[ruby/prism] Change ConstantPathNode#child to ConstantPathNode#{name,name_loc}

This has been requested for a long time, and I'm finally doing it
now. Unfortunately this is a breaking change for all of the APIs.

I've added in a Ruby method for `#child` that is deprecated so that
existing usage doesn't break, but for everyone else this is going
to be a bit of a pain.

https://github.com/ruby/prism/commit/9cbe74464e

5 files changed, 51 insertions, 19 deletions

diff --git a/lib/prism/node_ext.rb b/lib/prism/node_ext.rb
index 8674544065..10fc1decbf 100644
--- a/lib/prism/node_ext.rb
+++ b/lib/prism/node_ext.rb
@@ -143,11 +143,12 @@ module Prism
       current = self #: node?
 
       while current.is_a?(ConstantPathNode)
-        child = current.child
-        if child.is_a?(MissingNode)
+        name = current.name
+        if name.nil?
           raise MissingNodesInConstantPathError, "Constant path contains missing nodes. Cannot compute full name"
         end
-        parts.unshift(child.name)
+
+        parts.unshift(name)
         current = current.parent
       end
 
@@ -162,6 +163,20 @@ module Prism
     def full_name
       full_name_parts.join("::")
     end
+
+    # Previously, we had a child node on this class that contained either a
+    # constant read or a missing node. To not cause a breaking change, we
+    # continue to supply that API.
+    def child
+      warn(<<~MSG, category: :deprecated)
+        DEPRECATED: ConstantPathNode#child is deprecated and will be removed \
+        in the next major version. Use \
+        ConstantPathNode#name/ConstantPathNode#name_loc instead. Called from \
+        #{caller(1..1).first}.
+      MSG
+
+      name ? ConstantReadNode.new(source, name, name_loc) : MissingNode.new(source, location)
+    end
   end
 
   class ConstantPathTargetNode < Node
@@ -179,17 +194,31 @@ module Prism
           raise ConstantPathNode::DynamicPartsInConstantPathError, "Constant target path contains dynamic parts. Cannot compute full name"
         end
 
-      if child.is_a?(MissingNode)
+      if name.nil?
         raise ConstantPathNode::MissingNodesInConstantPathError, "Constant target path contains missing nodes. Cannot compute full name"
       end
 
-      parts.push(child.name)
+      parts.push(name)
     end
 
     # Returns the full name of this constant path. For example: "Foo::Bar"
     def full_name
       full_name_parts.join("::")
     end
+
+    # Previously, we had a child node on this class that contained either a
+    # constant read or a missing node. To not cause a breaking change, we
+    # continue to supply that API.
+    def child
+      warn(<<~MSG, category: :deprecated)
+        DEPRECATED: ConstantPathTargetNode#child is deprecated and will be \
+        removed in the next major version. Use \
+        ConstantPathTargetNode#name/ConstantPathTargetNode#name_loc instead. \
+        Called from #{caller(1..1).first}.
+      MSG
+
+      name ? ConstantReadNode.new(source, name, name_loc) : MissingNode.new(source, location)
+    end
   end
 
   class ConstantTargetNode < Node
diff --git a/lib/prism/pattern.rb b/lib/prism/pattern.rb
index e12cfd597f..91b23afe3e 100644
--- a/lib/prism/pattern.rb
+++ b/lib/prism/pattern.rb
@@ -149,7 +149,7 @@ module Prism
       parent = node.parent
 
       if parent.is_a?(ConstantReadNode) && parent.slice == "Prism"
-        compile_node(node.child)
+        compile_constant_name(node, node.name)
       else
         compile_error(node)
       end
@@ -158,14 +158,17 @@ module Prism
     # in ConstantReadNode
     # in String
     def compile_constant_read_node(node)
-      value = node.slice
+      compile_constant_name(node, node.name)
+    end
 
-      if Prism.const_defined?(value, false)
-        clazz = Prism.const_get(value)
+    # Compile a name associated with a constant.
+    def compile_constant_name(node, name)
+      if Prism.const_defined?(name, false)
+        clazz = Prism.const_get(name)
 
         ->(other) { clazz === other }
-      elsif Object.const_defined?(value, false)
-        clazz = Object.const_get(value)
+      elsif Object.const_defined?(name, false)
+        clazz = Object.const_get(name)
 
         ->(other) { clazz === other }
       else
diff --git a/lib/prism/translation/parser/compiler.rb b/lib/prism/translation/parser/compiler.rb
index a4aaa41d6f..c311613388 100644
--- a/lib/prism/translation/parser/compiler.rb
+++ b/lib/prism/translation/parser/compiler.rb
@@ -483,13 +483,13 @@ module Prism
           if node.parent.nil?
             builder.const_global(
               token(node.delimiter_loc),
-              [node.child.name, srange(node.child.location)]
+              [node.name, srange(node.name_loc)]
             )
           else
             builder.const_fetch(
               visit(node.parent),
               token(node.delimiter_loc),
-              [node.child.name, srange(node.child.location)]
+              [node.name, srange(node.name_loc)]
             )
           end
         end
diff --git a/lib/prism/translation/ripper.rb b/lib/prism/translation/ripper.rb
index 4e3b1b74fd..5cb6f6715d 100644
--- a/lib/prism/translation/ripper.rb
+++ b/lib/prism/translation/ripper.rb
@@ -1456,16 +1456,16 @@ module Prism
       # ^^^^^^^^
       def visit_constant_path_node(node)
         if node.parent.nil?
-          bounds(node.child.location)
-          child = on_const(node.child.name.to_s)
+          bounds(node.name_loc)
+          child = on_const(node.name.to_s)
 
           bounds(node.location)
           on_top_const_ref(child)
         else
           parent = visit(node.parent)
 
-          bounds(node.child.location)
-          child = on_const(node.child.name.to_s)
+          bounds(node.name_loc)
+          child = on_const(node.name.to_s)
 
           bounds(node.location)
           on_const_path_ref(parent, child)
diff --git a/lib/prism/translation/ruby_parser.rb b/lib/prism/translation/ruby_parser.rb
index f0a3bdd607..c6f741c8e5 100644
--- a/lib/prism/translation/ruby_parser.rb
+++ b/lib/prism/translation/ruby_parser.rb
@@ -442,9 +442,9 @@ module Prism
         # ^^^^^^^^
         def visit_constant_path_node(node)
           if node.parent.nil?
-            s(node, :colon3, node.child.name)
+            s(node, :colon3, node.name)
           else
-            s(node, :colon2, visit(node.parent), node.child.name)
+            s(node, :colon2, visit(node.parent), node.name)
           end
         end