brew-doctor: warning the external commands with conflicting names

Closes Homebrew/homebrew#34755.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/doctor.rb

@@ -1181,6 +1181,25 @@ end
     EOS
   end
 
+  def check_for_external_cmd_name_conflict
+    cmds = paths.map { |p| Dir["#{p}/brew-*"] }.flatten.uniq
+    cmds = cmds.select { |cmd| File.file?(cmd) && File.executable?(cmd) }
+    cmd_map = {}
+    cmds.each do |cmd|
+      cmd_name = File.basename(cmd, ".rb")
+      cmd_map[cmd_name] ||= []
+      cmd_map[cmd_name] << cmd
+    end
+    cmd_map.reject! { |cmd_name, cmd_paths| cmd_paths.size == 1 }
+    return if cmd_map.empty?
+    s = "You have external commands with conflicting names."
+    cmd_map.each do |cmd_name, cmd_paths|
+      s += "\n\nFound command `#{cmd_name}` in following places:\n"
+      s += cmd_paths.map { |f| "  #{f}" }.join("\n")
+    end
+    s
+  end
+
   def all
     methods.map(&:to_s).grep(/^check_/)
   end