feat(filters): Show similar filter names when missing filter(#186)

Tests/StencilTests/FilterSpec.swift

@@ -212,4 +212,36 @@ func testFilter() {
     }
   }
 
+
+  describe("filter suggestion") {
+
+    $0.it("made for unknown filter") {
+      let template = Template(templateString: "{{ value|unknownFilter }}")
+      let expectedError = TemplateSyntaxError("Unknown filter 'unknownFilter'. Found similar filters: 'knownFilter'")
+
+      let filterExtension = Extension()
+      filterExtension.registerFilter("knownFilter") { value, _ in value }
+
+      try expect(template.render(Context(dictionary: [:], environment: Environment(extensions: [filterExtension])))).toThrow(expectedError)
+    }
+
+    $0.it("made for multiple similar filters") {
+      let template = Template(templateString: "{{ value|lowerFirst }}")
+      let expectedError = TemplateSyntaxError("Unknown filter 'lowerFirst'. Found similar filters: 'lowerFirstWord', 'lowercase'")
+
+      let filterExtension = Extension()
+      filterExtension.registerFilter("lowerFirstWord") { value, _ in value }
+      filterExtension.registerFilter("lowerFirstLetter") { value, _ in value }
+
+      try expect(template.render(Context(dictionary: [:], environment: Environment(extensions: [filterExtension])))).toThrow(expectedError)
+    }
+
+    $0.it("not made when can't find similar filter") {
+      let template = Template(templateString: "{{ value|unknownFilter }}")
+      let expectedError = TemplateSyntaxError("Unknown filter 'unknownFilter'.")
+      try expect(template.render(Context(dictionary: [:]))).toThrow(expectedError)
+    }
+
+  }
+
 }