[ruby/prism] Autoload newlines and comment visitors

Having the @newline instance variable in every node adds up, and
since it is so rarely used, we only want to add it when necessary.

Moving this into an autoloaded file and moving the instance variable
out of the default initializers reduces allocated memory because the
nodes are now smaller and some fit into the compact list. On my
machine, I'm seeing about an 8% drop.

https://github.com/ruby/prism/commit/eea92c07d2

lib/prism.rb

@@ -71,8 +71,6 @@ require_relative "prism/polyfill/byteindex"
 require_relative "prism/node"
 require_relative "prism/node_ext"
 require_relative "prism/parse_result"
-require_relative "prism/parse_result/comments"
-require_relative "prism/parse_result/newlines"
 
 # This is a Ruby implementation of the prism parser. If we're running on CRuby
 # and we haven't explicitly set the PRISM_FFI_BACKEND environment variable, then

lib/prism/parse_result.rb

@@ -574,6 +574,12 @@ module Prism
 
   # This is a result specific to the `parse` and `parse_file` methods.
   class ParseResult < Result
+    autoload :Comments, "prism/parse_result/comments"
+    autoload :Newlines, "prism/parse_result/newlines"
+
+    private_constant :Comments
+    private_constant :Newlines
+
     # The syntax tree that was parsed from the source code.
     attr_reader :value
 
@@ -587,6 +593,17 @@ module Prism
     def deconstruct_keys(keys)
       super.merge!(value: value)
     end
+
+    # Attach the list of comments to their respective locations in the tree.
+    def attach_comments!
+      Comments.new(self).attach! # steep:ignore
+    end
+
+    # Walk the tree and mark nodes that are on a new line, loosely emulating
+    # the behavior of CRuby's `:line` tracepoint event.
+    def mark_newlines!
+      value.accept(Newlines.new(source.offsets.size)) # steep:ignore
+    end
   end
 
   # This is a result specific to the `lex` and `lex_file` methods.

lib/prism/parse_result/comments.rb

@@ -183,12 +183,5 @@ module Prism
         [preceding, NodeTarget.new(node), following]
       end
     end
-
-    private_constant :Comments
-
-    # Attach the list of comments to their respective locations in the tree.
-    def attach_comments!
-      Comments.new(self).attach! # steep:ignore
-    end
   end
 end

lib/prism/parse_result/newlines.rb

@@ -17,21 +17,26 @@ module Prism
     # Note that the logic in this file should be kept in sync with the Java
     # MarkNewlinesVisitor, since that visitor is responsible for marking the
     # newlines for JRuby/TruffleRuby.
+    #
+    # This file is autoloaded only when `mark_newlines!` is called, so the
+    # re-opening of the various nodes in this file will only be performed in
+    # that case. We do that to avoid storing the extra `@newline` instance
+    # variable on every node if we don't need it.
     class Newlines < Visitor
       # Create a new Newlines visitor with the given newline offsets.
-      def initialize(newline_marked)
+      def initialize(lines)
-        @newline_marked = newline_marked
+        @lines = Array.new(1 + lines, false)
       end
 
       # Permit block/lambda nodes to mark newlines within themselves.
       def visit_block_node(node)
-        old_newline_marked = @newline_marked
+        old_lines = @lines
-        @newline_marked = Array.new(old_newline_marked.size, false)
+        @lines = Array.new(old_lines.size, false)
 
         begin
           super(node)
         ensure
-          @newline_marked = old_newline_marked
+          @lines = old_lines
         end
       end
 
@@ -39,7 +44,7 @@ module Prism
 
       # Mark if/unless nodes as newlines.
       def visit_if_node(node)
-        node.set_newline_flag(@newline_marked)
+        node.newline!(@lines)
         super(node)
       end
 
@@ -48,17 +53,101 @@ module Prism
       # Permit statements lists to mark newlines within themselves.
       def visit_statements_node(node)
         node.body.each do |child|
-          child.set_newline_flag(@newline_marked)
+          child.newline!(@lines)
         end
         super(node)
       end
     end
+  end
 
-    private_constant :Newlines
+  class Node
+    def newline? # :nodoc:
+      @newline ? true : false
+    end
 
-    # Walk the tree and mark nodes that are on a new line.
+    def newline!(lines) # :nodoc:
-    def mark_newlines!
+      line = location.start_line
-      value.accept(Newlines.new(Array.new(1 + source.offsets.size, false))) # steep:ignore
+      unless lines[line]
+        lines[line] = true
+        @newline = true
+      end
+    end
+  end
+
+  class BeginNode < Node
+    def newline!(lines) # :nodoc:
+      # Never mark BeginNode with a newline flag, mark children instead.
+    end
+  end
+
+  class ParenthesesNode < Node
+    def newline!(lines) # :nodoc:
+      # Never mark ParenthesesNode with a newline flag, mark children instead.
+    end
+  end
+
+  class IfNode < Node
+    def newline!(lines) # :nodoc:
+      predicate.newline!(lines)
+    end
+  end
+
+  class UnlessNode < Node
+    def newline!(lines) # :nodoc:
+      predicate.newline!(lines)
+    end
+  end
+
+  class UntilNode < Node
+    def newline!(lines) # :nodoc:
+      predicate.newline!(lines)
+    end
+  end
+
+  class WhileNode < Node
+    def newline!(lines) # :nodoc:
+      predicate.newline!(lines)
+    end
+  end
+
+  class RescueModifierNode < Node
+    def newline!(lines) # :nodoc:
+      expression.newline!(lines)
+    end
+  end
+
+  class InterpolatedMatchLastLineNode < Node
+    def newline!(lines) # :nodoc:
+      first = parts.first
+      first.newline!(lines) if first
+    end
+  end
+
+  class InterpolatedRegularExpressionNode < Node
+    def newline!(lines) # :nodoc:
+      first = parts.first
+      first.newline!(lines) if first
+    end
+  end
+
+  class InterpolatedStringNode < Node
+    def newline!(lines) # :nodoc:
+      first = parts.first
+      first.newline!(lines) if first
+    end
+  end
+
+  class InterpolatedSymbolNode < Node
+    def newline!(lines) # :nodoc:
+      first = parts.first
+      first.newline!(lines) if first
+    end
+  end
+
+  class InterpolatedXStringNode < Node
+    def newline!(lines) # :nodoc:
+      first = parts.first
+      first.newline!(lines) if first
     end
   end
 end

prism/templates/lib/prism/inspect_visitor.rb.erb

@@ -116,13 +116,8 @@ module Prism
 
     # Compose a header for the given node.
     def inspect_node(name, node)
-      result = +"@ #{name} ("
-
       location = node.location
-      result << "location: (#{location.start_line},#{location.start_column})-(#{location.end_line},#{location.end_column})"
+      "@ #{name} (location: (#{location.start_line},#{location.start_column})-(#{location.end_line},#{location.end_column}))\n"
-      result << ", newline: true" if node.newline?
-
-      result << ")\n"
     end
 
     # Compose a string representing the given inner location field.

prism/templates/lib/prism/node.rb.erb

@@ -28,18 +28,6 @@ module Prism
       location.is_a?(Location) ? location.end_offset : ((location >> 32) + (location & 0xFFFFFFFF))
     end
 
-    def newline? # :nodoc:
-      @newline ? true : false
-    end
-
-    def set_newline_flag(newline_marked) # :nodoc:
-      line = location.start_line
-      unless newline_marked[line]
-        newline_marked[line] = true
-        @newline = true
-      end
-    end
-
     # Returns all of the lines of the source code associated with this node.
     def source_lines
       location.source_lines
@@ -181,7 +169,6 @@ module Prism
     # def initialize: (<%= (node.fields.map { |field| "#{field.rbs_class} #{field.name}" } + ["Location location"]).join(", ") %>) -> void
     def initialize(source, <%= (node.fields.map(&:name) + ["location"]).join(", ") %>)
       @source = source
-      @newline = false
       @location = location
       <%- node.fields.each do |field| -%>
       <%- if Prism::Template::CHECK_FIELD_KIND && field.respond_to?(:check_field_kind) -%>
@@ -195,25 +182,6 @@ module Prism
     def accept(visitor)
       visitor.visit_<%= node.human %>(self)
     end
-    <%- if node.newline == false -%>
-
-    def set_newline_flag(newline_marked) # :nodoc:
-      # Never mark <%= node.name %> with a newline flag, mark children instead
-    end
-    <%- elsif node.newline.is_a?(String) -%>
-
-    def set_newline_flag(newline_marked) # :nodoc:
-      <%- field = node.fields.find { |f| f.name == node.newline } or raise node.newline -%>
-      <%- case field -%>
-      <%- when Prism::Template::NodeField -%>
-      <%= field.name %>.set_newline_flag(newline_marked)
-      <%- when Prism::Template::NodeListField -%>
-      first = <%= field.name %>.first
-      first.set_newline_flag(newline_marked) if first
-      <%- else raise field.class.name -%>
-      <%- end -%>
-    end
-    <%- end -%>
 
     # def child_nodes: () -> Array[nil | Node]
     def child_nodes