Merge pull request #20414 from Homebrew/copilot/fix-18371

Don't allow installing formulae from paths without HOMEBREW_DEVELOPER

Library/Homebrew/env_config.rb

@@ -238,9 +238,10 @@ module Homebrew
         boolean:     true,
       },
       HOMEBREW_FORBID_PACKAGES_FROM_PATHS:       {
-        description: "If set, Homebrew will refuse to read formulae or casks provided from file paths, " \
-                     "e.g. `brew install ./package.rb`.",
-        boolean:     true,
+        description:  "If set, Homebrew will refuse to read formulae or casks provided from file paths, " \
+                      "e.g. `brew install ./package.rb`.",
+        boolean:      true,
+        default_text: "true unless `$HOMEBREW_DEVELOPER` is set.",
       },
       HOMEBREW_FORCE_API_AUTO_UPDATE:            {
         description: "If set, update the Homebrew API formula or cask data even if " \
@@ -552,6 +553,7 @@ module Homebrew
     CUSTOM_IMPLEMENTATIONS = T.let(Set.new([
       :HOMEBREW_MAKE_JOBS,
       :HOMEBREW_CASK_OPTS,
+      :HOMEBREW_FORBID_PACKAGES_FROM_PATHS,
     ]).freeze, T::Set[Symbol])
 
     ENVS.each do |env, hash|
@@ -628,6 +630,15 @@ module Homebrew
       cask_opts.include?("--require-sha")
     end
 
+    sig { returns(T::Boolean) }
+    def forbid_packages_from_paths?
+      return true if ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"].present?
+
+      # Provide an opt-out for tests and developers.
+      # Our testing framework installs formulae from file paths all over the place.
+      ENV["HOMEBREW_TESTS"].blank? && ENV["HOMEBREW_DEVELOPER"].blank?
+    end
+
     sig { returns(T::Boolean) }
     def automatically_set_no_install_from_api?
       ENV["HOMEBREW_AUTOMATICALLY_SET_NO_INSTALL_FROM_API"].present?

Library/Homebrew/test/env_config_spec.rb

@@ -69,4 +69,34 @@ RSpec.describe Homebrew::EnvConfig do
       expect(env_config.make_jobs).to eql("16")
     end
   end
+
+  describe ".forbid_packages_from_paths?" do
+    before do
+      ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"] = nil
+      ENV["HOMEBREW_DEVELOPER"] = nil
+      ENV["HOMEBREW_TESTS"] = nil
+    end
+
+    it "returns true if HOMEBREW_FORBID_PACKAGES_FROM_PATHS is set" do
+      ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"] = "1"
+      expect(env_config.forbid_packages_from_paths?).to be(true)
+    end
+
+    it "returns true if HOMEBREW_DEVELOPER is not set" do
+      ENV["HOMEBREW_DEVELOPER"] = nil
+      expect(env_config.forbid_packages_from_paths?).to be(true)
+    end
+
+    it "returns false if HOMEBREW_DEVELOPER is set and HOMEBREW_FORBID_PACKAGES_FROM_PATHS is not set" do
+      ENV["HOMEBREW_DEVELOPER"] = "1"
+      ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"] = nil
+      expect(env_config.forbid_packages_from_paths?).to be(false)
+    end
+
+    it "returns true if both HOMEBREW_DEVELOPER and HOMEBREW_FORBID_PACKAGES_FROM_PATHS are set" do
+      ENV["HOMEBREW_DEVELOPER"] = "1"
+      ENV["HOMEBREW_FORBID_PACKAGES_FROM_PATHS"] = "1"
+      expect(env_config.forbid_packages_from_paths?).to be(true)
+    end
+  end
 end