Support swift 5.0

Package@swift-5.swift

@@ -0,0 +1,23 @@
+// swift-tools-version:5.0
+import PackageDescription
+
+let package = Package(
+  name: "Stencil",
+  products: [
+    .library(name: "Stencil", targets: ["Stencil"])
+  ],
+  dependencies: [
+    .package(url: "https://github.com/kylef/PathKit.git", from: "0.9.0"),
+    .package(url: "https://github.com/kylef/Spectre.git", from: "0.9.0")
+  ],
+  targets: [
+    .target(name: "Stencil", dependencies: [
+      "PathKit"
+    ], path: "Sources"),
+    .testTarget(name: "StencilTests", dependencies: [
+      "Stencil",
+      "Spectre"
+    ])
+  ],
+  swiftLanguageVersions: [.v4, .v4_2, .v5]
+)

Sources/Node.swift

@@ -71,9 +71,15 @@ public class VariableNode: NodeType {
 
     if hasToken("if", at: 1) {
       let components = components.suffix(from: 2)
-      if let elseIndex = components.index(of: "else") {
+      #if swift(<5.0)
-        condition = try parser.compileExpression(components: Array(components.prefix(upTo: elseIndex)), token: token)
+      let elseIndex = components.index(of: "else")
-        let elseToken = components.suffix(from: elseIndex.advanced(by: 1)).joined(separator: " ")
+      #else
+      let elseIndex = components.firstIndex(of: "else")
+      #endif
+
+      if let safeElseIndex = elseIndex {
+        condition = try parser.compileExpression(components: Array(components.prefix(upTo: safeElseIndex)), token: token)
+        let elseToken = components.suffix(from: safeElseIndex.advanced(by: 1)).joined(separator: " ")
         elseExpression = try parser.compileResolvable(elseToken, containedIn: token)
       } else {
         condition = try parser.compileExpression(components: Array(components), token: token)