Use rdoc provided by bundled gems for generating ruby documentation

Merged: https://github.com/ruby/ruby/pull/12577

common.mk

@@ -64,7 +64,7 @@ LIBRUBY_EXTS  = ./.libruby-with-ext.time
 REVISION_H    = ./.revision.time
 PLATFORM_D    = $(TIMESTAMPDIR)/.$(PLATFORM_DIR).time
 ENC_TRANS_D   = $(TIMESTAMPDIR)/.enc-trans.time
-RDOC          = $(XRUBY) "$(tooldir)/rdoc-srcdir"
+RDOC          = $(XRUBY) "$(tooldir)/rdoc-srcdir" $(srcdir)
 RDOCOUT       = $(EXTOUT)/rdoc
 HTMLOUT       = $(EXTOUT)/html
 CAPIOUT       = doc/capi
@@ -676,6 +676,8 @@ do-install-dbg: $(PROGRAM) pre-install-dbg
 post-install-dbg::
 	@$(NULLCMD)
 
+srcs-doc: prepare-gems
+
 rdoc: PHONY main srcs-doc
 	@echo Generating RDoc documentation
 	$(Q) $(RDOC) --ri --op "$(RDOCOUT)" $(RDOC_GEN_OPTS) $(RDOCFLAGS) .

tool/lib/bundled_gem.rb

@@ -12,7 +12,8 @@ module BundledGem
     "singleton", # prime
     "ipaddr", # rinda
     "forwardable", # prime, rinda
-    "strscan" # rexml
+    "strscan", # rexml
+    "psych" # rdoc
   ]
 
   module_function

tool/rdoc-srcdir

@@ -1,6 +1,7 @@
 #!ruby -W0
 
-$:.unshift(File.expand_path("../lib", __dir__))
+rdoc_path = Dir.glob("#{ARGV[0]}/.bundle/gems/rdoc-*").first
+$LOAD_PATH.unshift("#{rdoc_path}/lib")
 require 'rdoc/rdoc'
 
 # Make only the output directory relative to the invoked directory.