Use Protobuf definition for determining JSON field names (#218)

This was previously relying on an auto-generated mapping layer, but since
the upstream patch was merged into protobuf 3.17.0 we can rely on the
upstream support instead.

See protocolbuffers/protobuf#8356

CHANGELOG.md

@@ -18,6 +18,10 @@
   - google-protobuf 3.15.x has a bug that causes a seg fault in Ruby under
     certain conditions (https://github.com/protocolbuffers/protobuf/pull/8639). Use
     google-protobuf 3.17.1 instead.
+* Use Protobuf definition for determining JSON field names
+  - Note you may see a breaking change if you were using `PgQuery::ParseResult.encode_json`
+    to map the protobuf result to JSON, since this now respects the intended JSON names
+    from the Proto3 definition (instead of the differently formatted Protobuf field names)
 
 
 ## 2.0.3     2021-04-05

Rakefile

@@ -86,18 +86,4 @@ task :update_source do
   system("cp -a #{libdir}/testdata/* #{testfilesdir}")
   # Copy back the custom ext files
   system("cp -a #{extbakdir}/pg_query_ruby.{c,sym} #{extbakdir}/extconf.rb #{extdir}")
-
-  # Generate JSON field name helper (workaround until https://github.com/protocolbuffers/protobuf/pull/8356 is merged)
-  str = "module PgQuery\n  INTERNAL_PROTO_FIELD_NAME_TO_JSON_NAME = {\n"
-  cur_type = nil
-  File.read(File.join(libdir, 'protobuf/pg_query.proto')).each_line do |line|
-    if line[/^message (\w+)/]
-      cur_type = $1
-      next
-    end
-    next unless line[/(repeated )?\w+ (\w+) = \d+( \[json_name="(\w+)"\])?;/]
-    str += format("    [%s, :%s] => '%s',\n", cur_type, $2, $4 || $2)
-  end
-  str += "  }\nend\n"
-  File.write(File.join(__dir__, 'lib/pg_query/json_field_names.rb'), str)
 end

lib/pg_query.rb

@@ -10,7 +10,6 @@
 require 'pg_query/treewalker'
 
 require 'pg_query/filter_columns'
-require 'pg_query/json_field_names'
 require 'pg_query/fingerprint'
 require 'pg_query/param_refs'
 require 'pg_query/deparse'

lib/pg_query/fingerprint.rb

@@ -60,9 +60,7 @@ def ignored_node_type?(node)
     end
 
     def node_protobuf_field_name_to_json_name(node_class, field)
-      # Use protobuf descriptor once json_name support is fixed: https://github.com/protocolbuffers/protobuf/pull/8356
-      # node_class.descriptor.find { |d| d.name == field.to_s }.json_name
-      INTERNAL_PROTO_FIELD_NAME_TO_JSON_NAME.fetch([node_class, field])
+      node_class.descriptor.find { |d| d.name == field.to_s }.json_name
     end
 
     def fingerprint_node(node, hash, parent_node_name = nil, parent_field_name = nil) # rubocop:disable Metrics/CyclomaticComplexity