Fix #8504 remove duplicate match exp from filter conversion (#8542)

* Demonstrate filter conversion outputting invalid match expression

* Filter duplicate values when outputting match expressions

* Use a sorting method less likely to blow up at big O

* Tighten up sort expression

src/style-spec/feature_filter/convert.js

@@ -187,7 +187,9 @@ function convertInOp(property: string, values: Array<any>, negate = false) {
     }
 
     if (uniformTypes && (type === 'string' || type === 'number')) {
-        return ['match', get, values, !negate, negate];
+        // Match expressions must have unique values.
+        const uniqueValues = values.sort().filter((v, i) => i === 0 || values[i - 1] !== v);
+        return ['match', get, uniqueValues, !negate, negate];
     }
 
     return [ negate ? 'all' : 'any' ].concat(

test/unit/style-spec/feature_filter.test.js

@@ -121,7 +121,7 @@ test('convert legacy filters to expressions', t => {
             [
                 "match",
                 ["geometry-type"],
-                ["Polygon", "LineString", "Point"],
+                ["LineString", "Point", "Polygon"],
                 true,
                 false
             ],
@@ -139,6 +139,30 @@ test('convert legacy filters to expressions', t => {
         t.end();
     });
 
+    t.test('removes duplicates when outputting match expressions', (t) => {
+        const filter = [
+            "in",
+            "$id",
+            1,
+            2,
+            3,
+            2,
+            1
+        ];
+
+        const expected = [
+            "match",
+            ["id"],
+            [1, 2, 3],
+            true,
+            false
+        ];
+
+        const converted = convertFilter(filter);
+        t.same(converted, expected);
+        t.end();
+    });
+
     t.end();
 });