Expand rdoc-ref targets at the end of ri output

There have been several document refactors in ruby/ruby that extract
individual methods/classes' documentation into separate files, like
ruby/ruby#6567

Because RI is not capable of rendering those references, RI users
are left with dramatically fewer documentation on those methods/classes.

This commit adds a new option `--expand-ref` (default: true) to expand
all the rdoc-ref targets at the end of the output.

Author: st0012

lib/rdoc/ri/driver.rb

@@ -79,6 +79,7 @@ def self.default_options
     options[:interactive] = false
     options[:profile]     = false
     options[:show_all]    = false
+    options[:expand_refs] = true
     options[:use_stdout]  = !$stdout.tty?
     options[:width]       = 72
 
@@ -245,6 +246,12 @@ def self.process_args argv
 
       opt.separator nil
 
+      opt.on("--[no-]expand-refs", "Expand rdoc-refs at the end of output") do |value|
+        options[:expand_refs] = value
+      end
+
+      opt.separator nil
+
       opt.on("--help", "-h",
              "Show help and exit.") do
         puts opts
@@ -425,6 +432,7 @@ def initialize initial_options = {}
     @use_stdout  = options[:use_stdout]
     @show_all    = options[:show_all]
     @width       = options[:width]
+    @expand_refs = options[:expand_refs]
   end
 
   ##
@@ -549,11 +557,8 @@ def add_includes out, includes
   # Looks up the method +name+ and adds it to +out+
 
   def add_method out, name
-    filtered   = lookup_method name
-
-    method_out = method_document name, filtered
-
-    out.concat method_out.parts
+    filtered = lookup_method name
+    method_document out, name, filtered
   end
 
   ##
@@ -645,6 +650,7 @@ def class_document name, found, klasses, includes, extends
 
     add_also_in out, also_in
 
+    expand_rdoc_refs_at_the_bottom(out)
     out
   end
 
@@ -824,6 +830,8 @@ def display_method name
 
     add_method out, name
 
+    expand_rdoc_refs_at_the_bottom(out)
+
     display out
   end
 
@@ -1255,9 +1263,7 @@ def lookup_method name
   ##
   # Builds a RDoc::Markup::Document from +found+, +klasses+ and +includes+
 
-  def method_document name, filtered
-    out = RDoc::Markup::Document.new
-
+  def method_document out, name, filtered
     out << RDoc::Markup::Heading.new(1, name)
     out << RDoc::Markup::BlankLine.new
 
@@ -1514,4 +1520,38 @@ def start_server
     server.start
   end
 
+  RDOC_REFS_REGEXP = /\[rdoc-ref:([\w.]+)(@.*)?\]/
+
+  def expand_rdoc_refs_at_the_bottom(out)
+    return unless @expand_refs
+
+    extracted_rdoc_refs = []
+
+    out.each do |part|
+      content = if part.respond_to?(:text)
+        part.text
+      else
+        next
+      end
+
+      rdoc_refs = content.scan(RDOC_REFS_REGEXP).uniq.map do |file_name, _anchor|
+        file_name
+      end
+
+      extracted_rdoc_refs.concat(rdoc_refs)
+    end
+
+    found_pages = extracted_rdoc_refs.map do |ref|
+      begin
+        @stores.first.load_page(ref)
+      rescue RDoc::Store::MissingFileError
+      end
+    end.compact
+
+    found_pages.each do |page|
+      out << RDoc::Markup::Heading.new(4, "Expanded from #{page.full_name}")
+      out << RDoc::Markup::BlankLine.new
+      out << page.comment
+    end
+  end
 end

test/rdoc/test_rdoc_ri_driver.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require_relative 'helper'
 
-class TestRDocRIDriver < RDoc::TestCase
+class RDocRIDriverTest < RDoc::TestCase
 
   def setup
     super
@@ -243,6 +243,29 @@ def test_add_method
     assert_equal expected, out
   end
 
+  def test_add_method_with_rdoc_ref_link
+    util_store
+
+    out = doc
+
+    @driver.add_method out, 'Foo::Bar#blah_with_rdoc_ref'
+
+    expected =
+      doc(
+        head(1, 'Foo::Bar#blah_with_rdoc_ref'),
+        blank_line,
+        para("(from #{@rdoc_home})"),
+        head(3, 'Implementation from Bar'),
+        rule(1),
+        verb("blah(5) => 5\n", "See also {Doc}[rdoc-ref:README.rdoc]\n"),
+        rule(1),
+        blank_line,
+        blank_line
+      )
+
+    assert_equal expected, out
+  end
+
   def test_add_method_that_is_alias_for_original
     util_store
 
@@ -598,7 +621,7 @@ def test_display_class
     assert_match %r%^= Attributes:%, out
     assert_match %r%^  attr_accessor attr%, out
 
-    assert_equal 1, out.scan(/^-{50,}$/).length, out
+    assert_equal 2, out.scan(/^-{50,}$/).length, out
 
     refute_match %r%Foo::Bar#blah%, out
   end
@@ -622,9 +645,29 @@ def test_display_class_all
     assert_match %r%^= Attributes:%, out
     assert_match %r%^  attr_accessor attr%, out
 
-    assert_equal 6, out.scan(/^-{50,}$/).length, out
+    assert_equal 9, out.scan(/^-{50,}$/).length, out
 
     assert_match %r%Foo::Bar#blah%, out
+    assert_match %r%Foo::Bar#blah_with_rdoc_ref%, out
+    # From Foo::Bar and Foo::Bar#blah_with_rdoc_ref
+    assert_equal 2, out.scan(/rdoc-ref:README.rdoc/).length
+    # But README.rdoc should only be displayed once
+    assert_equal 1, out.scan(/Expanded from README.rdoc/).length
+  end
+
+  def test_rdoc_refs_expansion_can_be_disabled
+    util_store
+
+    @driver.instance_variable_set :@expand_rdoc_refs, false
+
+    out, = capture_output do
+      @driver.display_class 'Foo::Bar'
+    end
+
+    # From Foo::Bar
+    assert_equal 1, out.scan(/rdoc-ref:README.rdoc/).length
+    # But README.rdoc should not be expanded
+    assert_empty out.scan(/Expanded from README.rdoc/)
   end
 
   def test_display_class_ambiguous
@@ -766,6 +809,7 @@ def test_display_name_not_found_method
 Foo::Bar#b not found, maybe you meant:
 
 Foo::Bar#blah
+Foo::Bar#blah_with_rdoc_ref
 Foo::Bar#bother
     EXPECTED
 
@@ -1141,6 +1185,7 @@ def test_list_methods_matching
     assert_equal %w[
         Foo::Bar#attr
         Foo::Bar#blah
+        Foo::Bar#blah_with_rdoc_ref
         Foo::Bar#bother
         Foo::Bar::new
       ],
@@ -1516,11 +1561,17 @@ def util_store
     @cFooInc.record_location @top_level
 
     @cFoo_Bar = @cFoo.add_class RDoc::NormalClass, 'Bar'
+    @cFoo_Bar.add_comment "See also {Doc}[rdoc-ref:README.rdoc]", @top_level
+    @cFoo_Bar.record_location @top_level
 
     @blah = @cFoo_Bar.add_method RDoc::AnyMethod.new(nil, 'blah')
     @blah.call_seq = "blah(5) => 5\nblah(6) => 6\n"
     @blah.record_location @top_level
 
+    @blah_with_rdoc_ref = @cFoo_Bar.add_method RDoc::AnyMethod.new(nil, 'blah_with_rdoc_ref')
+    @blah_with_rdoc_ref.call_seq = "blah(5) => 5\nSee also {Doc}[rdoc-ref:README.rdoc]"
+    @blah_with_rdoc_ref.record_location @top_level
+
     @bother = @cFoo_Bar.add_method RDoc::AnyMethod.new(nil, 'bother')
     @bother.block_params = "stuff"
     @bother.params = "(things)"