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hir: introduce QPath::LangItem
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This commit introduces `QPath::LangItem` to the HIR and uses it in AST
lowering instead of constructing a `hir::Path` from a slice of symbols.

This might be better for performance, but is also much cleaner as the
previous approach is fragile. In addition, it resolves a bug (#61019)
where an extern crate imported as "std" would result in the paths
created during AST lowering being resolved incorrectly (or not at all).

Co-authored-by: Matthew Jasper <mjjasper1@gmail.com>
Signed-off-by: David Wood <david@davidtw.co>
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@davidtwco @matthewjasper
davidtwco and matthewjasper committed Aug 16, 2020
1 parent 7dee5f8 commit 762137e
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Showing 21 changed files with 289 additions and 314 deletions.
161 changes: 60 additions & 101 deletions src/librustc_ast_lowering/expr.rs
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Expand Up @@ -449,7 +449,7 @@ impl<'hir> LoweringContext<'_, 'hir> {

// `::std::ops::Try::from_ok($tail_expr)`
block.expr = Some(this.wrap_in_try_constructor(
sym::from_ok,
hir::LangItem::TryFromOk,
try_span,
tail_expr,
ok_wrapped_span,
Expand All @@ -461,14 +461,13 @@ impl<'hir> LoweringContext<'_, 'hir> {

fn wrap_in_try_constructor(
&mut self,
method: Symbol,
lang_item: hir::LangItem,
method_span: Span,
expr: &'hir hir::Expr<'hir>,
overall_span: Span,
) -> &'hir hir::Expr<'hir> {
let path = &[sym::ops, sym::Try, method];
let constructor =
self.arena.alloc(self.expr_std_path(method_span, path, None, ThinVec::new()));
self.arena.alloc(self.expr_lang_item_path(method_span, lang_item, ThinVec::new()));
self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
}

Expand Down Expand Up @@ -558,12 +557,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
// `future::from_generator`:
let unstable_span =
self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
let gen_future = self.expr_std_path(
unstable_span,
&[sym::future, sym::from_generator],
None,
ThinVec::new(),
);
let gen_future =
self.expr_lang_item_path(unstable_span, hir::LangItem::FromGenerator, ThinVec::new());

// `future::from_generator(generator)`:
hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
Expand Down Expand Up @@ -630,23 +625,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
// Use of `await` outside of an async context, we cannot use `task_context` here.
self.expr_err(span)
};
let pin_ty_id = self.next_id();
let new_unchecked_expr_kind = self.expr_call_std_assoc_fn(
pin_ty_id,
let new_unchecked = self.expr_call_lang_item_fn_mut(
span,
&[sym::pin, sym::Pin],
"new_unchecked",
hir::LangItem::PinNewUnchecked,
arena_vec![self; ref_mut_pinned],
);
let new_unchecked = self.expr(span, new_unchecked_expr_kind, ThinVec::new());
let get_context = self.expr_call_std_path_mut(
let get_context = self.expr_call_lang_item_fn_mut(
gen_future_span,
&[sym::future, sym::get_context],
hir::LangItem::GetContext,
arena_vec![self; task_context],
);
let call = self.expr_call_std_path(
let call = self.expr_call_lang_item_fn(
span,
&[sym::future, sym::Future, sym::poll],
hir::LangItem::FuturePoll,
arena_vec![self; new_unchecked, get_context],
);
self.arena.alloc(self.expr_unsafe(call))
Expand All @@ -659,11 +650,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
let x_ident = Ident::with_dummy_span(sym::result);
let (x_pat, x_pat_hid) = self.pat_ident(span, x_ident);
let x_expr = self.expr_ident(span, x_ident, x_pat_hid);
let ready_pat = self.pat_std_enum(
span,
&[sym::task, sym::Poll, sym::Ready],
arena_vec![self; x_pat],
);
let ready_field = self.single_pat_field(span, x_pat);
let ready_pat = self.pat_lang_item_variant(span, hir::LangItem::PollReady, ready_field);
let break_x = self.with_loop_scope(loop_node_id, move |this| {
let expr_break =
hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
Expand All @@ -674,7 +662,7 @@ impl<'hir> LoweringContext<'_, 'hir> {

// `::std::task::Poll::Pending => {}`
let pending_arm = {
let pending_pat = self.pat_std_enum(span, &[sym::task, sym::Poll, sym::Pending], &[]);
let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
let empty_block = self.expr_block_empty(span);
self.arm(pending_pat, empty_block)
};
Expand Down Expand Up @@ -842,16 +830,12 @@ impl<'hir> LoweringContext<'_, 'hir> {

/// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
let id = self.next_id();
let e1 = self.lower_expr_mut(e1);
let e2 = self.lower_expr_mut(e2);
self.expr_call_std_assoc_fn(
id,
span,
&[sym::ops, sym::RangeInclusive],
"new",
arena_vec![self; e1, e2],
)
let fn_path = hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, span);
let fn_expr =
self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
}

fn lower_expr_range(
Expand All @@ -863,12 +847,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
) -> hir::ExprKind<'hir> {
use rustc_ast::ast::RangeLimits::*;

let path = match (e1, e2, lims) {
(None, None, HalfOpen) => sym::RangeFull,
(Some(..), None, HalfOpen) => sym::RangeFrom,
(None, Some(..), HalfOpen) => sym::RangeTo,
(Some(..), Some(..), HalfOpen) => sym::Range,
(None, Some(..), Closed) => sym::RangeToInclusive,
let lang_item = match (e1, e2, lims) {
(None, None, HalfOpen) => hir::LangItem::RangeFull,
(Some(..), None, HalfOpen) => hir::LangItem::RangeFrom,
(None, Some(..), HalfOpen) => hir::LangItem::RangeTo,
(Some(..), Some(..), HalfOpen) => hir::LangItem::Range,
(None, Some(..), Closed) => hir::LangItem::RangeToInclusive,
(Some(..), Some(..), Closed) => unreachable!(),
(_, None, Closed) => {
self.diagnostic().span_fatal(span, "inclusive range with no end").raise()
Expand All @@ -883,16 +867,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
}),
);

let is_unit = fields.is_empty();
let struct_path = [sym::ops, path];
let struct_path = self.std_path(span, &struct_path, None, is_unit);
let struct_path = hir::QPath::Resolved(None, struct_path);

if is_unit {
hir::ExprKind::Path(struct_path)
} else {
hir::ExprKind::Struct(self.arena.alloc(struct_path), fields, None)
}
hir::ExprKind::Struct(self.arena.alloc(hir::QPath::LangItem(lang_item, span)), fields, None)
}

fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
Expand Down Expand Up @@ -1412,9 +1387,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
let match_expr = {
let iter = self.expr_ident(desugared_span, iter, iter_pat_nid);
let ref_mut_iter = self.expr_mut_addr_of(desugared_span, iter);
let next_path = &[sym::iter, sym::Iterator, sym::next];
let next_expr =
self.expr_call_std_path(desugared_span, next_path, arena_vec![self; ref_mut_iter]);
let next_expr = self.expr_call_lang_item_fn(
desugared_span,
hir::LangItem::IteratorNext,
arena_vec![self; ref_mut_iter],
);
let arms = arena_vec![self; pat_arm, break_arm];

self.expr_match(desugared_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
Expand Down Expand Up @@ -1472,8 +1449,11 @@ impl<'hir> LoweringContext<'_, 'hir> {

// `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
let into_iter_expr = {
let into_iter_path = &[sym::iter, sym::IntoIterator, sym::into_iter];
self.expr_call_std_path(into_iter_span, into_iter_path, arena_vec![self; head])
self.expr_call_lang_item_fn(
into_iter_span,
hir::LangItem::IntoIterIntoIter,
arena_vec![self; head],
)
};

let match_expr = self.arena.alloc(self.expr_match(
Expand Down Expand Up @@ -1521,8 +1501,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
// expand <expr>
let sub_expr = self.lower_expr_mut(sub_expr);

let path = &[sym::ops, sym::Try, sym::into_result];
self.expr_call_std_path(unstable_span, path, arena_vec![self; sub_expr])
self.expr_call_lang_item_fn(
unstable_span,
hir::LangItem::TryIntoResult,
arena_vec![self; sub_expr],
)
};

// `#[allow(unreachable_code)]`
Expand Down Expand Up @@ -1558,12 +1541,19 @@ impl<'hir> LoweringContext<'_, 'hir> {
let err_ident = Ident::with_dummy_span(sym::err);
let (err_local, err_local_nid) = self.pat_ident(try_span, err_ident);
let from_expr = {
let from_path = &[sym::convert, sym::From, sym::from];
let err_expr = self.expr_ident_mut(try_span, err_ident, err_local_nid);
self.expr_call_std_path(try_span, from_path, arena_vec![self; err_expr])
self.expr_call_lang_item_fn(
try_span,
hir::LangItem::FromFrom,
arena_vec![self; err_expr],
)
};
let from_err_expr =
self.wrap_in_try_constructor(sym::from_error, unstable_span, from_expr, try_span);
let from_err_expr = self.wrap_in_try_constructor(
hir::LangItem::TryFromError,
unstable_span,
from_expr,
try_span,
);
let thin_attrs = ThinVec::from(attrs);
let catch_scope = self.catch_scopes.last().copied();
let ret_expr = if let Some(catch_node) = catch_scope {
Expand Down Expand Up @@ -1674,63 +1664,32 @@ impl<'hir> LoweringContext<'_, 'hir> {
self.arena.alloc(self.expr_call_mut(span, e, args))
}

// Note: associated functions must use `expr_call_std_path`.
fn expr_call_std_path_mut(
fn expr_call_lang_item_fn_mut(
&mut self,
span: Span,
path_components: &[Symbol],
lang_item: hir::LangItem,
args: &'hir [hir::Expr<'hir>],
) -> hir::Expr<'hir> {
let path =
self.arena.alloc(self.expr_std_path(span, path_components, None, ThinVec::new()));
let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item, ThinVec::new()));
self.expr_call_mut(span, path, args)
}

fn expr_call_std_path(
fn expr_call_lang_item_fn(
&mut self,
span: Span,
path_components: &[Symbol],
lang_item: hir::LangItem,
args: &'hir [hir::Expr<'hir>],
) -> &'hir hir::Expr<'hir> {
self.arena.alloc(self.expr_call_std_path_mut(span, path_components, args))
}

// Create an expression calling an associated function of an std type.
//
// Associated functions cannot be resolved through the normal `std_path` function,
// as they are resolved differently and so cannot use `expr_call_std_path`.
//
// This function accepts the path component (`ty_path_components`) separately from
// the name of the associated function (`assoc_fn_name`) in order to facilitate
// separate resolution of the type and creation of a path referring to its associated
// function.
fn expr_call_std_assoc_fn(
&mut self,
ty_path_id: hir::HirId,
span: Span,
ty_path_components: &[Symbol],
assoc_fn_name: &str,
args: &'hir [hir::Expr<'hir>],
) -> hir::ExprKind<'hir> {
let ty_path = self.std_path(span, ty_path_components, None, false);
let ty =
self.arena.alloc(self.ty_path(ty_path_id, span, hir::QPath::Resolved(None, ty_path)));
let fn_seg = self.arena.alloc(hir::PathSegment::from_ident(Ident::from_str(assoc_fn_name)));
let fn_path = hir::QPath::TypeRelative(ty, fn_seg);
let fn_expr =
self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
hir::ExprKind::Call(fn_expr, args)
self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args))
}

fn expr_std_path(
fn expr_lang_item_path(
&mut self,
span: Span,
components: &[Symbol],
params: Option<&'hir hir::GenericArgs<'hir>>,
lang_item: hir::LangItem,
attrs: AttrVec,
) -> hir::Expr<'hir> {
let path = self.std_path(span, components, params, true);
self.expr(span, hir::ExprKind::Path(hir::QPath::Resolved(None, path)), attrs)
self.expr(span, hir::ExprKind::Path(hir::QPath::LangItem(lang_item, span)), attrs)
}

pub(super) fn expr_ident(
Expand Down

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