Xml: Add #element_text method

This refactors verbose code in the `Sparkle` strategy where we access
element text into a reusable `Xml#element_text` method, replacing
chained calls like `item.elements["title"]&.text&.strip&.presence`
with `Xml.element_text(item, "title")`.

`#element_text` is only used to retrieve the text of a child element
in the `Sparkle` strategy but it can also retrieve the text from the
provided element if the `child_path` argument is omitted (i.e.,
`Xml.element_text(item)`). This will allow us to also avoid similar
calls like `item.text.strip.presence` in the future.

Library/Homebrew/livecheck/strategy/sparkle.rb

@@ -95,16 +95,16 @@ module Homebrew
               os = enclosure["os"].presence
             end
 
-            title = item.elements["title"]&.text&.strip&.presence
-            link = item.elements["link"]&.text&.strip&.presence
+            title = Xml.element_text(item, "title")
+            link = Xml.element_text(item, "link")
             url ||= link
-            channel = item.elements["channel"]&.text&.strip&.presence
-            release_notes_link = item.elements["releaseNotesLink"]&.text&.strip&.presence
-            short_version ||= item.elements["shortVersionString"]&.text&.strip&.presence
-            version ||= item.elements["version"]&.text&.strip&.presence
+            channel = Xml.element_text(item, "channel")
+            release_notes_link = Xml.element_text(item, "releaseNotesLink")
+            short_version ||= Xml.element_text(item, "shortVersionString")
+            version ||= Xml.element_text(item, "version")
 
             minimum_system_version_text =
-              item.elements["minimumSystemVersion"]&.text&.strip&.gsub(/\A\D+|\D+\z/, "")&.presence
+              Xml.element_text(item, "minimumSystemVersion")&.gsub(/\A\D+|\D+\z/, "")
             if minimum_system_version_text.present?
               minimum_system_version = begin
                 MacOSVersion.new(minimum_system_version_text)
@@ -113,7 +113,7 @@ module Homebrew
               end
             end
 
-            pub_date = item.elements["pubDate"]&.text&.strip&.presence&.then do |date_string|
+            pub_date = Xml.element_text(item, "pubDate")&.then do |date_string|
               Time.parse(date_string)
             rescue ArgumentError
               # Omit unparsable strings (e.g. non-English dates)

Library/Homebrew/livecheck/strategy/xml.rb

@@ -72,6 +72,30 @@ module Homebrew
           end
         end
 
+        # Retrieves the stripped inner text of an `REXML` element. Returns
+        # `nil` if the optional child element doesn't exist or the text is
+        # blank.
+        # @param element [REXML::Element] an `REXML` element to retrieve text
+        #   from, either directly or from a child element
+        # @param child_path [String, nil] the XPath of a child element to
+        #   retrieve text from
+        # @return [String, nil]
+        sig {
+          params(
+            element:    REXML::Element,
+            child_path: T.nilable(String),
+          ).returns(T.nilable(String))
+        }
+        def self.element_text(element, child_path = nil)
+          element = element.get_elements(child_path).first if child_path.present?
+          return if element.nil?
+
+          text = element.text
+          return if text.blank?
+
+          text.strip
+        end
+
         # Parses XML text and identifies versions using a `strategy` block.
         # If a regex is provided, it will be passed as the second argument to
         # the  `strategy` block (after the parsed XML data).

Library/Homebrew/test/livecheck/strategy/xml_spec.rb

@@ -79,6 +79,24 @@ describe Homebrew::Livecheck::Strategy::Xml do
     EOS
   end
 
+  let(:parent_child_text) { { parent: "1.2.3", child: "4.5.6" } }
+  let(:content_parent_child) do
+    # This XML deliberately includes unnecessary whitespace, to ensure that
+    # Xml#element_text properly strips the retrieved text.
+    <<~EOS
+      <?xml version="1.0" encoding="utf-8"?>
+      <elements>
+        <parent>
+          #{parent_child_text[:parent]}
+          <child> #{parent_child_text[:child]} </child>
+        </parent>
+        <blank-parent>
+          <blank-child></blank-child>
+        </blank-parent>
+      </elements>
+    EOS
+  end
+
   let(:content_matches) { ["1.1.2", "1.1.1", "1.1.0", "1.0.3", "1.0.2", "1.0.1", "1.0.0"] }
   let(:content_simple_matches) { ["1.2.3"] }
 
@@ -123,6 +141,29 @@ describe Homebrew::Livecheck::Strategy::Xml do
     end
   end
 
+  describe "::element_text" do
+    let(:parent_child_doc) { xml.parse_xml(content_parent_child) }
+    let(:parent) { parent_child_doc.get_elements("/elements/parent").first }
+    let(:blank_parent) { parent_child_doc.get_elements("/elements/blank-parent").first }
+
+    it "returns the element text if child_name is not provided" do
+      expect(xml.element_text(parent)).to eq(parent_child_text[:parent])
+    end
+
+    it "returns the child element text if child_name is provided" do
+      expect(xml.element_text(parent, "child")).to eq(parent_child_text[:child])
+    end
+
+    it "returns `nil` if the provided child element does not exist" do
+      expect(xml.element_text(parent, "nonexistent")).to be_nil
+    end
+
+    it "returns `nil` if the retrieved text is blank" do
+      expect(xml.element_text(blank_parent)).to be_nil
+      expect(xml.element_text(blank_parent, "blank-child")).to be_nil
+    end
+  end
+
   describe "::versions_from_content" do
     it "returns an empty array when given a block but content is blank" do
       expect(xml.versions_from_content("", regex) { "1.2.3" }).to eq([])