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Rollup merge of #78255 - dtolnay:match, r=lcnr

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Reduce diagram mess in 'match arms have incompatible types' error

I noticed this wild diagram in https://twitter.com/a_hoverbear/status/1318960787105353728 which I think does not benefit from the big outer vertical span.

This PR shrinks the outer span to cover just the `match` keyword and scrutinee expression *if* at least one of the highlighted match arms involved in the error is multiline.

**Before:**

<pre>
<b>error[E0308]: `match` arms have incompatible types</b>
   <b>--&gt;</b> src/topology/builder.rs:141:35
    <b>|</b>
<b>120 |</b>             let transform = match transform {
    <b>|    _________________________-</b>
<b>121 |   |</b>             Transform::Function(t) =&gt; {
    <b>|  _|_______________________________________-</b>
<b>122 | | |</b>                 filter_event_type(input_rx, input_type).compat().flat_map(|v| {
<b>123 | | |</b>                     futures::stream::iter(match v {
<b>124 | | |</b>                         Err(e) =&gt; {
<b>...   | |</b>
<b>139 | | |</b>                 .compat();
<b>140 | | |</b>             }
    <b>| |_|_____________- this is found to be of type `()`</b>
<b>141 |   |</b>             Transform::Task(t) =&gt; t
    <b>|  _|___________________________________^</b>
<b>142 | | |</b>                 .transform(filter_event_type(input_rx, input_type))
<b>143 | | |</b>                 .forward(output)
<b>144 | | |</b>                 .map(|_| debug!("Finished"))
<b>145 | | |</b>                 .compat(),
    <b>| |_|_________________________^ expected `()`, found struct `futures::compat::Compat01As03`</b>
<b>146 |   |</b>         };
    <b>|   |_________- `match` arms have incompatible types</b>
    <b>|</b>
    <b>= note:</b> expected type `<b>()</b>`
             found struct `<b>futures::compat::Compat01As03&lt;futures::Map&lt;futures::stream::Forward&lt;std::boxed::Box&lt;dyn futures::Stream&lt;Error = (), Item = event::Event&gt; + std::marker::Send&gt;, topology::fanout::Fanout&gt;, [closure@src/topology/builder.rs:144:22: 144:44]&gt;&gt;</b>`
</pre>

**After:**

<pre>
<b>error[E0308]: `match` arms have incompatible types</b>
   <b>--&gt;</b> src/topology/builder.rs:141:35
    <b>|</b>
<b>120 |</b>             let transform = match transform {
    <b>|                             --------------- `match` arms have incompatible types</b>
<b>121 |</b>                 Transform::Function(t) =&gt; {
    <b>|  _________________________________________-</b>
<b>122 | |</b>                   filter_event_type(input_rx, input_type).compat().flat_map(|v| {
<b>123 | |</b>                       futures::stream::iter(match v {
<b>124 | |</b>                           Err(e) =&gt; {
<b>...   |</b>
<b>139 | |</b>                   .compat();
<b>140 | |</b>               }
    <b>| |_______________- this is found to be of type `()`</b>
<b>141 |</b>                 Transform::Task(t) =&gt; t
    <b>|  _____________________________________^</b>
<b>142 | |</b>                   .transform(filter_event_type(input_rx, input_type))
<b>143 | |</b>                   .forward(output)
<b>144 | |</b>                   .map(|_| debug!("Finished"))
<b>145 | |</b>                   .compat(),
    <b>| |___________________________^ expected `()`, found struct `futures::compat::Compat01As03`</b>
    <b>|</b>
    <b>= note:</b> expected type `<b>()</b>`
             found struct `<b>futures::compat::Compat01As03&lt;futures::Map&lt;futures::stream::Forward&lt;std::boxed::Box&lt;dyn futures::Stream&lt;Error = (), Item = event::Event&gt; + std::marker::Send&gt;, topology::fanout::Fanout&gt;, [closure@src/topology/builder.rs:144:22: 144:44]&gt;&gt;</b>`
</pre>

FYI @Hoverbear
This commit is contained in:
Yuki Okushi 2020-10-23 18:26:40 +09:00 committed by GitHub
commit 7ba519ec50
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 53 additions and 15 deletions
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16
compiler/rustc_infer/src/infer/error_reporting/mod.rs
View File

@ -619,6 +619,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
scrut_hir_id,
opt_suggest_box_span,
arm_span,
scrut_span,
..
}) => match source {
hir::MatchSource::IfLetDesugar { .. } => {
@ -664,18 +665,29 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
Some(ty::error::ExpectedFound { expected, .. }) => expected,
_ => last_ty,
});
let msg = "`match` arms have incompatible types";
err.span_label(cause.span, msg);
let source_map = self.tcx.sess.source_map();
let mut any_multiline_arm = source_map.is_multiline(arm_span);
if prior_arms.len() <= 4 {
for sp in prior_arms {
any_multiline_arm |= source_map.is_multiline(*sp);
err.span_label(*sp, format!("this is found to be of type `{}`", t));
}
} else if let Some(sp) = prior_arms.last() {
any_multiline_arm |= source_map.is_multiline(*sp);
err.span_label(
*sp,
format!("this and all prior arms are found to be of type `{}`", t),
);
}
let outer_error_span = if any_multiline_arm {
// Cover just `match` and the scrutinee expression, not
// the entire match body, to reduce diagram noise.
cause.span.shrink_to_lo().to(scrut_span)
} else {
cause.span
};
let msg = "`match` arms have incompatible types";
err.span_label(outer_error_span, msg);
if let Some(sp) = semi_span {
err.span_suggestion_short(
sp,

1
compiler/rustc_middle/src/traits/mod.rs
View File

@ -343,6 +343,7 @@ static_assert_size!(ObligationCauseCode<'_>, 32);
#[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
pub struct MatchExpressionArmCause<'tcx> {
pub arm_span: Span,
pub scrut_span: Span,
pub semi_span: Option<Span>,
pub source: hir::MatchSource,
pub prior_arms: Vec<Span>,

1
compiler/rustc_typeck/src/check/_match.rs
View File

@ -201,6 +201,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
expr.span,
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
arm_span,
scrut_span: scrut.span,
semi_span,
source: match_src,
prior_arms: other_arms.clone(),

10
src/test/ui/match/match-incompat-type-semi.rs
View File

@ -39,4 +39,14 @@ fn main() {
None => { //~ ERROR incompatible types
},
};
let _ = match Some(42) {
Some(x) => "rust-lang.org"
.chars()
.skip(1)
.chain(Some(x as u8 as char))
.take(10)
.any(char::is_alphanumeric),
None => {} //~ ERROR incompatible types
};
}

40
src/test/ui/match/match-incompat-type-semi.stderr
View File

@ -56,19 +56,33 @@ LL | | };
error[E0308]: `match` arms have incompatible types
--> $DIR/match-incompat-type-semi.rs:39:17
|
LL | let _ = match Some(42) {
| _____________-
LL | | Some(x) => {
LL | | x
| | - this is found to be of type `{integer}`
LL | | },
LL | | None => {
| |_________________^
LL | || },
| ||_________^ expected integer, found `()`
LL | | };
| |_____- `match` arms have incompatible types
LL | let _ = match Some(42) {
| -------------- `match` arms have incompatible types
LL | Some(x) => {
LL | x
| - this is found to be of type `{integer}`
LL | },
LL | None => {
| _________________^
LL | | },
| |_________^ expected integer, found `()`
error: aborting due to 4 previous errors
error[E0308]: `match` arms have incompatible types
--> $DIR/match-incompat-type-semi.rs:50:17
|
LL | let _ = match Some(42) {
| -------------- `match` arms have incompatible types
LL | Some(x) => "rust-lang.org"
| ____________________-
LL | | .chars()
LL | | .skip(1)
LL | | .chain(Some(x as u8 as char))
LL | | .take(10)
LL | | .any(char::is_alphanumeric),
| |_______________________________________- this is found to be of type `bool`
LL | None => {}
| ^^ expected `bool`, found `()`
error: aborting due to 5 previous errors
For more information about this error, try `rustc --explain E0308`.