Collect errors which would be better as multiline errors

[mdinger]

This sorta seems like a metabug for a topic which doesn't exist...so I'm unsure if this is the right place for this. Either way, it still seems like a good idea though.

---

Errors such as #18946 would benefit from being multiline e.g. the second would be an improvement over the first:

<anon>:2:5: 2:10 error: mismatched types: expected `core::option::Option<int>`, found `core::result::Result<_, _>` (expected enum core::option::Option, found enum core::result::Result)

<anon>:2:5: 2:10 error: mismatched types: expected `core::option::Option<int>`,
                                             found `core::result::Result<_, _>`
                                         (expected enum `core::option::Option`,
                                             found enum `core::result::Result`)

Simple whitespace padding on single line errors cannot be implemented because of how it interacts with word wrapping (see #19203 (comment)). A better way would be to optionally enable multiline errors e.g. via compiler flags. However, a compiler flag for just one error may be overkill.

This bug is to collect errors which could be improved by being multiline errors and the way they should be improved. Then a more comprehensive fix can be enabled later.

cc @P1start @steveklabnik @jakub- @sinistersnare

---

Also might have other creative uses like improving #16619.

[mdinger]

Similar to #18946 :

struct S;

impl Iterator<uint> for S {
    fn next(&mut self) -> Result<uint, uint> { Ok(7) }
}

fn main() {}

---

Error:

<anon>:4:5: 4:55 error: method `next` has an incompatible type for trait: expected enum core::option::Option, found enum core::result::Result [E0053]
<anon>:4     fn next(&mut self) -> Result<uint, uint> { Ok(7) }
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error
playpen: application terminated with error code 101

---

Improved:

<anon>:4:5: 4:55 error: method `next` has an incompatible type for trait: expected enum `core::option::Option`,
                                                                             found enum `core::result::Result` [E0053]
<anon>:4     fn next(&mut self) -> Result<uint, uint> { Ok(7) }
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error
playpen: application terminated with error code 101

Comments:

• added backticks
• maybe should move [E0053]

[sinistersnare]

slight sidebar. Maybe the errors would look better as:

<anon>:4:5: 4:55 error [E0053]: method `next` has an incompatible type for trait: expected enum `core::option::Option`,
                                                                                     found enum `core::result::Result`
<anon>:4     fn next(&mut self) -> Result<uint, uint> { Ok(7) }
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error
playpen: application terminated with error code 101

I moved the error message to the beginning in the end. Although this is more of a general thing, and not for any specific errors.

[mdinger]

That seems sensible.

[mdinger]

struct S;

fn test() -> Option<int> {
    let s: S;

    s
}
fn main(){ 
    test();
}

---

Error:

<anon>:6:5: 6:6 error: mismatched types: expected `core::option::Option<int>`, found `S` (expected enum core::option::Option, found struct S)
<anon>:6     s
             ^
error: aborting due to previous error
playpen: application terminated with error code 101

---

Better:

<anon>:6:5: 6:6 error: mismatched types:
 expected `core::option::Option<int>`,
    found `S`
(expected enum `core::option::Option`,
    found struct `S`)
<anon>:6     s
             ^
error: aborting due to previous error
playpen: application terminated with error code 101

[mdinger]

#![feature(associated_types)]

pub trait Foo {
    type A;
    fn boo(&self) -> <Self as Foo>::A;
}

struct Bar;

impl Foo for int {
    type A = uint;
    fn boo(&self) -> uint {
        42
    }
}

fn foo1<I: Foo<A=Bar>>(x: I) {
    let _: Bar = x.boo();
}

fn foo2<I: Foo>(x: I) {
    let _: Bar = x.boo();
}


pub fn baz(x: &Foo<A=Bar>) {
    let _: Bar = x.boo();
}


pub fn main() {
    let a = 42i;
    foo1(a);
    baz(&a);
}

Poor:

<anon>:22:18: 22:25 error: mismatched types: expected `Bar`, found `<I as Foo>::A` (expected struct Bar, found associated type)
<anon>:22     let _: Bar = x.boo();
                           ^~~~~~~
<anon>:33:5: 33:9 error: type mismatch resolving `<int as Foo>::A == Bar`: expected uint, found struct Bar
<anon>:33     foo1(a);
              ^~~~
<anon>:33:5: 33:9 note: required by `foo1`
<anon>:33     foo1(a);
              ^~~~
<anon>:34:9: 34:11 error: type mismatch resolving `<int as Foo>::A == Bar`: expected uint, found struct Bar
<anon>:34     baz(&a);
                  ^~
<anon>:34:9: 34:11 note: required for the cast to the object type `Foo`
<anon>:34     baz(&a);
                  ^~
error: aborting due to 3 previous errors
playpen: application terminated with error code 101
Program ended.

Better:

<anon>:22:18: 22:25 error: mismatched types:
 expected `Bar`,
    found `<I as Foo>::A`
(expected struct Bar,
    found associated type)
<anon>:22     let _: Bar = x.boo();
                           ^~~~~~~
<anon>:33:5: 33:9 error: type mismatch resolving `<int as Foo>::A == Bar`:
 expected uint,
    found struct Bar
<anon>:33     foo1(a);
              ^~~~
<anon>:33:5: 33:9 note: required by `foo1`
<anon>:33     foo1(a);
              ^~~~
<anon>:34:9: 34:11 error: type mismatch resolving `<int as Foo>::A == Bar`:
 expected uint,
    found struct Bar
<anon>:34     baz(&a);
                  ^~
<anon>:34:9: 34:11 note: required for the cast to the object type `Foo`
<anon>:34     baz(&a);
                  ^~
error: aborting due to 3 previous errors
playpen: application terminated with error code 101
Program ended.

[mdinger]

fn take_any(_: ||) {
}

fn take_const_owned(_: ||:Sync+Send) {
}

fn give_any(f: ||) {
    take_any(f);
}

fn give_owned(f: ||:Send) {
    take_any(f);
    take_const_owned(f);
}

fn main() {}

Single line:

<anon>:13:22: 13:23 error: mismatched types: expected `'static ||:Send+Sync`, found `'static ||:Send` (expected bounds `Send+Sync`, found bounds `Send`)
<anon>:13     take_const_owned(f);
                               ^
error: aborting due to previous error
playpen: application terminated with error code 101

Multi-line:

<anon>:13:22: 13:23 error: mismatched types:
 expected `'static ||:Send+Sync`,
    found `'static ||:Send`
(expected bounds `Send+Sync`,
    found bounds `Send`)
<anon>:13     take_const_owned(f);
                               ^
error: aborting due to previous error
playpen: application terminated with error code 101

[mdinger]

Closed by #19870