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let-else: add hir::Let and type check it like a hir::Local
unify typeck of hir::Local and hir::Let remove extraneous pub(crate/super)
1 parent a0a4c7d commit af2f0e6

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13 files changed

+160
-92
lines changed

13 files changed

+160
-92
lines changed

‎compiler/rustc_ast_lowering/src/block.rs‎

Lines changed: 9 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,6 @@ use crate::{ImplTraitContext, ImplTraitPosition, LoweringContext};
22
use rustc_ast::{AttrVec, Block, BlockCheckMode, Expr, Local, LocalKind, Stmt, StmtKind};
33
use rustc_hir as hir;
44
use rustc_session::parse::feature_err;
5-
use rustc_span::symbol::Ident;
65
use rustc_span::{sym, DesugaringKind};
76

87
use smallvec::SmallVec;
@@ -39,8 +38,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
3938
let hir_id = self.lower_node_id(s.id);
4039
match &local.kind {
4140
LocalKind::InitElse(init, els) => {
42-
let (s, e) = self.lower_let_else(hir_id, local, init, els, tail);
43-
stmts.push(s);
41+
let e = self.lower_let_else(hir_id, local, init, els, tail);
4442
expr = Some(e);
4543
// remaining statements are in let-else expression
4644
break;
@@ -125,36 +123,25 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
125123
init: &Expr,
126124
els: &Block,
127125
tail: &[Stmt],
128-
) -> (hir::Stmt<'hir>, &'hir hir::Expr<'hir>) {
126+
) -> &'hir hir::Expr<'hir> {
129127
let ty = local
130128
.ty
131129
.as_ref()
132130
.map(|t| self.lower_ty(t, ImplTraitContext::Disallowed(ImplTraitPosition::Binding)));
133131
let span = self.lower_span(local.span);
134132
let span = self.mark_span_with_reason(DesugaringKind::LetElse, span, None);
135-
let init = Some(self.lower_expr(init));
136-
let val = Ident::with_dummy_span(sym::val);
137-
let (pat, val_id) =
138-
self.pat_ident_binding_mode(span, val, hir::BindingAnnotation::Unannotated);
133+
let init = self.lower_expr(init);
139134
let local_hir_id = self.lower_node_id(local.id);
140135
self.lower_attrs(local_hir_id, &local.attrs);
141-
// first statement which basically exists for the type annotation
142-
let stmt = {
143-
let local = self.arena.alloc(hir::Local {
136+
let let_expr = {
137+
let lex = self.arena.alloc(hir::Let {
144138
hir_id: local_hir_id,
139+
pat: self.lower_pat(&local.pat),
145140
ty,
146-
pat,
147141
init,
148142
span,
149-
source: hir::LocalSource::Normal,
150143
});
151-
let kind = hir::StmtKind::Local(local);
152-
hir::Stmt { hir_id: stmt_hir_id, kind, span }
153-
};
154-
let let_expr = {
155-
let scrutinee = self.expr_ident(span, val, val_id);
156-
let let_kind = hir::ExprKind::Let(self.lower_pat(&local.pat), scrutinee, span);
157-
self.arena.alloc(self.expr(span, let_kind, AttrVec::new()))
144+
self.arena.alloc(self.expr(span, hir::ExprKind::Let(lex), AttrVec::new()))
158145
};
159146
let then_expr = {
160147
let (stmts, expr) = self.lower_stmts(tail);
@@ -167,7 +154,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
167154
};
168155
self.alias_attrs(else_expr.hir_id, local_hir_id);
169156
let if_expr = self.arena.alloc(hir::Expr {
170-
hir_id: self.next_id(),
157+
hir_id: stmt_hir_id,
171158
span,
172159
kind: hir::ExprKind::If(let_expr, then_expr, Some(else_expr)),
173160
});
@@ -180,6 +167,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
180167
)
181168
.emit();
182169
}
183-
(stmt, if_expr)
170+
if_expr
184171
}
185172
}

‎compiler/rustc_ast_lowering/src/expr.rs‎

Lines changed: 9 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -92,11 +92,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
9292
let ohs = self.lower_expr(ohs);
9393
hir::ExprKind::AddrOf(k, m, ohs)
9494
}
95-
ExprKind::Let(ref pat, ref scrutinee, span) => hir::ExprKind::Let(
96-
self.lower_pat(pat),
97-
self.lower_expr(scrutinee),
98-
self.lower_span(span),
99-
),
95+
ExprKind::Let(ref pat, ref scrutinee, span) => {
96+
hir::ExprKind::Let(self.arena.alloc(hir::Let {
97+
hir_id: self.next_id(),
98+
span: self.lower_span(span),
99+
pat: self.lower_pat(pat),
100+
ty: None,
101+
init: self.lower_expr(scrutinee),
102+
}))
103+
}
100104
ExprKind::If(ref cond, ref then, ref else_opt) => {
101105
self.lower_expr_if(cond, then, else_opt.as_deref())
102106
}

‎compiler/rustc_hir/src/arena.rs‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -20,6 +20,7 @@ macro_rules! arena_types {
2020
[] generic_bound: rustc_hir::GenericBound<'tcx>,
2121
[] generic_param: rustc_hir::GenericParam<'tcx>,
2222
[] expr: rustc_hir::Expr<'tcx>,
23+
[] let_expr: rustc_hir::Let<'tcx>,
2324
[] expr_field: rustc_hir::ExprField<'tcx>,
2425
[] pat_field: rustc_hir::PatField<'tcx>,
2526
[] fn_decl: rustc_hir::FnDecl<'tcx>,

‎compiler/rustc_hir/src/hir.rs‎

Lines changed: 16 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1176,10 +1176,24 @@ pub struct Arm<'hir> {
11761176
pub body: &'hir Expr<'hir>,
11771177
}
11781178

1179+
/// Represents a `let <pat>[: <ty>] = <expr>` expression (not a Local), occurring in an `if-let` or
1180+
/// `let-else`, evaluating to a boolean. Typically the pattern is refutable.
1181+
///
1182+
/// In an if-let, imagine it as `if (let <pat> = <expr>) { ... }`; in a let-else, it is part of the
1183+
/// desugaring to if-let. Only let-else supports the type annotation at present.
1184+
#[derive(Debug, HashStable_Generic)]
1185+
pub struct Let<'hir> {
1186+
pub hir_id: HirId,
1187+
pub span: Span,
1188+
pub pat: &'hir Pat<'hir>,
1189+
pub ty: Option<&'hir Ty<'hir>>,
1190+
pub init: &'hir Expr<'hir>,
1191+
}
1192+
11791193
#[derive(Debug, HashStable_Generic)]
11801194
pub enum Guard<'hir> {
11811195
If(&'hir Expr<'hir>),
1182-
// FIXME use ExprKind::Let for this.
1196+
// FIXME use hir::Let for this.
11831197
IfLet(&'hir Pat<'hir>, &'hir Expr<'hir>),
11841198
}
11851199

@@ -1696,7 +1710,7 @@ pub enum ExprKind<'hir> {
16961710
///
16971711
/// These are not `Local` and only occur as expressions.
16981712
/// The `let Some(x) = foo()` in `if let Some(x) = foo()` is an example of `Let(..)`.
1699-
Let(&'hir Pat<'hir>, &'hir Expr<'hir>, Span),
1713+
Let(&'hir Let<'hir>),
17001714
/// An `if` block, with an optional else block.
17011715
///
17021716
/// I.e., `if <expr> { <expr> } else { <expr> }`.

‎compiler/rustc_hir/src/intravisit.rs‎

Lines changed: 12 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -389,6 +389,9 @@ pub trait Visitor<'v>: Sized {
389389
fn visit_expr(&mut self, ex: &'v Expr<'v>) {
390390
walk_expr(self, ex)
391391
}
392+
fn visit_let_expr(&mut self, lex: &'v Let<'v>) {
393+
walk_let_expr(self, lex)
394+
}
392395
fn visit_ty(&mut self, t: &'v Ty<'v>) {
393396
walk_ty(self, t)
394397
}
@@ -1126,6 +1129,14 @@ pub fn walk_anon_const<'v, V: Visitor<'v>>(visitor: &mut V, constant: &'v AnonCo
11261129
visitor.visit_nested_body(constant.body);
11271130
}
11281131

1132+
pub fn walk_let_expr<'v, V: Visitor<'v>>(visitor: &mut V, let_expr: &'v Let<'v>) {
1133+
// match the visit order in walk_local
1134+
visitor.visit_expr(let_expr.init);
1135+
visitor.visit_id(let_expr.hir_id);
1136+
visitor.visit_pat(let_expr.pat);
1137+
walk_list!(visitor, visit_ty, let_expr.ty);
1138+
}
1139+
11291140
pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>) {
11301141
visitor.visit_id(expression.hir_id);
11311142
match expression.kind {
@@ -1172,10 +1183,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
11721183
ExprKind::DropTemps(ref subexpression) => {
11731184
visitor.visit_expr(subexpression);
11741185
}
1175-
ExprKind::Let(ref pat, ref expr, _) => {
1176-
visitor.visit_expr(expr);
1177-
visitor.visit_pat(pat);
1178-
}
1186+
ExprKind::Let(ref let_expr) => visitor.visit_let_expr(let_expr),
11791187
ExprKind::If(ref cond, ref then, ref else_opt) => {
11801188
visitor.visit_expr(cond);
11811189
visitor.visit_expr(then);

‎compiler/rustc_hir_pretty/src/lib.rs‎

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1101,13 +1101,17 @@ impl<'a> State<'a> {
11011101
}
11021102

11031103
/// Print a `let pat = expr` expression.
1104-
fn print_let(&mut self, pat: &hir::Pat<'_>, expr: &hir::Expr<'_>) {
1105-
self.word("let ");
1104+
fn print_let(&mut self, pat: &hir::Pat<'_>, ty: Option<&hir::Ty<'_>>, init: &hir::Expr<'_>) {
1105+
self.word_space("let");
11061106
self.print_pat(pat);
1107+
if let Some(ty) = ty {
1108+
self.word_space(":");
1109+
self.print_type(ty);
1110+
}
11071111
self.space();
11081112
self.word_space("=");
1109-
let npals = || parser::needs_par_as_let_scrutinee(expr.precedence().order());
1110-
self.print_expr_cond_paren(expr, Self::cond_needs_par(expr) || npals())
1113+
let npals = || parser::needs_par_as_let_scrutinee(init.precedence().order());
1114+
self.print_expr_cond_paren(init, Self::cond_needs_par(init) || npals())
11111115
}
11121116

11131117
// Does `expr` need parentheses when printed in a condition position?
@@ -1462,8 +1466,8 @@ impl<'a> State<'a> {
14621466
// Print `}`:
14631467
self.bclose_maybe_open(expr.span, true);
14641468
}
1465-
hir::ExprKind::Let(ref pat, ref scrutinee, _) => {
1466-
self.print_let(pat, scrutinee);
1469+
hir::ExprKind::Let(hir::Let { pat, ty, init, .. }) => {
1470+
self.print_let(pat, *ty, init);
14671471
}
14681472
hir::ExprKind::If(ref test, ref blk, ref elseopt) => {
14691473
self.print_if(&test, &blk, elseopt.as_ref().map(|e| &**e));

‎compiler/rustc_mir_build/src/thir/cx/expr.rs‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -605,9 +605,10 @@ impl<'tcx> Cx<'tcx> {
605605
},
606606
Err(err) => bug!("invalid loop id for continue: {}", err),
607607
},
608-
hir::ExprKind::Let(ref pat, ref expr, _) => {
609-
ExprKind::Let { expr: self.mirror_expr(expr), pat: self.pattern_from_hir(pat) }
610-
}
608+
hir::ExprKind::Let(let_expr) => ExprKind::Let {
609+
expr: self.mirror_expr(let_expr.init),
610+
pat: self.pattern_from_hir(let_expr.pat),
611+
},
611612
hir::ExprKind::If(cond, then, else_opt) => ExprKind::If {
612613
if_then_scope: region::Scope {
613614
id: then.hir_id.local_id,

‎compiler/rustc_mir_build/src/thir/pattern/check_match.rs‎

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -64,7 +64,9 @@ impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, '_, 'tcx> {
6464
intravisit::walk_expr(self, ex);
6565
match &ex.kind {
6666
hir::ExprKind::Match(scrut, arms, source) => self.check_match(scrut, arms, *source),
67-
hir::ExprKind::Let(pat, scrut, span) => self.check_let(pat, scrut, *span),
67+
hir::ExprKind::Let(hir::Let { pat, init, span, .. }) => {
68+
self.check_let(pat, init, *span)
69+
}
6870
_ => {}
6971
}
7072
}
@@ -148,9 +150,9 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
148150
}
149151
}
150152

151-
fn check_let(&mut self, pat: &'tcx hir::Pat<'tcx>, expr: &hir::Expr<'_>, span: Span) {
153+
fn check_let(&mut self, pat: &'tcx hir::Pat<'tcx>, scrutinee: &hir::Expr<'_>, span: Span) {
152154
self.check_patterns(pat, Refutable);
153-
let mut cx = self.new_cx(expr.hir_id);
155+
let mut cx = self.new_cx(scrutinee.hir_id);
154156
let tpat = self.lower_pattern(&mut cx, pat, &mut false);
155157
check_let_reachability(&mut cx, pat.hir_id, tpat, span);
156158
}

‎compiler/rustc_passes/src/liveness.rs‎

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -429,8 +429,8 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
429429
intravisit::walk_expr(self, expr);
430430
}
431431

432-
hir::ExprKind::Let(ref pat, ..) => {
433-
self.add_from_pat(pat);
432+
hir::ExprKind::Let(let_expr) => {
433+
self.add_from_pat(let_expr.pat);
434434
intravisit::walk_expr(self, expr);
435435
}
436436

@@ -856,9 +856,9 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
856856
})
857857
}
858858

859-
hir::ExprKind::Let(ref pat, ref scrutinee, _) => {
860-
let succ = self.propagate_through_expr(scrutinee, succ);
861-
self.define_bindings_in_pat(pat, succ)
859+
hir::ExprKind::Let(let_expr) => {
860+
let succ = self.propagate_through_expr(let_expr.init, succ);
861+
self.define_bindings_in_pat(let_expr.pat, succ)
862862
}
863863

864864
// Note that labels have been resolved, so we don't need to look
@@ -1401,8 +1401,8 @@ fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
14011401
}
14021402
}
14031403

1404-
hir::ExprKind::Let(ref pat, ..) => {
1405-
this.check_unused_vars_in_pat(pat, None, |_, _, _, _| {});
1404+
hir::ExprKind::Let(let_expr) => {
1405+
this.check_unused_vars_in_pat(let_expr.pat, None, |_, _, _, _| {});
14061406
}
14071407

14081408
// no correctness conditions related to liveness

‎compiler/rustc_typeck/src/check/expr.rs‎

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -300,7 +300,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
300300
}
301301
}
302302
ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
303-
ExprKind::Let(pat, let_expr, _) => self.check_expr_let(let_expr, pat),
303+
ExprKind::Let(let_expr) => self.check_expr_let(let_expr),
304304
ExprKind::Loop(body, _, source, _) => {
305305
self.check_expr_loop(body, source, expected, expr)
306306
}
@@ -1048,10 +1048,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
10481048
}
10491049
}
10501050

1051-
fn check_expr_let(&self, expr: &'tcx hir::Expr<'tcx>, pat: &'tcx hir::Pat<'tcx>) -> Ty<'tcx> {
1052-
self.warn_if_unreachable(expr.hir_id, expr.span, "block in `let` expression");
1053-
let expr_ty = self.demand_scrutinee_type(expr, pat.contains_explicit_ref_binding(), false);
1054-
self.check_pat_top(pat, expr_ty, Some(expr.span), true);
1051+
fn check_expr_let(&self, let_expr: &'tcx hir::Let<'tcx>) -> Ty<'tcx> {
1052+
// for let statements, this is done in check_stmt
1053+
let init = let_expr.init;
1054+
self.warn_if_unreachable(init.hir_id, init.span, "block in `let` expression");
1055+
// otherwise check exactly as a let statement
1056+
self.check_decl(let_expr.into());
1057+
// but return a bool, for this is a boolean expression
10551058
self.tcx.types.bool
10561059
}
10571060

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