diff --git a/Library/Homebrew/compat.rb b/Library/Homebrew/compat.rb
index 7c444615b2..b860f73d03 100644
--- a/Library/Homebrew/compat.rb
+++ b/Library/Homebrew/compat.rb
@@ -1,4 +1,6 @@
 require "compat/os/mac"
+require "compat/requirements/x11_requirement"
+require "compat/requirements/xcode_requirement"
 require "compat/dependable"
 require "compat/dependency_collector"
 require "compat/download_strategy"
diff --git a/Library/Homebrew/compat/requirements/x11_requirement.rb b/Library/Homebrew/compat/requirements/x11_requirement.rb
new file mode 100644
index 0000000000..bad1f2c73c
--- /dev/null
+++ b/Library/Homebrew/compat/requirements/x11_requirement.rb
@@ -0,0 +1,17 @@
+require "requirement"
+
+class X11Requirement < Requirement
+  module Compat
+    def initialize(tags = [])
+      if tags.first.to_s.match?(/(\d\.)+\d/)
+        # TODO: deprecate when Homebrew/homebrew-core is fixed.
+        # odeprecated('depends_on :x11 => "X.Y.Z"')
+        tags.shift
+      end
+
+      super(tags)
+    end
+  end
+
+  prepend Compat
+end
diff --git a/Library/Homebrew/compat/requirements/xcode_requirement.rb b/Library/Homebrew/compat/requirements/xcode_requirement.rb
new file mode 100644
index 0000000000..1ceebd2e05
--- /dev/null
+++ b/Library/Homebrew/compat/requirements/xcode_requirement.rb
@@ -0,0 +1,22 @@
+require "requirement"
+
+class XcodeRequirement < Requirement
+  module Compat
+    def initialize(tags = [])
+      @version = if tags.first.to_s.match?(/(\d\.)+\d/)
+        tags.shift
+      else
+        tags.find do |tag|
+          next unless tag.to_s.match?(/(\d\.)+\d/)
+          # TODO: deprecate when Homebrew/homebrew-core is fixed.
+          # odeprecated('depends_on :xcode => [..., "X.Y.Z"]')
+          tags.delete(tag)
+        end
+      end
+
+      super(tags)
+    end
+  end
+
+  prepend Compat
+end
diff --git a/Library/Homebrew/dependency_collector.rb b/Library/Homebrew/dependency_collector.rb
index 9f22429ca5..b1fb6e4f92 100644
--- a/Library/Homebrew/dependency_collector.rb
+++ b/Library/Homebrew/dependency_collector.rb
@@ -116,15 +116,17 @@ class DependencyCollector
 
   def parse_symbol_spec(spec, tags)
     case spec
-    when :x11        then X11Requirement.new(spec.to_s, tags)
-    when :xcode      then XcodeRequirement.new(tags)
-    when :linux      then LinuxRequirement.new(tags)
-    when :macos      then MacOSRequirement.new(tags)
-    when :arch       then ArchRequirement.new(tags)
-    when :java       then JavaRequirement.new(tags)
-    when :osxfuse    then OsxfuseRequirement.new(tags)
-    when :tuntap     then TuntapRequirement.new(tags)
-    when :ld64       then ld64_dep_if_needed(tags)
+    when :arch          then ArchRequirement.new(tags)
+    when :codesign      then CodesignRequirement.new(tags)
+    when :java          then JavaRequirement.new(tags)
+    when :linux         then LinuxRequirement.new(tags)
+    when :macos         then MacOSRequirement.new(tags)
+    when :maximum_macos then MaximumMacOSRequirement.new(tags)
+    when :osxfuse       then OsxfuseRequirement.new(tags)
+    when :tuntap        then TuntapRequirement.new(tags)
+    when :x11           then X11Requirement.new(tags)
+    when :xcode         then XcodeRequirement.new(tags)
+    when :ld64          then ld64_dep_if_needed(tags)
     else
       raise ArgumentError, "Unsupported special dependency #{spec.inspect}"
     end
diff --git a/Library/Homebrew/extend/os/mac/requirements/non_binary_osxfuse_requirement.rb b/Library/Homebrew/extend/os/mac/requirements/non_binary_osxfuse_requirement.rb
deleted file mode 100644
index 39d638cf88..0000000000
--- a/Library/Homebrew/extend/os/mac/requirements/non_binary_osxfuse_requirement.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-require "requirement"
-
-class NonBinaryOsxfuseRequirement < Requirement
-  fatal true
-  satisfy(build_env: false) do
-    HOMEBREW_PREFIX.to_s != "/usr/local" || !OsxfuseRequirement.binary_osxfuse_installed?
-  end
-
-  def message
-    <<~EOS
-      osxfuse is already installed from the binary distribution and
-      conflicts with this formula.
-    EOS
-  end
-end
diff --git a/Library/Homebrew/extend/os/requirements/non_binary_osxfuse_requirement.rb b/Library/Homebrew/extend/os/requirements/non_binary_osxfuse_requirement.rb
deleted file mode 100644
index 099f29382c..0000000000
--- a/Library/Homebrew/extend/os/requirements/non_binary_osxfuse_requirement.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-if OS.mac?
-  require "extend/os/mac/requirements/non_binary_osxfuse_requirement"
-end
diff --git a/Library/Homebrew/requirements.rb b/Library/Homebrew/requirements.rb
index 6128db5163..0173017e87 100644
--- a/Library/Homebrew/requirements.rb
+++ b/Library/Homebrew/requirements.rb
@@ -1,11 +1,11 @@
 require "requirement"
+require "requirements/arch_requirement"
+require "requirements/codesign_requirement"
+require "requirements/java_requirement"
 require "requirements/linux_requirement"
 require "requirements/macos_requirement"
 require "requirements/maximum_macos_requirement"
 require "requirements/osxfuse_requirement"
-require "requirements/java_requirement"
 require "requirements/tuntap_requirement"
-require "requirements/unsigned_kext_requirement"
 require "requirements/x11_requirement"
-require "requirements/arch_requirement"
 require "requirements/xcode_requirement"
diff --git a/Library/Homebrew/requirements/arch_requirement.rb b/Library/Homebrew/requirements/arch_requirement.rb
index 0ff52dfa82..0fff93a9ef 100644
--- a/Library/Homebrew/requirements/arch_requirement.rb
+++ b/Library/Homebrew/requirements/arch_requirement.rb
@@ -3,9 +3,9 @@ require "requirement"
 class ArchRequirement < Requirement
   fatal true
 
-  def initialize(arch)
-    @arch = arch.pop
-    super
+  def initialize(tags)
+    @arch = tags.shift
+    super(tags)
   end
 
   satisfy(build_env: false) do
diff --git a/Library/Homebrew/requirements/codesign_requirement.rb b/Library/Homebrew/requirements/codesign_requirement.rb
new file mode 100644
index 0000000000..ed6c6988e8
--- /dev/null
+++ b/Library/Homebrew/requirements/codesign_requirement.rb
@@ -0,0 +1,32 @@
+class CodesignRequirement < Requirement
+  fatal true
+
+  def initialize(tags)
+    options = tags.shift
+    unless options.is_a?(Hash)
+      raise ArgumentError("CodesignRequirement requires an options Hash!")
+    end
+    unless options.key?(:identity)
+      raise ArgumentError("CodesignRequirement requires an identity key!")
+    end
+
+    @identity = options.fetch(:identity)
+    @with = options.fetch(:with, "code signing")
+    @url = options.fetch(:url, nil)
+    super(tags)
+  end
+
+  satisfy(build_env: false) do
+    mktemp do
+      FileUtils.cp "/usr/bin/false", "codesign_check"
+      quiet_system "/usr/bin/codesign", "-f", "-s", @identity,
+                                        "--dryrun", "codesign_check"
+    end
+  end
+
+  def message
+    message = "#{@identity} identity must be available to build with #{@with}"
+    message += ":\n#{@url}" if @url.present?
+    message
+  end
+end
diff --git a/Library/Homebrew/requirements/java_requirement.rb b/Library/Homebrew/requirements/java_requirement.rb
index fce7f57dbd..9c6062f0a3 100644
--- a/Library/Homebrew/requirements/java_requirement.rb
+++ b/Library/Homebrew/requirements/java_requirement.rb
@@ -27,7 +27,7 @@ class JavaRequirement < Requirement
 
   def initialize(tags = [])
     @version = tags.shift if /(\d+\.)+\d/ =~ tags.first
-    super
+    super(tags)
   end
 
   def message
@@ -39,7 +39,7 @@ class JavaRequirement < Requirement
   end
 
   def inspect
-    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+    "#<#{self.class.name}: #{tags.inspect} version=#{@version.inspect}>"
   end
 
   def display_s
diff --git a/Library/Homebrew/requirements/macos_requirement.rb b/Library/Homebrew/requirements/macos_requirement.rb
index 37c53cf108..7f40d37fed 100644
--- a/Library/Homebrew/requirements/macos_requirement.rb
+++ b/Library/Homebrew/requirements/macos_requirement.rb
@@ -4,8 +4,8 @@ class MacOSRequirement < Requirement
   fatal true
 
   def initialize(tags = [])
-    @version = MacOS::Version.from_symbol(tags.first) unless tags.empty?
-    super
+    @version = MacOS::Version.from_symbol(tags.shift) unless tags.empty?
+    super(tags)
   end
 
   def minimum_version_specified?
diff --git a/Library/Homebrew/requirements/maximum_macos_requirement.rb b/Library/Homebrew/requirements/maximum_macos_requirement.rb
index 9a8851390f..4dd7fd73d5 100644
--- a/Library/Homebrew/requirements/maximum_macos_requirement.rb
+++ b/Library/Homebrew/requirements/maximum_macos_requirement.rb
@@ -4,8 +4,8 @@ class MaximumMacOSRequirement < Requirement
   fatal true
 
   def initialize(tags)
-    @version = MacOS::Version.from_symbol(tags.first)
-    super
+    @version = MacOS::Version.from_symbol(tags.shift)
+    super(tags)
   end
 
   satisfy(build_env: false) { MacOS.version <= @version }
diff --git a/Library/Homebrew/requirements/non_binary_osxfuse_requirement.rb b/Library/Homebrew/requirements/non_binary_osxfuse_requirement.rb
deleted file mode 100644
index bb7788f487..0000000000
--- a/Library/Homebrew/requirements/non_binary_osxfuse_requirement.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-require "requirement"
-
-class NonBinaryOsxfuseRequirement < Requirement
-  fatal false
-end
-
-require "extend/os/requirements/non_binary_osxfuse_requirement"
diff --git a/Library/Homebrew/requirements/unsigned_kext_requirement.rb b/Library/Homebrew/requirements/unsigned_kext_requirement.rb
deleted file mode 100644
index b58a20ea6c..0000000000
--- a/Library/Homebrew/requirements/unsigned_kext_requirement.rb
+++ /dev/null
@@ -1,16 +0,0 @@
-require "requirement"
-
-class UnsignedKextRequirement < Requirement
-  fatal true
-
-  satisfy(build_env: false) { MacOS.version < :yosemite }
-
-  def message
-    s = <<~EOS
-      Building this formula from source isn't possible due to OS X
-      Yosemite (10.10) and above's strict unsigned kext ban.
-    EOS
-    s += super
-    s
-  end
-end
diff --git a/Library/Homebrew/requirements/x11_requirement.rb b/Library/Homebrew/requirements/x11_requirement.rb
index b7de5a2848..539d374804 100644
--- a/Library/Homebrew/requirements/x11_requirement.rb
+++ b/Library/Homebrew/requirements/x11_requirement.rb
@@ -10,13 +10,6 @@ class X11Requirement < Requirement
 
   env { ENV.x11 }
 
-  def initialize(name = "x11", tags = [])
-    @name = name
-    # no-op on version specified as a tag argument
-    tags.shift if /(\d\.)+\d/ =~ tags.first
-    super(tags)
-  end
-
   def min_version
     "1.12.2"
   end
@@ -51,7 +44,7 @@ class X11Requirement < Requirement
   end
 
   def inspect
-    "#<#{self.class.name}: #{name.inspect} #{tags.inspect}>"
+    "#<#{self.class.name}: #{tags.inspect}>"
   end
 end
 
diff --git a/Library/Homebrew/requirements/xcode_requirement.rb b/Library/Homebrew/requirements/xcode_requirement.rb
index ac6744e2a5..2cafe29d50 100644
--- a/Library/Homebrew/requirements/xcode_requirement.rb
+++ b/Library/Homebrew/requirements/xcode_requirement.rb
@@ -6,8 +6,8 @@ class XcodeRequirement < Requirement
   satisfy(build_env: false) { xcode_installed_version }
 
   def initialize(tags = [])
-    @version = tags.find { |tag| tags.delete(tag) if tag =~ /(\d\.)+\d/ }
-    super
+    @version = tags.shift if tags.first.to_s.match?(/(\d\.)+\d/)
+    super(tags)
   end
 
   def xcode_installed_version
@@ -40,6 +40,6 @@ class XcodeRequirement < Requirement
   end
 
   def inspect
-    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+    "#<#{self.class.name}: #{tags.inspect} version=#{@version.inspect}>"
   end
 end
diff --git a/Library/Homebrew/test/dependency_collector_spec.rb b/Library/Homebrew/test/dependency_collector_spec.rb
index a09d51eacc..37ee477b75 100644
--- a/Library/Homebrew/test/dependency_collector_spec.rb
+++ b/Library/Homebrew/test/dependency_collector_spec.rb
@@ -38,7 +38,7 @@ describe DependencyCollector do
     end
 
     specify "requirement tags" do
-      subject.add x11: "2.5.1"
+      subject.add :x11
       subject.add xcode: :build
       expect(find_requirement(X11Requirement).tags).to be_empty
       expect(find_requirement(XcodeRequirement)).to be_a_build_requirement
diff --git a/Library/Homebrew/test/formula_spec.rb b/Library/Homebrew/test/formula_spec.rb
index 060315fb03..3d4cb84cdf 100644
--- a/Library/Homebrew/test/formula_spec.rb
+++ b/Library/Homebrew/test/formula_spec.rb
@@ -798,7 +798,7 @@ describe Formula do
     stub_formula_loader(f1)
 
     java = JavaRequirement.new
-    x11 = X11Requirement.new("x11", [:recommended])
+    x11 = X11Requirement.new([:recommended])
     xcode = XcodeRequirement.new(["1.0", :optional])
 
     expect(Set.new(f1.recursive_requirements)).to eq(Set[java, x11])
diff --git a/Library/Homebrew/test/java_requirement_spec.rb b/Library/Homebrew/test/java_requirement_spec.rb
index b47593ab12..859c2d9fbb 100644
--- a/Library/Homebrew/test/java_requirement_spec.rb
+++ b/Library/Homebrew/test/java_requirement_spec.rb
@@ -14,7 +14,7 @@ describe JavaRequirement do
   describe "#inspect" do
     subject { described_class.new(%w[1.7+]) }
 
-    its(:inspect) { is_expected.to eq('#<JavaRequirement: "java" [] version="1.7+">') }
+    its(:inspect) { is_expected.to eq('#<JavaRequirement: [] version="1.7+">') }
   end
 
   describe "#display_s" do
diff --git a/Library/Homebrew/test/requirements/codesign_requirement_spec.rb b/Library/Homebrew/test/requirements/codesign_requirement_spec.rb
new file mode 100644
index 0000000000..5940c6d6f5
--- /dev/null
+++ b/Library/Homebrew/test/requirements/codesign_requirement_spec.rb
@@ -0,0 +1,21 @@
+require "requirements/codesign_requirement"
+
+describe CodesignRequirement do
+  subject(:requirement) {
+    described_class.new([{ identity: identity, with: with, url: url }])
+  }
+
+  let(:identity) { "lldb_codesign" }
+  let(:with) { "LLDB" }
+  let(:url) {
+    "https://llvm.org/svn/llvm-project/lldb/trunk/docs/code-signing.txt"
+  }
+
+  describe "#message" do
+    it "includes all parameters" do
+      expect(requirement.message).to include(identity)
+      expect(requirement.message).to include(with)
+      expect(requirement.message).to include(url)
+    end
+  end
+end
diff --git a/Library/Homebrew/test/requirements/non_binary_osxfuse_requirement_spec.rb b/Library/Homebrew/test/requirements/non_binary_osxfuse_requirement_spec.rb
deleted file mode 100644
index 84fb448740..0000000000
--- a/Library/Homebrew/test/requirements/non_binary_osxfuse_requirement_spec.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-require "requirements/non_binary_osxfuse_requirement"
-
-describe NonBinaryOsxfuseRequirement, :needs_macos do
-  subject { described_class.new([]) }
-
-  describe "#message" do
-    its(:message) { is_expected.to match("osxfuse is already installed from the binary distribution") }
-  end
-end
diff --git a/Library/Homebrew/test/requirements_spec.rb b/Library/Homebrew/test/requirements_spec.rb
index 3111a7c9c9..a4c9af3ad9 100644
--- a/Library/Homebrew/test/requirements_spec.rb
+++ b/Library/Homebrew/test/requirements_spec.rb
@@ -14,13 +14,13 @@ describe Requirements do
     end
 
     it "prefers the larger requirement when merging duplicates" do
-      subject << X11Requirement.new << X11Requirement.new("x11", %w[2.6])
-      expect(subject.to_a).to eq([X11Requirement.new("x11", %w[2.6])])
+      subject << X11Requirement.new << X11Requirement.new(%w[2.6])
+      expect(subject.to_a).to eq([X11Requirement.new(%w[2.6])])
     end
 
     it "does not use the smaller requirement when merging duplicates" do
-      subject << X11Requirement.new("x11", %w[2.6]) << X11Requirement.new
-      expect(subject.to_a).to eq([X11Requirement.new("x11", %w[2.6])])
+      subject << X11Requirement.new(%w[2.6]) << X11Requirement.new
+      expect(subject.to_a).to eq([X11Requirement.new(%w[2.6])])
     end
   end
 end
diff --git a/Library/Homebrew/test/x11_requirement_spec.rb b/Library/Homebrew/test/x11_requirement_spec.rb
index ef50fdc761..342394bb34 100644
--- a/Library/Homebrew/test/x11_requirement_spec.rb
+++ b/Library/Homebrew/test/x11_requirement_spec.rb
@@ -10,15 +10,10 @@ describe X11Requirement do
   end
 
   describe "#eql?" do
-    it "returns true if the names are equal" do
-      other = described_class.new(default_name)
+    it "returns true if the requirements are equal" do
+      other = described_class.new
       expect(subject).to eql(other)
     end
-
-    it "and returns false if the names differ" do
-      other = described_class.new("foo")
-      expect(subject).not_to eql(other)
-    end
   end
 
   describe "#modify_build_environment" do