From 071dd93ef2a5dfd180aad4a0ae8cc628be93582b Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 13:17:43 +0100
Subject: [PATCH 01/10] env_config: add `HOMEBREW_ALLOWED_TAPS`

This is the inverse of `HOMEBREW_FORBIDDEN_TAPS`.
---
 Library/Homebrew/env_config.rb                |  5 ++++
 Library/Homebrew/formula_installer.rb         | 29 ++++++++++++++-----
 .../sorbet/rbi/dsl/homebrew/env_config.rbi    |  3 ++
 3 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/Library/Homebrew/env_config.rb b/Library/Homebrew/env_config.rb
index ef9b72ea21..0424212119 100644
--- a/Library/Homebrew/env_config.rb
+++ b/Library/Homebrew/env_config.rb
@@ -11,6 +11,11 @@ module Homebrew
     module_function
 
     ENVS = {
+      HOMEBREW_ALLOWED_TAPS:                     {
+        description: "A space-separated list of taps. Homebrew will refuse to install a " \
+                     "formula unless it and all of its dependencies are in an official tap " \
+                     "or in a tap on this list.",
+      },
       HOMEBREW_API_AUTO_UPDATE_SECS:             {
         description: "Check Homebrew's API for new formulae or cask data every " \
                      "`HOMEBREW_API_AUTO_UPDATE_SECS` seconds. Alternatively, disable API auto-update " \
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index e038dd8f50..d73fc59797 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -1379,18 +1379,31 @@ on_request: installed_on_request?, options:)
     EOS
   end
 
+  sig { params(tap: Tap, allowed_taps: T::Set[Tap], forbidden_taps: T::Set[Tap]).returns(T::Boolean) }
+  def allowed_tap?(tap, allowed_taps, forbidden_taps)
+    (tap.official? || allowed_taps.blank? || allowed_taps.include?(tap)) && forbidden_taps.exclude?(tap)
+  end
+
   sig { void }
   def forbidden_tap_check
-    forbidden_taps = Homebrew::EnvConfig.forbidden_taps
-    return if forbidden_taps.blank?
+    forbidden_taps = Homebrew::EnvConfig.forbidden_taps.to_s.split
+    allowed_taps = Homebrew::EnvConfig.allowed_taps.to_s.split
+    return if forbidden_taps.blank? && allowed_taps.blank?
 
-    forbidden_taps_set = Set.new(forbidden_taps.split.filter_map do |tap|
+    forbidden_taps_set = Set.new(forbidden_taps.filter_map do |tap|
       Tap.fetch(tap)
     rescue Tap::InvalidNameError
       opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
       nil
     end)
 
+    allowed_taps_set = Set.new(allowed_taps.filter_map do |tap|
+      Tap.fetch(tap)
+    rescue Tap::InvalidNameError
+      opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
+      nil
+    end)
+
     owner = Homebrew::EnvConfig.forbidden_owner
     owner_contact = if (contact = Homebrew::EnvConfig.forbidden_owner_contact.presence)
       "\n#{contact}"
@@ -1400,11 +1413,12 @@ on_request: installed_on_request?, options:)
       compute_dependencies.each do |(dep, _options)|
         dep_tap = dep.tap
         next if dep_tap.blank?
-        next unless forbidden_taps_set.include?(dep_tap)
+        next if allowed_tap?(dep_tap, allowed_taps_set, forbidden_taps_set)
 
         raise CannotInstallFormulaError, <<~EOS
           The installation of #{formula.name} has a dependency #{dep.name}
-          but the #{dep_tap} tap was forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
+          but #{owner} has either not allowed the #{dep_tap} tap in `HOMEBREW_ALLOWED_TAPS` or
+          has forbidden the #{dep_tap} tap in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
         EOS
       end
     end
@@ -1413,11 +1427,12 @@ on_request: installed_on_request?, options:)
 
     formula_tap = formula.tap
     return if formula_tap.blank?
-    return unless forbidden_taps_set.include?(formula_tap)
+    return if allowed_tap?(formula_tap, allowed_taps_set, forbidden_taps_set)
 
     raise CannotInstallFormulaError, <<~EOS
       The installation of #{formula.full_name} has the tap #{formula_tap}
-      which was forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
+      which is either not allowed by #{owner} in `HOMEBREW_ALLOWED_TAPS` or
+      is forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
     EOS
   end
 
diff --git a/Library/Homebrew/sorbet/rbi/dsl/homebrew/env_config.rbi b/Library/Homebrew/sorbet/rbi/dsl/homebrew/env_config.rbi
index 938cd076f0..e6a1945bbe 100644
--- a/Library/Homebrew/sorbet/rbi/dsl/homebrew/env_config.rbi
+++ b/Library/Homebrew/sorbet/rbi/dsl/homebrew/env_config.rbi
@@ -9,6 +9,9 @@ module Homebrew::EnvConfig
     sig { returns(T.nilable(::String)) }
     def all_proxy; end
 
+    sig { returns(T.nilable(::String)) }
+    def allowed_taps; end
+
     sig { returns(Integer) }
     def api_auto_update_secs; end
 

From 6663516e7948f0f8402147b2c8e7b146500e6d33 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 14:42:16 +0100
Subject: [PATCH 02/10] tap: define `#allowed_by_env?`

---
 Library/Homebrew/formula_installer.rb | 29 +++--------------------
 Library/Homebrew/tap.rb               | 34 +++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index d73fc59797..f9734eb262 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -1379,30 +1379,9 @@ on_request: installed_on_request?, options:)
     EOS
   end
 
-  sig { params(tap: Tap, allowed_taps: T::Set[Tap], forbidden_taps: T::Set[Tap]).returns(T::Boolean) }
-  def allowed_tap?(tap, allowed_taps, forbidden_taps)
-    (tap.official? || allowed_taps.blank? || allowed_taps.include?(tap)) && forbidden_taps.exclude?(tap)
-  end
-
   sig { void }
   def forbidden_tap_check
-    forbidden_taps = Homebrew::EnvConfig.forbidden_taps.to_s.split
-    allowed_taps = Homebrew::EnvConfig.allowed_taps.to_s.split
-    return if forbidden_taps.blank? && allowed_taps.blank?
-
-    forbidden_taps_set = Set.new(forbidden_taps.filter_map do |tap|
-      Tap.fetch(tap)
-    rescue Tap::InvalidNameError
-      opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
-      nil
-    end)
-
-    allowed_taps_set = Set.new(allowed_taps.filter_map do |tap|
-      Tap.fetch(tap)
-    rescue Tap::InvalidNameError
-      opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
-      nil
-    end)
+    return if Homebrew::EnvConfig.forbidden_taps.blank? && Homebrew::EnvConfig.allowed_taps.blank?
 
     owner = Homebrew::EnvConfig.forbidden_owner
     owner_contact = if (contact = Homebrew::EnvConfig.forbidden_owner_contact.presence)
@@ -1412,8 +1391,7 @@ on_request: installed_on_request?, options:)
     unless ignore_deps?
       compute_dependencies.each do |(dep, _options)|
         dep_tap = dep.tap
-        next if dep_tap.blank?
-        next if allowed_tap?(dep_tap, allowed_taps_set, forbidden_taps_set)
+        next if dep_tap.blank? || dep_tap.allowed_by_env?
 
         raise CannotInstallFormulaError, <<~EOS
           The installation of #{formula.name} has a dependency #{dep.name}
@@ -1426,8 +1404,7 @@ on_request: installed_on_request?, options:)
     return if only_deps?
 
     formula_tap = formula.tap
-    return if formula_tap.blank?
-    return if allowed_tap?(formula_tap, allowed_taps_set, forbidden_taps_set)
+    return if formula_tap.blank? || formula_tap.allowed_by_env?
 
     raise CannotInstallFormulaError, <<~EOS
       The installation of #{formula.full_name} has the tap #{formula_tap}
diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index ab2046dae0..cf3da6e358 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -132,6 +132,30 @@ class Tap
     false
   end
 
+  sig { returns(T::Set[Tap]) }
+  def self.allowed_taps
+    allowed_tap_list = Homebrew::EnvConfig.allowed_taps.to_s.split
+
+    Set.new(allowed_tap_list.filter_map do |tap|
+      Tap.fetch(tap)
+    rescue Tap::InvalidNameError
+      opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
+      nil
+    end)
+  end
+
+  sig { returns(T::Set[Tap]) }
+  def self.forbidden_taps
+    forbidden_tap_list = Homebrew::EnvConfig.forbidden_taps.to_s.split
+
+    Set.new(forbidden_tap_list.filter_map do |tap|
+      Tap.fetch(tap)
+    rescue Tap::InvalidNameError
+      opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
+      nil
+    end)
+  end
+
   # @api public
   extend Enumerable
 
@@ -1056,6 +1080,16 @@ class Tap
     end
   end
 
+  sig { returns(T::Boolean) }
+  def allowed_by_env?
+    @allowed_by_env ||= begin
+      allowed_taps = self.class.allowed_taps
+      forbidden_taps = self.class.forbidden_taps
+
+      (official? || allowed_taps.blank? || allowed_taps.include?(self)) && forbidden_taps.exclude?(self)
+    end
+  end
+
   private
 
   sig { params(file: Pathname).returns(T.any(T::Array[String], Hash)) }

From 34e2c4ee97ba3484df7814ba323a9b767cb997f8 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 14:48:17 +0100
Subject: [PATCH 03/10] cask/installer: support `HOMEBREW_ALLOWED_TAPS`

---
 Library/Homebrew/cask/installer.rb | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/Library/Homebrew/cask/installer.rb b/Library/Homebrew/cask/installer.rb
index b7d4309ca9..0e2e89396c 100644
--- a/Library/Homebrew/cask/installer.rb
+++ b/Library/Homebrew/cask/installer.rb
@@ -574,15 +574,7 @@ on_request: true)
 
     sig { void }
     def forbidden_tap_check
-      forbidden_taps = Homebrew::EnvConfig.forbidden_taps
-      return if forbidden_taps.blank?
-
-      forbidden_taps_set = Set.new(forbidden_taps.split.filter_map do |tap|
-        Tap.fetch(tap)
-      rescue Tap::InvalidNameError
-        opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
-        nil
-      end)
+      return if Homebrew::EnvConfig.forbidden_taps.blank? && Homebrew::EnvConfig.allowed_taps.blank?
 
       owner = Homebrew::EnvConfig.forbidden_owner
       owner_contact = if (contact = Homebrew::EnvConfig.forbidden_owner_contact.presence)
@@ -592,25 +584,25 @@ on_request: true)
       unless skip_cask_deps?
         cask_and_formula_dependencies.each do |cask_or_formula|
           dep_tap = cask_or_formula.tap
-          next if dep_tap.blank?
-          next unless forbidden_taps_set.include?(dep_tap)
+          next if dep_tap.blank? || dep_tap.allowed_by_env?
 
           dep_full_name = cask_or_formula.full_name
           raise CaskCannotBeInstalledError.new(@cask, <<~EOS
             The installation of #{@cask} has a dependency #{dep_full_name}
-            but the #{dep_tap} tap was forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
+            but #{owner} has either not allowed the #{dep_tap} in `HOMEBREW_ALLOWED_TAPS` or
+            has forbidden the #{dep_tap} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
           EOS
           )
         end
       end
 
       cask_tap = @cask.tap
-      return if cask_tap.blank?
-      return unless forbidden_taps_set.include?(cask_tap)
+      return if cask_tap.blank? || cask_tap.allowed_by_env?
 
       raise CaskCannotBeInstalledError.new(@cask, <<~EOS
         The installation of #{@cask.full_name} has the tap #{cask_tap}
-        which was forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
+        which is either not allowed by #{owner} in `HOMEBREW_ALLOWED_TAPS` or
+        is forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
       EOS
       )
     end

From 7c9e8927e94e8637eb7c75ce87ca78ffe204f73c Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 16:08:22 +0100
Subject: [PATCH 04/10] tap: memoize allowed and forbidden taps

---
 Library/Homebrew/tap.rb | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index cf3da6e358..527fc0e156 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -132,29 +132,40 @@ class Tap
     false
   end
 
+  # rubocop:disable Style/ClassVars
+  # We want the the class variables below to be global to all `Tap` classes and subclasses.
   sig { returns(T::Set[Tap]) }
   def self.allowed_taps
-    allowed_tap_list = Homebrew::EnvConfig.allowed_taps.to_s.split
+    @@allowed_taps ||= begin
+      allowed_tap_list = Homebrew::EnvConfig.allowed_taps.to_s.split
 
-    Set.new(allowed_tap_list.filter_map do |tap|
-      Tap.fetch(tap)
-    rescue Tap::InvalidNameError
-      opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
-      nil
-    end)
+      Set.new(allowed_tap_list.filter_map do |tap|
+        Tap.fetch(tap)
+      rescue Tap::InvalidNameError
+        opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
+        nil
+      end)
+    end
+
+    @@allowed_taps.freeze
   end
 
   sig { returns(T::Set[Tap]) }
   def self.forbidden_taps
-    forbidden_tap_list = Homebrew::EnvConfig.forbidden_taps.to_s.split
+    @@forbidden_taps ||= begin
+      forbidden_tap_list = Homebrew::EnvConfig.forbidden_taps.to_s.split
 
-    Set.new(forbidden_tap_list.filter_map do |tap|
-      Tap.fetch(tap)
-    rescue Tap::InvalidNameError
-      opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
-      nil
-    end)
+      Set.new(forbidden_tap_list.filter_map do |tap|
+        Tap.fetch(tap)
+      rescue Tap::InvalidNameError
+        opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
+        nil
+      end)
+    end
+
+    @@forbidden_taps.freeze
   end
+  # rubocop:enable Style/ClassVars
 
   # @api public
   extend Enumerable

From 5222c9e32d1ab9eeb05a4ab3ef23c958ce56044a Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 16:08:42 +0100
Subject: [PATCH 05/10] Improve error message for allowed and forbidden taps

---
 Library/Homebrew/cask/installer.rb    | 30 ++++++++++++++-----------
 Library/Homebrew/formula_installer.rb | 32 ++++++++++++++++-----------
 Library/Homebrew/tap.rb               |  8 +++++--
 3 files changed, 42 insertions(+), 28 deletions(-)

diff --git a/Library/Homebrew/cask/installer.rb b/Library/Homebrew/cask/installer.rb
index 0e2e89396c..9b00efab5e 100644
--- a/Library/Homebrew/cask/installer.rb
+++ b/Library/Homebrew/cask/installer.rb
@@ -574,7 +574,7 @@ on_request: true)
 
     sig { void }
     def forbidden_tap_check
-      return if Homebrew::EnvConfig.forbidden_taps.blank? && Homebrew::EnvConfig.allowed_taps.blank?
+      return if Tap.allowed_taps.blank? && Tap.forbidden_taps.blank?
 
       owner = Homebrew::EnvConfig.forbidden_owner
       owner_contact = if (contact = Homebrew::EnvConfig.forbidden_owner_contact.presence)
@@ -587,24 +587,28 @@ on_request: true)
           next if dep_tap.blank? || dep_tap.allowed_by_env?
 
           dep_full_name = cask_or_formula.full_name
-          raise CaskCannotBeInstalledError.new(@cask, <<~EOS
-            The installation of #{@cask} has a dependency #{dep_full_name}
-            but #{owner} has either not allowed the #{dep_tap} in `HOMEBREW_ALLOWED_TAPS` or
-            has forbidden the #{dep_tap} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
-          EOS
-          )
+          error_message = +"The installation of #{@cask} has a dependency #{dep_full_name}\n" \
+                           "from the #{dep_tap} tap but #{owner} "
+          error_message << "has not allowed this tap in `HOMEBREW_ALLOWED_TAPS`" unless dep_tap.allowed_by_env?
+          error_message << " and\n" if !dep_tap.allowed_by_env? && dep_tap.forbidden_by_env?
+          error_message << "has forbidden this tap in `HOMEBREW_FORBIDDEN_TAPS`" if dep_tap.forbidden_by_env?
+          error_message << ".#{owner_contact}"
+
+          raise CaskCannotBeInstalledError.new(@cask, error_message)
         end
       end
 
       cask_tap = @cask.tap
       return if cask_tap.blank? || cask_tap.allowed_by_env?
 
-      raise CaskCannotBeInstalledError.new(@cask, <<~EOS
-        The installation of #{@cask.full_name} has the tap #{cask_tap}
-        which is either not allowed by #{owner} in `HOMEBREW_ALLOWED_TAPS` or
-        is forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
-      EOS
-      )
+      error_message = +"The installation of #{@cask.full_name} has the tap #{cask_tap}\n" \
+                       "but #{owner} "
+      error_message << "has not allowed this tap in `HOMEBREW_ALLOWED_TAPS`" unless cask_tap.allowed_by_env?
+      error_message << " and\n" if !cask_tap.allowed_by_env? && cask_tap.forbidden_by_env?
+      error_message << "has forbidden this tap in `HOMEBREW_FORBIDDEN_TAPS`" if cask_tap.forbidden_by_env?
+      error_message << ".#{owner_contact}"
+
+      raise CaskCannotBeInstalledError.new(@cask, error_message)
     end
 
     sig { void }
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index f9734eb262..b417b5d941 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -1381,7 +1381,7 @@ on_request: installed_on_request?, options:)
 
   sig { void }
   def forbidden_tap_check
-    return if Homebrew::EnvConfig.forbidden_taps.blank? && Homebrew::EnvConfig.allowed_taps.blank?
+    return if Tap.allowed_taps.blank? && Tap.forbidden_taps.blank?
 
     owner = Homebrew::EnvConfig.forbidden_owner
     owner_contact = if (contact = Homebrew::EnvConfig.forbidden_owner_contact.presence)
@@ -1391,26 +1391,32 @@ on_request: installed_on_request?, options:)
     unless ignore_deps?
       compute_dependencies.each do |(dep, _options)|
         dep_tap = dep.tap
-        next if dep_tap.blank? || dep_tap.allowed_by_env?
+        next if dep_tap.blank? || (dep_tap.allowed_by_env? && !dep_tap.forbidden_by_env?)
 
-        raise CannotInstallFormulaError, <<~EOS
-          The installation of #{formula.name} has a dependency #{dep.name}
-          but #{owner} has either not allowed the #{dep_tap} tap in `HOMEBREW_ALLOWED_TAPS` or
-          has forbidden the #{dep_tap} tap in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
-        EOS
+        error_message = +"The installation of #{formula.name} has a dependency #{dep.name}\n" \
+                         "from the #{dep_tap} tap but #{owner} "
+        error_message << "has not allowed this tap in `HOMEBREW_ALLOWED_TAPS`" unless dep_tap.allowed_by_env?
+        error_message << " and\n" if !dep_tap.allowed_by_env? && dep_tap.forbidden_by_env?
+        error_message << "has forbidden this tap in `HOMEBREW_FORBIDDEN_TAPS`" if dep_tap.forbidden_by_env?
+        error_message << ".#{owner_contact}"
+
+        raise CannotInstallFormulaError, error_message
       end
     end
 
     return if only_deps?
 
     formula_tap = formula.tap
-    return if formula_tap.blank? || formula_tap.allowed_by_env?
+    return if formula_tap.blank? || (formula_tap.allowed_by_env? && !formula_tap.forbidden_by_env?)
 
-    raise CannotInstallFormulaError, <<~EOS
-      The installation of #{formula.full_name} has the tap #{formula_tap}
-      which is either not allowed by #{owner} in `HOMEBREW_ALLOWED_TAPS` or
-      is forbidden by #{owner} in `HOMEBREW_FORBIDDEN_TAPS`.#{owner_contact}
-    EOS
+    error_message = +"The installation of #{formula.full_name} has the tap #{formula_tap}\n" \
+                     "but #{owner} "
+    error_message << "has not allowed this tap in `HOMEBREW_ALLOWED_TAPS`" unless formula_tap.allowed_by_env?
+    error_message << " and\n" if !formula_tap.allowed_by_env? && formula_tap.forbidden_by_env?
+    error_message << "has forbidden this tap in `HOMEBREW_FORBIDDEN_TAPS`" if formula_tap.forbidden_by_env?
+    error_message << ".#{owner_contact}"
+
+    raise CannotInstallFormulaError, error_message
   end
 
   sig { void }
diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index 527fc0e156..b386eaa985 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -1095,12 +1095,16 @@ class Tap
   def allowed_by_env?
     @allowed_by_env ||= begin
       allowed_taps = self.class.allowed_taps
-      forbidden_taps = self.class.forbidden_taps
 
-      (official? || allowed_taps.blank? || allowed_taps.include?(self)) && forbidden_taps.exclude?(self)
+      official? || allowed_taps.blank? || allowed_taps.include?(self)
     end
   end
 
+  sig { returns(T::Boolean) }
+  def forbidden_by_env?
+    @forbidden_by_env ||= self.class.forbidden_taps.include?(self)
+  end
+
   private
 
   sig { params(file: Pathname).returns(T.any(T::Array[String], Hash)) }

From 3555d09c1d4048caa27f585c979bed36b4ceda31 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 3 May 2024 16:43:39 +0100
Subject: [PATCH 06/10] formula_installer: fix failing test

---
 Library/Homebrew/test/formula_installer_spec.rb | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/Library/Homebrew/test/formula_installer_spec.rb b/Library/Homebrew/test/formula_installer_spec.rb
index e8be7f7cbb..611a5546b5 100644
--- a/Library/Homebrew/test/formula_installer_spec.rb
+++ b/Library/Homebrew/test/formula_installer_spec.rb
@@ -258,10 +258,17 @@ RSpec.describe FormulaInstaller do
   end
 
   describe "#forbidden_tap_check" do
+    before do
+      allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
+    end
+
+    let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }
+    let(:forbidden_taps_set) { Set.new([homebrew_forbidden]) }
+
     it "raises on forbidden tap on formula" do
-      ENV["HOMEBREW_FORBIDDEN_TAPS"] = f_tap = "homebrew/forbidden"
+      f_tap = homebrew_forbidden
       f_name = "homebrew-forbidden-tap"
-      f_path = Tap.fetch(f_tap).new_formula_path(f_name)
+      f_path = homebrew_forbidden.new_formula_path(f_name)
       f_path.parent.mkpath
       f_path.write <<~RUBY
         class #{Formulary.class_s(f_name)} < Formula
@@ -282,9 +289,9 @@ RSpec.describe FormulaInstaller do
     end
 
     it "raises on forbidden tap on dependency" do
-      ENV["HOMEBREW_FORBIDDEN_TAPS"] = dep_tap = "homebrew/forbidden"
+      dep_tap = homebrew_forbidden
       dep_name = "homebrew-forbidden-dependency-tap"
-      dep_path = Tap.fetch(dep_tap).new_formula_path(dep_name)
+      dep_path = homebrew_forbidden.new_formula_path(dep_name)
       dep_path.parent.mkpath
       dep_path.write <<~RUBY
         class #{Formulary.class_s(dep_name)} < Formula
@@ -310,7 +317,7 @@ RSpec.describe FormulaInstaller do
 
       expect do
         fi.forbidden_tap_check
-      end.to raise_error(CannotInstallFormulaError, /but the #{dep_tap} tap was forbidden/)
+      end.to raise_error(CannotInstallFormulaError, /from the #{dep_tap} tap but/)
     ensure
       dep_path.parent.parent.rmtree
     end

From 34387bfc8a355db698d181aff68bc779ae239d0d Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Sun, 5 May 2024 13:54:26 +0100
Subject: [PATCH 07/10] cask/installer: update to match formula_installer

---
 Library/Homebrew/cask/installer.rb           |  4 ++--
 Library/Homebrew/test/cask/installer_spec.rb | 19 ++++++++++++-------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/Library/Homebrew/cask/installer.rb b/Library/Homebrew/cask/installer.rb
index 9b00efab5e..123796b456 100644
--- a/Library/Homebrew/cask/installer.rb
+++ b/Library/Homebrew/cask/installer.rb
@@ -584,7 +584,7 @@ on_request: true)
       unless skip_cask_deps?
         cask_and_formula_dependencies.each do |cask_or_formula|
           dep_tap = cask_or_formula.tap
-          next if dep_tap.blank? || dep_tap.allowed_by_env?
+          next if dep_tap.blank? || (dep_tap.allowed_by_env? && !dep_tap.forbidden_by_env?)
 
           dep_full_name = cask_or_formula.full_name
           error_message = +"The installation of #{@cask} has a dependency #{dep_full_name}\n" \
@@ -599,7 +599,7 @@ on_request: true)
       end
 
       cask_tap = @cask.tap
-      return if cask_tap.blank? || cask_tap.allowed_by_env?
+      return if cask_tap.blank? || (cask_tap.allowed_by_env? && !cask_tap.forbidden_by_env?)
 
       error_message = +"The installation of #{@cask.full_name} has the tap #{cask_tap}\n" \
                        "but #{owner} "
diff --git a/Library/Homebrew/test/cask/installer_spec.rb b/Library/Homebrew/test/cask/installer_spec.rb
index 031b9d4a99..b453da9246 100644
--- a/Library/Homebrew/test/cask/installer_spec.rb
+++ b/Library/Homebrew/test/cask/installer_spec.rb
@@ -326,22 +326,27 @@ RSpec.describe Cask::Installer, :cask do
   end
 
   describe "#forbidden_tap_check" do
-    it "raises on forbidden tap on cask" do
-      ENV["HOMEBREW_FORBIDDEN_TAPS"] = tap = "homebrew/forbidden"
+    before do
+      allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
+    end
 
-      cask = Cask::Cask.new("homebrew-forbidden-tap", tap: Tap.fetch(tap)) do
+    let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }
+    let(:forbidden_taps_set) { Set.new([homebrew_forbidden]) }
+
+    it "raises on forbidden tap on cask" do
+      cask = Cask::Cask.new("homebrew-forbidden-tap", tap: homebrew_forbidden) do
         url "file://#{TEST_FIXTURE_DIR}/cask/container.tar.gz"
       end
 
       expect do
         described_class.new(cask).forbidden_tap_check
-      end.to raise_error(Cask::CaskCannotBeInstalledError, /has the tap #{tap}/)
+      end.to raise_error(Cask::CaskCannotBeInstalledError, /has the tap #{homebrew_forbidden}/)
     end
 
     it "raises on forbidden tap on dependency" do
-      ENV["HOMEBREW_FORBIDDEN_TAPS"] = dep_tap = "homebrew/forbidden"
+      dep_tap = homebrew_forbidden
       dep_name = "homebrew-forbidden-dependency-tap"
-      dep_path = Tap.fetch(dep_tap).new_formula_path(dep_name)
+      dep_path = dep_tap.new_formula_path(dep_name)
       dep_path.parent.mkpath
       dep_path.write <<~RUBY
         class #{Formulary.class_s(dep_name)} < Formula
@@ -358,7 +363,7 @@ RSpec.describe Cask::Installer, :cask do
 
       expect do
         described_class.new(cask).forbidden_tap_check
-      end.to raise_error(Cask::CaskCannotBeInstalledError, /but the #{dep_tap} tap was forbidden/)
+      end.to raise_error(Cask::CaskCannotBeInstalledError, /from the #{dep_tap} tap but/)
     ensure
       dep_path.parent.parent.rmtree
     end

From 078a328e8e221828080db50abcdbb3e94cb3ea07 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Mon, 6 May 2024 15:05:06 +0100
Subject: [PATCH 08/10] tap: avoid class vars

Avoiding them also allows us to write proper tests.
---
 Library/Homebrew/tap.rb           | 17 ++++++-----------
 Library/Homebrew/test/tap_spec.rb | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index b386eaa985..f66261d14b 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -132,11 +132,10 @@ class Tap
     false
   end
 
-  # rubocop:disable Style/ClassVars
-  # We want the the class variables below to be global to all `Tap` classes and subclasses.
   sig { returns(T::Set[Tap]) }
   def self.allowed_taps
-    @@allowed_taps ||= begin
+    cache_key = "allowed_taps_#{Homebrew::EnvConfig.allowed_taps.to_s.gsub(" ", "_")}".to_sym
+    cache[cache_key] ||= begin
       allowed_tap_list = Homebrew::EnvConfig.allowed_taps.to_s.split
 
       Set.new(allowed_tap_list.filter_map do |tap|
@@ -144,15 +143,14 @@ class Tap
       rescue Tap::InvalidNameError
         opoo "Invalid tap name in `HOMEBREW_ALLOWED_TAPS`: #{tap}"
         nil
-      end)
+      end).freeze
     end
-
-    @@allowed_taps.freeze
   end
 
   sig { returns(T::Set[Tap]) }
   def self.forbidden_taps
-    @@forbidden_taps ||= begin
+    cache_key = "forbidden_taps_#{Homebrew::EnvConfig.forbidden_taps.to_s.gsub(" ", "_")}".to_sym
+    cache[cache_key] ||= begin
       forbidden_tap_list = Homebrew::EnvConfig.forbidden_taps.to_s.split
 
       Set.new(forbidden_tap_list.filter_map do |tap|
@@ -160,12 +158,9 @@ class Tap
       rescue Tap::InvalidNameError
         opoo "Invalid tap name in `HOMEBREW_FORBIDDEN_TAPS`: #{tap}"
         nil
-      end)
+      end).freeze
     end
-
-    @@forbidden_taps.freeze
   end
-  # rubocop:enable Style/ClassVars
 
   # @api public
   extend Enumerable
diff --git a/Library/Homebrew/test/tap_spec.rb b/Library/Homebrew/test/tap_spec.rb
index a8cafb6799..940ac944f9 100644
--- a/Library/Homebrew/test/tap_spec.rb
+++ b/Library/Homebrew/test/tap_spec.rb
@@ -142,6 +142,24 @@ RSpec.describe Tap do
     end
   end
 
+  describe "::allowed_taps" do
+    before { allow(Homebrew::EnvConfig).to receive(:allowed_taps).and_return("homebrew/allowed") }
+
+    it "returns a set of allowed taps according to the environment" do
+      expect(described_class.allowed_taps)
+        .to contain_exactly(described_class.fetch("homebrew/allowed"))
+    end
+  end
+
+  describe "::forbidden_taps" do
+    before { allow(Homebrew::EnvConfig).to receive(:forbidden_taps).and_return("homebrew/forbidden") }
+
+    it "returns a set of forbidden taps according to the environment" do
+      expect(described_class.forbidden_taps)
+        .to contain_exactly(described_class.fetch("homebrew/forbidden"))
+    end
+  end
+
   specify "::names" do
     expect(described_class.names.sort).to eq(["homebrew/core", "homebrew/foo"])
   end

From 3b794fc6e895bca8997d61ccd0a1fd2a285a75a2 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Mon, 6 May 2024 15:22:48 +0100
Subject: [PATCH 09/10] formula_installer, cask/installer: add tests for
 `HOMEBREW_ALLOWED_TAPS`

---
 Library/Homebrew/test/cask/installer_spec.rb  | 22 +++++++++
 .../Homebrew/test/formula_installer_spec.rb   | 48 +++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/Library/Homebrew/test/cask/installer_spec.rb b/Library/Homebrew/test/cask/installer_spec.rb
index b453da9246..b0e22b9b92 100644
--- a/Library/Homebrew/test/cask/installer_spec.rb
+++ b/Library/Homebrew/test/cask/installer_spec.rb
@@ -327,10 +327,14 @@ RSpec.describe Cask::Installer, :cask do
 
   describe "#forbidden_tap_check" do
     before do
+      allow(Tap).to receive(:allowed_taps).and_return(allowed_taps_set)
       allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
     end
 
     let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }
+    let(:allowed_third_party) { Tap.fetch("nothomebrew/allowed") }
+    let(:disallowed_third_party) { Tap.fetch("nothomebrew/notallowed") }
+    let(:allowed_taps_set) { Set.new([allowed_third_party]) }
     let(:forbidden_taps_set) { Set.new([homebrew_forbidden]) }
 
     it "raises on forbidden tap on cask" do
@@ -343,6 +347,24 @@ RSpec.describe Cask::Installer, :cask do
       end.to raise_error(Cask::CaskCannotBeInstalledError, /has the tap #{homebrew_forbidden}/)
     end
 
+    it "raises on not allowed third-party tap on cask" do
+      cask = Cask::Cask.new("homebrew-not-allowed-tap", tap: disallowed_third_party) do
+        url "file://#{TEST_FIXTURE_DIR}/cask/container.tar.gz"
+      end
+
+      expect do
+        described_class.new(cask).forbidden_tap_check
+      end.to raise_error(Cask::CaskCannotBeInstalledError, /has the tap #{disallowed_third_party}/)
+    end
+
+    it "does not raise on allowed tap on cask" do
+      cask = Cask::Cask.new("third-party-allowed-tap", tap: allowed_third_party) do
+        url "file://#{TEST_FIXTURE_DIR}/cask/container.tar.gz"
+      end
+
+      expect { described_class.new(cask).forbidden_tap_check }.not_to raise_error
+    end
+
     it "raises on forbidden tap on dependency" do
       dep_tap = homebrew_forbidden
       dep_name = "homebrew-forbidden-dependency-tap"
diff --git a/Library/Homebrew/test/formula_installer_spec.rb b/Library/Homebrew/test/formula_installer_spec.rb
index 611a5546b5..d0878a3e3c 100644
--- a/Library/Homebrew/test/formula_installer_spec.rb
+++ b/Library/Homebrew/test/formula_installer_spec.rb
@@ -259,10 +259,14 @@ RSpec.describe FormulaInstaller do
 
   describe "#forbidden_tap_check" do
     before do
+      allow(Tap).to receive(:allowed_taps).and_return(allowed_taps_set)
       allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
     end
 
     let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }
+    let(:allowed_third_party) { Tap.fetch("nothomebrew/allowed") }
+    let(:disallowed_third_party) { Tap.fetch("nothomebrew/notallowed") }
+    let(:allowed_taps_set) { Set.new([allowed_third_party]) }
     let(:forbidden_taps_set) { Set.new([homebrew_forbidden]) }
 
     it "raises on forbidden tap on formula" do
@@ -288,6 +292,50 @@ RSpec.describe FormulaInstaller do
       f_path.parent.parent.rmtree
     end
 
+    it "raises on not allowed third-party tap on formula" do
+      f_tap = disallowed_third_party
+      f_name = "homebrew-not-allowed-tap"
+      f_path = disallowed_third_party.new_formula_path(f_name)
+      f_path.parent.mkpath
+      f_path.write <<~RUBY
+        class #{Formulary.class_s(f_name)} < Formula
+          url "foo"
+          version "0.1"
+        end
+      RUBY
+      Formulary.cache.delete(f_path)
+
+      f = Formulary.factory("#{f_tap}/#{f_name}")
+      fi = described_class.new(f)
+
+      expect do
+        fi.forbidden_tap_check
+      end.to raise_error(CannotInstallFormulaError, /has the tap #{f_tap}/)
+    ensure
+      f_path.parent.parent.parent.rmtree
+    end
+
+    it "does not raise on allowed tap on formula" do
+      f_tap = allowed_third_party
+      f_name = "homebrew-allowed-tap"
+      f_path = allowed_third_party.new_formula_path(f_name)
+      f_path.parent.mkpath
+      f_path.write <<~RUBY
+        class #{Formulary.class_s(f_name)} < Formula
+          url "foo"
+          version "0.1"
+        end
+      RUBY
+      Formulary.cache.delete(f_path)
+
+      f = Formulary.factory("#{f_tap}/#{f_name}")
+      fi = described_class.new(f)
+
+      expect { fi.forbidden_tap_check }.not_to raise_error
+    ensure
+      f_path.parent.parent.parent.rmtree
+    end
+
     it "raises on forbidden tap on dependency" do
       dep_tap = homebrew_forbidden
       dep_name = "homebrew-forbidden-dependency-tap"

From be29afa5f7f3845c8af836598ca6d2f3a3db8fb7 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Mon, 6 May 2024 15:26:29 +0100
Subject: [PATCH 10/10] Fix `brew style`

---
 Library/Homebrew/tap.rb                         | 4 ++--
 Library/Homebrew/test/cask/installer_spec.rb    | 3 +--
 Library/Homebrew/test/formula_installer_spec.rb | 3 +--
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index f66261d14b..ec38eb9292 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -134,7 +134,7 @@ class Tap
 
   sig { returns(T::Set[Tap]) }
   def self.allowed_taps
-    cache_key = "allowed_taps_#{Homebrew::EnvConfig.allowed_taps.to_s.gsub(" ", "_")}".to_sym
+    cache_key = :"allowed_taps_#{Homebrew::EnvConfig.allowed_taps.to_s.tr(" ", "_")}"
     cache[cache_key] ||= begin
       allowed_tap_list = Homebrew::EnvConfig.allowed_taps.to_s.split
 
@@ -149,7 +149,7 @@ class Tap
 
   sig { returns(T::Set[Tap]) }
   def self.forbidden_taps
-    cache_key = "forbidden_taps_#{Homebrew::EnvConfig.forbidden_taps.to_s.gsub(" ", "_")}".to_sym
+    cache_key = :"forbidden_taps_#{Homebrew::EnvConfig.forbidden_taps.to_s.tr(" ", "_")}"
     cache[cache_key] ||= begin
       forbidden_tap_list = Homebrew::EnvConfig.forbidden_taps.to_s.split
 
diff --git a/Library/Homebrew/test/cask/installer_spec.rb b/Library/Homebrew/test/cask/installer_spec.rb
index b0e22b9b92..568d848909 100644
--- a/Library/Homebrew/test/cask/installer_spec.rb
+++ b/Library/Homebrew/test/cask/installer_spec.rb
@@ -327,8 +327,7 @@ RSpec.describe Cask::Installer, :cask do
 
   describe "#forbidden_tap_check" do
     before do
-      allow(Tap).to receive(:allowed_taps).and_return(allowed_taps_set)
-      allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
+      allow(Tap).to receive_messages(allowed_taps: allowed_taps_set, forbidden_taps: forbidden_taps_set)
     end
 
     let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }
diff --git a/Library/Homebrew/test/formula_installer_spec.rb b/Library/Homebrew/test/formula_installer_spec.rb
index d0878a3e3c..e2655cd0c5 100644
--- a/Library/Homebrew/test/formula_installer_spec.rb
+++ b/Library/Homebrew/test/formula_installer_spec.rb
@@ -259,8 +259,7 @@ RSpec.describe FormulaInstaller do
 
   describe "#forbidden_tap_check" do
     before do
-      allow(Tap).to receive(:allowed_taps).and_return(allowed_taps_set)
-      allow(Tap).to receive(:forbidden_taps).and_return(forbidden_taps_set)
+      allow(Tap).to receive_messages(allowed_taps: allowed_taps_set, forbidden_taps: forbidden_taps_set)
     end
 
     let(:homebrew_forbidden) { Tap.fetch("homebrew/forbidden") }