Enhance compiler error for constraining builtin traits #93623

Pzixel · 2022-02-03T14:37:52Z

Given the following code:

fn foo<T>(t: Option<T>) {
    let _ = t == t;
}

It gives a nice error:

error[E0369]: binary operation `==` cannot be applied to type `Option<T>`
 --> src/main.rs:6:15
  |
6 |     let _ = t == t;
  |             - ^^ - Option<T>
  |             |
  |             Option<T>
  |
help: consider restricting type parameter `T`
  |
5 | fn duplicate<T: std::cmp::PartialEq>(t: Option<T>) {
  |               +++++++++++++++++++++

OTOH it doesn't work for say Copy:

fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) {
    (t, t)
}

which gives a somewhat unhelpful message:

error[E0382]: use of moved value: `t`
 --> src/main.rs:6:9
  |
5 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) {
  |                 - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait
6 |     (t, t)
  |      -  ^ value used here after move
  |      |
  |      value moved here

It would make sense to have this suggestion appearing here as well, e.g.

help: consider restricting type parameter `T`
  |
5 | fn duplicate<T: Copy>(t: Option<T>) {
  |               ++++++

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

WaffleLapkin · 2022-02-03T15:14:42Z

@rustbot label +A-diagnostics +A-suggestion-diagnostics +C-enhancement

Gordon01 · 2022-02-03T17:48:11Z

Maybe also mention about .clone() possibility?

WaffleLapkin · 2022-02-03T19:47:49Z

@rustbot claim

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? `@estebank` `@rustbot` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ``@estebank`` ``@rustbot`` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ```@estebank``` ```@rustbot``` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ````@estebank```` ````@rustbot```` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? `````@estebank````` `````@rustbot````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ``````@estebank`````` ``````@rustbot`````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ```````@estebank``````` ```````@rustbot``````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? ````````@estebank```````` ````````@rustbot```````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

…ebank Adt copy suggestions Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type - Can be copy - All predicates that need to be satisfied for that are based on type params i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`. An example: ```rust fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { (t, t) } ``` New error (current compiler doesn't provide `help`:): ```text error[E0382]: use of moved value: `t` --> t.rs:2:9 | 1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) { | - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait 2 | (t, t) | - ^ value used here after move | | | value moved here | help: consider restricting type parameter `T` | 1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) { | ++++++ ``` Fixes rust-lang#93623 r? `````````@estebank````````` `````````@rustbot````````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement ---- I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')

rustbot added A-diagnostics Area: Messages for errors, warnings, and lints A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` C-enhancement Category: An issue proposing an enhancement or a PR with one. labels Feb 3, 2022

rustbot assigned WaffleLapkin Feb 3, 2022

WaffleLapkin mentioned this issue Feb 25, 2022

Adt copy suggestions #94375

Merged

bors closed this as completed in 7537b20 Mar 3, 2022

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Enhance compiler error for constraining builtin traits #93623

Enhance compiler error for constraining builtin traits #93623

Pzixel commented Feb 3, 2022 •

edited by rustbot

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WaffleLapkin commented Feb 3, 2022

Gordon01 commented Feb 3, 2022

WaffleLapkin commented Feb 3, 2022

Enhance compiler error for constraining builtin traits #93623

Enhance compiler error for constraining builtin traits #93623

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Pzixel commented Feb 3, 2022 • edited by rustbot Loading

WaffleLapkin commented Feb 3, 2022

Gordon01 commented Feb 3, 2022

WaffleLapkin commented Feb 3, 2022

Pzixel commented Feb 3, 2022 •

edited by rustbot

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