Support Whitespace tags for Objects

This patch is the first step towards supporting the Whitespace Control tags.
It only implements support for the whitespace object tags `{{-` and `-}}`.

Support for the tags is more complicated since the `Tag.eval/3` function needs to support the `trim_previous` and `trim_next` arguments.
In some cases there are multiple of them and we need to forward them to further calls of `Solid.render/3`.

I'm very new to NimbleParsec and generally parsers so I'm posting this to get verification on the current path I have taken.
Some guidance would be appreciated if possible.

Needed by edgurgel#10

lib/solid.ex

@@ -74,6 +74,7 @@ defmodule Solid do
       Enum.reduce(text, {[], context}, fn entry, {acc, context} ->
         try do
           {result, context} = do_render(entry, context, options)
+          {result, acc, context} = maybe_trim(entry, result, acc, context)
           {[result | acc], context}
         catch
           {:break_exp, partial_result, context} ->
@@ -87,6 +88,55 @@ defmodule Solid do
     {Enum.reverse(result), context}
   end
 
+  defp maybe_trim({:text, _data}, result, acc, context) do
+    result = maybe_trim_current(result, context)
+    context = Map.put(context, :trim_next, false)
+    {result, acc, context}
+  end
+
+  defp maybe_trim({:object, data}, result, acc, context) do
+    [trim_previous] = Keyword.get(data, :trim_previous)
+    acc = maybe_trim_previous(acc, trim_previous)
+
+    result = maybe_trim_current(result, context)
+
+    [trim_next] = Keyword.get(data, :trim_next)
+    context = Map.put(context, :trim_next, trim_next)
+
+    {result, acc, context}
+  end
+
+  defp maybe_trim({:tag, _data}, result, acc, context) do
+    context = Map.put(context, :trim_next, false)
+    {result, acc, context}
+  end
+
+  defp maybe_trim_current(result, context) do
+    if context.trim_next do
+      trim_leading(result)
+    else
+      result
+    end
+  end
+
+  defp maybe_trim_previous(acc, flag) do
+    if flag && !Enum.empty?(acc) do
+      [prev | tail] = acc
+      trimmed_prev = trim_trailing(prev)
+      [trimmed_prev | tail]
+    else
+      acc
+    end
+  end
+
+  defp trim_trailing([value]) do
+    [String.trim_trailing(value)]
+  end
+
+  defp trim_leading([value]) do
+    [String.trim_leading(value)]
+  end
+
   defp do_render({:text, string}, context, _options), do: {string, context}
 
   defp do_render({:object, object}, context, options) do
@@ -95,11 +145,6 @@ defmodule Solid do
   end
 
   defp do_render({:tag, tag}, context, options) do
-    {tag_text, context} = render_tag(tag, context, options)
-    {tag_text, context}
-  end
-
-  defp render_tag(tag, context, options) do
     {result, context} = Tag.eval(tag, context, options)
 
     if result do

lib/solid/context.ex

@@ -1,11 +1,12 @@
 defmodule Solid.Context do
-  defstruct vars: %{}, counter_vars: %{}, iteration_vars: %{}, cycle_state: %{}
+  defstruct vars: %{}, counter_vars: %{}, iteration_vars: %{}, cycle_state: %{}, trim_next: false
 
   @type t :: %__MODULE__{
           vars: Map.t(),
           counter_vars: Map.t(),
           iteration_vars: %{optional(String.t()) => term},
-          cycle_state: Map.t()
+          cycle_state: Map.t(),
+          trim_next: boolean
         }
   @type scope :: :counter_vars | :vars | :iteration_vars
 

lib/solid/parser.ex

@@ -96,18 +96,25 @@ defmodule Solid.Parser.Base do
 
       argument = choice([value, field])
 
-      opening_object = string("{{")
-      closing_object = string("}}")
+      opening_tag = ignore(string("{%"))
+      closing_tag = ignore(string("%}"))
 
-      opening_tag = string("{%")
-      closing_tag = string("%}")
+      opening_objects = choice([
+        string("{{-") |> replace(true) |> tag(:trim_previous),
+        string("{{") |> replace(false) |> tag(:trim_previous)
+      ])
+
+      closing_objects = choice([
+        string("-}}") |> replace(true) |> tag(:trim_next),
+        string("}}") |> replace(false) |> tag(:trim_next)
+      ])
 
       space =
         string(" ")
         |> times(min: 0)
 
       text =
-        lookahead_not(choice([opening_object, opening_tag]))
+        lookahead_not(choice([opening_objects, opening_tag]))
         |> utf8_string([], 1)
         |> times(min: 1)
         |> reduce({Enum, :join, []})
@@ -136,21 +143,21 @@ defmodule Solid.Parser.Base do
         |> tag(:filter)
 
       object =
-        ignore(opening_object)
+        opening_objects
         |> ignore(space)
-        |> lookahead_not(closing_object)
+        |> lookahead_not(closing_objects)
         |> tag(argument, :argument)
         |> optional(tag(repeat(filter), :filters))
         |> ignore(space)
-        |> ignore(closing_object)
+        |> concat(closing_objects)
         |> tag(:object)
 
       comment = string("comment")
 
       end_comment = string("endcomment")
 
       comment_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(comment)
         |> ignore(space)
@@ -171,7 +178,7 @@ defmodule Solid.Parser.Base do
         |> replace({-1, -1})
 
       counter_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> concat(choice([increment, decrement]))
         |> ignore(space)
@@ -181,7 +188,7 @@ defmodule Solid.Parser.Base do
         |> tag(:counter_exp)
 
       case_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("case"))
         |> ignore(space)
@@ -190,7 +197,7 @@ defmodule Solid.Parser.Base do
         |> ignore(closing_tag)
 
       when_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("when"))
         |> ignore(space)
@@ -201,7 +208,7 @@ defmodule Solid.Parser.Base do
         |> tag(:when)
 
       else_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("else"))
         |> ignore(space)
@@ -258,15 +265,15 @@ defmodule Solid.Parser.Base do
         |> repeat(choice([bool_and, bool_or]) |> concat(expression))
 
       if_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("if"))
         |> tag(boolean_expression, :expression)
         |> ignore(closing_tag)
         |> tag(parsec(:liquid_entry), :result)
 
       elsif_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("elsif"))
         |> tag(boolean_expression, :expression)
@@ -275,7 +282,7 @@ defmodule Solid.Parser.Base do
         |> tag(:elsif_exp)
 
       unless_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("unless"))
         |> tag(boolean_expression, :expression)
@@ -304,7 +311,7 @@ defmodule Solid.Parser.Base do
         |> ignore(closing_tag)
 
       assign_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("assign"))
         |> ignore(space)
@@ -352,7 +359,7 @@ defmodule Solid.Parser.Base do
         |> reduce({Enum, :into, [%{}]})
 
       for_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("for"))
         |> ignore(space)
@@ -375,7 +382,7 @@ defmodule Solid.Parser.Base do
         |> tag(:for_exp)
 
       capture_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("capture"))
         |> ignore(space)
@@ -392,15 +399,15 @@ defmodule Solid.Parser.Base do
         |> tag(:capture_exp)
 
       break_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("break"))
         |> ignore(space)
         |> ignore(closing_tag)
         |> tag(:break_exp)
 
       continue_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("continue"))
         |> ignore(space)
@@ -415,7 +422,7 @@ defmodule Solid.Parser.Base do
         |> ignore(closing_tag)
 
       raw_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("raw"))
         |> ignore(space)
@@ -425,7 +432,7 @@ defmodule Solid.Parser.Base do
         |> tag(:raw_exp)
 
       cycle_tag =
-        ignore(opening_tag)
+        opening_tag
         |> ignore(space)
         |> ignore(string("cycle"))
         |> ignore(space)
@@ -475,7 +482,7 @@ defmodule Solid.Parser.Base do
       all_tags =
         if custom_tags != [] do
           custom_tag =
-            ignore(opening_tag)
+            opening_tag
             |> ignore(space)
             |> concat(choice(custom_tags))
             |> ignore(space)

test/cases/112/input.json

@@ -0,0 +1 @@
+{}

test/cases/112/input.liquid

@@ -0,0 +1,3 @@
+{% assign my_variable = "tomato" %}
+{% assign your_variable = "your" %}
+! {{ your_variable }} ! {{- my_variable -}} !