Bug 1706223 - Fix whitespace handling in clamp() parsing. r=xidorn

We should just restore the state when seeing whitespace and an unknown
token like when we do when finding any other token a few lines below.

This is not an issue for most callers (it's only an issue for clamp())
because the other callers use either `parse_comma_separated()` (for
min/max), or `parse_nested_block()` (for parens / nested calc()).

Both of those functions restrict the input in such a way that
is_exhausted returns true (a few lines above) and thus we parse
successfully.

Differential Revision: https://phabricator.services.mozilla.com/D112681

servo/components/style/values/specified/calc.rs

@@ -373,9 +373,9 @@ impl CalcNode {
                             rhs.negate();
                             sum.push(rhs);
                         },
-                        ref t => {
-                            let t = t.clone();
-                            return Err(input.new_unexpected_token_error(t));
+                        _ => {
+                            input.reset(&start);
+                            break;
                         },
                     }
                 },

testing/web-platform/tests/css/css-values/clamp-length-computed.html

@@ -22,6 +22,10 @@ function test_length_equals(value, expected) {
 test_length_equals('clamp(10px, 20px, 30px)', '20px');
 test_length_equals('clamp(10px, 5px, 30px)', '10px');
 test_length_equals('clamp(10px, 35px, 30px)', '30px');
+test_length_equals('clamp(10px, 35px , 30px)', '30px');
+test_length_equals('clamp(10px, 35px /*foo*/, 30px)', '30px');
+test_length_equals('clamp(10px /* foo */ , 35px, 30px)', '30px');
+test_length_equals('clamp(10px , 35px, 30px)', '30px');
 
 // clamp(MIN, VAL, MAX) is identical to max(MIN, min(VAL, MAX)),
 // so MIN wins over MAX if they are in the wrong order.