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Rollup merge of #126899 - GrigorenkoPV:suggest-const-block, r=davidtwco
Suggest inline const blocks for array initialization #126894
2 parents 9ce2a07 + ba5ec1f commit a7721a0

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+26
-66
lines changed

4 files changed

+26
-66
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‎compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs‎

Lines changed: 7 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -2915,54 +2915,28 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
29152915
}
29162916
ObligationCauseCode::RepeatElementCopy {
29172917
is_constable,
2918-
elt_type,
2918+
elt_type: _,
29192919
elt_span,
2920-
elt_stmt_span,
2920+
elt_stmt_span: _,
29212921
} => {
29222922
err.note(
29232923
"the `Copy` trait is required because this value will be copied for each element of the array",
29242924
);
2925-
let value_kind = match is_constable {
2926-
IsConstable::Fn => Some("the result of the function call"),
2927-
IsConstable::Ctor => Some("the result of the constructor"),
2928-
_ => None,
2929-
};
29302925
let sm = tcx.sess.source_map();
2931-
if let Some(value_kind) = value_kind
2926+
if matches!(is_constable, IsConstable::Fn | IsConstable::Ctor)
29322927
&& let Ok(snip) = sm.span_to_snippet(elt_span)
29332928
{
2934-
let help_msg = format!(
2935-
"consider creating a new `const` item and initializing it with {value_kind} \
2936-
to be used in the repeat position"
2937-
);
2938-
let indentation = sm.indentation_before(elt_stmt_span).unwrap_or_default();
2939-
err.multipart_suggestion(
2940-
help_msg,
2941-
vec![
2942-
(
2943-
elt_stmt_span.shrink_to_lo(),
2944-
format!(
2945-
"const ARRAY_REPEAT_VALUE: {elt_type} = {snip};\n{indentation}"
2946-
),
2947-
),
2948-
(elt_span, "ARRAY_REPEAT_VALUE".to_string()),
2949-
],
2929+
err.span_suggestion(
2930+
elt_span,
2931+
"create an inline `const` block",
2932+
format!("const {{ {snip} }}"),
29502933
Applicability::MachineApplicable,
29512934
);
29522935
} else {
29532936
// FIXME: we may suggest array::repeat instead
29542937
err.help("consider using `core::array::from_fn` to initialize the array");
29552938
err.help("see https://doc.rust-lang.org/stable/std/array/fn.from_fn.html for more information");
29562939
}
2957-
2958-
if tcx.sess.is_nightly_build()
2959-
&& matches!(is_constable, IsConstable::Fn | IsConstable::Ctor)
2960-
{
2961-
err.help(
2962-
"create an inline `const` block, see RFC #2920 \
2963-
<https://github.com/rust-lang/rfcs/pull/2920> for more information",
2964-
);
2965-
}
29662940
}
29672941
ObligationCauseCode::VariableType(hir_id) => {
29682942
if let Some(typeck_results) = &self.typeck_results

‎tests/ui/consts/const-blocks/fn-call-in-non-const.stderr‎

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -6,17 +6,15 @@ LL | let _: [Option<Bar>; 2] = [no_copy(); 2];
66
|
77
= note: required for `Option<Bar>` to implement `Copy`
88
= note: the `Copy` trait is required because this value will be copied for each element of the array
9-
= help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
109
help: consider annotating `Bar` with `#[derive(Copy)]`
1110
|
1211
LL + #[derive(Copy)]
1312
LL | struct Bar;
1413
|
15-
help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
16-
|
17-
LL ~ const ARRAY_REPEAT_VALUE: Option<Bar> = no_copy();
18-
LL ~ let _: [Option<Bar>; 2] = [ARRAY_REPEAT_VALUE; 2];
14+
help: create an inline `const` block
1915
|
16+
LL | let _: [Option<Bar>; 2] = [const { no_copy() }; 2];
17+
| ~~~~~~~~~~~~~~~~~~~
2018

2119
error: aborting due to 1 previous error
2220

‎tests/ui/consts/const-blocks/trait-error.stderr‎

Lines changed: 4 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -2,21 +2,18 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
22
--> $DIR/trait-error.rs:5:6
33
|
44
LL | [Foo(String::new()); 4];
5-
| ^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`, which is required by `Foo<String>: Copy`
5+
| ^^^^^^^^^^^^^^^^^^
6+
| |
7+
| the trait `Copy` is not implemented for `String`, which is required by `Foo<String>: Copy`
8+
| help: create an inline `const` block: `const { Foo(String::new()) }`
69
|
710
note: required for `Foo<String>` to implement `Copy`
811
--> $DIR/trait-error.rs:1:10
912
|
1013
LL | #[derive(Copy, Clone)]
1114
| ^^^^ unsatisfied trait bound introduced in this `derive` macro
1215
= note: the `Copy` trait is required because this value will be copied for each element of the array
13-
= help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
1416
= note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
15-
help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
16-
|
17-
LL ~ const ARRAY_REPEAT_VALUE: Foo<String> = Foo(String::new());
18-
LL ~ [ARRAY_REPEAT_VALUE; 4];
19-
|
2017

2118
error: aborting due to 1 previous error
2219

‎tests/ui/consts/const-fn-in-vec.stderr‎

Lines changed: 12 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -2,45 +2,36 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
22
--> $DIR/const-fn-in-vec.rs:1:47
33
|
44
LL | static _MAYBE_STRINGS: [Option<String>; 5] = [None; 5];
5-
| ^^^^ the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
5+
| ^^^^
6+
| |
7+
| the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
8+
| help: create an inline `const` block: `const { None }`
69
|
710
= note: required for `Option<String>` to implement `Copy`
811
= note: the `Copy` trait is required because this value will be copied for each element of the array
9-
= help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
10-
help: consider creating a new `const` item and initializing it with the result of the constructor to be used in the repeat position
11-
|
12-
LL + const ARRAY_REPEAT_VALUE: Option<String> = None;
13-
LL ~ static _MAYBE_STRINGS: [Option<String>; 5] = [ARRAY_REPEAT_VALUE; 5];
14-
|
1512

1613
error[E0277]: the trait bound `String: Copy` is not satisfied
1714
--> $DIR/const-fn-in-vec.rs:7:34
1815
|
1916
LL | let _strings: [String; 5] = [String::new(); 5];
20-
| ^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
17+
| ^^^^^^^^^^^^^
18+
| |
19+
| the trait `Copy` is not implemented for `String`
20+
| help: create an inline `const` block: `const { String::new() }`
2121
|
2222
= note: the `Copy` trait is required because this value will be copied for each element of the array
23-
= help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
24-
help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
25-
|
26-
LL ~ const ARRAY_REPEAT_VALUE: String = String::new();
27-
LL ~ let _strings: [String; 5] = [ARRAY_REPEAT_VALUE; 5];
28-
|
2923

3024
error[E0277]: the trait bound `String: Copy` is not satisfied
3125
--> $DIR/const-fn-in-vec.rs:9:48
3226
|
3327
LL | let _maybe_strings: [Option<String>; 5] = [None; 5];
34-
| ^^^^ the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
28+
| ^^^^
29+
| |
30+
| the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
31+
| help: create an inline `const` block: `const { None }`
3532
|
3633
= note: required for `Option<String>` to implement `Copy`
3734
= note: the `Copy` trait is required because this value will be copied for each element of the array
38-
= help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
39-
help: consider creating a new `const` item and initializing it with the result of the constructor to be used in the repeat position
40-
|
41-
LL ~ const ARRAY_REPEAT_VALUE: Option<String> = None;
42-
LL ~ let _maybe_strings: [Option<String>; 5] = [ARRAY_REPEAT_VALUE; 5];
43-
|
4435

4536
error: aborting due to 3 previous errors
4637

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