Fluid typography: PHP division by zero error when theme.json min and max viewport widths are equal

[ramonopoly]

When the same value is provided for min and max viewport widths in theme.json fluid typography config, PHP will throw a DivisionByZeroError.

This is because fluid typography calculates the linear scale denominator using minViewportWidth - maxViewportWidth.

See the two 1640px values:

{
	"$schema": "https://schemas.wp.org/trunk/theme.json",
	"version": 2,
	"settings": {

		"typography": {
			"fluid": {
				"minFontSize": "16px",
				"maxViewportWidth": "1640px",
				"minViewportWidth": "1640px"
			}
		}
	}
}

To avoid dividing by zero values, I propose returning null when minViewportWidth - maxViewportWidth is zero or some other falsey.

The consequence is that fluid font sizes will not be calculated.

The fluid typography clamp rule needs valid max and min viewport constraints.

Alternatives to this approach:

1. We could provide a fallback from the ​default values in gutenberg_get_typography_font_size_value(), e.g., 1600 - 320.

Syncs:

• ​https://github.com/WordPress/gutenberg/pull/57866

When the same value is provided for min and max viewport widths in the fluid typography config, set the linear scale factor to default 1.

To avoid dividing by zero values. PHP will throw an error and, besides, the fluid typography clamp rule needs valid max and min viewport constraints.

Trac ticket: https://core.trac.wordpress.org/ticket/60263

Those failing PHP 8 multisite tests look unrelated to me.

Just adding a similar comment as to the one I left on ​https://github.com/WordPress/gutenberg/pull/57866#pullrequestreview-1822541005, but I'm wondering if it'd be better to switch off fluid typography / return early if the min and max viewport sizes are the same?

but I'm wondering if it'd be better to switch off fluid typography / return early if the min and max viewport sizes are the same?

Thanks @andrewserong

I agree and I've updated accordingly.

The fluid typography clamp rule needs valid max and min viewport constraints to be "fluid" anyway, so returning early makes total sense.

🍺

This looks good to me. I restarted the failed phpunit test.

[audrasjb]

Moving to milestone 6.5.

Unit tests are passing now.

[isabel_brison]

In 57329:

Editor: fix fluid font division by zero error when min and max viewport widths are equal.

Fixes a division error by returning null when minViewportWidth - maxViewportWidth is zero in wp_get_computed_fluid_typography_value.

Props ramonopoly, mukesh27, andrewserong, audrasjb.
Fixes #60263.

Committed in r57329.