Add echo tag

lib/solid/tag/echo.ex

@@ -0,0 +1,26 @@
+defmodule Solid.Tag.Echo do
+  import NimbleParsec
+  alias Solid.Parser.{BaseTag, Literal, Argument}
+
+  @behaviour Solid.Tag
+
+  @impl true
+  def spec(_parser) do
+    space = Literal.whitespace(min: 0)
+
+    ignore(BaseTag.opening_tag())
+    |> ignore(string("echo"))
+    |> ignore(space)
+    |> tag(Argument.argument(), :argument)
+    |> optional(tag(repeat(Argument.filter()), :filters))
+    |> ignore(BaseTag.closing_tag())
+  end
+
+  @impl true
+  def render([argument: argument, filters: filters], context, options) do
+    {:ok, value, context} =
+      Solid.Argument.get(argument, context, [{:filters, filters} | options])
+
+    {[text: value], context}
+  end
+end

test/solid/tag/echo_test.exs

@@ -0,0 +1,16 @@
+defmodule Solid.Tag.EchoTest do
+  use ExUnit.Case, async: true
+  alias Solid.Tag.Echo
+  alias Solid.Context
+
+  defmodule Parser do
+    import NimbleParsec
+    defparsec(:parse, Echo.spec(__MODULE__) |> eos())
+  end
+
+  test "integration" do
+    {:ok, parsed, _, _, _, _} = "{% echo 'abc' | upcase %}" |> Parser.parse()
+
+    assert {[text: "ABC"], context} = Echo.render(parsed, %Context{}, [])
+  end
+end