[GR-18163] Fix Array#pack with x* to not output null characters

PullRequest: truffleruby/3221

Author: bjfish

CHANGELOG.md

@@ -16,6 +16,7 @@ Bug fixes:
 * `SIGINT`/`Interrupt`/`Ctrl+C` now shows the backtrace and exits as signaled, like CRuby (@eregon).
 * Update patch feature finding to prefer the longest matching load path (#2605, @bjfish).
 * Fix `Hash#{to_s,inspect}` for keys whose `#inspect` return a frozen String (#2613, @eregon).
+* Fix `Array#pack` with `x*` to not output null characters (#2614, @bjfish).
 
 Compatibility:
 

spec/ruby/core/array/pack/x_spec.rb

@@ -30,6 +30,7 @@
 
   it "does not add a NULL byte when passed the '*' modifier" do
     [].pack("x*").should == ""
+    [1, 2].pack("Cx*C").should == "\x01\x02"
   end
 end
 

src/main/java/org/truffleruby/core/format/pack/SimplePackTreeBuilder.java

@@ -235,10 +235,12 @@ public void back(int count) {
 
     @Override
     public void nullByte(int count) {
-        appendNode((sharedTreeBuilder.applyCount(
-                count,
-                WriteByteNodeGen.create(
-                        new LiteralFormatNode((byte) 0)))));
+        if (count != SimplePackParser.COUNT_STAR) {
+            appendNode((sharedTreeBuilder.applyCount(
+                    count,
+                    WriteByteNodeGen.create(
+                            new LiteralFormatNode((byte) 0)))));
+        }
     }
 
     @Override