Keep completion alive when RDoc document retrieval fails

lib/irb/input-method.rb

@@ -404,12 +404,29 @@ def easter_egg_dialog_contents
     end
 
     def rdoc_dialog_contents(name, width)
+      formatter = RDoc::Markup::ToAnsi.new
+      formatter.width = width
+
+      begin
+        document = retrieve_rdoc_document(name)
+      rescue RDoc::RI::Driver::NotFoundError
+        return
+      rescue => e
+        raise if $DEBUG
+        return rdoc_error_document(e).accept(formatter).split("\n")
+      end
+      return unless document
+
+      [PRESS_ALT_D_TO_READ_FULL_DOC] + document.accept(formatter).split("\n")
+    end
+
+    def retrieve_rdoc_document(name)
       driver = rdoc_ri_driver
       return unless driver
 
       name = driver.expand_name(name)
 
-      doc = if name =~ /#|\./
+      if name =~ /#|\./
         d = RDoc::Markup::Document.new
         driver.add_method(d, name)
         d
@@ -423,11 +440,15 @@ def rdoc_dialog_contents(name, width)
           driver.class_document(name, found, klasses, includes, extends)
         end
       end
+    end
 
-      formatter = RDoc::Markup::ToAnsi.new
-      formatter.width = width
-      [PRESS_ALT_D_TO_READ_FULL_DOC] + doc.accept(formatter).split("\n")
-    rescue RDoc::RI::Driver::NotFoundError
+    def rdoc_error_document(error)
+      document = RDoc::Markup::Document.new
+      document << RDoc::Markup::Paragraph.new("Failed to load the document:")
+      document << RDoc::Markup::Paragraph.new("#{error.class}: #{error.message}")
+      document << RDoc::Markup::BlankLine.new
+      document << RDoc::Markup::Paragraph.new("Restart IRB with -d to see the backtrace.")
+      document
     end
 
     def dialog_doc_position(cursor_pos_to_render, autocomplete_dialog, screen_width)

test/irb/test_input_method.rb

@@ -215,6 +215,82 @@ def has_rdoc_content?
     end
   end if defined?(RDoc)
 
+  class RdocDialogContentsTest < InputMethodTest
+    def test_shows_error_content_when_document_retrieval_raises
+      input_method = build_input_method(failing_driver(ArgumentError.new("undefined class/module RDoc::")))
+
+      contents = nil
+      assert_nothing_raised do
+        contents = input_method.rdoc_dialog_contents("1.foo", 40)
+      end
+
+      assert_not_nil contents
+      assert(contents.any? { |line| line.include?("ArgumentError") },
+             "expected the error to be shown in the dialog contents: #{contents.inspect}")
+      hint_index = contents.index { |line| line.include?("-d") }
+      assert_not_nil hint_index, "expected the hint to run with -d in the dialog contents: #{contents.inspect}"
+      assert_equal "", contents[hint_index - 1],
+                   "expected a blank line before the -d hint: #{contents.inspect}"
+      assert(contents.none? { |line| line.include?(IRB::RelineInputMethod::PRESS_ALT_D_TO_READ_FULL_DOC) },
+             "the full document hint must not be shown on error: #{contents.inspect}")
+    end
+
+    def test_raises_the_error_when_debug_is_enabled
+      input_method = build_input_method(failing_driver(ArgumentError.new("undefined class/module RDoc::")))
+
+      original_debug = $DEBUG
+      $DEBUG = true
+      # $DEBUG makes Ruby print raised exceptions to stderr; swallow that noise.
+      capture_output do
+        assert_raise(ArgumentError) do
+          input_method.rdoc_dialog_contents("1.foo", 40)
+        end
+      end
+    ensure
+      $DEBUG = original_debug
+    end
+
+    def test_includes_full_document_hint_when_document_is_available
+      input_method = build_input_method(documented_driver)
+
+      contents = input_method.rdoc_dialog_contents("1.foo", 40)
+
+      assert_equal IRB::RelineInputMethod::PRESS_ALT_D_TO_READ_FULL_DOC, contents.first
+    end
+
+    def test_returns_nil_when_document_not_found
+      input_method = build_input_method(failing_driver(RDoc::RI::Driver::NotFoundError.new("1.foo")))
+
+      assert_nil input_method.rdoc_dialog_contents("1.foo", 40)
+    end
+
+    private
+
+    def build_input_method(driver)
+      input_method = IRB::RelineInputMethod.new(IRB::RegexpCompletor.new)
+      input_method.instance_variable_set(:@rdoc_ri_driver, driver)
+      input_method
+    end
+
+    def failing_driver(error)
+      driver = Object.new
+      driver.define_singleton_method(:expand_name) { |name| name }
+      driver.define_singleton_method(:add_method) { |_document, _name| raise error }
+      driver.define_singleton_method(:classes_and_includes_and_extends_for) { |_name| raise error }
+      driver.define_singleton_method(:class_document) { |*| raise error }
+      driver
+    end
+
+    def documented_driver
+      driver = Object.new
+      driver.define_singleton_method(:expand_name) { |name| name }
+      driver.define_singleton_method(:add_method) do |document, _name|
+        document << RDoc::Markup::Paragraph.new("some documentation")
+      end
+      driver
+    end
+  end if defined?(RDoc)
+
   class CommandDocDialogContentTest < TestCase
     def setup
       @conf_backup = IRB.conf.dup