[GR-18163] Fix MatchData#[] with negative length argument

PullRequest: truffleruby/3737

Author: andrykonchin

CHANGELOG.md

@@ -44,6 +44,7 @@ Bug fixes:
 * Fix `StringIO#write` to transcode strings with encodings that don't match the `StringIO`'s `external_encoding`. (#2839, @flavorjones)
 * Fix processing of proc rest arguments located at the beginning if there are no actual arguments (#2921, @andrykonchin).
 * Fix `Monitor#exit` to raise `ThreadError` when monitor not owned by the current thread (#2922, @andrykonchin).
+* Fix `MatchData#[]` to support negative `length` argument (#2929, @andrykonchin).
 
 Compatibility:
 

spec/ruby/core/matchdata/element_reference_spec.rb

@@ -22,6 +22,11 @@
 
     # length argument larger than number of match values is capped to match value length
     /(.)(.)(\d+)(\d)/.match("THX1138.")[3, 10].should == %w|113 8|
+
+    /(.)(.)(\d+)(\d)/.match("THX1138.")[3, 0].should == []
+
+    /(.)(.)(\d+)(\d)/.match("THX1138.")[3, -1].should == nil
+    /(.)(.)(\d+)(\d)/.match("THX1138.")[3, -30].should == nil
   end
 
   it "supports ranges [start..end]" do

src/main/java/org/truffleruby/core/array/ArrayNodes.java

@@ -305,9 +305,6 @@ protected Object indexFallback(RubyArray array, Object index, NotProvided length
         protected Object slice(RubyArray array, int start, int length,
                 @Cached ReadSliceNormalizedNode readSliceNode,
                 @Cached ConditionProfile negativeIndexProfile) {
-            if (length < 0) {
-                return nil;
-            }
             if (negativeIndexProfile.profile(start < 0)) {
                 start += array.size;
             }

src/main/java/org/truffleruby/core/regexp/MatchDataNodes.java

@@ -273,11 +273,16 @@ protected Object getIndex(RubyMatchData matchData, int index, NotProvided length
 
         @Specialization
         protected Object getIndex(RubyMatchData matchData, int index, int length,
+                @Cached ConditionProfile negativeLengthProfile,
                 @Cached ConditionProfile normalizedIndexProfile,
                 @Cached ConditionProfile indexOutOfBoundsProfile,
                 @Cached ConditionProfile tooLargeTotalProfile) {
             final Object[] values = getValuesNode.execute(matchData);
 
+            if (negativeLengthProfile.profile(length < 0)) {
+                return nil;
+            }
+
             if (normalizedIndexProfile.profile(index < 0)) {
                 index += values.length;