False "Whitespace between a mixin name and parentheses for a mixin call" deprecation warning

[egonolieux]

I'm getting a lot of mixin related errors like these:

<w> DEPRECATED WARNING: Whitespace between a mixin name and parentheses for a mixin call is deprecated in /home/egonolieux/projects/some-project/assets/less/mixins/divider.less on line 50, column 20:
<w> 50     .divider-bottom(
<w> 

It seems like splitting the mixin arguments over multiple lines (for better readability) causes the issue:

.divider-bottom(
  @spacing-top,
  @spacing-bottom,
  @border-width,
  @border-color
);

This is confusing because there is no whitespace between the mixin name and parentheses here. However, when rewriting it like this:

.divider-bottom(@spacing-top,
                @spacing-bottom,
                @border-width,
                @border-color
);

Or like this:

.divider-bottom(@spacing-top, @spacing-bottom, @border-width, @border-color);

The deprecation warning no longer shows up. It seems this has been introduced since #4319.

[dosubot]

Hello @egonolieux! I'm Dosu, your friendly helper bot here to assist you with bugs, answer questions, and guide you toward becoming a contributor. I'm here while you wait for a human maintainer!

To resolve the deprecation warning about whitespace between a mixin name and parentheses for a mixin call in Less, ensure there is no whitespace between the mixin name and the opening parenthesis. Your initial example is actually correct and should not trigger a warning:

.divider-bottom(
  @spacing-top,
  @spacing-bottom,
  @border-width,
  @border-color
);

If you're still encountering warnings, it might be due to a bug or an issue with the specific version of Less.js you are using. The warning is intended to be triggered when there is whitespace directly between the mixin name and the parenthesis, like in .a ();, which is deprecated ^[1]. If the warning persists despite correct syntax, consider checking for updates or patches that might address this issue.

To continue talking to Dosu, mention @dosu.

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[puckowski]

Thank you for the bug report. I'll see if I can take a look this weekend.

[matthew-dean]

Oh oops. Yeah this shouldn't cause the warning.

[Y80]

How to disable this warning❓❓❓

[Svish]

How to disable this warning❓❓❓

Either remove the whitespace after the parenthesis as well, or wait for a fix. In our case, it was only a handful of issues, so I just fixed them all and warning is gone 👍

[puckowski]

You can try the newer --quiet flag to suppress the deprecation warnings when compiling Less.

@Y80

[hostep]

Any chance we'll see a fix for this soon-ish? Many thanks!

[puckowski]

I'll try to take a look at this issue this weekend.

[puckowski]

I think I have a fix in #4365

If anyone wants to patch their Less parser and confirm the fix corrects the behavior I would appreciate it.

[hostep]

Looks good @puckowski!

I just tried it in the ecosystem I'm active in, which is Magento2 ecommerce platform written in php, that uses less files for its frontend, and the amount of deprecated warnings dropped from 1220 to 39 after your changes, and those 39 seem like valid warnings. (example where warning went away, and example where warning still shows up, but that seems valid)

Many thanks!

[puckowski]

@hostep Thank you for testing!