diff --git a/Library/Homebrew/compat/dependency_collector.rb b/Library/Homebrew/compat/dependency_collector.rb
index fbcf1c2a0f..2e97d9d7fb 100644
--- a/Library/Homebrew/compat/dependency_collector.rb
+++ b/Library/Homebrew/compat/dependency_collector.rb
@@ -1,6 +1,21 @@
 require "dependency_collector"
 
 class DependencyCollector
+  alias _parse_string_spec parse_string_spec
+
+  # Define the languages that we can handle as external dependencies.
+  LANGUAGE_MODULES = Set[
+    :lua, :lua51, :perl, :python, :python3, :ruby
+  ].freeze
+
+  def parse_string_spec(spec, tags)
+    if (tag = tags.first) && LANGUAGE_MODULES.include?(tag)
+      LanguageModuleRequirement.new(tag, spec, tags[1])
+    else
+      _parse_string_spec(spec, tags)
+    end
+  end
+
   alias _parse_symbol_spec parse_symbol_spec
 
   def parse_symbol_spec(spec, tags)
@@ -20,6 +35,18 @@ class DependencyCollector
       tags << :run
       output_deprecation("libtool", tags)
       Dependency.new("libtool", tags)
+    when :mysql
+      # output_deprecation("mysql", tags)
+      MysqlRequirement.new(tags)
+    when :postgresql
+      # output_deprecation("postgresql", tags)
+      PostgresqlRequirement.new(tags)
+    when :gpg
+      # output_deprecation("gnupg", tags)
+      GPG2Requirement.new(tags)
+    when :rbenv
+      # output_deprecation("rbenv", tags)
+      RbenvRequirement.new(tags)
     else
       _parse_symbol_spec(spec, tags)
     end
diff --git a/Library/Homebrew/compat/requirements.rb b/Library/Homebrew/compat/requirements.rb
index 3886cd7c7e..da6d867b3d 100644
--- a/Library/Homebrew/compat/requirements.rb
+++ b/Library/Homebrew/compat/requirements.rb
@@ -1,4 +1,42 @@
 require "requirements"
+require "compat/requirements/language_module_requirement"
+require "compat/requirements/tex_requirement"
+
+class MysqlRequirement < Requirement
+  fatal true
+  default_formula "mysql"
+  satisfy { which "mysql_config" }
+end
+
+class PostgresqlRequirement < Requirement
+  fatal true
+  default_formula "postgresql"
+  satisfy { which "pg_config" }
+end
+
+class RbenvRequirement < Requirement
+  fatal true
+  default_formula "rbenv"
+  satisfy { which "rbenv" }
+end
+
+class CVSRequirement < Requirement
+  fatal true
+  default_formula "cvs"
+  satisfy { which "cvs" }
+end
+
+class MercurialRequirement < Requirement
+  fatal true
+  default_formula "mercurial"
+  satisfy { which "hg" }
+end
+
+class GPG2Requirement < Requirement
+  fatal true
+  default_formula "gnupg"
+  satisfy { which "gpg" }
+end
 
 XcodeDependency            = XcodeRequirement
 MysqlDependency            = MysqlRequirement
diff --git a/Library/Homebrew/requirements/language_module_requirement.rb b/Library/Homebrew/compat/requirements/language_module_requirement.rb
similarity index 100%
rename from Library/Homebrew/requirements/language_module_requirement.rb
rename to Library/Homebrew/compat/requirements/language_module_requirement.rb
diff --git a/Library/Homebrew/compat/requirements/tex_requirement.rb b/Library/Homebrew/compat/requirements/tex_requirement.rb
new file mode 100644
index 0000000000..cb26a84779
--- /dev/null
+++ b/Library/Homebrew/compat/requirements/tex_requirement.rb
@@ -0,0 +1,20 @@
+require "requirement"
+
+class TeXRequirement < Requirement
+  fatal true
+  cask "mactex"
+  download "https://www.tug.org/mactex/"
+
+  satisfy { which("tex") || which("latex") }
+
+  def message
+    s = <<~EOS
+      A LaTeX distribution is required for Homebrew to install this formula.
+
+      Make sure that "/usr/texbin", or the location you installed it to, is in
+      your PATH before proceeding.
+    EOS
+    s += super
+    s
+  end
+end
diff --git a/Library/Homebrew/dependency_collector.rb b/Library/Homebrew/dependency_collector.rb
index f8edbab069..5fe3aef30e 100644
--- a/Library/Homebrew/dependency_collector.rb
+++ b/Library/Homebrew/dependency_collector.rb
@@ -19,11 +19,6 @@ require "extend/cachable"
 class DependencyCollector
   extend Cachable
 
-  # Define the languages that we can handle as external dependencies.
-  LANGUAGE_MODULES = Set[
-    :lua, :lua51, :perl, :python, :python3, :ruby
-  ].freeze
-
   attr_reader :deps, :requirements
 
   def initialize
@@ -58,16 +53,28 @@ class DependencyCollector
     parse_spec(spec, Array(tags))
   end
 
-  def ant_dep(tags)
+  def ant_dep_if_needed(tags)
     Dependency.new("ant", tags)
   end
 
-  def xz_dep(tags)
+  def cvs_dep_if_needed(tags)
+    Dependency.new("cvs", tags)
+  end
+
+  def xz_dep_if_needed(tags)
     Dependency.new("xz", tags)
   end
 
+  def expat_dep_if_needed(tags)
+    Dependency.new("expat", tags)
+  end
+
+  def ld64_dep_if_needed(*)
+    LD64Dependency.new
+  end
+
   def self.tar_needs_xz_dependency?
-    !new.xz_dep([]).nil?
+    !new.xz_dep_if_needed([]).nil?
   end
 
   private
@@ -94,8 +101,6 @@ class DependencyCollector
       TapDependency.new(spec, tags)
     elsif tags.empty?
       Dependency.new(spec, tags)
-    elsif (tag = tags.first) && LANGUAGE_MODULES.include?(tag)
-      LanguageModuleRequirement.new(tag, spec, tags[1])
     else
       Dependency.new(spec, tags)
     end
@@ -107,30 +112,23 @@ class DependencyCollector
     when :xcode      then XcodeRequirement.new(tags)
     when :linux      then LinuxRequirement.new(tags)
     when :macos      then MacOSRequirement.new(tags)
-    when :mysql      then MysqlRequirement.new(tags)
-    when :postgresql then PostgresqlRequirement.new(tags)
-    when :gpg        then GPG2Requirement.new(tags)
     when :fortran    then FortranRequirement.new(tags)
     when :mpi        then MPIRequirement.new(*tags)
     when :tex        then TeXRequirement.new(tags)
     when :arch       then ArchRequirement.new(tags)
     when :hg         then MercurialRequirement.new(tags)
     when :python     then PythonRequirement.new(tags)
+    when :python2    then PythonRequirement.new(tags)
     when :python3    then Python3Requirement.new(tags)
     when :java       then JavaRequirement.new(tags)
-    when :rbenv      then RbenvRequirement.new(tags)
     when :ruby       then RubyRequirement.new(tags)
     when :osxfuse    then OsxfuseRequirement.new(tags)
     when :perl       then PerlRequirement.new(tags)
     when :tuntap     then TuntapRequirement.new(tags)
-    when :ant        then ant_dep(tags)
+    when :ant        then ant_dep_if_needed(tags)
     when :emacs      then EmacsRequirement.new(tags)
-    # Tiger's ld is too old to properly link some software
-    when :ld64       then LD64Dependency.new if MacOS.version < :leopard
-    # Tiger doesn't ship expat in /usr/lib
-    when :expat      then Dependency.new("expat", tag) if MacOS.version < :leopard
-    when :python2
-      PythonRequirement.new(tags)
+    when :ld64       then ld64_dep_if_needed(tags)
+    when :expat      then expat_dep_if_needed(tags)
     else
       raise ArgumentError, "Unsupported special dependency #{spec.inspect}"
     end
@@ -152,16 +150,16 @@ class DependencyCollector
       parse_url_spec(spec.url, tags)
     elsif strategy <= GitDownloadStrategy
       GitRequirement.new(tags)
+    elsif strategy <= SubversionDownloadStrategy
+      SubversionRequirement.new(tags)
     elsif strategy <= MercurialDownloadStrategy
-      MercurialRequirement.new(tags)
+      Dependency.new("hg", tags)
     elsif strategy <= FossilDownloadStrategy
       Dependency.new("fossil", tags)
     elsif strategy <= BazaarDownloadStrategy
       Dependency.new("bazaar", tags)
     elsif strategy <= CVSDownloadStrategy
-      CVSRequirement.new(tags)
-    elsif strategy <= SubversionDownloadStrategy
-      SubversionRequirement.new(tags)
+      cvs_dep_if_needed(tags)
     elsif strategy < AbstractDownloadStrategy
       # allow unknown strategies to pass through
     else
@@ -172,7 +170,7 @@ class DependencyCollector
 
   def parse_url_spec(url, tags)
     case File.extname(url)
-    when ".xz"          then xz_dep(tags)
+    when ".xz"          then xz_dep_if_needed(tags)
     when ".lha", ".lzh" then Dependency.new("lha", tags)
     when ".lz"          then Dependency.new("lzip", tags)
     when ".rar"         then Dependency.new("unrar", tags)
diff --git a/Library/Homebrew/extend/os/mac/dependency_collector.rb b/Library/Homebrew/extend/os/mac/dependency_collector.rb
index 8d660321e6..66dcf3afe6 100644
--- a/Library/Homebrew/extend/os/mac/dependency_collector.rb
+++ b/Library/Homebrew/extend/os/mac/dependency_collector.rb
@@ -1,11 +1,28 @@
 class DependencyCollector
-  def ant_dep(tags)
+  def ant_dep_if_needed(tags)
     return if MacOS.version < :mavericks
     Dependency.new("ant", tags)
   end
 
-  def xz_dep(tags)
+  def cvs_dep_if_needed(tags)
+    return if MacOS.version < :lion
+    Dependency.new("cvs", tags)
+  end
+
+  def xz_dep_if_needed(tags)
     return if MacOS.version >= :mavericks
     Dependency.new("xz", tags)
   end
+
+  def expat_dep_if_needed(tags)
+    # Tiger doesn't ship expat in /usr/lib
+    return if MacOS.version > :tiger
+    Dependency.new("expat", tags)
+  end
+
+  def ld64_dep_if_needed(*)
+    # Tiger's ld is too old to properly link some software
+    return if MacOS.version > :tiger
+    LD64Dependency.new
+  end
 end
diff --git a/Library/Homebrew/gpg.rb b/Library/Homebrew/gpg.rb
index 83b525b444..f1b989a165 100644
--- a/Library/Homebrew/gpg.rb
+++ b/Library/Homebrew/gpg.rb
@@ -1,29 +1,17 @@
 require "utils"
 
 class Gpg
-  def self.find_gpg(executable)
-    which_all(executable).detect do |gpg|
-      gpg_short_version = Utils.popen_read(gpg, "--version")[/\d\.\d/, 0]
-      next unless gpg_short_version
-      gpg_version = Version.create(gpg_short_version.to_s)
-      @version = gpg_version
-      gpg_version >= Version.create("2.0")
-    end
+  module_function
+
+  def executable
+    which "gpg"
   end
 
-  def self.executable
-    find_gpg("gpg") || find_gpg("gpg2")
-  end
-
-  def self.available?
+  def available?
     File.executable?(executable.to_s)
   end
 
-  def self.version
-    @version if available?
-  end
-
-  def self.create_test_key(path)
+  def create_test_key(path)
     odie "No GPG present to test against!" unless available?
 
     (path/"batch.gpg").write <<~EOS
@@ -40,8 +28,9 @@ class Gpg
     system executable, "--batch", "--gen-key", "batch.gpg"
   end
 
-  def self.cleanup_test_processes!
+  def cleanup_test_processes!
     odie "No GPG present to test against!" unless available?
+
     gpgconf = Pathname.new(executable).parent/"gpgconf"
 
     system gpgconf, "--kill", "gpg-agent"
@@ -49,7 +38,7 @@ class Gpg
                                  "gpg-agent"
   end
 
-  def self.test(path)
+  def test(path)
     create_test_key(path)
     begin
       yield
diff --git a/Library/Homebrew/requirements.rb b/Library/Homebrew/requirements.rb
index d5992b88d9..456dabd0a7 100644
--- a/Library/Homebrew/requirements.rb
+++ b/Library/Homebrew/requirements.rb
@@ -1,7 +1,5 @@
 require "requirement"
 require "requirements/fortran_requirement"
-require "requirements/gpg2_requirement"
-require "requirements/language_module_requirement"
 require "requirements/linux_requirement"
 require "requirements/macos_requirement"
 require "requirements/maximum_macos_requirement"
@@ -15,116 +13,8 @@ require "requirements/tuntap_requirement"
 require "requirements/unsigned_kext_requirement"
 require "requirements/x11_requirement"
 require "requirements/emacs_requirement"
-
-class XcodeRequirement < Requirement
-  fatal true
-
-  satisfy(build_env: false) { xcode_installed_version }
-
-  def initialize(tags)
-    @version = tags.find { |tag| tags.delete(tag) if tag =~ /(\d\.)+\d/ }
-    super
-  end
-
-  def xcode_installed_version
-    return false unless MacOS::Xcode.installed?
-    return true unless @version
-    MacOS::Xcode.version >= @version
-  end
-
-  def message
-    version = " #{@version}" if @version
-    message = <<~EOS
-      A full installation of Xcode.app#{version} is required to compile this software.
-      Installing just the Command Line Tools is not sufficient.
-    EOS
-    if MacOS.version >= :lion
-      message + <<~EOS
-        Xcode can be installed from the App Store.
-      EOS
-    else
-      message + <<~EOS
-        Xcode can be installed from #{Formatter.url("https://developer.apple.com/download/more/")}.
-      EOS
-    end
-  end
-
-  def inspect
-    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
-  end
-end
-
-class MysqlRequirement < Requirement
-  fatal true
-  default_formula "mysql"
-
-  satisfy { which "mysql_config" }
-end
-
-class PostgresqlRequirement < Requirement
-  fatal true
-  default_formula "postgresql"
-
-  satisfy { which "pg_config" }
-end
-
-class RbenvRequirement < Requirement
-  fatal true
-  default_formula "rbenv"
-
-  satisfy { which "rbenv" }
-end
-
-class TeXRequirement < Requirement
-  fatal true
-  cask "mactex"
-  download "https://www.tug.org/mactex/"
-
-  satisfy { which("tex") || which("latex") }
-
-  def message
-    s = <<~EOS
-      A LaTeX distribution is required for Homebrew to install this formula.
-
-      Make sure that "/usr/texbin", or the location you installed it to, is in
-      your PATH before proceeding.
-    EOS
-    s += super
-    s
-  end
-end
-
-class ArchRequirement < Requirement
-  fatal true
-
-  def initialize(arch)
-    @arch = arch.pop
-    super
-  end
-
-  satisfy(build_env: false) do
-    case @arch
-    when :x86_64 then MacOS.prefer_64_bit?
-    when :intel, :ppc then Hardware::CPU.type == @arch
-    end
-  end
-
-  def message
-    "This formula requires an #{@arch} architecture."
-  end
-end
-
-class CVSRequirement < Requirement
-  fatal true
-  default_formula "cvs"
-  satisfy { which "cvs" }
-end
-
-class MercurialRequirement < Requirement
-  fatal true
-  default_formula "mercurial"
-  satisfy { which("hg") }
-end
+require "requirements/arch_requirement"
+require "requirements/xcode_requirement"
 
 class GitRequirement < Requirement
   fatal true
diff --git a/Library/Homebrew/requirements/arch_requirement.rb b/Library/Homebrew/requirements/arch_requirement.rb
new file mode 100644
index 0000000000..0ff52dfa82
--- /dev/null
+++ b/Library/Homebrew/requirements/arch_requirement.rb
@@ -0,0 +1,21 @@
+require "requirement"
+
+class ArchRequirement < Requirement
+  fatal true
+
+  def initialize(arch)
+    @arch = arch.pop
+    super
+  end
+
+  satisfy(build_env: false) do
+    case @arch
+    when :x86_64 then MacOS.prefer_64_bit?
+    when :intel, :ppc then Hardware::CPU.type == @arch
+    end
+  end
+
+  def message
+    "This formula requires an #{@arch} architecture."
+  end
+end
diff --git a/Library/Homebrew/requirements/gpg2_requirement.rb b/Library/Homebrew/requirements/gpg2_requirement.rb
deleted file mode 100644
index 04097f9be9..0000000000
--- a/Library/Homebrew/requirements/gpg2_requirement.rb
+++ /dev/null
@@ -1,12 +0,0 @@
-require "requirement"
-require "gpg"
-
-class GPG2Requirement < Requirement
-  fatal true
-  default_formula "gnupg"
-
-  # GPGTools installs GnuPG 2.0.x as a `gpg` symlink pointing
-  # to `gpg2`. Our `gnupg` installs only a non-symlink `gpg`.
-  # The aim is to retain support for any version above 2.0.
-  satisfy(build_env: false) { Gpg.available? }
-end
diff --git a/Library/Homebrew/requirements/xcode_requirement.rb b/Library/Homebrew/requirements/xcode_requirement.rb
new file mode 100644
index 0000000000..ff167c6fdf
--- /dev/null
+++ b/Library/Homebrew/requirements/xcode_requirement.rb
@@ -0,0 +1,39 @@
+require "requirement"
+
+class XcodeRequirement < Requirement
+  fatal true
+
+  satisfy(build_env: false) { xcode_installed_version }
+
+  def initialize(tags)
+    @version = tags.find { |tag| tags.delete(tag) if tag =~ /(\d\.)+\d/ }
+    super
+  end
+
+  def xcode_installed_version
+    return false unless MacOS::Xcode.installed?
+    return true unless @version
+    MacOS::Xcode.version >= @version
+  end
+
+  def message
+    version = " #{@version}" if @version
+    message = <<~EOS
+      A full installation of Xcode.app#{version} is required to compile this software.
+      Installing just the Command Line Tools is not sufficient.
+    EOS
+    if MacOS.version >= :lion
+      message + <<~EOS
+        Xcode can be installed from the App Store.
+      EOS
+    else
+      message + <<~EOS
+        Xcode can be installed from #{Formatter.url("https://developer.apple.com/download/more/")}.
+      EOS
+    end
+  end
+
+  def inspect
+    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+  end
+end
diff --git a/Library/Homebrew/rubocops/lines_cop.rb b/Library/Homebrew/rubocops/lines_cop.rb
index fdc31078f3..c96efd0b1c 100644
--- a/Library/Homebrew/rubocops/lines_cop.rb
+++ b/Library/Homebrew/rubocops/lines_cop.rb
@@ -6,12 +6,16 @@ module RuboCop
       # This cop checks for various miscellaneous Homebrew coding styles
       class Lines < FormulaCop
         def audit_formula(_node, _class_node, _parent_class_node, _body_node)
-          [:automake, :autoconf, :libtool].each do |dependency|
+          [:automake, :autoconf, :libtool, :mysql, :postgresql, :rbenv].each do |dependency|
             next unless depends_on?(dependency)
             problem ":#{dependency} is deprecated. Usage should be \"#{dependency}\"."
           end
 
-          problem ':apr is deprecated. Usage should be "apr-util".' if depends_on?(:apr)
+          { apr: "apr-util", gpg: "gnupg" }.each do |requirement, dependency|
+            next unless depends_on?(requirement)
+            problem ":#{requirement} is deprecated. Usage should be \"#{dependency}\"."
+          end
+
           problem ":tex is deprecated." if depends_on?(:tex)
         end
       end
diff --git a/Library/Homebrew/test/dependency_collector_spec.rb b/Library/Homebrew/test/dependency_collector_spec.rb
index 3905717ad0..5ba3c20bdc 100644
--- a/Library/Homebrew/test/dependency_collector_spec.rb
+++ b/Library/Homebrew/test/dependency_collector_spec.rb
@@ -87,7 +87,7 @@ describe DependencyCollector do
     it "creates a resource dependency from a CVS URL" do
       resource = Resource.new
       resource.url(":pserver:anonymous:@example.com:/cvsroot/foo/bar", using: :cvs)
-      expect(subject.add(resource)).to be_an_instance_of(CVSRequirement)
+      expect(subject.add(resource)).to eq(Dependency.new("cvs", [:build]))
     end
 
     it "creates a resource dependency from a Subversion URL" do
diff --git a/Library/Homebrew/test/gpg2_requirement_spec.rb b/Library/Homebrew/test/gpg2_requirement_spec.rb
deleted file mode 100644
index 8b9040b82e..0000000000
--- a/Library/Homebrew/test/gpg2_requirement_spec.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-require "requirements/gpg2_requirement"
-require "fileutils"
-
-describe GPG2Requirement do
-  let(:dir) { mktmpdir }
-
-  describe "#satisfied?" do
-    it "returns true if GPG2 is installed" do
-      ENV["PATH"] = dir/"bin"
-      (dir/"bin/gpg").write <<~EOS
-        #!/bin/bash
-        echo 2.1.20
-      EOS
-      FileUtils.chmod 0755, dir/"bin/gpg"
-
-      expect(subject).to be_satisfied
-    end
-  end
-end
diff --git a/Library/Homebrew/test/language_module_requirement_spec.rb b/Library/Homebrew/test/language_module_requirement_spec.rb
index 7f2666855a..6ca8cbd0e8 100644
--- a/Library/Homebrew/test/language_module_requirement_spec.rb
+++ b/Library/Homebrew/test/language_module_requirement_spec.rb
@@ -1,6 +1,6 @@
-require "requirements/language_module_requirement"
+require "compat/requirements/language_module_requirement"
 
-describe LanguageModuleRequirement do
+describe LanguageModuleRequirement, :needs_compat do
   specify "unique dependencies are not equal" do
     x = described_class.new(:node, "less")
     y = described_class.new(:node, "coffee-script")