Engine: Don't compile <% # coments %> (marcoroth#826)

Follow up to marcoroth#825.

This pull request improves the engine by not compiling `<% # coments %>
comments as part of the template. Outputting `# coments` could lead to
some cases, where the template could be compiled but couldn't be
rendered, because it would comment out important pieces of the template.

```erb
<% if true %><% # comment %><%= "Hello World" %><% end %>
```

**Before**

`exe/herb compile test.html.erb`
```ruby
__herb = ::Herb::Engine; _buf = ::String.new;
 if true; # comment
 _buf << __herb.h(("Hello World")); end; _buf << '
'.freeze;
_buf.to_s
```


**After**

`exe/herb compile test.html.erb`
```ruby
__herb = ::Herb::Engine; _buf = ::String.new;
 if true; _buf << __herb.h(("Hello World")); end; _buf << '
'.freeze;
_buf.to_s
```


### For reference

`bin/erubi-compile test.html.erb`
```ruby
__erubi = ::Erubi; _buf = ::String.new; if true ; # comment ; _buf << __erubi.h(( "Hello World" )); end ; _buf << '
'.freeze;
_buf.to_s
```

`bin/erubi-render test.html.erb`
```
bin/erubi-render:117:in 'Kernel#eval': (eval at bin/erubi-render:117):2: syntax errors found (SyntaxError)
  1 | __erubi = ::Erubi; _buf = ::String.new; if true ; # comment ; _buf << __erubi.h(( "Hello World" )); end ; _buf << '
> 2 | '.freeze;
    | ^ unterminated string meets end of file
  3 | _buf.to_s
> 4 |
    | ^ expected an `end` to close the conditional clause

    | ^ unexpected end-of-input, assuming it is closing the parent top level context

        from bin/erubi-render:117:in 'ErubiRenderer#render_template'
        from bin/erubi-render:31:in 'ErubiRenderer#run'
        from bin/erubi-render:152:in '<main>'
```

`exe/herb render test.html.erb`
```
Hello World
```

Author: marcoroth

lib/herb/ast/helpers.rb

@@ -21,6 +21,17 @@ def erb_comment?(opening)
       def erb_output?(opening)
         opening.include?("=")
       end
+
+      #: (Herb::AST::ERBContentNode) -> bool
+      def inline_ruby_comment?(node)
+        return false unless node.is_a?(Herb::AST::ERBContentNode)
+        return false if erb_comment?(node.tag_opening&.value || "")
+
+        content = node.content&.value || ""
+        stripped = content.lstrip
+
+        stripped.start_with?("#") && node.location.start.line == node.location.end.line
+      end
     end
   end
 end

lib/herb/engine/compiler.rb

@@ -162,6 +162,8 @@ def visit_cdata_node(node)
       end
 
       def visit_erb_content_node(node)
+        return if inline_ruby_comment?(node)
+
         process_erb_tag(node)
       end
 

sig/herb/ast/helpers.rbs

@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require_relative "../test_helper"
+require_relative "../snapshot_utils"
+require_relative "../../lib/herb/engine"
+
+module Engine
+  class ERBCommentsTest < Minitest::Spec
+    include SnapshotUtils
+
+    test "inline ruby comment on same line" do
+      template = %(<% if true %><% # Comment here %><% end %>)
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "inline ruby comment with newline" do
+      template = "<% if true %><% # Comment here %>\n<% end %>"
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "inline ruby comment between code" do
+      template = %(<% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "inline ruby comment before and between code" do
+      template = %(<% # Comment here %><% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "inline ruby comment with spaces" do
+      template = %(<%  # Comment %> <% code = "test" %><%= code %>)
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "inline ruby comment multiline" do
+      template = "<% # Comment\nmore %> <% code = \"test\" %><%= code %>"
+
+      assert_compiled_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment on same line" do
+      template = %(<% if true %><% # Comment here %><% end %>)
+
+      assert_evaluated_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment with newline" do
+      template = "<% if true %><% # Comment here %>\n<% end %>"
+
+      assert_evaluated_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment between code" do
+      template = %(<% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_evaluated_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment before and between code" do
+      template = %(<% # Comment here %><% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_evaluated_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment with spaces" do
+      template = %(<%  # Comment %> <% code = "test" %><%= code %>)
+
+      assert_evaluated_snapshot(template)
+    end
+
+    test "evaluation: inline ruby comment multiline" do
+      template = "<% # Comment\nmore %> <% code = \"test\" %><%= code %>"
+
+      assert_evaluated_snapshot(template, { more: "ignored" })
+    end
+  end
+end

test/engine/erb_comments_test.rb

@@ -398,5 +398,41 @@ class EvaluationTest < Minitest::Spec
 
       assert_evaluated_snapshot(template, {}, { escape: false })
     end
+
+    test "inline ruby comment on same line" do
+      template = %(<% if true %><% # Comment here %><% end %>)
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "inline ruby comment with newline" do
+      template = "<% if true %><% # Comment here %>\n<% end %>"
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "inline ruby comment between code" do
+      template = %(<% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "inline ruby comment before and between code" do
+      template = %(<% # Comment here %><% if true %><% # Comment here %><%= "hello" %><% end %>)
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "inline ruby comment with spaces" do
+      template = %(<%  # Comment %> <% code = "test" %><%= code %>)
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "inline ruby comment multiline" do
+      template = "<% # Comment\nmore %> <% code = \"test\" %><%= code %>"
+
+      assert_evaluated_snapshot(template, { more: "ignored" }, { escape: false })
+    end
   end
 end