Json: Add #parse_json method

This setup mimics the `#parse_xml` method that was implemented in the
`Xml` strategy. Isolating the parsing code means that other strategies
can take only what they need from `Json` (i.e., it's not required for
them to use `Json#find_versions`).

Library/Homebrew/livecheck/strategy/json.rb

@@ -46,6 +46,19 @@ module Homebrew
           URL_MATCH_REGEX.match?(url)
         end
 
+        # Parses JSON text and returns the parsed data.
+        # @param content [String] the JSON text to parse
+        sig { params(content: String).returns(T.untyped) }
+        def self.parse_json(content)
+          require "json"
+
+          begin
+            JSON.parse(content)
+          rescue JSON::ParserError
+            raise "Content could not be parsed as JSON."
+          end
+        end
+
         # Parses JSON 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 JSON data).
@@ -63,12 +76,8 @@ module Homebrew
         def self.versions_from_content(content, regex = nil, &block)
           return [] if content.blank? || block.blank?
 
-          require "json"
+          json = parse_json(content)
-          json = begin
+          return [] if json.blank?
-            JSON.parse(content)
-          rescue JSON::ParserError
-            raise "Content could not be parsed as JSON."
-          end
 
           block_return_value = if regex.present?
             yield(json, regex)

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

@@ -74,6 +74,12 @@ describe Homebrew::Livecheck::Strategy::Json do
     end
   end
 
+  describe "::parse_json" do
+    it "returns an object when given valid content" do
+      expect(json.parse_json(content_simple)).to be_an_instance_of(Hash)
+    end
+  end
+
   describe "::versions_from_content" do
     it "returns an empty array when given a block but content is blank" do
       expect(json.versions_from_content("", regex) { "1.2.3" }).to eq([])