Handle nested calc values. Fixes MoOx#23.

Author: ben-eb

parser.jison

@@ -37,6 +37,9 @@
 ([0-9]+("."[0-9]+)?|"."[0-9]+)\%       return 'PERCENTAGE';
 ([0-9]+("."[0-9]+)?|"."[0-9]+)\b       return 'NUMBER';
 
+(calc)                                 return 'NESTED_CALC';
+([a-z]+)                               return 'PREFIX';
+
 "("                                    return 'LPAREN';
 ")"                                    return 'RPAREN';
 
@@ -63,6 +66,8 @@ expression
   	| math_expression MUL math_expression { $$ = { type: 'MathExpression', operator: $2, left: $1, right: $3 }; }
   	| math_expression DIV math_expression { $$ = { type: 'MathExpression', operator: $2, left: $1, right: $3 }; }
   	| LPAREN math_expression RPAREN { $$ = $2; }
+    | NESTED_CALC LPAREN math_expression RPAREN { $$ = $3; }
+    | SUB PREFIX SUB NESTED_CALC LPAREN math_expression RPAREN { $$ = $6; }
   	| css_value { $$ = $1; }
   	| value { $$ = $1; }
     ;

src/__tests__/index.js

@@ -70,6 +70,20 @@ test(
   'a 2px b 3em c'
 )
 
+test(
+  'should reduce nested calc',
+  testFixture,
+  'calc(100% - calc(50% + 25px))',
+  'calc(50% - 25px)'
+)
+
+test(
+  'should reduce prefixed nested calc',
+  testFixture,
+  '-webkit-calc(100% - -webkit-calc(50% + 25px))',
+  '-webkit-calc(50% - 25px)'
+)
+
 test(
   'should reduce calc with newline characters',
   testFixture,