Port fix for "at" expression off-by-1 error (#11375)

* Port fix for "at" expression off-by-1 error

Refs https://github.com/mapbox/mapbox-gl-js/pull/6269

* Consistency

* Add ignores for symbol positiong differences in real-world tests

1 files changed, 10 insertions, 4 deletions

diff --git a/src/mbgl/style/expression/at.cpp b/src/mbgl/style/expression/at.cpp
index e447d33bc7..725e5ddb51 100644
--- a/src/mbgl/style/expression/at.cpp
+++ b/src/mbgl/style/expression/at.cpp
@@ -19,15 +19,21 @@ EvaluationResult At::evaluate(const EvaluationContext& params) const {
     const auto i = evaluatedIndex->get<double>();
     const auto inputArray = evaluatedInput->get<std::vector<Value>>();
     
-    if (i < 0 || i >= inputArray.size()) {
+    if (i < 0) {
         return EvaluationError {
-            "Array index out of bounds: " + stringify(i) +
-            " > " + util::toString(inputArray.size()) + "."
+            "Array index out of bounds: " + util::toString(i) + " < 0."
+        };
+    }
+    
+    if (i >= inputArray.size()) {
+        return EvaluationError {
+            "Array index out of bounds: " + util::toString(i) +
+            " > " + util::toString(inputArray.size() - 1) + "."
         };
     }
     if (i != std::floor(i)) {
         return EvaluationError {
-            "Array index must be an integer, but found " + stringify(i) + " instead."
+            "Array index must be an integer, but found " + util::toString(i) + " instead."
         };
     }
     return inputArray[static_cast<std::size_t>(i)];