Truffleruby: "Rescuing" failed `require` doesn't work as expected

[palkan]

Context

In Ruby Next, I want to be able to "catch" syntax errors occurred while requiring a file to transpile this file on-the-fly and evaluate (ruby -ruby-next some_ruby_file_with_edge_syntax.rb, see uby-next.rb).

Problem

To make this work I use at_exit hook and check whether $! is a SyntaxError, try to re-load the transpiled version and call exit!(0) if that works.

In TruffleRuby, at_exit block is called, we can access the exception via $! but calling exit!(0) has no effect—the exit status is still >0.
Also, the exception message is printed as well (in MRI, if we "caught" the exception, there is no err output).

Here is the minimal reproduction: https://github.com/palkan/ruby-compatibility-examples/blob/master/examples/at_exit_rescue.rb

And here is the failing CI build with the output: https://github.com/palkan/ruby-compatibility-examples/runs/864905161?check_suite_focus=true

P.S. There you can find how MRI and JRuby handle this. (JRuby sets the correct exit status but still prints the error message).

/cc @ssnickolay

[chrisseaton]

try to re-load the transpiled version and call exit!(0) if that works.

I don't understand this bit - if you can successfully transpile and reload... you then exit? Why don't you then keep going with the transpiled code?

[eregon]

The exit!(0) is a way to suppress the original SyntaxError, which would otherwise be shown.

[chrisseaton]

But the exit!(0) doesn't actually cause the process to exit? I thought after transpiling you'd want to continue?

[eregon]

There is an eval() and then it exits: https://github.com/ruby-next/ruby-next/blob/d3d075fa60b3da82d1f949ca4ad5ec2ca5b2ae96/lib/uby-next.rb#L66-L67

[ssnickolay]

I've tested locally and didn't see the error (note: the TR build includes not released fix for refine_include_super.rb):

p.s. for JRuby I see described behaviour (print error stack trace but correct exit status)

SyntaxError: /Users/ssnickolay/Projects/oss/ruby-compatibility-examples/support/invalid_syntax.rb:1: syntax error, unexpected '}'
invalid_hash = {x: }
                   ^
           require at org/jruby/RubyKernel.java:974
  require_relative at org/jruby/RubyKernel.java:1002
            <main> at examples/at_exit_rescue.rb:8
We catched it!

[eregon]

@ssnickolay https://github.com/palkan/ruby-compatibility-examples/blob/master/run-all.rb assumes you're running with the ruby to test in PATH.

I can reproduce on master, I'm working on a fix.

[ssnickolay]

assumes you're running with the ruby to test in PATH.

Yeah, I didn't read carefully run-all.rb

[eregon]

Fixed in e9dce4a8d216454de7273fb3780a17c18a811574, thanks for the report and reproducer!

[palkan]

Sorry, but I broke it again 🙃

Here is a bit more complex example: https://github.com/palkan/ruby-compatibility-examples/commit/f92c69c0366e1c3b656d2ef7aead4a1a79bb5c0b (and the corresponding CI build: https://github.com/palkan/ruby-compatibility-examples/runs/884982846?check_suite_focus=true).

This time, we define at_exit hook in the required file (-r), not the one we execute. That could be the reason.

P.S. I can open a new issue if you'd like.

[eregon]

I'll take a look, thanks for the reproducer :smiley:

Run examples/cli_require_at_exit.rb:  💥 truffleruby:
examples/../support/typo.rb:1: syntax error, unexpected tRCURLY (SyntaxError)
examples/cli_require_at_exit.rb:2:in `<main>': Assertion failed:  (RuntimeError)

[eregon]

It seems the issue in that case is that the SyntaxError happens in the "main script file" and so before TruffleRuby enters TopLevelRaiseHandler.

[eregon]

That example is fixed with efa38abf2be8e55900f92259c56f90cda8f896bf.