feat(editor): add support for trailing whitespace rendering

[alevinval]

Context

Adds a new render configuration value Trailing, which can be used to selectively enable trailing whitespace of certain whitespace characters as requested in #2719

[pascalkuthe]

This will messup diagnostic and selection. The style can frequently differ, you should only be updating the text while leaving cell style unchanged

[alevinval]

How can I render something without being forced to provide a style?

[alevinval]

I'm still not sure how to apply this feedback. I've changed the code to always apply whitespace_style though. I think this is basically the last pending thing to address.

[m0ar]

@pascalkuthe Would it be possible to the next round of review on this? 🙏 It's a feature I have been running a fork for and it would be great to see it included in the main editor, I'm sure @alevinval feels similarly :)

[kmicklas]

When testing this I noticed that with many themes the trailing whitespace indicators are not particularly visible, which makes sense since they share a style with the "all" whitespace render feature. However, it's counterproductive if the goal is to have a very clear visible indicator of trailing whitespace. Is it worth considering a separate style class for this?

[alevinval]

Hi @kmicklas, any pointers on where I should look in the codebase to land a custom style? So far I've pushed to keep this PR up-to-date with the latest master changes, which now also deal with narrow non-breaking spaces.

[alevinval]

@kmicklas I realize now that adding the style appears to be quite trivial. I've just pushed 970122f, and with the following update on the config of my current theme:

diff --git a/runtime/themes/onelight.toml b/runtime/themes/onelight.toml
index e395716d..2f089060 100644
--- a/runtime/themes/onelight.toml
+++ b/runtime/themes/onelight.toml
@@ -138,6 +138,7 @@
 "ui.virtual.ruler" = { bg = "grey-200" }
 "ui.virtual.wrap" = { fg = "grey-500" }
 "ui.virtual.whitespace" = { fg = "grey-400" }
+"ui.virtual.trailing_whitespace" = { fg = "grey-300", bg = "red" }
 "ui.virtual.indent-guide" = { fg = "grey-500" }
 "ui.virtual.inlay-hint" = { fg = "grey-500" }
 "ui.virtual.inlay-hint.parameter" = { fg = "grey-500", modifiers = ["italic"] }

Results in the following:

I presume I don't have to update any theme here, and that theme owners can choose how to best style it.

[gamma-delta]

Hi, just putting here that I'd love this feature -- I write a lot of code for my job that I can't run a formatter on (because we don't have consistent formatting, or because it's some in-house language), and having this display immediately without needing to scour through the whole thing with all the whitespace symbols on or using git diff would be great.

[inducer]

I've been using this, and I greatly appreciate the feature. I did notice an issue (though I am not meaning to hold up a potential merge):

If a line is truncated at the edge of the editor window, any spaces that happen to be at the end are flagged as trailing. This disappears once you scroll to the right.

Before scrolling:

After scrolling:

[daedroza]

Can this feature be rebased on current HEAD instead of using merge tag?

[ElYaiko]

This works good, will this be merged on main?

[alevinval]

Long time no code, I've updated this branch to latest master changes.

[kanashimia]

1. Typing while having this option enabled is very distracting, especially if you set the highlighter to red background, your editor will blink every time you enter next word, as trailing whitespace is shown immediately. It works ok like that for regular whitespace.render = "all", but here it just isn't good, there needs to be some delay at least. You can also not render it on the same line as the primary cursor, but that will make it slightly confusing when you try delete the whitespace.

2. Whitespace marker isn't rendered where it should be with tabs. Easier to see on the picture.

   whitespace.render="all":

   

   whitespace.render="trailing":

   

   Gray rectangle is the cursor.

3. Trailing whitespace isn't rendered on the line with no newline.

[daedroza]

Long time no code, I've updated this branch to latest master changes.

Hey, inside trailing_whitespace.rs

        WhitespaceKind::Tab => {
            let grapheme_tab_width = char_to_byte_idx(&palette.tab, 1);
            &palette.tab[..grapheme_tab_width]
        }

For grapheme_tab_width should be char_to_byte_idx(&palette.tab, palette.tab.len()). The default 1 value renders incorrectly when the character for tab is also space.

Indeed there are some other bugs but I'm happy with current changes.

[ntzm]

Works well for me, can you also add the new value into the docs https://github.com/helix-editor/helix/blob/master/book/src/editor.md#editorwhitespace-section

[nik-rev]

If there is some whitespace and your cursor is on the whitespace, it will become fully highlighted

So naturally I would expect that if I pressed d it would delete the entire highlighted region, but this isn't the case as just one newline is deleted, the whitespace isn't.

So I think it makes sense if the entire whitespace didn't get highlighted, OR the highlighted region was treated as a selection and would delete the whitespace

[senekor]

Hi, just putting here that I'd love this feature -- I write a lot of code for my job that I can't run a formatter on (because we don't have consistent formatting, or because it's some in-house language), and having this display immediately without needing to scour through the whole thing with all the whitespace symbols on or using git diff would be great.

@gamma-delta For your use case, it might be even better to configure a custom formatter that only trims trailing whitespace. Less annoying visually, less manual work. A sed command can do this, alternatively I made ec2hx which has that built-in. I also commented about this here and here.