Support functions calls in CSS variable value after first comma

See https://github.com/less/less.js/pull/4237/files

Bug: T386079
Change-Id: Ifdbd79ad445bff1bedbc21c76be53132e128e57f

Author: anny21

lib/Less/Parser.php

@@ -2538,6 +2538,11 @@ private function parsePermissiveValue( $untilTokens = null ) {
 			if ( $e ) {
 				$value[] = $e;
 			}
+			// NOTE: Comma handling backported from Less.js 4.2.1 (T386077)
+			if ( $this->peekChar( ',' ) ) {
+				$value[] = new Less_Tree_Anonymous( ',' );
+				$this->matchChar( ',' );
+			}
 		} while ( $e );
 		$done = $testCurrentChar( $this->input[$this->pos] );
 		if ( $value ) {

lib/Less/Tree/Expression.php

@@ -69,7 +69,12 @@ public function genCSS( $output ) {
 		for ( $i = 0; $i < $val_len; $i++ ) {
 			$this->value[$i]->genCSS( $output );
 			if ( !$this->noSpacing && ( $i + 1 < $val_len ) ) {
-				$output->add( ' ' );
+				// NOTE: Comma handling backported from Less.js 4.2.1 (T386077)
+				if ( !( $this->value[$i + 1] instanceof Less_Tree_Anonymous )
+					|| ( $this->value[$i + 1] instanceof Less_Tree_Anonymous && $this->value[$i + 1]->value !== ',' )
+				) {
+					$output->add( ' ' );
+				}
 			}
 		}
 	}

test/Fixtures/less.php/css/T386079-fix-function-call.css

@@ -0,0 +1,3 @@
+.test {
+  --background: linear-gradient(270deg, rgba(0, 0, 0, 0) 36.5%, #000 98%), linear-gradient(180deg, rgba(0, 0, 0, 0.9) 0%, rgba(0, 0, 0, 0) 35%);
+}

test/Fixtures/less.php/less/T386079-fix-function-call.less

@@ -0,0 +1,7 @@
+@color-black: #000;
+
+.test {
+  --background: 
+    linear-gradient(270deg, fade(@color-black, 0%) 36.5%, @color-black 98%),
+   linear-gradient(180deg, fade(@color-black, 90%) 0%, fade(@color-black, 0%) 35%);
+}