mruby-rr is an exprimental Time Traveling Debugger for mruby that based on Mozilla's rr. mruby-rr supports record and replay of mruby program execution. We can record the tough bug using mruby-rr for just once. Afterwards we can playback the execution as many times as we want. mruby-rr can also do time traveling operations like reverse-next and evaluating expressions.

1. install rr https://rr-project.org
2. Compile mruby with following settings in build_config.rb

MRuby::Build.new do |conf|
...
  enable_debug # Enable debug symbols
  conf.cc.defines = %w(MRB_ENABLE_DEBUG_HOOK) # Enable debug hook
  conf.gem :git => 'https://github.com/johnlinvc/mruby-rr.git' # Install mruby-rr tracepoint
...
end

3. clone this project

./mruby-rr record program.rb to record the execution of the mruby program. Current implementation requires typing mrdb command run and Control-d to leave the mrdb in mruby-rr.

./mruby-rr replay to replay the last recorded session. Current implementation require to do a break and continue before others commands can work. Use Control + d to leave the current debug session.

break "filename" line : Break at the line of the specified file. For example, 'mrb-break "hello.rb" 3'. notice the double quote around the filename.

continue: Continue execution until reaching the next breakpoint.

next: Continue execution until reaching the next line in the same file.

reverse-continue: Continue execution in reverse order until reaching the previous breakpoint.

reverse-next: Continue execution in reverse order until reaching the previous line in the same file.

print "mruby expression": Execute the mruby expression in current context. All the side effects like variable mutation will be discarded after execution continues. For example, mrb-print "p a" prints the value of a.

info break: List current breakpoints

list: Show the file contents around current line.

restart: Replay the recorded session from the beginning.