feat(for loop): Support range literals (#192)

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Added support for iterating arrays of tuples
 - Added support for ranges in if-in expression
 - Added property `forloop.length` to get number of items in the loop
+- Now you can construct ranges for loops using `a...b` syntax, i.e. `for i in 1...array.count`
 
 ### Bug Fixes
 

Sources/ForTag.swift

@@ -10,9 +10,15 @@ class ForNode : NodeType {
   class func parse(_ parser:TokenParser, token:Token) throws -> NodeType {
     let components = token.components()
 
-    guard components.count >= 3 && components[2] == "in" &&
-        (components.count == 4 || (components.count >= 6 && components[4] == "where")) else {
-      throw TemplateSyntaxError("'for' statements should use the following 'for x in y where condition' `\(token.contents)`.")
+    func hasToken(_ token: String, at index: Int) -> Bool {
+      return components.count > (index + 1) && components[index] == token
+    }
+    func endsOrHasToken(_ token: String, at index: Int) -> Bool {
+      return components.count == index || hasToken(token, at: index)
+    }
+
+    guard hasToken("in", at: 2) && endsOrHasToken("where", at: 4) else {
+      throw TemplateSyntaxError("'for' statements should use the syntax: `for <x> in <y> [where <condition>]")
     }
 
     let loopVariables = components[1].characters
@@ -20,8 +26,6 @@ class ForNode : NodeType {
       .map(String.init)
       .map { $0.trimmingCharacters(in: CharacterSet.whitespaces) }
 
-    let variable = components[3]
-
     var emptyNodes = [NodeType]()
 
     let forNodes = try parser.parse(until(["endfor", "empty"]))
@@ -35,14 +39,13 @@ class ForNode : NodeType {
       _ = parser.nextToken()
     }
 
-    let filter = try parser.compileFilter(variable)
-    let `where`: Expression?
-    if components.count >= 6 {
-      `where` = try parseExpression(components: Array(components.suffix(from: 5)), tokenParser: parser)
-    } else {
-      `where` = nil
-    }
-    return ForNode(resolvable: filter, loopVariables: loopVariables, nodes: forNodes, emptyNodes:emptyNodes, where: `where`)
+    let resolvable = try parser.compileResolvable(components[3])
+
+    let `where` = hasToken("where", at: 4)
+      ? try parseExpression(components: Array(components.suffix(from: 5)), tokenParser: parser)
+      : nil
+
+    return ForNode(resolvable: resolvable, loopVariables: loopVariables, nodes: forNodes, emptyNodes:emptyNodes, where: `where`)
   }
 
   init(resolvable: Resolvable, loopVariables: [String], nodes:[NodeType], emptyNodes:[NodeType], where: Expression? = nil) {

Sources/IfTag.swift

@@ -111,7 +111,7 @@ final class IfExpressionParser {
         }
       }
 
-      return .variable(try tokenParser.compileFilter(component))
+      return .variable(try tokenParser.compileResolvable(component))
     }
   }
 

Sources/Parser.swift

@@ -40,7 +40,7 @@ public class TokenParser {
       case .text(let text):
         nodes.append(TextNode(text: text))
       case .variable:
-        nodes.append(VariableNode(variable: try compileFilter(token.contents)))
+        nodes.append(VariableNode(variable: try compileResolvable(token.contents)))
       case .block:
         if let parse_until = parse_until , parse_until(self, token) {
           prependToken(token)
@@ -114,6 +114,11 @@ public class TokenParser {
     return try FilterExpression(token: token, parser: self)
   }
 
+  public func compileResolvable(_ token: String) throws -> Resolvable {
+    return try RangeVariable(token, parser: self)
+      ?? compileFilter(token)
+  }
+
 }
 
 // https://en.wikipedia.org/wiki/Levenshtein_distance#Iterative_with_two_matrix_rows

Sources/Variable.swift

@@ -130,6 +130,42 @@ public func ==(lhs: Variable, rhs: Variable) -> Bool {
   return lhs.variable == rhs.variable
 }
 
+/// A structure used to represet range of two integer values expressed as `from...to`.
+/// Values should be numbers (they will be converted to integers).
+/// Rendering this variable produces array from range `from...to`.
+/// If `from` is more than `to` array will contain values of reversed range.
+public struct RangeVariable: Resolvable {
+  public let from: Resolvable
+  public let to: Resolvable
+
+  public init?(_ token: String, parser: TokenParser) throws {
+    let components = token.components(separatedBy: "...")
+    guard components.count == 2 else {
+      return nil
+    }
+
+    self.from = try parser.compileFilter(components[0])
+    self.to = try parser.compileFilter(components[1])
+  }
+
+  public func resolve(_ context: Context) throws -> Any? {
+    let fromResolved = try from.resolve(context)
+    let toResolved = try to.resolve(context)
+
+    guard let from = fromResolved.flatMap(toNumber(value:)).flatMap(Int.init) else {
+      throw TemplateSyntaxError("'from' value is not an Integer (\(fromResolved ?? "nil"))")
+    }
+
+    guard let to = toResolved.flatMap(toNumber(value:)).flatMap(Int.init) else {
+      throw TemplateSyntaxError("'to' value is not an Integer (\(toResolved ?? "nil") )")
+    }
+
+    let range = min(from, to)...max(from, to)
+    return from > to ? Array(range.reversed()) : Array(range)
+  }
+
+}
+
 
 func normalize(_ current: Any?) -> Any? {
   if let current = current as? Normalizable {

Tests/StencilTests/ForNodeSpec.swift

@@ -227,7 +227,7 @@ func testForNode() {
           .block(value: "for i"),
       ]
       let parser = TokenParser(tokens: tokens, environment: Environment())
-      let error = TemplateSyntaxError("'for' statements should use the following 'for x in y where condition' `for i`.")
+      let error = TemplateSyntaxError("'for' statements should use the syntax: `for <x> in <y> [where <condition>]")
       try expect(try parser.parse()).toThrow(error)
     }
 
@@ -306,6 +306,11 @@ func testForNode() {
       try expect(result) == "childString=child\nbaseString=base\nbaseInt=1\n"
     }
 
+    $0.it("can iterate in range of variables") {
+      let template: Template = "{% for i in 1...j %}{{ i }}{% endfor %}"
+      try expect(try template.render(Context(dictionary: ["j": 3]))) == "123"
+    }
+
   }
 
 }

Tests/StencilTests/IfNodeSpec.swift

@@ -270,5 +270,22 @@ func testIfNode() {
       let result = try renderNodes(nodes, Context(dictionary: ["instance": SomeType()]))
       try expect(result) == ""
     }
+
+    $0.it("supports closed range variables") {
+      let tokens: [Token] = [
+        .block(value: "if value in 1...3"),
+        .text(value: "true"),
+        .block(value: "else"),
+        .text(value: "false"),
+        .block(value: "endif")
+      ]
+
+      let parser = TokenParser(tokens: tokens, environment: Environment())
+      let nodes = try parser.parse()
+
+      try expect(renderNodes(nodes, Context(dictionary: ["value": 3]))) == "true"
+      try expect(renderNodes(nodes, Context(dictionary: ["value": 4]))) == "false"
+    }
+
   }
 }

Tests/StencilTests/VariableSpec.swift

@@ -189,4 +189,52 @@ func testVariable() {
       try expect(result) == 2
     }
   }
+
+  describe("RangeVariable") {
+
+    let context: Context = {
+      let ext = Extension()
+      ext.registerFilter("incr", filter: { (arg: Any?) in toNumber(value: arg!)! + 1 })
+      let environment = Environment(extensions: [ext])
+      return Context(dictionary: [:], environment: environment)
+    }()
+
+    func makeVariable(_ token: String) throws -> RangeVariable? {
+      return try RangeVariable(token, parser: TokenParser(tokens: [], environment: context.environment))
+    }
+
+    $0.it("can resolve closed range as array") {
+      let result = try makeVariable("1...3")?.resolve(context) as? [Int]
+      try expect(result) == [1, 2, 3]
+    }
+
+    $0.it("can resolve decreasing closed range as reversed array") {
+      let result = try makeVariable("3...1")?.resolve(context) as? [Int]
+      try expect(result) == [3, 2, 1]
+    }
+
+    $0.it("can use filter on range variables") {
+      let result = try makeVariable("1|incr...3|incr")?.resolve(context) as? [Int]
+      try expect(result) == [2, 3, 4]
+    }
+
+    $0.it("throws when left value is not int") {
+      let template: Template = "{% for i in k...j %}{{ i }}{% endfor %}"
+      try expect(try template.render(Context(dictionary: ["j": 3, "k": "1"]))).toThrow()
+    }
+
+    $0.it("throws when right value is not int") {
+      let variable = try makeVariable("k...j")
+      try expect(try variable?.resolve(Context(dictionary: ["j": "3", "k": 1]))).toThrow()
+    }
+
+    $0.it("throws is left range value is missing") {
+      try  expect(makeVariable("...1")).toThrow()
+    }
+
+    $0.it("throws is right range value is missing") {
+      try  expect(makeVariable("1...")).toThrow()
+    }
+
+  }
 }