Improve Ripper compatibiliy layer and emit :on_embexpr_end for unmatched closing brace

lib/prism/lex_compat.rb

@@ -846,6 +846,8 @@ def post_process_tokens(tokens, source, data_loc, bom, eof_token)
 
       cache = Translation::Ripper::LineAndColumnCache.new(source)
 
+      brace_depth = 0
+
       tokens.each do |token|
         # Skip missing heredoc ends.
         next if token[1] == :on_heredoc_end && token[2] == ""
@@ -854,6 +856,24 @@ def post_process_tokens(tokens, source, data_loc, bom, eof_token)
         line, column = token[0]
         start_offset = source.byte_offset(line, column)
 
+        # Replicate a Ripper quirk where exactly the first unmatched closing
+        # brace is emitted as :on_embexpr_end, and any subsequent ones are :on_rbrace.
+        #
+        # Track brace nesting depth to handle unmatched closing braces.
+        # :on_lbrace (hashes/blocks), :on_embexpr_beg (interpolation), and :on_tlambeg (lambdas)
+        # all start a curly brace context balanced by a closing }.
+        case token[1]
+        when :on_lbrace, :on_embexpr_beg, :on_tlambeg
+          brace_depth += 1
+        when :on_rbrace
+          if brace_depth == 0
+            token = [token[0], :on_embexpr_end, token[2], prev_token_state]
+          end
+          brace_depth -= 1
+        when :on_embexpr_end
+          brace_depth -= 1
+        end
+
         # Ripper reports columns on line 1 without counting the BOM, so we
         # adjust to get the real offset
         start_offset += 3 if line == 1 && bom

test/prism/ruby/ripper_test.rb

@@ -219,6 +219,14 @@ def test_lex_invalid_syntax
       assert_equal(Ripper.lex('if;)'), Translation::Ripper.lex('if;)'))
     end
 
+    def test_unmatched_braces
+      assert_ripper_lex("} }")
+      assert_ripper_lex("{ b: 1 } }")
+      assert_ripper_lex("[].each { } }")
+      assert_ripper_lex('"#{1}" }')
+      assert_ripper_lex("-> { } }")
+    end
+
     def test_tokenize
       source = "foo;1;BAZ"
       assert_equal(Ripper.tokenize(source), Translation::Ripper.tokenize(source))