Require spaces around operators in calc() (fixes #15486)

tests/unit/style/parsing/length.rs

@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use parsing::parse;
+use style::parser::Parse;
+use style::values::specified::length::Length;
+
+#[test]
+fn test_calc() {
+    assert!(parse(Length::parse, "calc(1px+ 2px)").is_err());
+}

tests/unit/style/parsing/mod.rs

@@ -87,6 +87,7 @@ mod font;
 mod image;
 mod inherited_box;
 mod inherited_text;
+mod length;
 mod mask;
 mod outline;
 mod position;