Raise on ruby 2.7 deprecation warnings

Break tests if we introduce any ruby 2.7 deprecation warnings.

.github/workflows/ci.yml

@@ -88,6 +88,7 @@ jobs:
         run: |
           docker run \
             --env "CI=true" \
+            --env "RAISE_ON_WARNINGS=true" \
             --env "DEPENDABOT_TEST_ACCESS_TOKEN=${{ secrets.GITHUB_TOKEN }}" \
             --env "SUITE_NAME=${{ matrix.suite.name }}" \
             --rm "$CORE_CI_IMAGE" bash -c \

common/spec/spec_helper.rb

@@ -10,6 +10,7 @@
 
 require "dependabot/dependency_file"
 require_relative "dummy_package_manager/dummy"
+require_relative "warning_monkey_patch"
 
 if ENV["COVERAGE"]
   SimpleCov::Formatter::Console.output_style = "block"

common/spec/warning_monkey_patch.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+ALLOW_PATTERNS = [
+  # Ignore parser warnings for ruby 2.7 minor version mismatches
+  # TODO: Fix these by upgrading to ruby 2.7.3 (requires ubuntu upgrade)
+  %r{parser/current is loading parser/ruby27},
+  /2.7.\d-compliant syntax, but you are running 2.7.\d/,
+  %r{whitequark/parser}
+].freeze
+
+# Called internally by Ruby for all warnings
+module Warning
+  def self.warn(message)
+    $stderr.print(message)
+
+    raise message if ENV["RAISE_ON_WARNINGS"].to_s == "true" && ALLOW_PATTERNS.none? { |pattern| pattern =~ message }
+
+    return unless ENV["DEBUG_WARNINGS"]
+
+    warn caller
+    $stderr.puts
+  end
+end