diff --git a/lib/prism/node_ext.rb b/lib/prism/node_ext.rb
index 688e60a15957a6..36a43b6327e4c9 100644
--- a/lib/prism/node_ext.rb
+++ b/lib/prism/node_ext.rb
@@ -169,14 +169,17 @@ def full_name
   class ParametersNode < Node
     # Mirrors the Method#parameters method.
     def signature
-      names = [] #: Array[[:req | :opt | :rest | :keyreq | :key | :keyrest | :block, Symbol] | [:rest | :keyrest | :nokey]]
+      names = [] #: Array[[:req | :opt | :rest | :keyreq | :key | :keyrest | :block, Symbol] | [:req | :rest | :keyrest | :nokey]]
 
       requireds.each do |param|
         names << (param.is_a?(MultiTargetNode) ? [:req] : [:req, param.name])
       end
 
       optionals.each { |param| names << [:opt, param.name] }
-      names << [:rest, rest.name || :*] if rest
+
+      if rest && rest.is_a?(RestParameterNode)
+        names << [:rest, rest.name || :*]
+      end
 
       posts.each do |param|
         names << (param.is_a?(MultiTargetNode) ? [:req] : [:req, param.name])
diff --git a/lib/prism/pack.rb b/lib/prism/pack.rb
index 0168e5e7496ada..31c768612328bd 100644
--- a/lib/prism/pack.rb
+++ b/lib/prism/pack.rb
@@ -216,6 +216,7 @@ def describe
           else
             source = directive.source
           end
+          # @type var source_width: Integer
           "  #{source.ljust(source_width)}  #{directive.describe}"
         end
 
diff --git a/lib/prism/parse_result.rb b/lib/prism/parse_result.rb
index 7cb982e69981f6..1d9e7008822faa 100644
--- a/lib/prism/parse_result.rb
+++ b/lib/prism/parse_result.rb
@@ -30,7 +30,7 @@ def encoding
     # Perform a byteslice on the source code using the given byte offset and
     # byte length.
     def slice(byte_offset, length)
-      source.byteslice(byte_offset, length)
+      source.byteslice(byte_offset, length) or raise
     end
 
     # Binary search through the offsets to find the line number for the given
@@ -52,7 +52,7 @@ def column(byte_offset)
 
     # Return the character offset for the given byte offset.
     def character_offset(byte_offset)
-      source.byteslice(0, byte_offset).length
+      (source.byteslice(0, byte_offset) or raise).length
     end
 
     # Return the column number in characters for the given byte offset.
@@ -157,12 +157,8 @@ def comments
     end
 
     # Create a new location object with the given options.
-    def copy(**options)
-      Location.new(
-        options.fetch(:source) { source },
-        options.fetch(:start_offset) { start_offset },
-        options.fetch(:length) { length }
-      )
+    def copy(source: self.source, start_offset: self.start_offset, length: self.length)
+      Location.new(source, start_offset, length)
     end
 
     # Returns a string representation of this location.
diff --git a/lib/prism/parse_result/comments.rb b/lib/prism/parse_result/comments.rb
index 0f1522deade01c..314261ea470721 100644
--- a/lib/prism/parse_result/comments.rb
+++ b/lib/prism/parse_result/comments.rb
@@ -150,6 +150,7 @@ def nearest_targets(node, comment)
           target_end = target.end_offset
 
           if target.encloses?(comment)
+            # @type var target: NodeTarget
             # The comment is completely contained by this target. Abandon the
             # binary search at this level.
             return nearest_targets(target.node, comment)
diff --git a/lib/prism/parse_result/newlines.rb b/lib/prism/parse_result/newlines.rb
index ca05f5b7026767..96c97646ff141a 100644
--- a/lib/prism/parse_result/newlines.rb
+++ b/lib/prism/parse_result/newlines.rb
@@ -58,7 +58,11 @@ def visit_statements_node(node)
 
     # Walk the tree and mark nodes that are on a new line.
     def mark_newlines!
-      value.accept(Newlines.new(Array.new(1 + source.offsets.size, false)))
+      if ProgramNode === value
+        value.accept(Newlines.new(Array.new(1 + source.offsets.size, false)))
+      else
+        raise "ParseResult does not contain ProgramNode value"
+      end
     end
   end
 end
diff --git a/lib/prism/pattern.rb b/lib/prism/pattern.rb
index e1643671ec1131..8e0d235796cd2b 100644
--- a/lib/prism/pattern.rb
+++ b/lib/prism/pattern.rb
@@ -69,7 +69,14 @@ def initialize(query)
     # nodes.
     def compile
       result = Prism.parse("case nil\nin #{query}\nend")
-      compile_node(result.value.statements.body.last.conditions.last.pattern)
+
+      case_match_node = result.value.statements.body.last
+      raise CompilationError, case_match_node.inspect unless case_match_node.is_a?(CaseMatchNode)
+
+      in_node = case_match_node.conditions.last
+      raise CompilationError, in_node.inspect unless in_node.is_a?(InNode)
+
+      compile_node(in_node.pattern)
     end
 
     # Scan the given node and all of its children for nodes that match the
@@ -77,13 +84,14 @@ def compile
     # matches the pattern. If no block is given, an enumerator will be returned
     # that will yield each node that matches the pattern.
     def scan(root)
-      return to_enum(__method__, root) unless block_given?
+      return to_enum(__method__ || raise, root) unless block_given?
 
       @compiled ||= compile
+      compiled = @compiled #: Proc
       queue = [root]
 
       while (node = queue.shift)
-        yield node if @compiled.call(node)
+        yield node if compiled.call(node)
         queue.concat(node.compact_child_nodes)
       end
     end
@@ -174,7 +182,13 @@ def compile_hash_pattern_node(node)
 
       preprocessed =
         node.elements.to_h do |element|
-          [element.key.unescaped.to_sym, compile_node(element.value)]
+          key = element.key
+          if key.respond_to?(:unescaped)
+            # @type var key: SymbolNode
+            [key.unescaped.to_sym, compile_node(element.value)]
+          else
+            raise CompilationError, element.inspect
+          end
         end
 
       compiled_keywords = ->(other) do
diff --git a/lib/prism/prism.gemspec b/lib/prism/prism.gemspec
index 8e642192a5a07d..16ae553e323501 100644
--- a/lib/prism/prism.gemspec
+++ b/lib/prism/prism.gemspec
@@ -125,19 +125,14 @@ Gem::Specification.new do |spec|
     "sig/manifest.yaml",
     "sig/prism.rbs",
     "sig/prism/compiler.rbs",
-    "sig/prism/debug.rbs",
-    "sig/prism/desugar_compiler.rbs",
     "sig/prism/dispatcher.rbs",
     "sig/prism/dot_visitor.rbs",
     "sig/prism/dsl.rbs",
-    "sig/prism/lex_compat.rbs",
     "sig/prism/mutation_compiler.rbs",
-    "sig/prism/node_ext.rbs",
-    "sig/prism/node_inspector.rbs",
     "sig/prism/node.rbs",
+    "sig/prism/node_ext.rbs",
     "sig/prism/pack.rbs",
-    "sig/prism/parse_result/comments.rbs",
-    "sig/prism/parse_result/newlines.rbs",
+    "sig/prism/parse_result.rbs",
     "sig/prism/pattern.rbs",
     "sig/prism/ripper_compat.rbs",
     "sig/prism/serialize.rbs",
diff --git a/prism/config.yml b/prism/config.yml
index 9a959c9cb88828..a89052d7699992 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -692,7 +692,6 @@ nodes:
         type: constant[]
       - name: parameters
         type: node?
-        kind: BlockParametersNode
       - name: body
         type: node?
       - name: opening_loc
@@ -1583,8 +1582,12 @@ nodes:
         type: node?
       - name: elements
         type: node[]
+        kind: AssocNode
       - name: rest
         type: node?
+        kind:
+          - AssocSplatNode
+          - NoKeywordsParameterNode
       - name: opening_loc
         type: location?
       - name: closing_loc
diff --git a/prism/templates/lib/prism/dot_visitor.rb.erb b/prism/templates/lib/prism/dot_visitor.rb.erb
index 56f116b8d3944e..5a9b4954442884 100644
--- a/prism/templates/lib/prism/dot_visitor.rb.erb
+++ b/prism/templates/lib/prism/dot_visitor.rb.erb
@@ -17,7 +17,7 @@ module Prism
         if port
           "<tr><td align=\"left\" colspan=\"2\" port=\"#{name}\">#{name}</td></tr>"
         else
-          "<tr><td align=\"left\">#{name}</td><td>#{CGI.escapeHTML(value)}</td></tr>"
+          "<tr><td align=\"left\">#{name}</td><td>#{CGI.escapeHTML(value || raise)}</td></tr>"
         end
       end
     end
diff --git a/prism/templates/lib/prism/node.rb.erb b/prism/templates/lib/prism/node.rb.erb
index 99d89712cfb350..98048989f29157 100644
--- a/prism/templates/lib/prism/node.rb.erb
+++ b/prism/templates/lib/prism/node.rb.erb
@@ -182,14 +182,9 @@ module Prism
       }.compact.join(", ") %>] #: Array[Prism::node | Location]
     end
 
-    # def copy: (**params) -> <%= node.name %>
-    def copy(**params)
-      <%= node.name %>.new(
-        source,
-        <%- (node.fields.map(&:name) + ["location"]).map do |name| -%>
-        params.fetch(:<%= name %>) { <%= name %> },
-        <%- end -%>
-      )
+    # def copy: (<%= (node.fields.map { |field| "?#{field.name}: #{field.rbs_class}" } + ["?location: Location"]).join(", ") %>) -> <%= node.name %>
+    def copy(<%= (node.fields.map(&:name) + ["location"]).map { |field| "#{field}: self.#{field}" }.join(", ") %>)
+      <%= node.name %>.new(<%= ["source", *node.fields.map(&:name), "location"].join(", ") %>)
     end
 
     # def deconstruct: () -> Array[nil | Node]
diff --git a/prism/templates/template.rb b/prism/templates/template.rb
index 18806901e1a777..aba909bdc3b770 100755
--- a/prism/templates/template.rb
+++ b/prism/templates/template.rb
@@ -99,11 +99,11 @@ def java_cast
     end
 
     def specific_kind
-      @options[:kind] unless @options[:kind].is_a?(Array)
+      options[:kind] unless options[:kind].is_a?(Array)
     end
 
     def union_kind
-      options[:kind] if @options[:kind].is_a?(Array)
+      options[:kind] if options[:kind].is_a?(Array)
     end
   end
 
@@ -132,7 +132,7 @@ def rbs_class
       if specific_kind
         "#{specific_kind}?"
       elsif union_kind
-        [union_kind, "nil"].join(" | ")
+        [*union_kind, "nil"].join(" | ")
       else
         "Prism::node?"
       end
@@ -147,7 +147,13 @@ def rbi_class
   # references and store them directly on the struct.
   class NodeListField < Field
     def rbs_class
-      "Array[Prism::node]"
+      if specific_kind
+        "Array[#{specific_kind}]"
+      elsif union_kind
+        "Array[#{union_kind.join(" | ")}]"
+      else
+        "Array[Prism::node]"
+      end
     end
 
     def rbi_class
@@ -157,6 +163,15 @@ def rbi_class
     def java_type
       "Node[]"
     end
+
+    # TODO: unduplicate with NodeKindField
+    def specific_kind
+      options[:kind] unless options[:kind].is_a?(Array)
+    end
+
+    def union_kind
+      options[:kind] if options[:kind].is_a?(Array)
+    end
   end
 
   # This represents a field on a node that is the ID of a string interned
@@ -569,12 +584,12 @@ def locals
     "src/token_type.c",
     "rbi/prism.rbi",
     "sig/prism.rbs",
-    "sig/prism/dot_visitor.rbs",
     "sig/prism/dsl.rbs",
     "sig/prism/mutation_compiler.rbs",
     "sig/prism/node.rbs",
-    "sig/prism/ripper_compat.rbs",
     "sig/prism/visitor.rbs",
+    "sig/prism/_private/dot_visitor.rbs",
+    "sig/prism/_private/ripper_compat.rbs",
   ]
 end