setup:static-content:deploy fails minifying CSS

Magento's built-in CSS minification is generally not required for Hyvä themes, as Hyvä generates minified CSS when running the build-prod command.

However, if Hyvä and Luma themes coexist, disabling Magento's global CSS minification might not be an option (Magento does not support store-view or website scope for this setting). In such scenarios, depending on the Tailwind CSS version and classes used, Magento's minification process can fail during bin/magento setup:static-content:deploy.

To resolve this, enable CSS minification globally and apply the patch below.

To enable CSS minification, run the command:

bin/magento config:set dev/css/minify_files 1

The following patch, contributed by Thomas Negeli (Limesoda), resolves the issue:

--- a/vendor/tubalmartin/cssmin/src/Minifier.php
+++ b/vendor/tubalmartin/cssmin/src/Minifier.php
@@ -298,43 +298,61 @@ class Minifier
         $css = $this->processDataUrls($css);

         // Process comments
-        $css = preg_replace_callback(
+        $newCss = preg_replace_callback(
             '/(?<!\\\\)\/\*(.*?)\*(?<!\\\\)\//Ss',
             array($this, 'processCommentsCallback'),
-            $css
+            (string)$css
         );
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // IE7: Process Microsoft matrix filters (whitespaces between Matrix parameters). Can contain strings inside.
-        $css = preg_replace_callback(
+        $newCss = preg_replace_callback(
             '/filter:\s*progid:DXImageTransform\.Microsoft\.Matrix\(([^)]+)\)/Ss',
             array($this, 'processOldIeSpecificMatrixDefinitionCallback'),
-            $css
+            (string)$css
         );
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // Process quoted unquotable attribute selectors to unquote them. Covers most common cases.
         // Likelyhood of a quoted attribute selector being a substring in a string: Very very low.
-        $css = preg_replace(
+        $newCss = preg_replace(
             '/\[\s*([a-z][a-z-]+)\s*([\*\|\^\$~]?=)\s*[\'"](-?[a-z_][a-z0-9-_]+)[\'"]\s*\]/Ssi',
             '[$1$2$3]',
-            $css
+            (string)$css
         );
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // Process strings so their content doesn't get accidentally minified
-        $css = preg_replace_callback(
+        $newCss = preg_replace_callback(
             '/(?:"(?:[^\\\\"]|\\\\.|\\\\)*")|'."(?:'(?:[^\\\\']|\\\\.|\\\\)*')/S",
             array($this, 'processStringsCallback'),
-            $css
+            (string)$css
         );
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // Normalize all whitespace strings to single spaces. Easier to work with that way.
-        $css = preg_replace('/\s+/S', ' ', $css);
+        $newCss = preg_replace('/\s+/S', ' ', (string)$css);
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // Process import At-rules with unquoted URLs so URI reserved characters such as a semicolon may be used safely.
-        $css = preg_replace_callback(
+        $newCss = preg_replace_callback(
             '/@import url\(([^\'"]+?)\)( |;)/Si',
             array($this, 'processImportUnquotedUrlAtRulesCallback'),
-            $css
+            (string)$css
         );
+        if(!is_null($newCss)) {
+            $css = $newCss;
+        }

         // Process comments
         $css = $this->processComments($css);