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Rollup merge of rust-lang#40224 - nikomatsakis:issue-39808, r=eddyb
change the strategy for diverging types The new strategy is as follows. First, the `!` type is assigned in two cases: - a block with a diverging statement and no tail expression (e.g., `{return;}`); - any expression with the type `!` is considered diverging. Second, we track when we are in a diverging state, and we permit a value of any type to be coerced **into** `!` if the expression that produced it is diverging. This means that `fn foo() -> ! { panic!(); 22 }` type-checks, even though the block has a type of `usize`. Finally, coercions **from** the `!` type to any other are always permitted. Fixes rust-lang#39808. Fixes rust-lang#39984.
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‎src/librustc/cfg/construct.rs

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -74,11 +74,11 @@ pub fn construct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
7474

7575
impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
7676
fn block(&mut self, blk: &hir::Block, pred: CFGIndex) -> CFGIndex {
77-
if let Some(break_to_expr_id) = blk.break_to_expr_id {
77+
if blk.targeted_by_break {
7878
let expr_exit = self.add_ast_node(blk.id, &[]);
7979

8080
self.breakable_block_scopes.push(BlockScope {
81-
block_expr_id: break_to_expr_id,
81+
block_expr_id: blk.id,
8282
break_index: expr_exit,
8383
});
8484

@@ -195,7 +195,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
195195
// [..expr..]
196196
//
197197
let cond_exit = self.expr(&cond, pred); // 1
198-
let then_exit = self.block(&then, cond_exit); // 2
198+
let then_exit = self.expr(&then, cond_exit); // 2
199199
self.add_ast_node(expr.id, &[cond_exit, then_exit]) // 3,4
200200
}
201201

@@ -215,7 +215,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
215215
// [..expr..]
216216
//
217217
let cond_exit = self.expr(&cond, pred); // 1
218-
let then_exit = self.block(&then, cond_exit); // 2
218+
let then_exit = self.expr(&then, cond_exit); // 2
219219
let else_exit = self.expr(&otherwise, cond_exit); // 3
220220
self.add_ast_node(expr.id, &[then_exit, else_exit]) // 4, 5
221221
}

‎src/librustc/hir/intravisit.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -960,7 +960,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
960960
}
961961
ExprIf(ref head_expression, ref if_block, ref optional_else) => {
962962
visitor.visit_expr(head_expression);
963-
visitor.visit_block(if_block);
963+
visitor.visit_expr(if_block);
964964
walk_list!(visitor, visit_expr, optional_else);
965965
}
966966
ExprWhile(ref subexpression, ref block, ref opt_sp_name) => {

‎src/librustc/hir/lowering.rs

Lines changed: 21 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -1146,7 +1146,7 @@ impl<'a> LoweringContext<'a> {
11461146
bounds.iter().map(|bound| self.lower_ty_param_bound(bound)).collect()
11471147
}
11481148

1149-
fn lower_block(&mut self, b: &Block, break_to: Option<NodeId>) -> P<hir::Block> {
1149+
fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
11501150
let mut expr = None;
11511151

11521152
let mut stmts = vec![];
@@ -1169,7 +1169,7 @@ impl<'a> LoweringContext<'a> {
11691169
expr: expr,
11701170
rules: self.lower_block_check_mode(&b.rules),
11711171
span: b.span,
1172-
break_to_expr_id: break_to,
1172+
targeted_by_break: targeted_by_break,
11731173
})
11741174
}
11751175

@@ -1264,7 +1264,7 @@ impl<'a> LoweringContext<'a> {
12641264
}
12651265
ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
12661266
self.with_new_scopes(|this| {
1267-
let body = this.lower_block(body, None);
1267+
let body = this.lower_block(body, false);
12681268
let body = this.expr_block(body, ThinVec::new());
12691269
let body_id = this.record_body(body, Some(decl));
12701270
hir::ItemFn(this.lower_fn_decl(decl),
@@ -1358,7 +1358,7 @@ impl<'a> LoweringContext<'a> {
13581358
hir::TraitMethod::Required(names))
13591359
}
13601360
TraitItemKind::Method(ref sig, Some(ref body)) => {
1361-
let body = this.lower_block(body, None);
1361+
let body = this.lower_block(body, false);
13621362
let expr = this.expr_block(body, ThinVec::new());
13631363
let body_id = this.record_body(expr, Some(&sig.decl));
13641364
hir::TraitItemKind::Method(this.lower_method_sig(sig),
@@ -1414,7 +1414,7 @@ impl<'a> LoweringContext<'a> {
14141414
hir::ImplItemKind::Const(this.lower_ty(ty), body_id)
14151415
}
14161416
ImplItemKind::Method(ref sig, ref body) => {
1417-
let body = this.lower_block(body, None);
1417+
let body = this.lower_block(body, false);
14181418
let expr = this.expr_block(body, ThinVec::new());
14191419
let body_id = this.record_body(expr, Some(&sig.decl));
14201420
hir::ImplItemKind::Method(this.lower_method_sig(sig), body_id)
@@ -1838,32 +1838,35 @@ impl<'a> LoweringContext<'a> {
18381838
id: id,
18391839
rules: hir::DefaultBlock,
18401840
span: span,
1841-
break_to_expr_id: None,
1841+
targeted_by_break: false,
18421842
});
18431843
P(self.expr_block(blk, ThinVec::new()))
18441844
}
18451845
_ => P(self.lower_expr(els)),
18461846
}
18471847
});
18481848

1849-
hir::ExprIf(P(self.lower_expr(cond)), self.lower_block(blk, None), else_opt)
1849+
let then_blk = self.lower_block(blk, false);
1850+
let then_expr = self.expr_block(then_blk, ThinVec::new());
1851+
1852+
hir::ExprIf(P(self.lower_expr(cond)), P(then_expr), else_opt)
18501853
}
18511854
ExprKind::While(ref cond, ref body, opt_ident) => {
18521855
self.with_loop_scope(e.id, |this|
18531856
hir::ExprWhile(
18541857
this.with_loop_condition_scope(|this| P(this.lower_expr(cond))),
1855-
this.lower_block(body, None),
1858+
this.lower_block(body, false),
18561859
this.lower_opt_sp_ident(opt_ident)))
18571860
}
18581861
ExprKind::Loop(ref body, opt_ident) => {
18591862
self.with_loop_scope(e.id, |this|
1860-
hir::ExprLoop(this.lower_block(body, None),
1863+
hir::ExprLoop(this.lower_block(body, false),
18611864
this.lower_opt_sp_ident(opt_ident),
18621865
hir::LoopSource::Loop))
18631866
}
18641867
ExprKind::Catch(ref body) => {
1865-
self.with_catch_scope(e.id, |this|
1866-
hir::ExprBlock(this.lower_block(body, Some(e.id))))
1868+
self.with_catch_scope(body.id, |this|
1869+
hir::ExprBlock(this.lower_block(body, true)))
18671870
}
18681871
ExprKind::Match(ref expr, ref arms) => {
18691872
hir::ExprMatch(P(self.lower_expr(expr)),
@@ -1881,7 +1884,7 @@ impl<'a> LoweringContext<'a> {
18811884
})
18821885
})
18831886
}
1884-
ExprKind::Block(ref blk) => hir::ExprBlock(self.lower_block(blk, None)),
1887+
ExprKind::Block(ref blk) => hir::ExprBlock(self.lower_block(blk, false)),
18851888
ExprKind::Assign(ref el, ref er) => {
18861889
hir::ExprAssign(P(self.lower_expr(el)), P(self.lower_expr(er)))
18871890
}
@@ -2027,7 +2030,7 @@ impl<'a> LoweringContext<'a> {
20272030

20282031
// `<pat> => <body>`
20292032
{
2030-
let body = self.lower_block(body, None);
2033+
let body = self.lower_block(body, false);
20312034
let body_expr = P(self.expr_block(body, ThinVec::new()));
20322035
let pat = self.lower_pat(pat);
20332036
arms.push(self.arm(hir_vec![pat], body_expr));
@@ -2099,7 +2102,7 @@ impl<'a> LoweringContext<'a> {
20992102
let (guard, body) = if let ExprKind::If(ref cond,
21002103
ref then,
21012104
_) = else_expr.node {
2102-
let then = self.lower_block(then, None);
2105+
let then = self.lower_block(then, false);
21032106
(Some(cond),
21042107
self.expr_block(then, ThinVec::new()))
21052108
} else {
@@ -2149,7 +2152,7 @@ impl<'a> LoweringContext<'a> {
21492152
// Note that the block AND the condition are evaluated in the loop scope.
21502153
// This is done to allow `break` from inside the condition of the loop.
21512154
let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| (
2152-
this.lower_block(body, None),
2155+
this.lower_block(body, false),
21532156
this.expr_break(e.span, ThinVec::new()),
21542157
this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
21552158
));
@@ -2210,7 +2213,7 @@ impl<'a> LoweringContext<'a> {
22102213
// `::std::option::Option::Some(<pat>) => <body>`
22112214
let pat_arm = {
22122215
let body_block = self.with_loop_scope(e.id,
2213-
|this| this.lower_block(body, None));
2216+
|this| this.lower_block(body, false));
22142217
let body_expr = P(self.expr_block(body_block, ThinVec::new()));
22152218
let pat = self.lower_pat(pat);
22162219
let some_pat = self.pat_some(e.span, pat);
@@ -2642,7 +2645,7 @@ impl<'a> LoweringContext<'a> {
26422645
id: self.next_id(),
26432646
rules: hir::DefaultBlock,
26442647
span: span,
2645-
break_to_expr_id: None,
2648+
targeted_by_break: false,
26462649
}
26472650
}
26482651

@@ -2750,7 +2753,7 @@ impl<'a> LoweringContext<'a> {
27502753
id: id,
27512754
stmts: stmts,
27522755
expr: Some(expr),
2753-
break_to_expr_id: None,
2756+
targeted_by_break: false,
27542757
});
27552758
self.expr_block(block, attrs)
27562759
}

‎src/librustc/hir/mod.rs

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -548,9 +548,11 @@ pub struct Block {
548548
/// Distinguishes between `unsafe { ... }` and `{ ... }`
549549
pub rules: BlockCheckMode,
550550
pub span: Span,
551-
/// The id of the expression that `break` breaks to if the block can be broken out of.
552-
/// Currently only `Some(_)` for `catch {}` blocks
553-
pub break_to_expr_id: Option<NodeId>,
551+
/// If true, then there may exist `break 'a` values that aim to
552+
/// break out of this block early. As of this writing, this is not
553+
/// currently permitted in Rust itself, but it is generated as
554+
/// part of `catch` statements.
555+
pub targeted_by_break: bool,
554556
}
555557

556558
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
@@ -992,8 +994,8 @@ pub enum Expr_ {
992994
ExprType(P<Expr>, P<Ty>),
993995
/// An `if` block, with an optional else block
994996
///
995-
/// `if expr { block } else { expr }`
996-
ExprIf(P<Expr>, P<Block>, Option<P<Expr>>),
997+
/// `if expr { expr } else { expr }`
998+
ExprIf(P<Expr>, P<Expr>, Option<P<Expr>>),
997999
/// A while loop, with an optional label
9981000
///
9991001
/// `'label: while expr { block }`

‎src/librustc/hir/print.rs

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1036,7 +1036,7 @@ impl<'a> State<'a> {
10361036
word(&mut self.s, " else if ")?;
10371037
self.print_expr(&i)?;
10381038
space(&mut self.s)?;
1039-
self.print_block(&then)?;
1039+
self.print_expr(&then)?;
10401040
self.print_else(e.as_ref().map(|e| &**e))
10411041
}
10421042
// "final else"
@@ -1058,13 +1058,13 @@ impl<'a> State<'a> {
10581058

10591059
pub fn print_if(&mut self,
10601060
test: &hir::Expr,
1061-
blk: &hir::Block,
1061+
blk: &hir::Expr,
10621062
elseopt: Option<&hir::Expr>)
10631063
-> io::Result<()> {
10641064
self.head("if")?;
10651065
self.print_expr(test)?;
10661066
space(&mut self.s)?;
1067-
self.print_block(blk)?;
1067+
self.print_expr(blk)?;
10681068
self.print_else(elseopt)
10691069
}
10701070

‎src/librustc/infer/type_variable.rs

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,7 @@ pub struct TypeVariableTable<'tcx> {
3030
}
3131

3232
/// Reasons to create a type inference variable
33+
#[derive(Debug)]
3334
pub enum TypeVariableOrigin {
3435
MiscVariable(Span),
3536
NormalizeProjectionType(Span),
@@ -41,6 +42,7 @@ pub enum TypeVariableOrigin {
4142
AdjustmentType(Span),
4243
DivergingStmt(Span),
4344
DivergingBlockExpr(Span),
45+
DivergingFn(Span),
4446
LatticeVariable(Span),
4547
}
4648

@@ -196,14 +198,15 @@ impl<'tcx> TypeVariableTable<'tcx> {
196198
diverging: bool,
197199
origin: TypeVariableOrigin,
198200
default: Option<Default<'tcx>>,) -> ty::TyVid {
201+
debug!("new_var(diverging={:?}, origin={:?})", diverging, origin);
199202
self.eq_relations.new_key(());
200203
let index = self.values.push(TypeVariableData {
201204
value: Bounded { relations: vec![], default: default },
202205
origin: origin,
203206
diverging: diverging
204207
});
205208
let v = ty::TyVid { index: index as u32 };
206-
debug!("new_var() -> {:?}", v);
209+
debug!("new_var: diverging={:?} index={:?}", diverging, v);
207210
v
208211
}
209212

‎src/librustc/middle/expr_use_visitor.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -414,9 +414,9 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
414414
self.consume_exprs(exprs);
415415
}
416416

417-
hir::ExprIf(ref cond_expr, ref then_blk, ref opt_else_expr) => {
417+
hir::ExprIf(ref cond_expr, ref then_expr, ref opt_else_expr) => {
418418
self.consume_expr(&cond_expr);
419-
self.walk_block(&then_blk);
419+
self.walk_expr(&then_expr);
420420
if let Some(ref else_expr) = *opt_else_expr {
421421
self.consume_expr(&else_expr);
422422
}

‎src/librustc/middle/liveness.rs

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -821,8 +821,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
821821

822822
fn propagate_through_block(&mut self, blk: &hir::Block, succ: LiveNode)
823823
-> LiveNode {
824-
if let Some(break_to_expr_id) = blk.break_to_expr_id {
825-
self.breakable_block_ln.insert(break_to_expr_id, succ);
824+
if blk.targeted_by_break {
825+
self.breakable_block_ln.insert(blk.id, succ);
826826
}
827827
let succ = self.propagate_through_opt_expr(blk.expr.as_ref().map(|e| &**e), succ);
828828
blk.stmts.iter().rev().fold(succ, |succ, stmt| {
@@ -951,7 +951,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
951951
// ( succ )
952952
//
953953
let else_ln = self.propagate_through_opt_expr(els.as_ref().map(|e| &**e), succ);
954-
let then_ln = self.propagate_through_block(&then, succ);
954+
let then_ln = self.propagate_through_expr(&then, succ);
955955
let ln = self.live_node(expr.id, expr.span);
956956
self.init_from_succ(ln, else_ln);
957957
self.merge_from_succ(ln, then_ln, false);

‎src/librustc/traits/error_reporting.rs

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -904,6 +904,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
904904
ObligationCauseCode::StartFunctionType |
905905
ObligationCauseCode::IntrinsicType |
906906
ObligationCauseCode::MethodReceiver |
907+
ObligationCauseCode::ReturnNoExpression |
907908
ObligationCauseCode::MiscObligation => {
908909
}
909910
ObligationCauseCode::SliceOrArrayElem => {

‎src/librustc/traits/mod.rs

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -173,6 +173,9 @@ pub enum ObligationCauseCode<'tcx> {
173173

174174
// method receiver
175175
MethodReceiver,
176+
177+
// `return` with no expression
178+
ReturnNoExpression,
176179
}
177180

178181
#[derive(Clone, Debug, PartialEq, Eq)]

‎src/librustc/traits/structural_impls.rs

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -167,6 +167,7 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
167167
type Lifted = traits::ObligationCauseCode<'tcx>;
168168
fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<Self::Lifted> {
169169
match *self {
170+
super::ReturnNoExpression => Some(super::ReturnNoExpression),
170171
super::MiscObligation => Some(super::MiscObligation),
171172
super::SliceOrArrayElem => Some(super::SliceOrArrayElem),
172173
super::TupleElem => Some(super::TupleElem),
@@ -489,6 +490,7 @@ impl<'tcx> TypeFoldable<'tcx> for traits::ObligationCauseCode<'tcx> {
489490
super::StructInitializerSized |
490491
super::VariableType(_) |
491492
super::ReturnType |
493+
super::ReturnNoExpression |
492494
super::RepeatVec |
493495
super::FieldSized |
494496
super::ConstSized |
@@ -533,6 +535,7 @@ impl<'tcx> TypeFoldable<'tcx> for traits::ObligationCauseCode<'tcx> {
533535
super::StructInitializerSized |
534536
super::VariableType(_) |
535537
super::ReturnType |
538+
super::ReturnNoExpression |
536539
super::RepeatVec |
537540
super::FieldSized |
538541
super::ConstSized |

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