feat(filter): Support filter tag

CHANGELOG.md

@@ -13,6 +13,15 @@
   path. Any template names that try to escape the base path will raise a
   `SuspiciousFileOperation` error.
 
+- New `{% filter %}` tag allowing you to perform a filter across the contents
+  of a block.
+
+    ```html+django
+    {% filter lowercase %}
+      This Text Will Be Lowercased.
+    {% endfilter %}
+    ```
+
 
 ## 0.7.1
 

Sources/FilterTag.swift

@@ -0,0 +1,35 @@
+class FilterNode : NodeType {
+  let resolvable: Resolvable
+  let nodes: [NodeType]
+
+  class func parse(_ parser: TokenParser, token: Token) throws -> NodeType {
+    let bits = token.components()
+
+    guard bits.count == 2 else {
+      throw TemplateSyntaxError("'filter' tag takes one argument, the filter expression")
+    }
+
+    let blocks = try parser.parse(until(["endfilter"]))
+
+    guard let token = parser.nextToken() else {
+      throw TemplateSyntaxError("`endfilter` was not found.")
+    }
+
+    let resolvable = try parser.compileFilter("filter_value|\(bits[1])")
+    return FilterNode(nodes: blocks, resolvable: resolvable)
+  }
+
+  init(nodes: [NodeType], resolvable: Resolvable) {
+    self.nodes = nodes
+    self.resolvable = resolvable
+  }
+
+  func render(_ context: Context) throws -> String {
+    let value = try renderNodes(nodes, context)
+
+    return try context.push(dictionary: ["filter_value": value]) {
+      return try VariableNode(variable: resolvable).render(context)
+    }
+  }
+}
+

Sources/Namespace.swift

@@ -42,6 +42,7 @@ public class Namespace {
     registerTag("include", parser: IncludeNode.parse)
     registerTag("extends", parser: ExtendsNode.parse)
     registerTag("block", parser: BlockNode.parse)
+    registerTag("filter", parser: FilterNode.parse)
   }
 
   fileprivate func registerDefaultFilters() {

Tests/StencilTests/FilterTagSpec.swift

@@ -0,0 +1,25 @@
+import Spectre
+import Stencil
+
+
+func testFilterTag() {
+  describe("Filter Tag") {
+    $0.it("allows you to use a filter") {
+      let template = Template(templateString: "{% filter uppercase %}Test{% endfilter %}")
+      let result = try template.render()
+      try expect(result) == "TEST"
+    }
+
+    $0.it("allows you to chain filters") {
+      let template = Template(templateString: "{% filter lowercase|capitalize %}TEST{% endfilter %}")
+      let result = try template.render()
+      try expect(result) == "Test"
+    }
+
+    $0.it("errors without a filter") {
+      let template = Template(templateString: "{% filter %}Test{% endfilter %}")
+      try expect(try template.render()).toThrow()
+    }
+
+  }
+}

Tests/StencilTests/XCTest.swift

@@ -17,6 +17,7 @@ public func stencilTests() {
   testNowNode()
   testInclude()
   testInheritence()
+  testFilterTag()
   testStencil()
 }
 

docs/builtins.rst

@@ -177,6 +177,26 @@ Will be treated as:
 ``now``
 ~~~~~~~
 
+``filter``
+~~~~~~~~~~
+
+Filters the contents of the block.
+
+.. code-block:: html+django
+
+    {% filter lowercase %}
+      This Text Will Be Lowercased.
+    {% endfilter %}
+
+You can chain multiple filters with a pipe (`|`).
+
+.. code-block:: html+django
+
+    {% filter lowercase|capitalize %}
+      This Text Will First Be Lowercased, Then The First Character Will BE
+      Capitalised.
+    {% endfilter %}
+
 ``include``
 ~~~~~~~~~~~