Suggest inline const blocks for array initialization

4 files changed, 26 insertions, 66 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index b2fa3489dda..f9cdca6360e 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2915,38 +2915,21 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             }
             ObligationCauseCode::RepeatElementCopy {
                 is_constable,
-                elt_type,
+                elt_type: _,
                 elt_span,
-                elt_stmt_span,
+                elt_stmt_span: _,
             } => {
                 err.note(
                     "the `Copy` trait is required because this value will be copied for each element of the array",
                 );
-                let value_kind = match is_constable {
-                    IsConstable::Fn => Some("the result of the function call"),
-                    IsConstable::Ctor => Some("the result of the constructor"),
-                    _ => None,
-                };
                 let sm = tcx.sess.source_map();
-                if let Some(value_kind) = value_kind
+                if matches!(is_constable, IsConstable::Fn | IsConstable::Ctor)
                     && let Ok(snip) = sm.span_to_snippet(elt_span)
                 {
-                    let help_msg = format!(
-                        "consider creating a new `const` item and initializing it with {value_kind} \
-                        to be used in the repeat position"
-                    );
-                    let indentation = sm.indentation_before(elt_stmt_span).unwrap_or_default();
-                    err.multipart_suggestion(
-                        help_msg,
-                        vec![
-                            (
-                                elt_stmt_span.shrink_to_lo(),
-                                format!(
-                                    "const ARRAY_REPEAT_VALUE: {elt_type} = {snip};\n{indentation}"
-                                ),
-                            ),
-                            (elt_span, "ARRAY_REPEAT_VALUE".to_string()),
-                        ],
+                    err.span_suggestion(
+                        elt_span,
+                        "create an inline `const` block",
+                        format!("const {{ {snip} }}"),
                         Applicability::MachineApplicable,
                     );
                 } else {
@@ -2954,15 +2937,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     err.help("consider using `core::array::from_fn` to initialize the array");
                     err.help("see https://doc.rust-lang.org/stable/std/array/fn.from_fn.html for more information");
                 }
-
-                if tcx.sess.is_nightly_build()
-                    && matches!(is_constable, IsConstable::Fn | IsConstable::Ctor)
-                {
-                    err.help(
-                        "create an inline `const` block, see RFC #2920 \
-                         <https://github.com/rust-lang/rfcs/pull/2920> for more information",
-                    );
-                }
             }
             ObligationCauseCode::VariableType(hir_id) => {
                 if let Some(typeck_results) = &self.typeck_results
diff --git a/tests/ui/consts/const-blocks/fn-call-in-non-const.stderr b/tests/ui/consts/const-blocks/fn-call-in-non-const.stderr
index 14bce10f787..9dce29732ac 100644
--- a/tests/ui/consts/const-blocks/fn-call-in-non-const.stderr
+++ b/tests/ui/consts/const-blocks/fn-call-in-non-const.stderr
@@ -6,17 +6,15 @@ LL |     let _: [Option<Bar>; 2] = [no_copy(); 2];
    |
    = note: required for `Option<Bar>` to implement `Copy`
    = note: the `Copy` trait is required because this value will be copied for each element of the array
-   = help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
 help: consider annotating `Bar` with `#[derive(Copy)]`
    |
 LL + #[derive(Copy)]
 LL | struct Bar;
    |
-help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
-   |
-LL ~     const ARRAY_REPEAT_VALUE: Option<Bar> = no_copy();
-LL ~     let _: [Option<Bar>; 2] = [ARRAY_REPEAT_VALUE; 2];
+help: create an inline `const` block
    |
+LL |     let _: [Option<Bar>; 2] = [const { no_copy() }; 2];
+   |                                ~~~~~~~~~~~~~~~~~~~
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/consts/const-blocks/trait-error.stderr b/tests/ui/consts/const-blocks/trait-error.stderr
index b0b1378bb7d..8f00f14dfb9 100644
--- a/tests/ui/consts/const-blocks/trait-error.stderr
+++ b/tests/ui/consts/const-blocks/trait-error.stderr
@@ -2,7 +2,10 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
   --> $DIR/trait-error.rs:5:6
    |
 LL |     [Foo(String::new()); 4];
-   |      ^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`, which is required by `Foo<String>: Copy`
+   |      ^^^^^^^^^^^^^^^^^^
+   |      |
+   |      the trait `Copy` is not implemented for `String`, which is required by `Foo<String>: Copy`
+   |      help: create an inline `const` block: `const { Foo(String::new()) }`
    |
 note: required for `Foo<String>` to implement `Copy`
   --> $DIR/trait-error.rs:1:10
@@ -10,13 +13,7 @@ note: required for `Foo<String>` to implement `Copy`
 LL | #[derive(Copy, Clone)]
    |          ^^^^ unsatisfied trait bound introduced in this `derive` macro
    = note: the `Copy` trait is required because this value will be copied for each element of the array
-   = help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
-   |
-LL ~     const ARRAY_REPEAT_VALUE: Foo<String> = Foo(String::new());
-LL ~     [ARRAY_REPEAT_VALUE; 4];
-   |
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/consts/const-fn-in-vec.stderr b/tests/ui/consts/const-fn-in-vec.stderr
index 12098e8199c..7c6b3bee940 100644
--- a/tests/ui/consts/const-fn-in-vec.stderr
+++ b/tests/ui/consts/const-fn-in-vec.stderr
@@ -2,45 +2,36 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
   --> $DIR/const-fn-in-vec.rs:1:47
    |
 LL | static _MAYBE_STRINGS: [Option<String>; 5] = [None; 5];
-   |                                               ^^^^ the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
+   |                                               ^^^^
+   |                                               |
+   |                                               the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
+   |                                               help: create an inline `const` block: `const { None }`
    |
    = note: required for `Option<String>` to implement `Copy`
    = note: the `Copy` trait is required because this value will be copied for each element of the array
-   = help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
-help: consider creating a new `const` item and initializing it with the result of the constructor to be used in the repeat position
-   |
-LL + const ARRAY_REPEAT_VALUE: Option<String> = None;
-LL ~ static _MAYBE_STRINGS: [Option<String>; 5] = [ARRAY_REPEAT_VALUE; 5];
-   |
 
 error[E0277]: the trait bound `String: Copy` is not satisfied
   --> $DIR/const-fn-in-vec.rs:7:34
    |
 LL |     let _strings: [String; 5] = [String::new(); 5];
-   |                                  ^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
+   |                                  ^^^^^^^^^^^^^
+   |                                  |
+   |                                  the trait `Copy` is not implemented for `String`
+   |                                  help: create an inline `const` block: `const { String::new() }`
    |
    = note: the `Copy` trait is required because this value will be copied for each element of the array
-   = help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
-help: consider creating a new `const` item and initializing it with the result of the function call to be used in the repeat position
-   |
-LL ~     const ARRAY_REPEAT_VALUE: String = String::new();
-LL ~     let _strings: [String; 5] = [ARRAY_REPEAT_VALUE; 5];
-   |
 
 error[E0277]: the trait bound `String: Copy` is not satisfied
   --> $DIR/const-fn-in-vec.rs:9:48
    |
 LL |     let _maybe_strings: [Option<String>; 5] = [None; 5];
-   |                                                ^^^^ the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
+   |                                                ^^^^
+   |                                                |
+   |                                                the trait `Copy` is not implemented for `String`, which is required by `Option<String>: Copy`
+   |                                                help: create an inline `const` block: `const { None }`
    |
    = note: required for `Option<String>` to implement `Copy`
    = note: the `Copy` trait is required because this value will be copied for each element of the array
-   = help: create an inline `const` block, see RFC #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
-help: consider creating a new `const` item and initializing it with the result of the constructor to be used in the repeat position
-   |
-LL ~     const ARRAY_REPEAT_VALUE: Option<String> = None;
-LL ~     let _maybe_strings: [Option<String>; 5] = [ARRAY_REPEAT_VALUE; 5];
-   |
 
 error: aborting due to 3 previous errors