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Add diagnostics to "while loop" and "for loop" that note that it is always determined that it might iterate zero times.
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9 files changed

+175
-8
lines changed

9 files changed

+175
-8
lines changed

‎compiler/rustc_hir_typeck/src/coercion.rs‎

Lines changed: 31 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -40,6 +40,8 @@ use crate::FnCtxt;
4040
use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag};
4141
use rustc_hir as hir;
4242
use rustc_hir::def_id::{DefId, LocalDefId};
43+
use rustc_hir::intravisit::{self, Visitor};
44+
use rustc_hir::Expr;
4345
use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
4446
use rustc_infer::infer::relate::RelateResult;
4547
use rustc_infer::infer::{Coercion, DefineOpaqueTypes, InferOk, InferResult};
@@ -1702,10 +1704,10 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
17021704

17031705
if let Some(expr) = expression {
17041706
if let hir::ExprKind::Loop(
1705-
_,
1707+
loop_blk,
17061708
_,
17071709
loop_src @ (hir::LoopSource::While | hir::LoopSource::ForLoop),
1708-
_,
1710+
loop_span,
17091711
) = expr.kind
17101712
{
17111713
let loop_type = if loop_src == hir::LoopSource::While {
@@ -1715,6 +1717,33 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
17151717
};
17161718

17171719
err.note(format!("{loop_type} evaluate to unit type `()`"));
1720+
1721+
struct RetExprChecker {
1722+
contains_ret_expr: bool,
1723+
}
1724+
impl<'v> Visitor<'v> for RetExprChecker {
1725+
fn visit_expr(&mut self, ex: &'v Expr<'v>) {
1726+
if let hir::ExprKind::Ret(_) = ex.kind {
1727+
self.contains_ret_expr = true;
1728+
return;
1729+
}
1730+
intravisit::walk_expr(self, ex);
1731+
}
1732+
}
1733+
let mut visitor = RetExprChecker { contains_ret_expr: false };
1734+
intravisit::walk_block(&mut visitor, loop_blk);
1735+
if visitor.contains_ret_expr {
1736+
let loop_header = if loop_src == hir::LoopSource::While {
1737+
"loop condition expression or pattern"
1738+
} else {
1739+
"iterator expression"
1740+
};
1741+
err.span_note(
1742+
loop_span,
1743+
format!("It is determined that this might iterate zero times, regardless of the {loop_header}.")
1744+
);
1745+
err.span_help(loop_span, "If you are assuming that it will iterate more than once, consider using a `loop` expression instead.");
1746+
}
17181747
}
17191748

17201749
fcx.emit_coerce_suggestions(

‎tests/ui/coercion/coerce-loop-issue-122561.stderr‎

Lines changed: 70 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -98,6 +98,16 @@ LL | | }
9898
| |_____^ expected `bool`, found `()`
9999
|
100100
= note: `for` loops evaluate to unit type `()`
101+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
102+
--> $DIR/coerce-loop-issue-122561.rs:4:5
103+
|
104+
LL | for i in 0.. {
105+
| ^^^^^^^^^^^^
106+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
107+
--> $DIR/coerce-loop-issue-122561.rs:4:5
108+
|
109+
LL | for i in 0.. {
110+
| ^^^^^^^^^^^^
101111
help: consider returning a value here
102112
|
103113
LL ~ }
@@ -116,6 +126,16 @@ LL | | }
116126
| |_____^ expected `String`, found `()`
117127
|
118128
= note: `for` loops evaluate to unit type `()`
129+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
130+
--> $DIR/coerce-loop-issue-122561.rs:11:5
131+
|
132+
LL | for i in 0..5 {
133+
| ^^^^^^^^^^^^^
134+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
135+
--> $DIR/coerce-loop-issue-122561.rs:11:5
136+
|
137+
LL | for i in 0..5 {
138+
| ^^^^^^^^^^^^^
119139
help: consider returning a value here
120140
|
121141
LL ~ }
@@ -134,6 +154,16 @@ LL | | }
134154
| |_____^ expected `bool`, found `()`
135155
|
136156
= note: `for` loops evaluate to unit type `()`
157+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
158+
--> $DIR/coerce-loop-issue-122561.rs:18:5
159+
|
160+
LL | for i in 0..0 {
161+
| ^^^^^^^^^^^^^
162+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
163+
--> $DIR/coerce-loop-issue-122561.rs:18:5
164+
|
165+
LL | for i in 0..0 {
166+
| ^^^^^^^^^^^^^
137167
help: consider returning a value here
138168
|
139169
LL ~ }
@@ -168,6 +198,16 @@ LL | fn for_single_line() -> bool { for i in 0.. { return false; } }
168198
| expected `bool` because of return type
169199
|
170200
= note: `for` loops evaluate to unit type `()`
201+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
202+
--> $DIR/coerce-loop-issue-122561.rs:33:32
203+
|
204+
LL | fn for_single_line() -> bool { for i in 0.. { return false; } }
205+
| ^^^^^^^^^^^^
206+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
207+
--> $DIR/coerce-loop-issue-122561.rs:33:32
208+
|
209+
LL | fn for_single_line() -> bool { for i in 0.. { return false; } }
210+
| ^^^^^^^^^^^^
171211
help: consider returning a value here
172212
|
173213
LL | fn for_single_line() -> bool { for i in 0.. { return false; } /* `bool` value */ }
@@ -186,6 +226,16 @@ LL | | }
186226
| |_____^ expected `bool`, found `()`
187227
|
188228
= note: `while` loops evaluate to unit type `()`
229+
note: It is determined that this might iterate zero times, regardless of the loop condition expression or pattern.
230+
--> $DIR/coerce-loop-issue-122561.rs:48:5
231+
|
232+
LL | while true {
233+
| ^^^^^^^^^^
234+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
235+
--> $DIR/coerce-loop-issue-122561.rs:48:5
236+
|
237+
LL | while true {
238+
| ^^^^^^^^^^
189239
help: consider returning a value here
190240
|
191241
LL ~ }
@@ -206,6 +256,16 @@ LL | | }
206256
| |_____^ expected `bool`, found `()`
207257
|
208258
= note: `while` loops evaluate to unit type `()`
259+
note: It is determined that this might iterate zero times, regardless of the loop condition expression or pattern.
260+
--> $DIR/coerce-loop-issue-122561.rs:57:5
261+
|
262+
LL | while i < 3 {
263+
| ^^^^^^^^^^^
264+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
265+
--> $DIR/coerce-loop-issue-122561.rs:57:5
266+
|
267+
LL | while i < 3 {
268+
| ^^^^^^^^^^^
209269
help: consider returning a value here
210270
|
211271
LL ~ }
@@ -224,6 +284,16 @@ LL | | }
224284
| |_____^ expected `bool`, found `()`
225285
|
226286
= note: `while` loops evaluate to unit type `()`
287+
note: It is determined that this might iterate zero times, regardless of the loop condition expression or pattern.
288+
--> $DIR/coerce-loop-issue-122561.rs:65:5
289+
|
290+
LL | while false {
291+
| ^^^^^^^^^^^
292+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
293+
--> $DIR/coerce-loop-issue-122561.rs:65:5
294+
|
295+
LL | while false {
296+
| ^^^^^^^^^^^
227297
help: consider returning a value here
228298
|
229299
LL ~ }

‎tests/ui/for-loop-while/break-while-condition.stderr‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -38,6 +38,16 @@ LL | | }
3838
= note: expected type `!`
3939
found unit type `()`
4040
= note: `while` loops evaluate to unit type `()`
41+
note: It is determined that this might iterate zero times, regardless of the loop condition expression or pattern.
42+
--> $DIR/break-while-condition.rs:24:13
43+
|
44+
LL | while false {
45+
| ^^^^^^^^^^^
46+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
47+
--> $DIR/break-while-condition.rs:24:13
48+
|
49+
LL | while false {
50+
| ^^^^^^^^^^^
4151
help: consider adding a diverging expression here
4252
|
4353
LL ~ }

‎tests/ui/typeck/issue-100285.rs‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -13,8 +13,7 @@ fn foo(n: i32) -> i32 {
1313
} else {
1414
return 5;
1515
}
16-
17-
} //~ HELP consider returning a value here
16+
}
1817
}
1918

2019
fn main() {}

‎tests/ui/typeck/issue-100285.stderr‎

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,15 +8,25 @@ LL | | if n < 0 {
88
LL | | return i;
99
LL | | } else if n < 10 {
1010
... |
11-
LL | |
11+
LL | | }
1212
LL | | }
1313
| |_____^ expected `i32`, found `()`
1414
|
1515
= note: `for` loops evaluate to unit type `()`
16+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
17+
--> $DIR/issue-100285.rs:2:5
18+
|
19+
LL | for i in 0..0 {
20+
| ^^^^^^^^^^^^^
21+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
22+
--> $DIR/issue-100285.rs:2:5
23+
|
24+
LL | for i in 0..0 {
25+
| ^^^^^^^^^^^^^
1626
help: consider returning a value here
1727
|
1828
LL ~ }
19-
LL ~ /* `i32` value */
29+
LL + /* `i32` value */
2030
|
2131

2232
error: aborting due to 1 previous error

‎tests/ui/typeck/issue-116572.rs‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
fn main() {}
2+
3+
fn foo() -> bool {
4+
while let x = 0 {
5+
//~^ 4:5: 7:6: mismatched types [E0308]
6+
return true;
7+
}
8+
}

‎tests/ui/typeck/issue-116572.stderr‎

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,31 @@
1+
error[E0308]: mismatched types
2+
--> $DIR/issue-116572.rs:4:5
3+
|
4+
LL | fn foo() -> bool {
5+
| ---- expected `bool` because of return type
6+
LL | / while let x = 0 {
7+
LL | |
8+
LL | | return true;
9+
LL | | }
10+
| |_____^ expected `bool`, found `()`
11+
|
12+
= note: `while` loops evaluate to unit type `()`
13+
note: It is determined that this might iterate zero times, regardless of the loop condition expression or pattern.
14+
--> $DIR/issue-116572.rs:4:5
15+
|
16+
LL | while let x = 0 {
17+
| ^^^^^^^^^^^^^^^
18+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
19+
--> $DIR/issue-116572.rs:4:5
20+
|
21+
LL | while let x = 0 {
22+
| ^^^^^^^^^^^^^^^
23+
help: consider returning a value here
24+
|
25+
LL ~ }
26+
LL + /* `bool` value */
27+
|
28+
29+
error: aborting due to 1 previous error
30+
31+
For more information about this error, try `rustc --explain E0308`.

‎tests/ui/typeck/issue-98982.rs‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,7 @@
11
fn foo() -> i32 {
22
for i in 0..0 { //~ ERROR mismatched types [E0308]
33
return i;
4-
} //~ HELP consider returning a value here
4+
}
55
}
66

77
fn main() {}

‎tests/ui/typeck/issue-98982.stderr‎

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -9,10 +9,20 @@ LL | | }
99
| |_____^ expected `i32`, found `()`
1010
|
1111
= note: `for` loops evaluate to unit type `()`
12+
note: It is determined that this might iterate zero times, regardless of the iterator expression.
13+
--> $DIR/issue-98982.rs:2:5
14+
|
15+
LL | for i in 0..0 {
16+
| ^^^^^^^^^^^^^
17+
help: If you are assuming that it will iterate more than once, consider using a `loop` expression instead.
18+
--> $DIR/issue-98982.rs:2:5
19+
|
20+
LL | for i in 0..0 {
21+
| ^^^^^^^^^^^^^
1222
help: consider returning a value here
1323
|
1424
LL ~ }
15-
LL ~ /* `i32` value */
25+
LL + /* `i32` value */
1626
|
1727

1828
error: aborting due to 1 previous error

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