syntax error on empty variable tag

CHANGELOG.md

@@ -23,6 +23,10 @@ _None_
   [Ilya Puchka](https://github.com/ilyapuchka)
   [#254](https://github.com/stencilproject/Stencil/pull/254)
 
+- Throw syntax error on empty variable tags (`{{ }}`) instead `fatalError`.  
+  [Ilya Puchka](https://github.com/ilyapuchka)
+  [#263](https://github.com/stencilproject/Stencil/pull/263)
+
 ### Internal Changes
 
 - `Token` type converted to struct to allow computing token components only once.  

Sources/Extension.swift

@@ -89,7 +89,7 @@ enum Filter: FilterType {
     switch self {
     case let .simple(filter):
       if !arguments.isEmpty {
-        throw TemplateSyntaxError("cannot invoke filter with an argument")
+        throw TemplateSyntaxError("Can't invoke filter with an argument")
       }
       return try filter(value)
     case let .arguments(filter):

Sources/Node.swift

@@ -84,7 +84,10 @@ public class VariableNode: NodeType {
       elseExpression = nil
     }
 
-    let filter = try parser.compileResolvable(components[0], containedIn: token)
+    guard let resolvable = components.first else {
+      throw TemplateSyntaxError(reason: "Missing variable name", token: token)
+    }
+    let filter = try parser.compileResolvable(resolvable, containedIn: token)
     return VariableNode(variable: filter, token: token, condition: condition, elseExpression: elseExpression)
   }
 

Tests/StencilTests/EnvironmentSpec.swift

@@ -133,6 +133,11 @@ final class EnvironmentTests: XCTestCase {
         token: "name|unknown"
       )
     }
+    
+    it("reports error in variable tag") {
+      self.template = "{{ }}"
+      try self.expectError(reason: "Missing variable name", token: " ")
+    }
   }
 
   func testRenderingError() {
@@ -153,7 +158,7 @@ final class EnvironmentTests: XCTestCase {
 
     it("reports passing argument to simple filter") {
       self.template = "{{ name|uppercase:5 }}"
-      try self.expectError(reason: "cannot invoke filter with an argument", token: "name|uppercase:5")
+      try self.expectError(reason: "Can't invoke filter with an argument", token: "name|uppercase:5")
     }
 
     it("reports rendering error in custom tag") {