Support macro expressions within templates

spec/instance_template/macro_for_spec.cr

@@ -0,0 +1,31 @@
+require "../spec_helper"
+
+module ToHtml::InstanceTemplate::MacroForSpec
+  class MyView
+    getter a : String
+    getter b : String
+
+    def initialize(@a, @b); end
+
+    ToHtml.instance_template do
+      form do
+        {% for ivar in @type.instance_vars %}
+          input type: :text, name: {{ivar.name.stringify}}, value: {{ivar.name.id}}
+        {% end %}
+      end
+    end
+  end
+
+  describe "MyView#to_html" do
+    it "should return the correct HTML" do
+      expected = <<-HTML.squish
+      <form>
+        <input type="text" name="a" value="foo">
+        <input type="text" name="b" value="bar">
+      </form>
+      HTML
+
+      MyView.new(a: "foo", b: "bar").to_html.should eq(expected)
+    end
+  end
+end

spec/instance_template/macro_if_spec.cr

@@ -0,0 +1,27 @@
+require "../spec_helper"
+
+module ToHtml::InstanceTemplate::MacroIfSpec
+  class MyView
+    ToHtml.class_template do
+      {% if false %}
+        p do
+          "Not shown"
+        end
+      {% else %}
+        p do
+          "Shown"
+        end
+      {% end %}
+    end
+  end
+
+  describe "MyView#to_html" do
+    it "should return the correct HTML" do
+      expected = <<-HTML.squish
+      <p>Shown</p>
+      HTML
+
+      MyView.to_html.should eq(expected)
+    end
+  end
+end

src/instance_template.cr

@@ -112,6 +112,25 @@ module ToHtml
           {% end %}
       {% end %}
       end
+    {% elsif blk.body.is_a?(MacroIf) %}
+      \{% if {{blk.body.cond}} %}
+        ToHtml.to_html_eval_exps({{io}}, {{indent_level}}) do
+          {{blk.body.then}}
+        end
+      \{% else %}
+        ToHtml.to_html_eval_exps({{io}}, {{indent_level}}) do
+          {{blk.body.else}}
+        end
+      \{% end %}
+    {% elsif blk.body.is_a?(MacroFor) %}
+      \{% for {{blk.body.vars.splat}} in {{blk.body.exp}} %}
+        ToHtml.to_html_eval_exps({{io}}, {{indent_level}}) do
+          # Crystal seems to insert a newline after each macro variable for some reason
+          {{blk.body.body.stringify.gsub(/\n/, "").id}}
+        end
+      \{% end %}
+    {% elsif blk.body.is_a?(MacroExpression) || blk.body.is_a?(MacroLiteral) %}
+      {{blk.body}}
     {% elsif blk.body.is_a?(Assign) %}
       # Don't print this to the IO
       {{blk.body}}