Account for unicode char width when calculating vertical label lines

[estebank]

In ui/terminal-width/non-whitespace-trimming-unicode.stderr we account for the visible char width when calculating the label and span positions, but we do not do so for the vertical bar tying them together, causing the following output:

error[E0308]: mismatched types
  --> $DIR/non-whitespace-trimming-unicode.rs:4:415
   |
LL | ...♬♭♮♯♰♱♲♳♴♵♶♷♸♹♺♻♼♽♾♿⚀⚁⚂⚃⚄⚅⚆⚈⚉4"; let _: () = 42;  let _: &str = "🦀☀☁☂☃☄★☆☇☈☉☊☋☌☍☎☏☐☑☒☓  ☖☗☘☙☚☛☜☝☞☟☠☡☢☣☤☥☦☧☨☩☪☫☬☭☮☯☰☱☲☳☴☵☶☷☸☹☺☻☼☽☾☿♀♁♂♃...
   |                                             --   ^^ expected (), found integer
   |                                                      |
   |                                             expected due to this
   |
   = note: expected type `()`
              found type `{integer}`

error: aborting due to previous error

where it should be

error[E0308]: mismatched types
  --> $DIR/non-whitespace-trimming-unicode.rs:4:415
   |
LL | ...♬♭♮♯♰♱♲♳♴♵♶♷♸♹♺♻♼♽♾♿⚀⚁⚂⚃⚄⚅⚆⚈⚉4"; let _: () = 42;  let _: &str = "🦀☀☁☂☃☄★☆☇☈☉☊☋☌☍☎☏☐☑☒☓  ☖☗☘☙☚☛☜☝☞☟☠☡☢☣☤☥☦☧☨☩☪☫☬☭☮☯☰☱☲☳☴☵☶☷☸☹☺☻☼☽☾☿♀♁♂♃...
   |                                             --   ^^ expected (), found integer
   |                                             |
   |                                             expected due to this
   |
   = note: expected type `()`
              found type `{integer}`

error: aborting due to previous error

(Found during #66539)

[TheSamsa]

I would like to solve this as a first time issue. Best with some pointers where to start :)

[estebank]

@TheSamsa the code that draws the vertical lines is at

rust/src/librustc_errors/emitter.rs

Lines 901 to 927 in 3f93ffc

	// Write the vertical lines for labels that are on a different line as the underline.
	//
	// After this we will have:
	//
	// 2 | fn foo() {
	// | __________
	// | | |
	// | |
	// 3 |
	// 4 | | }
	// | |_
	for &(pos, annotation) in &annotations_position {
	let style = if annotation.is_primary {
	Style::UnderlinePrimary
	} else {
	Style::UnderlineSecondary
	};
	let pos = pos + 1;
	if pos > 1 && (annotation.has_label() || annotation.takes_space()) {
	for p in line_offset + 1..=line_offset + pos {
	buffer.putc(p,
	code_offset + annotation.start_col - margin.computed_left,
	'|',
	style);
	}
	}

and the one that draws the span labels is right below

rust/src/librustc_errors/emitter.rs

Lines 949 to 974 in 3f93ffc

	// Write the labels on the annotations that actually have a label.
	//
	// After this we will have:
	//
	// 2 | fn foo() {
	// | __________
	// | |
	// | something about `foo`
	// 3 |
	// 4 | }
	// | _ test
	for &(pos, annotation) in &annotations_position {
	let style = if annotation.is_primary {
	Style::LabelPrimary
	} else {
	Style::LabelSecondary
	};
	let (pos, col) = if pos == 0 {
	(pos + 1, (annotation.end_col + 1).saturating_sub(left))
	} else {
	(pos + 2, annotation.start_col.saturating_sub(left))
	};
	if let Some(ref label) = annotation.label {
	buffer.puts(line_offset + pos, code_offset + col, &label, style);
	}
	}

I think the error might be using margin.computed_left instead of left, but I'm not entirely certain.

If this is your first time compiling rustc, you probably want to read the rustc guide, but the TL;DR: is "run ./x.py test src/test/ui --stage 1 --bless to build the compiler up to the first stage and update the stderr test output files".

You might also want to wait until the linked PR is merged so you have a test case, unless you wish to come up with a new one (look for a test that has multiple labels in the same span and pad the source to the left with unicode chars on non-1 width).

[TheSamsa]

Thank you!
I did read the rustc guide, and even compiled it on my own once. But thanks for the direction, and the note to the PR.
I'll do my best 😉