Proposal: Discorage use of currently unused font faces / familes

[notlee]

Problem

If a typography mixin such as oTypographySans is used to output a family/weight/style combination which does not have a font face in o-fonts an error is thrown.

However there is no notice when a font face exists in o-fonts but hasn't been included in the project. Neither is there a way to "deprecate" the use of a font face within a project, which may have been included previously.

This is a problem because it would be expensive to load all our font families on ft.com, and when one has been included but rarely used it's difficult to remove. For example one font that has slipped into use on ft.com is MetricWeb medium (500). It is very rarely used and doesn't justify downloading another custom font.

Proposal

1. Throw an error when a font face is used by o-typography which exists in o-fonts but has not been output by o-fonts.

• This will require a change to o-fonts to keep track of which fonts have been output (or output and deprecated in the project, see proposal 2).
• The error should discourage adding new fonts for performance reasons. It should list which fonts have already been output and are available to use freely.
• It should be possible to dismiss the error globally per font face or totally, for cases where the fonts faces are included in a different Sass entry point. (@i-like-robots, this isn't the case for PageKit projects?)

2. Add a deprecated parameter to the oFonts mixin, so projects may deprecate and eventually remove the use of a font face (which may continue to exist in o-fonts for other projects in the brand).

// Pagekit?
@include oFonts($opts: (
    'metric': (
            ('weight': 'regular', 'style': 'normal'),
            ('weight': 'semibold', 'style': 'normal')
-           ('weight': 'medium', 'style': 'normal')
+           ('weight': 'medium', 'style': 'normal', 'deprecated': 'is being removed from ft.com, use semibold instead maybe')
    ),
    'financier-display': (
            ('weight': 'regular', 'style': 'normal')
    )
));

[i-like-robots]

Throw an error when a font face is used by o-typography which exists in o-fonts but has not been output by o-fonts

+1

for cases where the fonts faces are included in a different Sass entry point

Yes that's correct, we have two Sass entrypoints - global shared stuff (which includes fonts, normalise, grid, header, footer, layout) and an app specific one.

Add a deprecated parameter to the oFonts mixin

That's a good idea, although I doubt the efficacy or Sass warnings.

[notlee]

Yes that's correct, we have two Sass entrypoints - global shared stuff (which includes fonts, normalise, grid, header, footer, layout) and an app specific one.

Ah that's a bit annoying. We'd have to tell o-fonts in the second entry point what fonts have been included in the first, something like this:

@include oFontsAllowedFonts($allowed-fonts: (
    'metric': (
            ('weight': 'regular', 'style': 'normal'),
            ('weight': 'semibold', 'style': 'normal')
           ('weight': 'medium', 'style': 'normal', 'deprecated': 'is being removed from ft.com, use semibold instead maybe')
    ),
    'financier-display': (
            ('weight': 'regular', 'style': 'normal')
    )
));

If the map is the same as for the oFonts mixin at least a variable can be shared between the two entry points

[notlee]

Actually this isn't going to work out simply:

• it's a breaking change to error if the fonts aren't output (and I want to avoid a typography major, unless we make major cascades easier)
• origami components don't include fonts (builds will fail)

Let's:

• Add an o-fonts mixin as the above to log which fonts have been included for cases of CSS splitting. But let's name it oFontsVariantsIncluded
• Add an o-fonts function oFontsVariantIncluded to check which fonts have been included (to go along with the existing oFontsVariantExists function, which checks if the font is available in o-fonts at all)
• Add an o-typography variable $o-typography-error-on-missing-font: false that defaults to false, so this isn't breaking and doesn't break component builds. If a project sets $o-typography-error-on-missing-font: true, it will use oFontsVariantIncluded and error if the font being used has not been included

[notlee]

Closing in favour of: https://github.com/Financial-Times/o-fonts/issues/109 https://github.com/Financial-Times/o-typography/issues/249