Added filter to apply dynamic filters

CHANGELOG.md

@@ -8,7 +8,10 @@ _None_
 
 ### Enhancements
 
-_None_
+- Added support for dynamic filter using `filter` filter. With that you can define a variable with a name of filter
+, i.e. `myfilter = "uppercase"` and then use it to invoke this filter with `{{ string|filter:myfilter }}`.  
+  [Ilya Puchka](https://github.com/ilyapuchka)
+  [#203](https://github.com/stencilproject/Stencil/pull/203)
 
 ### Deprecations
 

Sources/Expression.swift

@@ -1,4 +1,4 @@
-protocol Expression: CustomStringConvertible {
+public protocol Expression: CustomStringConvertible {
   func evaluate(context: Context) throws -> Bool
 }
 

Sources/Extension.swift

@@ -35,6 +35,11 @@ open class Extension {
 
   /// Registers a template filter with the given name
   public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?]) throws -> Any?) {
+    filters[name] = .arguments({ value, args, _ in try filter(value, args) })
+  }
+
+  /// Registers a template filter with the given name
+  public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?], Context) throws -> Any?) {
     filters[name] = .arguments(filter)
   }
 }
@@ -68,28 +73,28 @@ class DefaultExtension: Extension {
     registerFilter("join", filter: joinFilter)
     registerFilter("split", filter: splitFilter)
     registerFilter("indent", filter: indentFilter)
+    registerFilter("filter", filter: filterFilter)
   }
 }
 
 
 protocol FilterType {
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any?
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any?
 }
 
 enum Filter: FilterType {
   case simple(((Any?) throws -> Any?))
-  case arguments(((Any?, [Any?]) throws -> Any?))
+  case arguments(((Any?, [Any?], Context) throws -> Any?))
 
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any? {
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any? {
     switch self {
     case let .simple(filter):
       if !arguments.isEmpty {
         throw TemplateSyntaxError("cannot invoke filter with an argument")
       }
-
       return try filter(value)
     case let .arguments(filter):
-      return try filter(value, arguments)
+      return try filter(value, arguments, context)
     }
   }
 }

Sources/Filters.swift

@@ -39,7 +39,7 @@ func defaultFilter(value: Any?, arguments: [Any?]) -> Any? {
 
 func joinFilter(value: Any?, arguments: [Any?]) throws -> Any? {
   guard arguments.count < 2 else {
-    throw TemplateSyntaxError("'join' filter takes a single argument")
+    throw TemplateSyntaxError("'join' filter takes at most one argument")
   }
 
   let separator = stringify(arguments.first ?? "")
@@ -55,7 +55,7 @@ func joinFilter(value: Any?, arguments: [Any?]) throws -> Any? {
 
 func splitFilter(value: Any?, arguments: [Any?]) throws -> Any? {
   guard arguments.count < 2 else {
-    throw TemplateSyntaxError("'split' filter takes a single argument")
+    throw TemplateSyntaxError("'split' filter takes at most one argument")
   }
 
   let separator = stringify(arguments.first ?? " ")
@@ -115,3 +115,16 @@ func indent(_ content: String, indentation: String, indentFirst: Bool) -> String
   return result.joined(separator: "\n")
 }
 
+func filterFilter(value: Any?, arguments: [Any?], context: Context) throws -> Any? {
+  guard let value = value else { return nil }
+  guard arguments.count == 1 else {
+    throw TemplateSyntaxError("'filter' filter takes one argument")
+  }
+
+  let attribute = stringify(arguments[0])
+
+  let expr = try context.environment.compileFilter("$0|\(attribute)")
+  return try context.push(dictionary: ["$0": value]) {
+    try expr.resolve(context)
+  }
+}

Sources/ForTag.swift

@@ -31,7 +31,7 @@ class ForNode : NodeType {
     let resolvable = try parser.compileResolvable(components[3], containedIn: token)
 
     let `where` = hasToken("where", at: 4)
-      ? try parseExpression(components: Array(components.suffix(from: 5)), tokenParser: parser, token: token)
+      ? try parser.compileExpression(components: Array(components.suffix(from: 5)), token: token)
       : nil
 
     let forNodes = try parser.parse(until(["endfor", "empty"]))

Sources/IfTag.swift

@@ -111,11 +111,11 @@ final class IfExpressionParser {
     self.tokens = tokens
   }
 
-  static func parser(components: [String], tokenParser: TokenParser, token: Token) throws -> IfExpressionParser {
-    return try IfExpressionParser(components: ArraySlice(components), tokenParser: tokenParser, token: token)
+  static func parser(components: [String], environment: Environment, token: Token) throws -> IfExpressionParser {
+    return try IfExpressionParser(components: ArraySlice(components), environment: environment, token: token)
   }
 
-  private init(components: ArraySlice<String>, tokenParser: TokenParser, token: Token) throws {
+  private init(components: ArraySlice<String>, environment: Environment, token: Token) throws {
     var parsedComponents = Set<Int>()
     var bracketsBalance = 0
     self.tokens = try zip(components.indices, components).compactMap { (index, component) in
@@ -125,7 +125,7 @@ final class IfExpressionParser {
         bracketsBalance += 1
         let (expression, parsedCount) = try IfExpressionParser.subExpression(
           from: components.suffix(from: index + 1),
-          tokenParser: tokenParser,
+          environment: environment,
           token: token
         )
         parsedComponents.formUnion(Set(index...(index + parsedCount)))
@@ -147,12 +147,12 @@ final class IfExpressionParser {
             return .prefix(name: name, bindingPower: bindingPower, operatorType: operatorType)
           }
         }
-        return .variable(try tokenParser.compileResolvable(component, containedIn: token))
+        return .variable(try environment.compileResolvable(component, containedIn: token))
       }
     }
   }
 
-  private static func subExpression(from components: ArraySlice<String>, tokenParser: TokenParser, token: Token) throws -> (Expression, Int) {
+  private static func subExpression(from components: ArraySlice<String>, environment: Environment, token: Token) throws -> (Expression, Int) {
     var bracketsBalance = 1
     let subComponents = components
       .prefix(while: {
@@ -167,7 +167,7 @@ final class IfExpressionParser {
       throw TemplateSyntaxError("'if' expression error: missing closing bracket")
     }
 
-    let expressionParser = try IfExpressionParser(components: subComponents, tokenParser: tokenParser, token: token)
+    let expressionParser = try IfExpressionParser(components: subComponents, environment: environment, token: token)
     let expression = try expressionParser.parse()
     return (expression, subComponents.count)
   }
@@ -211,10 +211,6 @@ final class IfExpressionParser {
   }
 }
 
-func parseExpression(components: [String], tokenParser: TokenParser, token: Token) throws -> Expression {
-  let parser = try IfExpressionParser.parser(components: components, tokenParser: tokenParser, token: token)
-  return try parser.parse()
-}
 
 /// Represents an if condition and the associated nodes when the condition
 /// evaluates
@@ -243,7 +239,7 @@ class IfNode : NodeType {
     var components = token.components
     components.removeFirst()
 
-    let expression = try parseExpression(components: components, tokenParser: parser, token: token)
+    let expression = try parser.compileExpression(components: components, token: token)
     let nodes = try parser.parse(until(["endif", "elif", "else"]))
     var conditions: [IfCondition] = [
       IfCondition(expression: expression, nodes: nodes)
@@ -253,7 +249,7 @@ class IfNode : NodeType {
     while let current = nextToken, current.contents.hasPrefix("elif") {
       var components = current.components
       components.removeFirst()
-      let expression = try parseExpression(components: components, tokenParser: parser, token: current)
+      let expression = try parser.compileExpression(components: components, token: current)
 
       let nodes = try parser.parse(until(["endif", "elif", "else"]))
       nextToken = parser.nextToken()
@@ -281,7 +277,7 @@ class IfNode : NodeType {
     var trueNodes = [NodeType]()
     var falseNodes = [NodeType]()
 
-    let expression = try parseExpression(components: components, tokenParser: parser, token: token)
+    let expression = try parser.compileExpression(components: components, token: token)
     falseNodes = try parser.parse(until(["endif", "else"]))
 
     guard let token = parser.nextToken() else {

Sources/Node.swift

@@ -74,11 +74,11 @@ public class VariableNode : NodeType {
     if hasToken("if", at: 1) {
       let components = components.suffix(from: 2)
       if let elseIndex = components.index(of: "else") {
-        condition = try parseExpression(components: Array(components.prefix(upTo: elseIndex)), tokenParser: parser, token: token)
+        condition = try parser.compileExpression(components: Array(components.prefix(upTo: elseIndex)), token: token)
         let elseToken = components.suffix(from: elseIndex.advanced(by: 1)).joined(separator: " ")
         elseExpression = try parser.compileResolvable(elseToken, containedIn: token)
       } else {
-        condition = try parseExpression(components: Array(components), tokenParser: parser, token: token)
+        condition = try parser.compileExpression(components: Array(components), token: token)
         elseExpression = nil
       }
     } else {

Sources/Parser.swift

@@ -49,7 +49,7 @@ public class TokenParser {
 
         if let tag = token.components.first {
           do {
-            let parser = try findTag(name: tag)
+            let parser = try environment.findTag(name: tag)
             let node = try parser(self, token)
             nodes.append(node)
           } catch {
@@ -76,8 +76,27 @@ public class TokenParser {
     tokens.insert(token, at: 0)
   }
 
+  /// Create filter expression from a string contained in provided token
+  public func compileFilter(_ filterToken: String, containedIn token: Token) throws -> Resolvable {
+    return try environment.compileFilter(filterToken, containedIn: token)
+  }
+
+  /// Create boolean expression from components contained in provided token
+  public func compileExpression(components: [String], token: Token) throws -> Expression {
+    return try environment.compileExpression(components: components, containedIn: token)
+  }
+
+  /// Create resolvable (i.e. range variable or filter expression) from a string contained in provided token
+  public func compileResolvable(_ token: String, containedIn containingToken: Token) throws -> Resolvable {
+    return try environment.compileResolvable(token, containedIn: containingToken)
+  }
+
+}
+
+extension Environment {
+
   func findTag(name: String) throws -> Extension.TagParser {
-    for ext in environment.extensions {
+    for ext in extensions {
       if let filter = ext.tags[name] {
         return filter
       }
@@ -87,7 +106,7 @@ public class TokenParser {
   }
 
   func findFilter(_ name: String) throws -> FilterType {
-    for ext in environment.extensions {
+    for ext in extensions {
       if let filter = ext.filters[name] {
         return filter
       }
@@ -105,7 +124,7 @@ public class TokenParser {
   }
 
   private func suggestedFilters(for name: String) -> [String] {
-    let allFilters = environment.extensions.flatMap({ $0.filters.keys })
+    let allFilters = extensions.flatMap({ $0.filters.keys })
 
     let filtersWithDistance = allFilters
                 .map({ (filterName: $0, distance: $0.levenshteinDistance(name)) })
@@ -118,9 +137,15 @@ public class TokenParser {
     return filtersWithDistance.filter({ $0.distance == minDistance }).map({ $0.filterName })
   }
 
+  /// Create filter expression from a string
+  public func compileFilter(_ token: String) throws -> Resolvable {
+    return try FilterExpression(token: token, environment: self)
+  }
+
+  /// Create filter expression from a string contained in provided token
   public func compileFilter(_ filterToken: String, containedIn containingToken: Token) throws -> Resolvable {
     do {
-      return try FilterExpression(token: filterToken, parser: self)
+      return try FilterExpression(token: filterToken, environment: self)
     } catch {
       guard var syntaxError = error as? TemplateSyntaxError, syntaxError.token == nil else {
         throw error
@@ -137,22 +162,23 @@ public class TokenParser {
     }
   }
 
-  @available(*, deprecated, message: "Use compileFilter(_:containedIn:)")
-  public func compileFilter(_ token: String) throws -> Resolvable {
-    return try FilterExpression(token: token, parser: self)
-  }
-
-  @available(*, deprecated, message: "Use compileResolvable(_:containedIn:)")
+  /// Create resolvable (i.e. range variable or filter expression) from a string
   public func compileResolvable(_ token: String) throws -> Resolvable {
-    return try RangeVariable(token, parser: self)
+    return try RangeVariable(token, environment: self)
       ?? compileFilter(token)
   }
 
+  /// Create resolvable (i.e. range variable or filter expression) from a string contained in provided token
   public func compileResolvable(_ token: String, containedIn containingToken: Token) throws -> Resolvable {
-    return try RangeVariable(token, parser: self, containedIn: containingToken)
+    return try RangeVariable(token, environment: self, containedIn: containingToken)
         ?? compileFilter(token, containedIn: containingToken)
   }
 
+  /// Create boolean expression from components contained in provided token
+  public func compileExpression(components: [String], containedIn token: Token) throws -> Expression {
+    return try IfExpressionParser.parser(components: components, environment: self, token: token).parse()
+  }
+
 }
 
 // https://en.wikipedia.org/wiki/Levenshtein_distance#Iterative_with_two_matrix_rows

Sources/Variable.swift

@@ -8,8 +8,8 @@ class FilterExpression : Resolvable {
   let filters: [(FilterType, [Variable])]
   let variable: Variable
 
-  init(token: String, parser: TokenParser) throws {
-    let bits = token.split(separator: "|").map({ String($0).trim(character: " ") })
+  init(token: String, environment: Environment) throws {
+    let bits = token.smartSplit(separator: "|").map({ String($0).trim(character: " ") })
     if bits.isEmpty {
       throw TemplateSyntaxError("Variable tags must include at least 1 argument")
     }
@@ -20,7 +20,7 @@ class FilterExpression : Resolvable {
     do {
       filters = try filterBits.map {
         let (name, arguments) = parseFilterComponents(token: $0)
-        let filter = try parser.findFilter(name)
+        let filter = try environment.findFilter(name)
         return (filter, arguments)
       }
     } catch {
@@ -34,7 +34,7 @@ class FilterExpression : Resolvable {
 
     return try filters.reduce(result) { x, y in
       let arguments = try y.1.map { try $0.resolve(context) }
-      return try y.0.invoke(value: x, arguments: arguments)
+      return try y.0.invoke(value: x, arguments: arguments, context: context)
     }
   }
 }
@@ -144,25 +144,24 @@ public struct RangeVariable: Resolvable {
   public let from: Resolvable
   public let to: Resolvable
 
-  @available(*, deprecated, message: "Use init?(_:parser:containedIn:)")
-  public init?(_ token: String, parser: TokenParser) throws {
+  public init?(_ token: String, environment: Environment) 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])
+    self.from = try environment.compileFilter(components[0])
+    self.to = try environment.compileFilter(components[1])
   }
 
-  public init?(_ token: String, parser: TokenParser, containedIn containingToken: Token) throws {
+  public init?(_ token: String, environment: Environment, containedIn containingToken: Token) throws {
     let components = token.components(separatedBy: "...")
     guard components.count == 2 else {
       return nil
     }
 
-    self.from = try parser.compileFilter(components[0], containedIn: containingToken)
-    self.to = try parser.compileFilter(components[1], containedIn: containingToken)
+    self.from = try environment.compileFilter(components[0], containedIn: containingToken)
+    self.to = try environment.compileFilter(components[1], containedIn: containingToken)
   }
 
   public func resolve(_ context: Context) throws -> Any? {

Tests/StencilTests/ExpressionSpec.swift

@@ -5,10 +5,9 @@ import Spectre
 class ExpressionsTests: XCTestCase {
   func testExpressions() {
     describe("Expression") {
-      let parser = TokenParser(tokens: [], environment: Environment())
 
       func parseExpression(components: [String]) throws -> Expression {
-        let parser = try IfExpressionParser.parser(components: components, tokenParser: parser, token: .text(value: "", at: .unknown))
+        let parser = try IfExpressionParser.parser(components: components, environment: Environment(), token: .text(value: "", at: .unknown))
         return try parser.parse()
       }