Display command description in doc dialog on tab completion

lib/irb/command/base.rb

@@ -37,11 +37,46 @@ def execute(irb_context, arg)
           puts e.message
         end
 
+        # Returns formatted lines for display in the doc dialog popup.
+        def doc_dialog_content(name, width)
+          lines = []
+          lines << Color.colorize(name, [:BOLD, :BLUE]) + Color.colorize(" (command)", [:CYAN])
+          lines << ""
+          lines.concat(wrap_lines(description, width))
+          if help_message
+            lines << ""
+            lines.concat(wrap_lines(help_message, width))
+          end
+          lines
+        end
+
         private
 
         def highlight(text)
           Color.colorize(text, [:BOLD, :BLUE])
         end
+
+        def wrap_lines(text, width)
+          text.lines.flat_map do |line|
+            line = line.chomp
+            next [''] if line.empty?
+            next [line] if line.length <= width
+
+            indent = line[/\A\s*/]
+            parts = line.strip.split(/(\s+)/)
+            result = []
+            current = indent.dup
+            parts.each do |part|
+              if current != indent && current.length + part.length > width
+                result << current.rstrip
+                current = indent.dup
+              end
+              current << part unless current == indent && part.match?(/\A\s+\z/)
+            end
+            result << current.rstrip unless current == indent
+            result
+          end
+        end
       end
 
       def initialize(irb_context)

lib/irb/completion.rb

@@ -8,6 +8,29 @@
 require_relative 'ruby-lex'
 
 module IRB
+  class DocumentTarget # :nodoc:
+    attr_reader :name
+
+    def initialize(name)
+      @name = name
+    end
+  end
+
+  class CommandDocument < DocumentTarget # :nodoc:
+  end
+
+  # Represents a method/class documentation target. May hold multiple names
+  # when the receiver is ambiguous (e.g. `{}.any?` could be Hash#any? or Proc#any?).
+  # The dialog popup uses only the first name; the full-screen display renders all.
+  class MethodDocument < DocumentTarget # :nodoc:
+    attr_reader :names
+
+    def initialize(*names)
+      super(names.first)
+      @names = names
+    end
+  end
+
   class BaseCompletor # :nodoc:
 
     # Set of reserved words used by Ruby, you should not use these for
@@ -76,6 +99,12 @@ def command_candidates(target)
       end
     end
 
+    def command_document_target(preposing, matched)
+      if preposing.empty? && IRB::Command.command_names.include?(matched)
+        CommandDocument.new(matched)
+      end
+    end
+
     def retrieve_files_to_require_relative_from_current_dir
       @files_from_current_dir ||= Dir.glob("**/*.{rb,#{RbConfig::CONFIG['DLEXT']}}", base: '.').map { |path|
         path.sub(/\.(rb|#{RbConfig::CONFIG['DLEXT']})\z/, '')
@@ -118,8 +147,10 @@ def completion_candidates(preposing, target, _postposing, bind:)
     end
 
     def doc_namespace(preposing, matched, _postposing, bind:)
-      result = ReplTypeCompletor.analyze(preposing + matched, binding: bind, filename: @context.irb_path)
-      result&.doc_namespace('')
+      command_document_target(preposing, matched) || begin
+        result = ReplTypeCompletor.analyze(preposing + matched, binding: bind, filename: @context.irb_path)
+        result&.doc_namespace('')
+      end
     end
   end
 
@@ -201,8 +232,8 @@ def completion_candidates(preposing, target, postposing, bind:)
       commands | completion_data
     end
 
-    def doc_namespace(_preposing, matched, _postposing, bind:)
-      retrieve_completion_data(matched, bind: bind, doc_namespace: true)
+    def doc_namespace(preposing, matched, _postposing, bind:)
+      command_document_target(preposing, matched) || retrieve_completion_data(matched, bind: bind, doc_namespace: true)
     end
 
     def retrieve_completion_data(input, bind:, doc_namespace:)