Add audit check to see if both version and checksum changed.

Library/Homebrew/utils/git.rb

@@ -1,3 +1,31 @@
+require "open3"
+
+module Git
+  module_function
+
+  def last_revision_commit_of_file(repo, file, before_commit: nil)
+    args = [before_commit.nil? ? "--skip=1" : before_commit.split("..").first]
+
+    out, = Open3.capture3(
+      HOMEBREW_SHIMS_PATH/"scm/git", "-C", repo,
+      "log", "--oneline", "--max-count=1", *args, "--", file
+    )
+    out.split(" ").first
+  end
+
+  def last_revision_of_file(repo, file, before_commit: nil)
+    relative_file = Pathname(file).relative_path_from(repo)
+
+    commit_hash = last_revision_commit_of_file(repo, file, before_commit: before_commit)
+
+    out, = Open3.capture3(
+      HOMEBREW_SHIMS_PATH/"scm/git", "-C", repo,
+      "show", "#{commit_hash}:#{relative_file}"
+    )
+    out
+  end
+end
+
 module Utils
   def self.git_available?
     return @git if instance_variable_defined?(:@git)