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# frozen_string_literal: true
# Monkey patch of Enumerator#next to get better stack traces
# when an error is raised from within a Fiber.
# https://bugs.ruby-lang.org/issues/16829
module EnumeratorNextPatch
%w(next next_values peek peek_values).each do |name|
define_method(name) do |*args|
gitlab_patch_backtrace_marker { super(*args) }
rescue Exception => err # rubocop: disable Lint/RescueException
err.set_backtrace(err.backtrace + caller) unless
has_gitlab_patch_backtrace_marker?(err.backtrace) && backtrace_matches_caller?(err.backtrace)
raise
end
end
private
def gitlab_patch_backtrace_marker
yield
end
# This function tells us whether the exception was generated by #next itself or by something in
# the Fiber that it invokes. If it's generated by #next, then the backtrace will have
# #gitlab_patch_backtrace_marker as the third item down the trace (since
# #gitlab_patch_backtrace_marker calls a block, which in turn calls #next.) If it's generated
# by the Fiber that #next invokes, then it won't contain this marker.
def has_gitlab_patch_backtrace_marker?(backtrace)
match = %r(^(.*):[0-9]+:in `gitlab_patch_backtrace_marker'$).match(backtrace[2])
!!match && match[1] == __FILE__
end
# This function makes sure that the rest of the stack trace matches in order to avoid missing
# an exception that was generated by calling #next on another Enumerator inside the Fiber.
# This might miss some *very* contrived scenarios involving recursion, but exceptions don't
# provide Fiber information, so it's the best we can do.
def backtrace_matches_caller?(backtrace)
backtrace[3..] == caller[1..]
end
end
Enumerator.prepend(EnumeratorNextPatch)
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