MDL-56959 theme: SCSS file is inherited from parent

Also added support for the SCSS property to be a Closure
and return content rather than simply being the name of a file.

theme/boost/config.php

@@ -27,9 +27,11 @@ defined('MOODLE_INTERNAL') || die();
 require_once(__DIR__ . '/lib.php');
 
 $THEME->name = 'boost';
-$THEME->scssfile = 'preset';
 $THEME->sheets = [];
 $THEME->editor_sheets = [];
+$THEME->scss = function($theme) {
+    return theme_boost_get_main_scss_content($theme);
+};
 
 $THEME->layouts = [
     // Most backwards compatible layout without the blocks - this is the layout used by default.

theme/boost/lib.php

@@ -46,38 +46,16 @@ function theme_boost_get_extra_scss($theme) {
 }
 
 /**
- * Get SCSS to prepend.
+ * Returns the main SCSS content.
  *
  * @param theme_config $theme The theme config object.
- * @return array
+ * @return string
  */
-function theme_boost_get_pre_scss($theme) {
+function theme_boost_get_main_scss_content($theme) {
     global $CFG;
 
     $scss = '';
-    $configurable = [
-        // Config key => [variableName, ...].
-        'brandcolor' => ['brand-primary'],
-    ];
-
-    // Prepend variables first.
-    foreach ($configurable as $configkey => $targets) {
-        $value = $theme->settings->{$configkey};
-        if (empty($value)) {
-            continue;
-        }
-        array_map(function($target) use (&$scss, $value) {
-            $scss .= '$' . $target . ': ' . $value . ";\n";
-        }, (array) $targets);
-    }
-
-    // Prepend pre-scss.
-    if (!empty($theme->settings->scsspre)) {
-        $scss .= $theme->settings->scsspre;
-    }
-
-    // Now append the preset.
-    $filename = $theme->settings->preset;
+    $filename = !empty($theme->settings->preset) ? $theme->settings->preset : null;
     $fs = get_file_storage();
 
     $context = context_system::instance();
@@ -94,3 +72,37 @@ function theme_boost_get_pre_scss($theme) {
 
     return $scss;
 }
+
+/**
+ * Get SCSS to prepend.
+ *
+ * @param theme_config $theme The theme config object.
+ * @return array
+ */
+function theme_boost_get_pre_scss($theme) {
+    global $CFG;
+
+    $scss = '';
+    $configurable = [
+        // Config key => [variableName, ...].
+        'brandcolor' => ['brand-primary'],
+    ];
+
+    // Prepend variables first.
+    foreach ($configurable as $configkey => $targets) {
+        $value = isset($theme->settings->{$configkey}) ? $theme->settings->{$configkey} : null;
+        if (empty($value)) {
+            continue;
+        }
+        array_map(function($target) use (&$scss, $value) {
+            $scss .= '$' . $target . ': ' . $value . ";\n";
+        }, (array) $targets);
+    }
+
+    // Prepend pre-scss.
+    if (!empty($theme->settings->scsspre)) {
+        $scss .= $theme->settings->scsspre;
+    }
+
+    return $scss;
+}

theme/upgrade.txt

@@ -19,9 +19,10 @@ Removed themes:
  * CLI svgtool.php has moved from theme/base/cli to admin/cli and paths should be relative to the new location.
 * Bootstrap 4 was added as part of a the new theme 'boost'.
 * Themes can now automatically compile SCSS on the fly. This works the same way as it
-  does compiling LESS on the fly, effecitvely adding $THEME->scssfile to your config.
+  does compiling LESS on the fly, effecitvely adding $THEME->scss to your config.
 * Two new callbacks allow themes to inject SCSS code before and after the content provided
-  by the SCSS file $THEME->scssfile. See $THEME->prescsscallback and $THEME->extrascsscallback.
+  by the SCSS file $THEME->scss. See $THEME->prescsscallback and $THEME->extrascsscallback.
+* $THEME->scss can also be a Closure which will return the main SCSS content.
 * Using .dir-rtl for RTL styling is deprecated and should not be used any more. From now
   the styles are automatically flipped when the language is right-to-left. However,
   as this is not always perfect, you can define exceptions. Please refer to the documentation