Handle HAML filter blank lines

lib/syntax_tree/haml.rb

@@ -82,10 +82,30 @@ def accept(visitor)
     end
   end
 
+  # This is our entrypoint for the formatter. We effectively delegate this to
+  # accepting the Format visitor.
   def format(q)
     accept(SyntaxTree::Haml::Format.new(q))
   end
 
+  # When we're formatting a list of children, we need to know the last line a
+  # node is on. This is because the next node in the list of children should be
+  # at most 1 blank line below the last line of the previous node. We cache this
+  # because at worst it requires walking the entire tree because filter nodes
+  # can take up multiple lines.
+  def last_line
+    @last_line ||=
+      if children.any?
+        children.last.last_line
+      elsif type == :filter
+        line + value[:text].rstrip.count("\n") + 1
+      else
+        line
+      end
+  end
+
+  # This is our entrypoint for the pretty printer. We effectively delegate this
+  # to accepting the PrettyPrint visitor.
   def pretty_print(q)
     accept(SyntaxTree::Haml::PrettyPrint.new(q))
   end

lib/syntax_tree/haml/format.rb

@@ -69,15 +69,17 @@ def visit_filter(node)
             q.breakable_force
             first = true
 
-            node.value[:text].each_line(chomp: true) do |line|
-              if first
-                first = false
-              else
-                q.breakable_force
-              end
+            node.value[:text]
+              .rstrip
+              .each_line(chomp: true) do |line|
+                if first
+                  first = false
+                else
+                  q.breakable_force
+                end
 
-              q.text(line)
-            end
+                q.text(line)
+              end
           end
         end
       end
@@ -124,8 +126,7 @@ def visit_root(node)
 
         node.children.each do |child|
           q.breakable_force if previous_line && (child.line - previous_line) > 1
-          previous_line =
-            child.children.any? ? child.children.last.line : child.line
+          previous_line = child.last_line
 
           visit(child)
           q.breakable_force
@@ -513,10 +514,8 @@ def with_children(node)
                   q.breakable_force
                 end
 
-                previous_line =
-                  child.children.any? ? child.children.last.line : child.line
-
                 visit(child)
+                previous_line = child.last_line
               end
             end
           end

test/filter_test.rb

@@ -24,4 +24,27 @@ def test_javascript
         1 + 1;
     HAML
   end
+
+  def test_does_not_add_blank_lines
+    assert_format(<<~HAML)
+      %html
+        %head
+          :javascript
+            console.log("This is inline script.");
+        %body
+          = yield
+    HAML
+  end
+
+  def test_maintains_blank_lines
+    assert_format(<<~HAML)
+      %html
+        %head
+          :javascript
+            console.log("This is inline script.");
+
+        %body
+          = yield
+    HAML
+  end
 end