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.


git-svn-id: https://develop.svn.wordpress.org/trunk@57329 602fd350-edb4-49c9-b593-d223f7449a82

Author: tellthemachines

src/wp-includes/block-supports/typography.php

@@ -398,6 +398,7 @@ function wp_get_typography_value_and_unit( $raw_value, $options = array() ) {
  *
  * @since 6.1.0
  * @since 6.3.0 Checks for unsupported min/max viewport values that cause invalid clamp values.
+ * @since 6.5.0 Returns early when min and max viewport subtraction is zero to avoid division by zero.
  * @access private
  *
  * @param array $args {
@@ -468,12 +469,18 @@ function wp_get_computed_fluid_typography_value( $args = array() ) {
 		return null;
 	}
 
+	// Calculates the linear factor denominator. If it's 0, we cannot calculate a fluid value.
+	$linear_factor_denominator = $maximum_viewport_width['value'] - $minimum_viewport_width['value'];
+	if ( empty( $linear_factor_denominator ) ) {
+		return null;
+	}
+
 	/*
 	 * Build CSS rule.
 	 * Borrowed from https://websemantics.uk/tools/responsive-font-calculator/.
 	 */
 	$view_port_width_offset = round( $minimum_viewport_width['value'] / 100, 3 ) . $font_size_unit;
-	$linear_factor          = 100 * ( ( $maximum_font_size['value'] - $minimum_font_size['value'] ) / ( $maximum_viewport_width['value'] - $minimum_viewport_width['value'] ) );
+	$linear_factor          = 100 * ( ( $maximum_font_size['value'] - $minimum_font_size['value'] ) / ( $linear_factor_denominator ) );
 	$linear_factor_scaled   = round( $linear_factor * $scale_factor, 3 );
 	$linear_factor_scaled   = empty( $linear_factor_scaled ) ? 1 : $linear_factor_scaled;
 	$fluid_target_font_size = implode( '', $minimum_font_size_rem ) . " + ((1vw - $view_port_width_offset) * $linear_factor_scaled)";

tests/phpunit/tests/block-supports/typography.php

@@ -913,6 +913,7 @@ public function data_invalid_size_wp_get_typography_value_and_unit() {
 	 * Tests computed font size values.
 	 *
 	 * @ticket 58522
+	 * @ticket 60263
 	 *
 	 * @covers ::wp_get_computed_fluid_typography_value
 	 *
@@ -951,6 +952,16 @@ public function data_wp_get_computed_fluid_typography_value() {
 				),
 				'expected_output' => 'clamp(50px, 3.125rem + ((1vw - 3.2px) * 7.353), 100px)',
 			),
+			'returns `null` when maximum and minimum viewport width are equal' => array(
+				'args'            => array(
+					'minimum_viewport_width' => '800px',
+					'maximum_viewport_width' => '800px',
+					'minimum_font_size'      => '50px',
+					'maximum_font_size'      => '100px',
+					'scale_factor'           => 1,
+				),
+				'expected_output' => null,
+			),
 			'returns `null` when `maximum_viewport_width` is an unsupported unit' => array(
 				'args'            => array(
 					'minimum_viewport_width' => '320px',