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Auto merge of rust-lang#75656 - tirr-c:match-suggest-semi, r=estebank
Provide better spans for the match arm without tail expression Resolves rust-lang#75418. Applied the same logic in the `if`-`else` type mismatch case. r? @estebank
2 parents 0ec9459 + c4fb3f2 commit 5180f3d

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5 files changed

+154
-22
lines changed

5 files changed

+154
-22
lines changed

‎src/librustc_infer/infer/error_reporting/mod.rs

+9
Original file line numberDiff line numberDiff line change
@@ -609,6 +609,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
609609
err.span_label(span, "expected due to this");
610610
}
611611
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
612+
semi_span,
612613
source,
613614
ref prior_arms,
614615
last_ty,
@@ -663,6 +664,14 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
663664
format!("this and all prior arms are found to be of type `{}`", t),
664665
);
665666
}
667+
if let Some(sp) = semi_span {
668+
err.span_suggestion_short(
669+
sp,
670+
"consider removing this semicolon",
671+
String::new(),
672+
Applicability::MachineApplicable,
673+
);
674+
}
666675
}
667676
},
668677
ObligationCauseCode::IfExpression(box IfExpressionCause { then, outer, semicolon }) => {

‎src/librustc_middle/traits/mod.rs

+1
Original file line numberDiff line numberDiff line change
@@ -345,6 +345,7 @@ static_assert_size!(ObligationCauseCode<'_>, 32);
345345
#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
346346
pub struct MatchExpressionArmCause<'tcx> {
347347
pub arm_span: Span,
348+
pub semi_span: Option<Span>,
348349
pub source: hir::MatchSource,
349350
pub prior_arms: Vec<Span>,
350351
pub last_ty: Ty<'tcx>,

‎src/librustc_typeck/check/_match.rs

+28-22
Original file line numberDiff line numberDiff line change
@@ -124,11 +124,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
124124
}
125125
}
126126
} else {
127-
let arm_span = if let hir::ExprKind::Block(blk, _) = &arm.body.kind {
128-
// Point at the block expr instead of the entire block
129-
blk.expr.as_ref().map(|e| e.span).unwrap_or(arm.body.span)
127+
let (arm_span, semi_span) = if let hir::ExprKind::Block(blk, _) = &arm.body.kind {
128+
self.find_block_span(blk, prior_arm_ty)
130129
} else {
131-
arm.body.span
130+
(arm.body.span, None)
132131
};
133132
let (span, code) = match i {
134133
// The reason for the first arm to fail is not that the match arms diverge,
@@ -138,6 +137,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
138137
expr.span,
139138
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
140139
arm_span,
140+
semi_span,
141141
source: match_src,
142142
prior_arms: other_arms.clone(),
143143
last_ty: prior_arm_ty.unwrap(),
@@ -295,14 +295,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
295295

296296
let mut remove_semicolon = None;
297297
let error_sp = if let ExprKind::Block(block, _) = &else_expr.kind {
298-
if let Some(expr) = &block.expr {
299-
expr.span
300-
} else if let Some(stmt) = block.stmts.last() {
301-
// possibly incorrect trailing `;` in the else arm
302-
remove_semicolon = self.could_remove_semicolon(block, then_ty);
303-
stmt.span
304-
} else {
305-
// empty block; point at its entirety
298+
let (error_sp, semi_sp) = self.find_block_span(block, Some(then_ty));
299+
remove_semicolon = semi_sp;
300+
if block.expr.is_none() && block.stmts.is_empty() {
306301
// Avoid overlapping spans that aren't as readable:
307302
// ```
308303
// 2 | let x = if true {
@@ -333,26 +328,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
333328
if outer_sp.is_some() {
334329
outer_sp = Some(self.tcx.sess.source_map().guess_head_span(span));
335330
}
336-
else_expr.span
337331
}
332+
error_sp
338333
} else {
339334
// shouldn't happen unless the parser has done something weird
340335
else_expr.span
341336
};
342337

343338
// Compute `Span` of `then` part of `if`-expression.
344339
let then_sp = if let ExprKind::Block(block, _) = &then_expr.kind {
345-
if let Some(expr) = &block.expr {
346-
expr.span
347-
} else if let Some(stmt) = block.stmts.last() {
348-
// possibly incorrect trailing `;` in the else arm
349-
remove_semicolon = remove_semicolon.or(self.could_remove_semicolon(block, else_ty));
350-
stmt.span
351-
} else {
352-
// empty block; point at its entirety
340+
let (then_sp, semi_sp) = self.find_block_span(block, Some(else_ty));
341+
remove_semicolon = remove_semicolon.or(semi_sp);
342+
if block.expr.is_none() && block.stmts.is_empty() {
353343
outer_sp = None; // same as in `error_sp`; cleanup output
354-
then_expr.span
355344
}
345+
then_sp
356346
} else {
357347
// shouldn't happen unless the parser has done something weird
358348
then_expr.span
@@ -450,4 +440,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
450440
scrut_ty
451441
}
452442
}
443+
444+
fn find_block_span(
445+
&self,
446+
block: &'tcx hir::Block<'tcx>,
447+
expected_ty: Option<Ty<'tcx>>,
448+
) -> (Span, Option<Span>) {
449+
if let Some(expr) = &block.expr {
450+
(expr.span, None)
451+
} else if let Some(stmt) = block.stmts.last() {
452+
// possibly incorrect trailing `;` in the else arm
453+
(stmt.span, expected_ty.and_then(|ty| self.could_remove_semicolon(block, ty)))
454+
} else {
455+
// empty block; point at its entirety
456+
(block.span, None)
457+
}
458+
}
453459
}

‎src/test/ui/match/match-incompat-type-semi.rs

+42
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,42 @@
1+
// Diagnostic enhancement explained in issue #75418.
2+
// Point at the last statement in the block if there's no tail expression,
3+
// and suggest removing the semicolon if appropriate.
4+
5+
fn main() {
6+
let _ = match Some(42) {
7+
Some(x) => {
8+
x
9+
},
10+
None => {
11+
0;
12+
//~^ ERROR incompatible types
13+
//~| HELP consider removing this semicolon
14+
},
15+
};
16+
17+
let _ = if let Some(x) = Some(42) {
18+
x
19+
} else {
20+
0;
21+
//~^ ERROR incompatible types
22+
//~| HELP consider removing this semicolon
23+
};
24+
25+
let _ = match Some(42) {
26+
Some(x) => {
27+
x
28+
},
29+
None => {
30+
();
31+
//~^ ERROR incompatible types
32+
},
33+
};
34+
35+
let _ = match Some(42) {
36+
Some(x) => {
37+
x
38+
},
39+
None => { //~ ERROR incompatible types
40+
},
41+
};
42+
}

‎src/test/ui/match/match-incompat-type-semi.stderr

+74
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,74 @@
1+
error[E0308]: `match` arms have incompatible types
2+
--> $DIR/match-incompat-type-semi.rs:11:13
3+
|
4+
LL | let _ = match Some(42) {
5+
| _____________-
6+
LL | | Some(x) => {
7+
LL | | x
8+
| | - this is found to be of type `{integer}`
9+
LL | | },
10+
LL | | None => {
11+
LL | | 0;
12+
| | ^-
13+
| | ||
14+
| | |help: consider removing this semicolon
15+
| | expected integer, found `()`
16+
... |
17+
LL | | },
18+
LL | | };
19+
| |_____- `match` arms have incompatible types
20+
21+
error[E0308]: `if` and `else` have incompatible types
22+
--> $DIR/match-incompat-type-semi.rs:20:9
23+
|
24+
LL | let _ = if let Some(x) = Some(42) {
25+
| _____________-
26+
LL | | x
27+
| | - expected because of this
28+
LL | | } else {
29+
LL | | 0;
30+
| | ^-
31+
| | ||
32+
| | |help: consider removing this semicolon
33+
| | expected integer, found `()`
34+
LL | |
35+
LL | |
36+
LL | | };
37+
| |_____- `if` and `else` have incompatible types
38+
39+
error[E0308]: `match` arms have incompatible types
40+
--> $DIR/match-incompat-type-semi.rs:30:13
41+
|
42+
LL | let _ = match Some(42) {
43+
| _____________-
44+
LL | | Some(x) => {
45+
LL | | x
46+
| | - this is found to be of type `{integer}`
47+
LL | | },
48+
LL | | None => {
49+
LL | | ();
50+
| | ^^^ expected integer, found `()`
51+
LL | |
52+
LL | | },
53+
LL | | };
54+
| |_____- `match` arms have incompatible types
55+
56+
error[E0308]: `match` arms have incompatible types
57+
--> $DIR/match-incompat-type-semi.rs:39:17
58+
|
59+
LL | let _ = match Some(42) {
60+
| _____________-
61+
LL | | Some(x) => {
62+
LL | | x
63+
| | - this is found to be of type `{integer}`
64+
LL | | },
65+
LL | | None => {
66+
| |_________________^
67+
LL | || },
68+
| ||_________^ expected integer, found `()`
69+
LL | | };
70+
| |_____- `match` arms have incompatible types
71+
72+
error: aborting due to 4 previous errors
73+
74+
For more information about this error, try `rustc --explain E0308`.

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