Beta regression in span printing with tabs involved

[est31]

This code (containing tabs) gives an error (playground):

	let b = "hello";
	let _a = b + ", World!";

The error works fine on stable:

  |
3 |  let _a = b + ", World!";
  |           ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
  |
3 |  let _a = b.to_owned() + ", World!";
  |           ^^^^^^^^^^^^

But is mispositioned on rustc 1.25.0-nightly (73ac5d6 2018-01-11) as well as on rustc 1.24.0-beta.2 (a19122c 2018-01-10):

  |
3 |     let _a = b + ", World!";
  |              ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
  |
3 |     let _a = b.to_owned() + ", World!";
  |           ^^^^^^^^^^^^

cc @estebank

[BubbaSheen]

Interesting. Im new to code work so following you guys has been extremely helpful thanks

…

On Jan 12, 2018 4:44 AM, "est31" ***@***.***> wrote: This code (containing tabs) gives an error (playground <https://play.rust-lang.org/?gist=7fbea34512455179a57ca244b297ba26&version=nightly> ): let b = "hello"; let _a = b + ", World!"; The error works fine on stable: | 3 | let _a = b + ", World!"; | ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left | 3 | let _a = b.to_owned() + ", World!"; | ^^^^^^^^^^^^ But is mispositioned on rustc 1.25.0-nightly (73ac5d6 <73ac5d6> 2018-01-11) as well as on rustc 1.24.0-beta.2 (a19122c <a19122c> 2018-01-10): | 3 | let _a = b + ", World!"; | ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left | 3 | let _a = b.to_owned() + ", World!"; | ^^^^^^^^^^^^ cc @estebank <https://github.com/estebank> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#47377>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AhXLZpW96E-kEteWrOLXG8iE-oM4vZhDks5tJylzgaJpZM4RcCkz> .

[est31]

Using bisect-rust I could see that the issue started with #45953, but probably the actual issue is somewhere else (e.g. in the machinery added in #45711 that #45953 starts using for tabs).

[est31]

Yeah, the issue also exists when emojis are involved (no tabs):

    let b = "hello";
    println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";

Gives:

4 |     println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
  |                                 ^^^^^^^^^^^^

The emoji manifestation of the issue is no beta regression, seems to exist on stable as well.

[est31]

I've created #47380 for the emoji/unicode issue.

[estebank]

It seems to me that the issue only manifests itself in suggestions, and that is handled separately from the main diagnostics.

---

Mentoring instructions:

emit_suggestion_default needs to be modified to use col_display instead of col.0, the start being span_start_pos.col_display + start and the end being span_start_pos.col_display + start + sub_len (sub_len already accounts for unicode chars). This change should fix both this and #47380.

[gaurikholkar-zz]

Will pick this up