Should not throw an exception when unknow function exist in calc

Fix #34

parser.jison

@@ -39,6 +39,7 @@
 
 (calc) return 'NESTED_CALC';
 (var\([^\)]*\)) return 'CSS_VAR';
+([a-z]+\([a-z0-9-]+\)) return 'UNKNOW_FUNCTION'
 ([a-z]+) return 'PREFIX';
 
 "(" return 'LPAREN';
@@ -72,6 +73,7 @@ expression
  | css_variable { $$ = $1; }
  | css_value { $$ = $1; }
  | value { $$ = $1; }
+ | UNKNOW_FUNCTION { $$ = { type: 'Unknow', value: $1 }; }
  ;
 
  value

src/__tests__/index.js

@@ -324,3 +324,10 @@ test(
  'calc( (1em - calc( 10px + 1em)) / 2)',
  '-5px'
 )
+
+test(
+ 'should not throw an exception when unknow function exist in calc',
+ testFixture,
+ 'calc(constant(safe-area-inset-left) + 100px - 50px)',
+ 'calc(constant(safe-area-inset-left) + 50px)'
+)

src/lib/stringifier.js

@@ -36,6 +36,7 @@ function stringify(node, prec) {
  case "Value":
  return round(node.value, prec)
  case 'CssVariable':
+ case 'Unknow':
  return node.value
  default:
  return round(node.value, prec) + node.unit