Fix NoMethodError when encoding with invalid: :replace option

khasinski · khasinski · commit d66b260ad5ce · 2026-01-18T19:37:33.000+01:00
When encoding a string with `invalid: :replace` and `replace:` options but without `undef: :replace`, JRuby was incorrectly throwing NoMethodError instead of Encoding::UndefinedConversionError. The bug occurred because when `ecopts` hash exists (due to `:replace` option) but doesn't contain a `:fallback` key, the code was setting `fallbackFunc` to `AREF_FALLBACK` with a nil `fallback` value. When an undefined conversion was encountered, it tried to call `nil.[]()` which raised NoMethodError. The fix adds a check for `!fallback.isNil()` before assigning the fallback function, ensuring that the fallback is only used when explicitly provided. Fixes #9009
diff --git a/core/src/main/java/org/jruby/util/io/EncodingUtils.java b/core/src/main/java/org/jruby/util/io/EncodingUtils.java
@@ -1515,14 +1515,16 @@ public static void transcodeLoop(ThreadContext context, byte[] inBytes, Ptr inPo
 
         if (!ecopts.isNil() && ecopts instanceof RubyHash) {
             fallback = ((RubyHash)ecopts).op_aref(context, asSymbol(context, "fallback"));
-            if (fallback instanceof RubyHash) {
-                fallbackFunc = HASH_FALLBACK;
-            } else if (fallback instanceof RubyProc) { // not quite same check as MRI
-                fallbackFunc = PROC_FALLBACK;
-            } else if (fallback instanceof RubyMethod) { // not quite same check as MRI
-                fallbackFunc = METHOD_FALLBACK;
-            } else {
-                fallbackFunc = AREF_FALLBACK;
+            if (!fallback.isNil()) {
+                if (fallback instanceof RubyHash) {
+                    fallbackFunc = HASH_FALLBACK;
+                } else if (fallback instanceof RubyProc) { // not quite same check as MRI
+                    fallbackFunc = PROC_FALLBACK;
+                } else if (fallback instanceof RubyMethod) { // not quite same check as MRI
+                    fallbackFunc = METHOD_FALLBACK;
+                } else {
+                    fallbackFunc = AREF_FALLBACK;
+                }
             }
         }
 
diff --git a/test/jruby/test_string.rb b/test/jruby/test_string.rb
@@ -274,4 +274,25 @@ def test_strange_printf
     opponent = '41181 jpa:awh'.scan("jpa")[0]
     assert_equal('jpa', sprintf("%s", opponent))
   end
+
+  # GH-9009: encoding with invalid: :replace but without undef: :replace
+  # should raise UndefinedConversionError, not NoMethodError
+  def test_encode_undefined_conversion_with_invalid_replace
+    # "&#256;" (U+0100) is valid UTF-8 but not representable in windows-1252
+    str = "1&#256;&#381;2"
+
+    # With only invalid: :replace (no undef:), should raise UndefinedConversionError
+    assert_raises(Encoding::UndefinedConversionError) do
+      str.encode("windows-1252", invalid: :replace, replace: "")
+    end
+
+    # With undef: :replace, should replace undefined chars
+    result = str.encode("windows-1252", undef: :replace, replace: "")
+    assert_equal "1\x8E2".force_encoding("windows-1252"), result
+
+    # Without any options, should also raise UndefinedConversionError
+    assert_raises(Encoding::UndefinedConversionError) do
+      str.encode("windows-1252")
+    end
+  end
 end
