rubocops/livecheck: Rework LivecheckUrlProvided

The existing `LivecheckUrlProvided` RuboCop requires a `url` for all
`livecheck` blocks except those using `skip`, `formula`, or `cask`,
as those only appear in a `livecheck` block with no other DSL methods.

We now have a `throttle` method that can be used alongside other DSL
methods (e.g., `url`, `regex`, `strategy`) or by itself. `brew style`
currently fails when `throttle` is used by itself, so this reworks
the conditions to allow this usage.

Library/Homebrew/rubocops/livecheck.rb

@@ -45,20 +45,19 @@ def audit_formula(_node, _class_node, _parent_class_node, body_node)
       class LivecheckUrlProvided < FormulaCop
         def audit_formula(_node, _class_node, _parent_class_node, body_node)
           livecheck_node = find_block(body_node, :livecheck)
-          return if livecheck_node.blank?
-
-          skip = find_every_method_call_by_name(livecheck_node, :skip).first
-          return if skip.present?
+          return unless livecheck_node
 
-          formula_node = find_every_method_call_by_name(livecheck_node, :formula).first
-          cask_node = find_every_method_call_by_name(livecheck_node, :cask).first
-          return if formula_node.present? || cask_node.present?
+          url_node = find_every_method_call_by_name(livecheck_node, :url).first
+          return if url_node
 
-          livecheck_url = find_every_method_call_by_name(livecheck_node, :url).first
-          return if livecheck_url.present?
+          # A regex and/or strategy is specific to a particular URL, so we
+          # should require an explicit URL.
+          regex_node = find_every_method_call_by_name(livecheck_node, :regex).first
+          strategy_node = find_every_method_call_by_name(livecheck_node, :strategy).first
+          return if !regex_node && !strategy_node
 
           offending_node(livecheck_node)
-          problem "A `url` must be provided to livecheck."
+          problem "A `url` should be provided when `regex` or `strategy` are used."
         end
       end
 

Library/Homebrew/test/rubocops/livecheck/url_provided_spec.rb

@@ -5,20 +5,31 @@
 RSpec.describe RuboCop::Cop::FormulaAudit::LivecheckUrlProvided do
   subject(:cop) { described_class.new }
 
-  it "reports an offense when a `url` is not specified in the livecheck block" do
+  it "reports an offense when a `url` is not specified in a livecheck block" do
     expect_offense(<<~RUBY)
       class Foo < Formula
         url "https://brew.sh/foo-1.0.tgz"
 
         livecheck do
-        ^^^^^^^^^^^^ FormulaAudit/LivecheckUrlProvided: A `url` must be provided to livecheck.
+        ^^^^^^^^^^^^ FormulaAudit/LivecheckUrlProvided: A `url` should be provided when `regex` or `strategy` are used.
           regex(%r{href=.*?/formula[._-]v?(\\d+(?:\\.\\d+)+)\\.t}i)
         end
       end
     RUBY
+
+    expect_offense(<<~RUBY)
+      class Foo < Formula
+        url "https://brew.sh/foo-1.0.tgz"
+
+        livecheck do
+        ^^^^^^^^^^^^ FormulaAudit/LivecheckUrlProvided: A `url` should be provided when `regex` or `strategy` are used.
+          strategy :page_match
+        end
+      end
+    RUBY
   end
 
-  it "reports no offenses when a `url` is specified in the livecheck block" do
+  it "reports no offenses when a `url` and `regex` are specified in the livecheck block" do
     expect_no_offenses(<<~RUBY)
       class Foo < Formula
         url "https://brew.sh/foo-1.0.tgz"
@@ -30,4 +41,17 @@ class Foo < Formula
       end
     RUBY
   end
+
+  it "reports no offenses when a `url` and `strategy` are specified in the livecheck block" do
+    expect_no_offenses(<<~RUBY)
+      class Foo < Formula
+        url "https://brew.sh/foo-1.0.tgz"
+
+        livecheck do
+          url :stable
+          strategy :page_match
+        end
+      end
+    RUBY
+  end
 end