Deprecate installing casks/formulae from paths.

We've already disabled installing casks/formulae from URLs and we
regularly tell people not to install from paths so let's just deprecate
this behaviour entirely.

Even Homebrew developers do not need to work this way.

Library/Homebrew/brew.rb

@@ -211,9 +211,14 @@ rescue Exception => e # rubocop:disable Lint/RescueException
     $stderr.puts "If reporting this issue please do so at (not Homebrew/brew or Homebrew/homebrew-core):"
     $stderr.puts "  #{Formatter.url(issues_url)}"
   elsif internal_cmd
+    if e.is_a?(MethodDeprecatedError) && (first_backtrace = e.backtrace&.first.presence) &&
+       (first_backtrace.include?("/formulary.rb") || first_backtrace.include?("/cask_loader.rb"))
+      $stderr.puts Utils::Backtrace.clean(e) if ARGV.include?("--debug") || args.debug?
+    else
       $stderr.puts "#{Tty.bold}Please report this issue:#{Tty.reset}"
       $stderr.puts "  #{Formatter.url(OS::ISSUES_URL)}"
     end
+  end
 
   exit 1
 else

Library/Homebrew/cask/cask_loader.rb

@@ -105,10 +105,19 @@ module Cask
         end
 
         return if %w[.rb .json].exclude?(path.extname)
+        return if path.to_s.include?("/Formula/")
         return unless path.expand_path.exist?
 
-        return if Homebrew::EnvConfig.forbid_packages_from_paths? &&
+        unless path.realpath.to_s.start_with?("#{Caskroom.path}/", "#{HOMEBREW_LIBRARY}/Taps/",
-                  !path.realpath.to_s.start_with?("#{Caskroom.path}/", "#{HOMEBREW_LIBRARY}/Taps/")
+                                              "#{HOMEBREW_LIBRARY_PATH}/test/support/fixtures/")
+          return if Homebrew::EnvConfig.forbid_packages_from_paths?
+
+          # So many tests legimately use casks from paths that we can't warn about them all.
+          # Let's focus on end-users for now.
+          unless ENV["HOMEBREW_TESTS"]
+            odeprecated "installing formulae from paths or URLs", "installing formulae from taps"
+          end
+        end
 
         new(path)
       end
@@ -195,6 +204,8 @@ module Cask
       def load(config:)
         path.dirname.mkpath
 
+        odeprecated "installing casks from paths or URLs", "installing casks from taps"
+
         if ALLOWED_URL_SCHEMES.exclude?(url.scheme)
           raise UnsupportedInstallationMethod,
                 "Non-checksummed download of #{name} formula file from an arbitrary URL is unsupported! " \

Library/Homebrew/formulary.rb

@@ -646,9 +646,6 @@ module Formulary
 
       return unless path.expand_path.exist?
 
-      return if Homebrew::EnvConfig.forbid_packages_from_paths? &&
-                !path.realpath.to_s.start_with?("#{HOMEBREW_CELLAR}/", "#{HOMEBREW_LIBRARY}/Taps/")
-
       options = if (tap = Tap.from_path(path))
         # Only treat symlinks in taps as aliases.
         if path.symlink?
@@ -675,6 +672,17 @@ module Formulary
 
       return if path.extname != ".rb"
 
+      unless path.realpath.to_s.start_with?("#{HOMEBREW_CELLAR}/", "#{HOMEBREW_TAP_DIRECTORY}/",
+                                            "#{HOMEBREW_LIBRARY_PATH}/test/support/fixtures/")
+        return if Homebrew::EnvConfig.forbid_packages_from_paths?
+
+        # So many tests legimately use formulae from paths that we can't warn about them all.
+        # Let's focus on end-users for now.
+        unless ENV["HOMEBREW_TESTS"]
+          odeprecated "installing formulae from paths or URLs", "installing formulae from taps"
+        end
+      end
+
       new(path, **options)
     end
 
@@ -716,6 +724,8 @@ module Formulary
       return unless uri.path
       return unless uri.scheme.present?
 
+      odeprecated "installing formulae from paths or URLs", "installing formulae from taps"
+
       new(uri, from:)
     end
 

Library/Homebrew/test/cask/cask_loader/from_uri_loader_spec.rb

@@ -29,28 +29,28 @@ RSpec.describe Cask::CaskLoader::FromURILoader do
       loader = described_class.new("https://brew.sh/foo.rb")
       expect do
         loader.load(config: nil)
-      end.to raise_error(UnsupportedInstallationMethod)
+      end.to raise_error(MethodDeprecatedError)
     end
 
     it "raises an error when given an ftp URL" do
       loader = described_class.new("ftp://brew.sh/foo.rb")
       expect do
         loader.load(config: nil)
-      end.to raise_error(UnsupportedInstallationMethod)
+      end.to raise_error(MethodDeprecatedError)
     end
 
     it "raises an error when given an sftp URL" do
       loader = described_class.new("sftp://brew.sh/foo.rb")
       expect do
         loader.load(config: nil)
-      end.to raise_error(UnsupportedInstallationMethod)
+      end.to raise_error(MethodDeprecatedError)
     end
 
-    it "does not raise an error when given a file URL" do
+    it "raises an error when given a file URL" do
       loader = described_class.new("file://#{TEST_FIXTURE_DIR}/cask/Casks/local-caffeine.rb")
       expect do
         loader.load(config: nil)
-      end.not_to raise_error(UnsupportedInstallationMethod)
+      end.to raise_error(MethodDeprecatedError)
     end
   end
 end

Library/Homebrew/test/cask/cask_spec.rb

@@ -46,16 +46,10 @@ RSpec.describe Cask::Cask, :cask do
       expect(c.token).to eq("caffeine")
     end
 
-    it "returns an instance of the Cask from a URL", :needs_utils_curl, :no_api do
-      c = Cask::CaskLoader.load("file://#{tap_path}/Casks/local-caffeine.rb")
-      expect(c).to be_a(described_class)
-      expect(c.token).to eq("local-caffeine")
-    end
-
     it "raises an error when failing to download a Cask from a URL", :needs_utils_curl, :no_api do
       expect do
         Cask::CaskLoader.load("file://#{tap_path}/Casks/notacask.rb")
-      end.to raise_error(Cask::CaskUnavailableError)
+      end.to raise_error(MethodDeprecatedError)
     end
 
     it "returns an instance of the Cask from a relative file location" do

Library/Homebrew/test/formulary_spec.rb

@@ -129,11 +129,6 @@ RSpec.describe Formulary do
         end.to raise_error(FormulaUnavailableError)
       end
 
-      it "returns a Formula when given a URL", :needs_utils_curl, :no_api do
-        formula = described_class.factory("file://#{formula_path}")
-        expect(formula).to be_a(Formula)
-      end
-
       it "errors when given a URL but paths are disabled" do
         ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"] = "1"
         expect do
@@ -546,31 +541,31 @@ RSpec.describe Formulary do
       it "raises an error when given an https URL" do
         expect do
           described_class.factory("https://brew.sh/foo.rb")
-        end.to raise_error(UnsupportedInstallationMethod)
+        end.to raise_error(MethodDeprecatedError)
       end
 
       it "raises an error when given a bottle URL" do
         expect do
           described_class.factory("https://brew.sh/foo-1.0.arm64_catalina.bottle.tar.gz")
-        end.to raise_error(UnsupportedInstallationMethod)
+        end.to raise_error(MethodDeprecatedError)
       end
 
       it "raises an error when given an ftp URL" do
         expect do
           described_class.factory("ftp://brew.sh/foo.rb")
-        end.to raise_error(UnsupportedInstallationMethod)
+        end.to raise_error(MethodDeprecatedError)
       end
 
       it "raises an error when given an sftp URL" do
         expect do
           described_class.factory("sftp://brew.sh/foo.rb")
-        end.to raise_error(UnsupportedInstallationMethod)
+        end.to raise_error(MethodDeprecatedError)
       end
 
-      it "does not raise an error when given a file URL" do
+      it "raises an error when given a file URL" do
         expect do
           described_class.factory("file://#{TEST_FIXTURE_DIR}/testball.rb")
-        end.not_to raise_error(UnsupportedInstallationMethod)
+        end.to raise_error(MethodDeprecatedError)
       end
     end