Modify env in Utils::Curl instead of bin/brew

Library/Homebrew/test/utils/curl_spec.rb

@@ -410,6 +410,20 @@
     end
   end
 
+  describe "extra_curl_args" do
+    it "doesn't set CURL_HOME when HOMEBREW_CURLRC is unset" do
+      expect(extra_curl_env).not_to include("CURL_HOME")
+    end
+
+    it "sets CURL_HOME when HOMEBREW_CURLRC and HOMEBREW_CURL_HOME are set" do
+      ENV["HOMEBREW_CURLRC"] = "1"
+      ENV["HOMEBREW_CURL_HOME"] = "/tmp/curl_home"
+      expect(extra_curl_env).to include("CURL_HOME" => "/tmp/curl_home")
+    ensure
+      ENV["HOMEBREW_CURLRC"] = nil
+    end
+  end
+
   describe "url_protected_by_cloudflare?" do
     it "returns `true` when a URL is protected by Cloudflare" do
       expect(url_protected_by_cloudflare?(details[:cloudflare][:single_cookie])).to be(true)

Library/Homebrew/utils/curl.rb

@@ -130,7 +130,7 @@ def curl_with_workarounds(
 
       result = system_command curl_executable(use_homebrew_curl: use_homebrew_curl),
                               args:    curl_args(*args, **options),
-                              env:     env,
+                              env:     env.merge(extra_curl_env),
                               timeout: end_time&.remaining,
                               **command_options
 
@@ -557,6 +557,17 @@ def curl_response_follow_redirections(responses, base_url)
 
     private
 
+    # Determines extra environment variables to set based on global configuration
+    # @return [Hash] A hash containing the environment variables to set for `curl`
+    def extra_curl_env
+      env = {}
+      if Homebrew::EnvConfig.curlrc? && !Homebrew::EnvConfig.curl_home.nil?
+        env["CURL_HOME"] = Homebrew::EnvConfig.curl_home
+      end
+
+      env
+    end
+
     # Parses HTTP response text from `curl` output into a hash containing the
     # information from the status line (status code and, optionally,
     # descriptive text) and headers.

bin/brew

@@ -205,13 +205,6 @@ ENV_VAR_NAMES=(
   HOME SHELL PATH TERM TERMINFO TERMINFO_DIRS COLUMNS DISPLAY LOGNAME USER CI SSH_AUTH_SOCK SUDO_ASKPASS
   http_proxy https_proxy ftp_proxy no_proxy all_proxy HTTPS_PROXY FTP_PROXY ALL_PROXY
 )
-
-# When using .curlrc is permitted, also allow setting CURL_HOME
-if [[ -n "${HOMEBREW_CURLRC-}" && -n "${HOMEBREW_CURL_HOME-}" ]]
-then
-  FILTERED_ENV+=("CURL_HOME=${HOMEBREW_CURL_HOME}")
-fi
-
 # Filter all but the specific variables.
 for VAR in "${ENV_VAR_NAMES[@]}" "${!HOMEBREW_@}"
 do