commands/exec: allow customising environment.

Provide `HOMEBREW_BUNDLE_EXEC_ALL_KEG_ONLY_DEPS` and
`HOMEBREW_BUNDLE_EXEC_FORMULA_VERSION_*` variables to allow adjusting
the environment variables that are set in `brew bundle exec`.

lib/bundle/commands/exec.rb

@@ -35,7 +35,15 @@ def run(*args, global: false, file: nil)
 
           Formulary.factory(entry.name)
         end
-        ENV.keg_only_deps = ENV.deps.select(&:keg_only?)
+
+        # Allow setting all dependencies to be keg-only
+        # (i.e. should be explicitly in HOMEBREW_*PATHs ahead of HOMEBREW_PREFIX)
+        ENV.keg_only_deps = if ENV["HOMEBREW_BUNDLE_EXEC_ALL_KEG_ONLY_DEPS"].present?
+          ENV.delete("HOMEBREW_BUNDLE_EXEC_ALL_KEG_ONLY_DEPS")
+          ENV.deps
+        else
+          ENV.deps.select(&:keg_only?)
+        end
         ENV.setup_build_environment
 
         # Enable compiler flag filtering
@@ -58,6 +66,27 @@ def run(*args, global: false, file: nil)
         # Ensure the Ruby path we saved goes before anything else, if the command was in the PATH
         ENV.prepend_path "PATH", command_path if command_path.present?
 
+        # Replace the formula versions from the environment variables
+        formula_versions = {}
+        ENV.each do |key, value|
+          match = key.match(/^HOMEBREW_BUNDLE_EXEC_FORMULA_VERSION_(.+)$/)
+          next if match.blank?
+
+          formula_name = match[1]
+          next if formula_name.blank?
+
+          ENV.delete(key)
+          formula_versions[formula_name.downcase] = value
+        end
+        formula_versions.each do |formula_name, formula_version|
+          ENV.each do |key, value|
+            opt = %r{/opt/#{formula_name}([/:$])}
+            next unless value.match(opt)
+
+            ENV[key] = value.gsub(opt, "/Cellar/#{formula_name}/#{formula_version}\\1")
+          end
+        end
+
         exec(*args)
       end
     end

spec/bundle/commands/exec_command_spec.rb

@@ -10,35 +10,47 @@
   end
 
   context "when a Brewfile is found" do
-    it "does not raise an error" do
-      allow(described_class).to receive(:exec).and_return(nil)
-      allow_any_instance_of(Pathname).to receive(:read)
-        .and_return("brew 'openssl'")
+    let(:brewfile_contents) { "brew 'openssl'" }
 
-      expect { described_class.run("bundle", "install") }.not_to raise_error
+    before do
+      allow_any_instance_of(Pathname).to receive(:read)
+        .and_return(brewfile_contents)
     end
 
-    it "is able to run without bundle arguments" do
-      allow(described_class).to receive(:exec).with("bundle", "install").and_return(nil)
-      allow_any_instance_of(Pathname).to receive(:read)
-        .and_return("brew 'openssl'")
+    context "with valid command setup" do
+      before do
+        allow(described_class).to receive(:exec).and_return(nil)
+      end
 
-      expect { described_class.run("bundle", "install") }.not_to raise_error
-    end
+      it "does not raise an error" do
+        expect { described_class.run("bundle", "install") }.not_to raise_error
+      end
 
-    it "raises an exception if called without a command" do
-      allow(described_class).to receive(:exec).and_return(nil)
-      allow_any_instance_of(Pathname).to receive(:read)
-        .and_return("brew 'openssl'")
+      it "does not raise an error when HOMEBREW_BUNDLE_EXEC_ALL_KEG_ONLY_DEPS is set" do
+        ENV["HOMEBREW_BUNDLE_EXEC_ALL_KEG_ONLY_DEPS"] = "1"
+        expect { described_class.run("bundle", "install") }.not_to raise_error
+      end
 
-      expect { described_class.run }.to raise_error(RuntimeError)
+      it "uses the formula version from the environment variable" do
+        openssl_version = "1.1.1"
+        ENV["PATH"] = "/opt/homebrew/opt/openssl/bin"
+        ENV["HOMEBREW_BUNDLE_EXEC_FORMULA_VERSION_OPENSSL"] = openssl_version
+        described_class.run("bundle", "install")
+        expect(ENV.fetch("PATH")).to include("/Cellar/openssl/1.1.1/bin")
+      end
+
+      it "is able to run without bundle arguments" do
+        allow(described_class).to receive(:exec).with("bundle", "install").and_return(nil)
+        expect { described_class.run("bundle", "install") }.not_to raise_error
+      end
+
+      it "raises an exception if called without a command" do
+        expect { described_class.run }.to raise_error(RuntimeError)
+      end
     end
 
     it "raises if called with a command that's not on the PATH" do
       allow(described_class).to receive_messages(exec: nil, which: nil)
-      allow_any_instance_of(Pathname).to receive(:read)
-        .and_return("brew 'openssl'")
-
       expect { described_class.run("bundle", "install") }.to raise_error(RuntimeError)
     end
 
@@ -47,49 +59,35 @@
       expect(described_class).to receive(:which).and_return(Pathname("/usr/local/bin/bundle"))
       allow(ENV).to receive(:prepend_path).with(any_args).and_call_original
       expect(ENV).to receive(:prepend_path).with("PATH", "/usr/local/bin").once.and_call_original
-      allow_any_instance_of(Pathname).to receive(:read)
-        .and_return("brew 'openssl'")
       described_class.run("bundle", "install")
     end
 
     describe "when running a command which exists but is not on the PATH" do
-      it "does not raise if the command is a relative path with current directory indicator" do
-        allow(described_class).to receive(:exec).with("./configure").and_return(nil)
-        expect(described_class).not_to receive(:which)
-        allow_any_instance_of(Pathname).to receive(:read)
-          .and_return("brew 'zlib'")
-
-        expect { described_class.run("./configure") }.not_to raise_error
+      let(:brewfile_contents) { "brew 'zlib'" }
+
+      shared_examples "allows command execution" do |command|
+        it "does not raise" do
+          allow(described_class).to receive(:exec).with(command).and_return(nil)
+          expect(described_class).not_to receive(:which)
+          expect { described_class.run(command) }.not_to raise_error
+        end
       end
 
-      it "does not raise if the command is a relative path without current directory indicator" do
-        allow(described_class).to receive(:exec).with("bin/install").and_return(nil)
-        expect(described_class).not_to receive(:which)
-        allow_any_instance_of(Pathname).to receive(:read)
-          .and_return("brew 'zlib'")
-
-        expect { described_class.run("bin/install") }.not_to raise_error
-      end
-
-      it "does not raise if the command is an absolute path" do
-        allow(described_class).to receive(:exec).with("/Users/admin/Downloads/command").and_return(nil)
-        expect(described_class).not_to receive(:which)
-        allow_any_instance_of(Pathname).to receive(:read)
-          .and_return("brew 'zlib'")
-
-        expect { described_class.run("/Users/admin/Downloads/command") }.not_to raise_error
-      end
+      it_behaves_like "allows command execution", "./configure"
+      it_behaves_like "allows command execution", "bin/install"
+      it_behaves_like "allows command execution", "/Users/admin/Downloads/command"
     end
 
     describe "when the Brewfile contains rbenv" do
-      before { ENV["HOMEBREW_RBENV_ROOT"] = rbenv_root.to_s }
-
       let(:rbenv_root) { Pathname.new("/tmp/.rbenv") }
+      let(:brewfile_contents) { "brew 'rbenv'" }
+
+      before do
+        ENV["HOMEBREW_RBENV_ROOT"] = rbenv_root.to_s
+      end
 
       it "prepends the path of the rbenv shims to PATH before running" do
         allow(described_class).to receive(:exec).with("/usr/bin/true").and_return(0)
-        allow_any_instance_of(Pathname).to receive(:read)
-          .and_return("brew 'rbenv'")
         allow(ENV).to receive(:fetch).with(any_args).and_call_original
         allow(ENV).to receive(:prepend_path).with(any_args).once.and_call_original