Preserve extra RUBYOPT in precompile hook

Author: justin808

react_on_rails/lib/generators/react_on_rails/templates/base/base/bin/shakapacker-precompile-hook

@@ -55,15 +55,19 @@ def utf8_subprocess_env(extra = {})
   return extra.dup unless [Encoding::US_ASCII, Encoding::ASCII_8BIT].include?(Encoding.find("locale"))
 
   # Merge the UTF-8 widening last so it is authoritative: a caller-supplied key cannot accidentally
-  # drop the pin (callers pass functional flags like REACT_ON_RAILS_SKIP_VALIDATION here, not locale
-  # vars). The pin is derived from the parent's own RUBYOPT, so existing non-encoding flags survive.
+  # drop the pin. The pin is derived from the parent's RUBYOPT plus any caller-supplied RUBYOPT, so
+  # existing non-encoding flags survive and explicit per-call flags are preserved.
   extra.merge(
     "LANG" => "C.UTF-8",
     "LC_ALL" => "C.UTF-8",
-    "RUBYOPT" => utf8_widened_rubyopt(ENV.fetch("RUBYOPT", ""))
+    "RUBYOPT" => utf8_widened_rubyopt(subprocess_rubyopt(extra))
   )
 end
 
+def subprocess_rubyopt(extra)
+  [ENV.fetch("RUBYOPT", nil), extra["RUBYOPT"]].compact.join(" ")
+end
+
 # Prepend a UTF-8 external-encoding pin to RUBYOPT for the C/POSIX widening case — a portable
 # fallback for systems where the C.UTF-8 locale is not installed and LANG/LC_ALL alone would not
 # take effect. If RUBYOPT already pins an encoding it is an explicit, deliberate request that we

react_on_rails/spec/react_on_rails/shakapacker_precompile_hook_shared_spec.rb

@@ -283,11 +283,13 @@ def bad_overrides.each_key
         end
       end
 
-      it "keeps the UTF-8 pin even when a caller passes RUBYOPT in extra" do
-        # The widening is applied last (authoritative), so an extra RUBYOPT key cannot silently drop
-        # the pin and leave the child on US-ASCII.
+      it "keeps the UTF-8 pin while preserving caller-supplied RUBYOPT in extra" do
+        # The widening is applied last (authoritative), and the caller's extra RUBYOPT is folded
+        # into the widened value rather than silently dropping either set of flags.
         with_locale_encoding(Encoding::US_ASCII) do
           with_env("RUBYOPT" => "-W0") do
+            expect(utf8_subprocess_env("RUBYOPT" => "-rbundler/setup")["RUBYOPT"])
+              .to eq("-EUTF-8 -W0 -rbundler/setup")
             expect(utf8_subprocess_env("RUBYOPT" => nil)["RUBYOPT"]).to eq("-EUTF-8 -W0")
           end
         end

react_on_rails/spec/support/shakapacker_precompile_hook_shared.rb

@@ -61,15 +61,19 @@ def utf8_subprocess_env(extra = {})
   return extra.dup unless [Encoding::US_ASCII, Encoding::ASCII_8BIT].include?(Encoding.find("locale"))
 
   # Merge the UTF-8 widening last so it is authoritative: a caller-supplied key cannot accidentally
-  # drop the pin (callers pass functional flags like REACT_ON_RAILS_SKIP_VALIDATION here, not locale
-  # vars). The pin is derived from the parent's own RUBYOPT, so existing non-encoding flags survive.
+  # drop the pin. The pin is derived from the parent's RUBYOPT plus any caller-supplied RUBYOPT, so
+  # existing non-encoding flags survive and explicit per-call flags are preserved.
   extra.merge(
     "LANG" => "C.UTF-8",
     "LC_ALL" => "C.UTF-8",
-    "RUBYOPT" => utf8_widened_rubyopt(ENV.fetch("RUBYOPT", ""))
+    "RUBYOPT" => utf8_widened_rubyopt(subprocess_rubyopt(extra))
   )
 end
 
+def subprocess_rubyopt(extra)
+  [ENV.fetch("RUBYOPT", nil), extra["RUBYOPT"]].compact.join(" ")
+end
+
 # Prepend a UTF-8 external-encoding pin to RUBYOPT for the C/POSIX widening case — a portable
 # fallback for systems where the C.UTF-8 locale is not installed and LANG/LC_ALL alone would not
 # take effect. If RUBYOPT already pins an encoding it is an explicit, deliberate request that we