fix(variable): Prevent crash on unknown index in array

CHANGELOG.md

@@ -1,4 +1,14 @@
 # Stencil Changelog
+
+## Master
+
+### Bug Fixes
+
+- Variables (`{{ variable.5 }}`) that reference an array index at an unknown
+  index will now resolve to `nil` instead of causing a crash.
+  [#72](https://github.com/kylef/Stencil/issues/72)
+
+
 ## 0.6.0
 
 ### Enhancements

Sources/Variable.swift

@@ -64,7 +64,11 @@ public struct Variable : Equatable, Resolvable {
         current = dictionary[bit]
       } else if let array = current as? [Any] {
         if let index = Int(bit) {
-          current = array[index]
+          if index >= 0 && index < array.count {
+            current = array[index]
+          } else {
+            current = nil
+          }
         } else if bit == "first" {
           current = array.first
         } else if bit == "last" {

Tests/StencilTests/VariableSpec.swift

@@ -52,6 +52,20 @@ func testVariable() {
       let variable = Variable("contacts.0")
       let result = try variable.resolve(context) as? String
       try expect(result) == "Katie"
+
+        let variable1 = Variable("contacts.1")
+        let result1 = try variable1.resolve(context) as? String
+        try expect(result1) == "Carlton"
+    }
+
+    $0.it("can resolve an item from an array via unknown index") {
+      let variable = Variable("contacts.5")
+      let result = try variable.resolve(context) as? String
+      try expect(result).to.beNil()
+
+      let variable1 = Variable("contacts.-5")
+      let result1 = try variable1.resolve(context) as? String
+      try expect(result1).to.beNil()
     }
 
     $0.it("can resolve the first item from an array") {