From 7ddbfa2d374d1bab63abbb6ec405ba751895164e Mon Sep 17 00:00:00 2001
From: Eli Fitch <elifitch@users.noreply.github.com>
Date: Thu, 6 Dec 2018 13:36:13 -0500
Subject: [PATCH] Flattens nested single element all expressions when
 converting to expressions (#7679)

---
 src/style-spec/feature_filter/convert.js    |  2 +-
 test/unit/style-spec/feature_filter.test.js | 39 +++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/style-spec/feature_filter/convert.js b/src/style-spec/feature_filter/convert.js
index 574c64779d1..1998eabc87a 100644
--- a/src/style-spec/feature_filter/convert.js
+++ b/src/style-spec/feature_filter/convert.js
@@ -92,7 +92,7 @@ function _convertFilter(filter: FilterSpecification, expectedTypes: ExpectedType
         return ['any'].concat(children);
     } else if (op === 'all') {
         const children = (filter: any).slice(1).map(f => _convertFilter(f, expectedTypes));
-        return ['all'].concat(children);
+        return children.length > 1 ? ['all'].concat(children) : [].concat(...children);
     } else if (op === 'none') {
         return ['!', _convertFilter(['any'].concat(filter.slice(1)), {})];
     } else if (op === 'in') {
diff --git a/test/unit/style-spec/feature_filter.test.js b/test/unit/style-spec/feature_filter.test.js
index d1624ca4487..6621b2dd713 100644
--- a/test/unit/style-spec/feature_filter.test.js
+++ b/test/unit/style-spec/feature_filter.test.js
@@ -100,6 +100,45 @@ test('convert legacy filters to expressions', t => {
         t.end();
     });
 
+    t.test('flattens nested, single child all expressions', (t) => {
+        const filter = [
+            "all",
+            [
+                "in",
+                "$type",
+                "Polygon",
+                "LineString",
+                "Point"
+            ],
+            [
+                "all",
+                ["in", "type", "island"]
+            ]
+        ];
+
+        const expected = [
+            "all",
+            [
+                "match",
+                ["geometry-type"],
+                ["Polygon", "LineString", "Point"],
+                true,
+                false
+            ],
+            [
+                "match",
+                ["get", "type"],
+                ["island"],
+                true,
+                false
+            ]
+        ];
+
+        const converted = convertFilter(filter);
+        t.same(converted, expected);
+        t.end();
+    });
+
     t.end();
 });