resource: automatic determine mirrors for PyPI resources

Library/Homebrew/env_config.rb

@@ -474,5 +474,12 @@ def cask_opts_quarantine?
     def cask_opts_require_sha?
       cask_opts.include?("--require-sha")
     end
+
+    sig { returns(T::Array[String]) }
+    def pip_index_urls
+      "#{ENV.fetch("PIP_INDEX_URL", "")} #{ENV.fetch("PIP_EXTRA_INDEX_URL", "")}".split.map do |url|
+        url.chomp("/")
+      end.uniq
+    end
   end
 end

Library/Homebrew/resource.rb

@@ -294,6 +294,14 @@ def determine_mirror_urls
       end
     end
 
+    # PyPI (PEP 503): https://peps.python.org/pep-0503
+    if url.start_with?("https://files.pythonhosted.org/packages")
+      extra_urls = Homebrew::EnvConfig.pip_index_urls.map do |pip_index_url|
+        url.sub("https://files.pythonhosted.org", pip_index_url.chomp("/simple"))
+      end
+      urls = extra_urls + urls
+    end
+
     urls
   end
 

bin/brew

@@ -129,6 +129,7 @@ PATH="/usr/bin:/bin:/usr/sbin:/sbin"
 FILTERED_ENV=()
 ENV_VAR_NAMES=(
   HOME SHELL PATH TERM TERMINFO TERMINFO_DIRS COLUMNS DISPLAY LOGNAME USER CI SSH_AUTH_SOCK SUDO_ASKPASS
+  PIP_INDEX_URL PIP_EXTRA_INDEX_URL
   http_proxy https_proxy ftp_proxy no_proxy all_proxy HTTPS_PROXY FTP_PROXY ALL_PROXY
   GITHUB_ACTIONS GITHUB_WORKSPACE GITHUB_ACTIONS_HOMEBREW_SELF_HOSTED
   GITHUB_REPOSITORY GITHUB_RUN_ID GITHUB_RUN_ATTEMPT GITHUB_SHA GITHUB_HEAD_REF GITHUB_BASE_REF GITHUB_REF