Tracking Issue for improving suggestion rendering in diagnostics #141973

estebank · 2025-06-03T16:29:09Z

This is a tracking issue for the prioritizing "verbose" or "hidden" suggestions over "inline" (the default given by span_suggestion suggestions.

Inline suggestions have several issues that make them less readable than verbose ones:

I've seen people get confused by them
Small differences caused by typos are much better seen on the verbose output, where the highlighting now points at the exact character, instead of having to visually notice the different text in non-aligned places
The inline output was the original implementation, but since we've introduced the diff output which is clearer on what we expect the user to write
For additions, things like "add a type parameter: " are even more unclear
Relying on the inline suggestions have lead us to use worse spans on purpose because otherwise the rendering would be bad (like skipping whitespace in some cases) and has a tendency to make suggestion mistakes harder to notice (broken suggestions making it in because we couldn't tell during review)
When a single suggestion is in the diagnostic, the default renders inline, but if there are two, then both get rendered as verbose, which makes the output sometimes sensitive to what was emitted and can cause two similar errors to look very different.

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Steps

Audit all cases of span_suggestion uses.
Adjust individual cases to be either span_suggestion_verbose, span_suggestion_hidden or span_suggestion_tool_only
Change span_suggestion to span_suggestion_inline and span_suggestion_verbose to span_suggestion

Implementation history

https://rust-lang.zulipchat.com/#narrow/channel/147480-t-compiler.2Fdiagnostics/topic/Why.20are.20we.20making.20suggestions.20verbose.3F

The text was updated successfully, but these errors were encountered:

compiler-errors · 2025-06-03T16:31:56Z

This work is also enabled by:

which improve the presentation of verbose suggestions when they're "purely additive", which should help reduce the impact of this work.

…-suggestion, r=compiler-errors Make E0621 missing lifetime suggestion verbose ``` error[E0621]: explicit lifetime required in the type of `x` --> $DIR/42701_one_named_and_one_anonymous.rs:10:9 | LL | &*x | ^^^ lifetime `'a` required | help: add explicit lifetime `'a` to the type of `x` | LL | fn foo2<'a>(a: &'a Foo, x: &'a i32) -> &'a i32 { | ++ ``` Part of rust-lang#141973.

…ywiser Verbose suggestion to make param `const` ``` error[E0747]: type provided when a constant was expected --> $DIR/invalid-const-arguments.rs:10:19 | LL | impl<N> Foo for B<N> {} | ^ | help: consider changing this type parameter to a const parameter | LL - impl<N> Foo for B<N> {} LL + impl<const N: u8> Foo for B<N> {} | ``` Part of rust-lang#141973.

Rollup merge of #142043 - estebank:const-suggestion, r=wesleywiser Verbose suggestion to make param `const` ``` error[E0747]: type provided when a constant was expected --> $DIR/invalid-const-arguments.rs:10:19 | LL | impl<N> Foo for B<N> {} | ^ | help: consider changing this type parameter to a const parameter | LL - impl<N> Foo for B<N> {} LL + impl<const N: u8> Foo for B<N> {} | ``` Part of #141973.

Verbose suggestion to make param `const` ``` error[E0747]: type provided when a constant was expected --> $DIR/invalid-const-arguments.rs:10:19 | LL | impl<N> Foo for B<N> {} | ^ | help: consider changing this type parameter to a const parameter | LL - impl<N> Foo for B<N> {} LL + impl<const N: u8> Foo for B<N> {} | ``` Part of rust-lang/rust#141973.

…gestion, r=compiler-errors Make obligation cause code suggestions verbose ``` error[E0277]: `()` is not a future --> $DIR/unnecessary-await.rs:28:10 | LL | e!().await; | ^^^^^ `()` is not a future | = help: the trait `Future` is not implemented for `()` = note: () must be a future or must implement `IntoFuture` to be awaited = note: required for `()` to implement `IntoFuture` help: remove the `.await` | LL - e!().await; LL + e!(); | ``` ``` 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` | = 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 | LL | static _MAYBE_STRINGS: [Option<String>; 5] = [const { None }; 5]; | +++++++ + ``` Part of rust-lang#141973

Make cast suggestions verbose ``` error[E0604]: only `u8` can be cast as `char`, not `u32` --> $DIR/E0604.rs:2:5 | LL | 1u32 as char; | ^^^^^^^^^^^^ invalid cast | help: try `char::from_u32` instead | LL - 1u32 as char; LL + char::from_u32(1u32); | ``` ``` error[E0620]: cast to unsized type: `&[u8]` as `[char]` --> $DIR/cast-to-slice.rs:6:5 | LL | arr as [char]; | ^^^^^^^^^^^^^ | help: try casting to a reference instead | LL | arr as &[char]; | + ``` ``` error[E0620]: cast to unsized type: `Box<{integer}>` as `dyn Send` --> $DIR/cast-to-unsized-trait-object-suggestion.rs:3:5 | LL | Box::new(1) as dyn Send; | ^^^^^^^^^^^^^^^^^^^^^^^ | help: you can cast to a `Box` instead | LL | Box::new(1) as Box<dyn Send>; | ++++ + ``` Part of rust-lang#141973.

…gestion, r=compiler-errors Make obligation cause code suggestions verbose ``` error[E0277]: `()` is not a future --> $DIR/unnecessary-await.rs:28:10 | LL | e!().await; | ^^^^^ `()` is not a future | = help: the trait `Future` is not implemented for `()` = note: () must be a future or must implement `IntoFuture` to be awaited = note: required for `()` to implement `IntoFuture` help: remove the `.await` | LL - e!().await; LL + e!(); | ``` ``` 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` | = 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 | LL | static _MAYBE_STRINGS: [Option<String>; 5] = [const { None }; 5]; | +++++++ + ``` Part of rust-lang#141973

Make cast suggestions verbose ``` error[E0604]: only `u8` can be cast as `char`, not `u32` --> $DIR/E0604.rs:2:5 | LL | 1u32 as char; | ^^^^^^^^^^^^ invalid cast | help: try `char::from_u32` instead | LL - 1u32 as char; LL + char::from_u32(1u32); | ``` ``` error[E0620]: cast to unsized type: `&[u8]` as `[char]` --> $DIR/cast-to-slice.rs:6:5 | LL | arr as [char]; | ^^^^^^^^^^^^^ | help: try casting to a reference instead | LL | arr as &[char]; | + ``` ``` error[E0620]: cast to unsized type: `Box<{integer}>` as `dyn Send` --> $DIR/cast-to-unsized-trait-object-suggestion.rs:3:5 | LL | Box::new(1) as dyn Send; | ^^^^^^^^^^^^^^^^^^^^^^^ | help: you can cast to a `Box` instead | LL | Box::new(1) as Box<dyn Send>; | ++++ + ``` Part of rust-lang#141973.

Rollup merge of #142131 - estebank:cast-sugg, r=Urgau Make cast suggestions verbose ``` error[E0604]: only `u8` can be cast as `char`, not `u32` --> $DIR/E0604.rs:2:5 | LL | 1u32 as char; | ^^^^^^^^^^^^ invalid cast | help: try `char::from_u32` instead | LL - 1u32 as char; LL + char::from_u32(1u32); | ``` ``` error[E0620]: cast to unsized type: `&[u8]` as `[char]` --> $DIR/cast-to-slice.rs:6:5 | LL | arr as [char]; | ^^^^^^^^^^^^^ | help: try casting to a reference instead | LL | arr as &[char]; | + ``` ``` error[E0620]: cast to unsized type: `Box<{integer}>` as `dyn Send` --> $DIR/cast-to-unsized-trait-object-suggestion.rs:3:5 | LL | Box::new(1) as dyn Send; | ^^^^^^^^^^^^^^^^^^^^^^^ | help: you can cast to a `Box` instead | LL | Box::new(1) as Box<dyn Send>; | ++++ + ``` Part of #141973.

Rollup merge of #142045 - estebank:obligation-cause-code-suggestion, r=compiler-errors Make obligation cause code suggestions verbose ``` error[E0277]: `()` is not a future --> $DIR/unnecessary-await.rs:28:10 | LL | e!().await; | ^^^^^ `()` is not a future | = help: the trait `Future` is not implemented for `()` = note: () must be a future or must implement `IntoFuture` to be awaited = note: required for `()` to implement `IntoFuture` help: remove the `.await` | LL - e!().await; LL + e!(); | ``` ``` 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` | = 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 | LL | static _MAYBE_STRINGS: [Option<String>; 5] = [const { None }; 5]; | +++++++ + ``` Part of #141973

compiler-errors assigned estebank Jun 3, 2025

fmease added the WG-diagnostics Working group: Diagnostics label Jun 3, 2025

This was referenced Jun 4, 2025

Make E0621 missing lifetime suggestion verbose #142042

Open

Verbose suggestion to make param const #142043

Merged

Make obligation cause code suggestions verbose #142045

Merged

estebank mentioned this issue Jun 6, 2025

Make cast suggestions verbose #142131

Merged

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Tracking Issue for improving suggestion rendering in diagnostics #141973

Tracking Issue for improving suggestion rendering in diagnostics #141973

estebank commented Jun 3, 2025 •

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compiler-errors commented Jun 3, 2025

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Tracking Issue for improving suggestion rendering in diagnostics #141973

Tracking Issue for improving suggestion rendering in diagnostics #141973

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estebank commented Jun 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Implementation history

compiler-errors commented Jun 3, 2025

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estebank commented Jun 3, 2025 •

edited

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