feat: Add a default filter

CHANGELOG.md

@@ -12,6 +12,11 @@
 ### Enhancements
 
 - You may now register custom template filters which make use of arguments.
+- There is now a `default` filter.
+
+    ```html+django
+    Hello {{ name|default:"World" }}
+    ```
 
 ### Bug Fixes
 

Sources/Filters.swift

@@ -31,3 +31,7 @@ func lowercase(_ value: Any?) -> Any? {
 
   return value
 }
+
+func defaultFilter(value: Any?, arguments: [Any?]) -> Any? {
+  return value ?? arguments.first as Any
+}

Sources/Namespace.swift

@@ -45,6 +45,7 @@ public class Namespace {
   }
 
   fileprivate func registerDefaultFilters() {
+    registerFilter("default", filter: defaultFilter)
     registerFilter("capitalize", filter: capitalise)
     registerFilter("uppercase", filter: uppercase)
     registerFilter("lowercase", filter: lowercase)

Tests/StencilTests/FilterSpec.swift

@@ -89,4 +89,18 @@ func testFilter() {
       try expect(result) == "kyle"
     }
   }
+
+  describe("default filter") {
+    let template = Template(templateString: "Hello {{ name|default:\"World\" }}")
+
+    $0.it("shows the variable value") {
+      let result = try template.render(Context(dictionary: ["name": "Kyle"]))
+      try expect(result) == "Hello Kyle"
+    }
+
+    $0.it("shows the default value") {
+      let result = try template.render(Context(dictionary: [:]))
+      try expect(result) == "Hello World"
+    }
+  }
 }

docs/builtins.rst

@@ -120,3 +120,13 @@ For example, `Stencil` to `stencil`.
 .. code-block:: html+django
 
     {{ "Stencil"|lowercase }}
+
+``default``
+~~~~~~~~~~~
+
+If a variable not present in the context, use given default. Otherwise, use the
+value of the variable. For example:
+
+.. code-block:: html+django
+
+    Hello {{ name|default:"World" }}