utils: add `tar`

Includes `validate_file` method to be used by `bump-formula-pr`

Library/Homebrew/dev-cmd/bump-formula-pr.rb

@@ -3,6 +3,7 @@
 require "formula"
 require "cli/parser"
 require "utils/pypi"
+require "utils/tar"
 
 module Homebrew
   module_function
@@ -205,19 +206,8 @@ module Homebrew
       end
       check_closed_pull_requests(formula, tap_full_name, url: new_url, args: args) unless new_version
       resource_path, forced_version = fetch_resource(formula, new_version, new_url)
-      tar_file_extensions = %w[.tar .tb2 .tbz .tbz2 .tgz .tlz .txz .tZ]
-      if tar_file_extensions.any? { |extension| new_url.include? extension }
-        gnu_tar_gtar_path = HOMEBREW_PREFIX/"opt/gnu-tar/bin/gtar"
-        gnu_tar_gtar = gnu_tar_gtar_path if gnu_tar_gtar_path.executable?
-        tar = which("gtar") || gnu_tar_gtar || which("tar")
-        if Utils.popen_read(tar, "-tf", resource_path).match?(%r{/.*\.})
-          new_hash = resource_path.sha256
-        else
-          odie "#{resource_path} is not a valid tar file!"
-        end
-      else
-        new_hash = resource_path.sha256
-      end
+      Utils::Tar.validate_file(resource_path)
+      new_hash = resource_path.sha256
     end
 
     replacement_pairs = []

Library/Homebrew/test/utils/tar_spec.rb

+# frozen_string_literal: true
+
+require "utils/tar"
+
+describe Utils::Tar do
+  before do
+    described_class.clear_executable_cache
+  end
+
+  describe ".available?" do
+    it "returns true if tar or gnu-tar is available" do
+      if described_class.executable.present?
+        expect(described_class).to be_available
+      else
+        expect(described_class).not_to be_available
+      end
+    end
+  end
+
+  describe ".validate_file" do
+    it "does not raise an error when tar and gnu-tar are unavailable" do
+      allow(described_class).to receive(:available?).and_return false
+      expect { described_class.validate_file "blah" }.not_to raise_error
+    end
+
+    context "when tar or gnu-tar is available" do
+      let(:testball_resource) { "#{TEST_FIXTURE_DIR}/tarballs/testball-0.1.tbz" }
+      let(:invalid_resource) { "#{TEST_TMPDIR}/invalid.tgz" }
+
+      before do
+        allow(described_class).to receive(:available?).and_return true
+      end
+
+      it "does not raise an error if file is not a tar file" do
+        expect { described_class.validate_file "blah" }.not_to raise_error
+      end
+
+      it "does not raise an error if file is valid tar file" do
+        expect { described_class.validate_file testball_resource }.not_to raise_error
+      end
+
+      it "raises an error if file is an invalid tar file" do
+        FileUtils.touch invalid_resource
+        expect { described_class.validate_file invalid_resource }.to raise_error SystemExit
+        FileUtils.rm_f invalid_resource
+      end
+    end
+  end
+end

Library/Homebrew/utils/tar.rb

+# frozen_string_literal: true
+
+module Utils
+  # Helper functions for interacting with tar files.
+  #
+  # @api private
+  module Tar
+    module_function
+
+    TAR_FILE_EXTENSIONS = %w[.tar .tb2 .tbz .tbz2 .tgz .tlz .txz .tZ].freeze
+
+    def available?
+      executable.present?
+    end
+
+    def executable
+      return @executable if defined?(@executable)
+
+      gnu_tar_gtar_path = HOMEBREW_PREFIX/"opt/gnu-tar/bin/gtar"
+      gnu_tar_gtar = gnu_tar_gtar_path if gnu_tar_gtar_path.executable?
+      @executable = which("gtar") || gnu_tar_gtar || which("tar")
+    end
+
+    def validate_file(path)
+      return unless available?
+
+      path = Pathname.new(path)
+      return unless TAR_FILE_EXTENSIONS.include? path.extname
+      return if Utils.popen_read(executable, "-tf", path).match?(%r{/.*\.})
+
+      odie "#{path} is not a valid tar file!"
+    end
+
+    def clear_executable_cache
+      remove_instance_variable(:@executable) if defined?(@executable)
+    end
+  end
+end