[ruby/prism] wip: node unions

https://github.com/ruby/prism/commit/99a71675d4

prism/config.yml

@@ -692,6 +692,7 @@ nodes:
         type: constant[]
       - name: parameters
         type: node?
+        kind: BlockParametersNode
       - name: body
         type: node?
       - name: opening_loc
@@ -727,6 +728,7 @@ nodes:
         kind: ParametersNode
       - name: locals
         type: node[]
+        kind: BlockLocalVariableNode
       - name: opening_loc
         type: location?
       - name: closing_loc
@@ -1134,6 +1136,9 @@ nodes:
         type: node?
       - name: child
         type: node
+        kind:
+          - ConstantReadNode
+          - MissingNode
       - name: delimiter_loc
         type: location
     comment: |
@@ -1177,6 +1182,9 @@ nodes:
         type: node?
       - name: child
         type: node
+        kind:
+          - ConstantReadNode
+          - MissingNode
       - name: delimiter_loc
         type: location
     comment: |
@@ -1617,6 +1625,10 @@ nodes:
     fields:
       - name: numeric
         type: node
+        kind:
+          - FloatNode
+          - IntegerNode
+          - RationalNode
     comment: |
       Represents an imaginary number literal.
 
@@ -2370,16 +2382,36 @@ nodes:
     fields:
       - name: requireds
         type: node[]
+        kind:
+          - RequiredParameterNode
+          - MultiTargetNode
       - name: optionals
         type: node[]
+        kind: OptionalParameterNode
       - name: rest
         type: node?
+        kind:
+          - RestParameterNode
+          - ImplicitRestNode # Only in block parameters
       - name: posts
         type: node[]
+        kind:
+          - RequiredParameterNode
+          - MultiTargetNode
+          # On parsing error of `f(**kwargs, ...)` or `f(**nil, ...)`, the keyword_rest value is moved here:
+          - KeywordRestParameterNode
+          - NoKeywordsParameterNode
       - name: keywords
         type: node[]
+        kind:
+          - RequiredKeywordParameterNode
+          - OptionalKeywordParameterNode
       - name: keyword_rest
         type: node?
+        kind:
+          - KeywordRestParameterNode
+          - ForwardingParameterNode
+          - NoKeywordsParameterNode
       - name: block
         type: node?
         kind: BlockParameterNode

prism/templates/template.rb

@@ -75,35 +75,49 @@ module Prism
   # node and not just a generic node.
   class NodeKindField < Field
     def c_type
-      if options[:kind]
+      if specific_kind
-        "pm_#{options[:kind].gsub(/(?<=.)[A-Z]/, "_\\0").downcase}"
+        "pm_#{specific_kind.gsub(/(?<=.)[A-Z]/, "_\\0").downcase}"
       else
         "pm_node"
       end
     end
 
     def ruby_type
-      options[:kind] || "Node"
+      specific_kind || "Node"
     end
 
     def java_type
-      options[:kind] || "Node"
+      specific_kind || "Node"
     end
 
     def java_cast
-      if options[:kind]
+      if specific_kind
         "(Nodes.#{options[:kind]}) "
       else
         ""
       end
     end
+
+    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 itself a node. We pass them as
   # references and store them as references.
   class NodeField < NodeKindField
     def rbs_class
-      options[:kind] || "Prism::node"
+      if specific_kind
+        specific_kind
+      elsif union_kind
+        union_kind.join(" | ")
+      else
+        "Prism::node"
+      end
     end
 
     def rbi_class
@@ -115,7 +129,13 @@ module Prism
   # optionally null. We pass them as references and store them as references.
   class OptionalNodeField < NodeKindField
     def rbs_class
-      "#{options[:kind] || "Prism::node"}?"
+      if specific_kind
+        "#{specific_kind}?"
+      elsif union_kind
+        [union_kind, "nil"].join(" | ")
+      else
+        "Prism::node?"
+      end
     end
 
     def rbi_class