hir::BindingAnnotation,
) -> (hir::Pat<'hir>, hir::HirId) {
let hir_id = self.next_id();
(
hir::Pat {
hir_id,
kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
span: self.lower_span(span),
default_binding_modes: true,
},
hir_id,
)
}
fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
self.arena.alloc(hir::Pat {
hir_id: self.next_id(),
kind,
span: self.lower_span(span),
default_binding_modes: true,
})
}
fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
hir::Pat {
hir_id: self.next_id(),
kind,
span: self.lower_span(span),
default_binding_modes: false,
}
}
fn ty_path(
&mut self,
mut hir_id: hir::HirId,
span: Span,
qpath: hir::QPath<'hir>,
) -> hir::Ty<'hir> {
let kind = match qpath {
hir::QPath::Resolved(None, path) => {
// Turn trait object paths into `TyKind::TraitObject` instead.
match path.res {
Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
let principal = hir::PolyTraitRef {
bound_generic_params: &[],
trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
span: self.lower_span(span),
};
// The original ID is taken by the `PolyTraitRef`,
// so the `Ty` itself needs a different one.
hir_id = self.next_id();
hir::TyKind::TraitObject(
arena_vec![self; principal],
self.elided_dyn_bound(span),
TraitObjectSyntax::None,
)
}
_ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
}
}
_ => hir::TyKind::Path(qpath),
};
hir::Ty { hir_id, kind, span: self.lower_span(span) }
}
/// Invoked to create the lifetime argument(s) for an elided trait object
/// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
/// when the bound is written, even if it is written with `'_` like in
/// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
let r = hir::Lifetime {
hir_id: self.next_id(),
span: self.lower_span(span),
name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
};
debug!("elided_dyn_bound: r={:?}", r);
r
}
}
/// Helper struct for delayed construction of GenericArgs.
struct GenericArgsCtor<'hir> {
args: SmallVec<[hir::GenericArg<'hir>; 4]>,
bindings: &'hir [hir::TypeBinding<'hir>],
parenthesized: bool,
span: Span,
}
impl<'hir> GenericArgsCtor<'hir> {
fn is_empty(&self) -> bool {
self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
}
fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
let ga = hir::GenericArgs {
args: this.arena.alloc_from_iter(self.args),
bindings: self.bindings,
parenthesized: self.parenthesized,
span_ext: this.lower_span(self.span),
};
this.arena.alloc(ga)
}
}
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