test(melange): show crash when melange.emit depends on transitive PPX

[anmonteiro]

• This is a regression introduced in test(melange): demonstrate melange.emit doesn't respect -p #7849

[anmonteiro]

I'm not sure why the error is fixed by not pushing the stack frames.

For reference, the error is:

  Description:
    ("Implicit_output.produce called without any handler in dynamic scope",
    { type = "Rules" })
  Raised at Stdune__Code_error.raise in file
    "otherlibs/stdune/src/code_error.ml", line 11, characters 30-62
  Called from Fiber__Core.O.(>>|).(fun) in file "otherlibs/fiber/src/core.ml",
    line 250, characters 36-41

    ...

  -> required by ("<unnamed>", ())
  -> required by ("<unnamed>", ())
  -> required by ("<unnamed>", ())
  -> required by ("<unnamed>", ())
  -> required by
     ("load-dir", In_build_dir "default/lib/test/dist/lib/test/.dist.mobjs")
  -> required by
     ("build-file",
     In_build_dir "default/lib/test/dist/lib/test/.dist.mobjs/melange.js")
  -> required by ("<unnamed>", ())
  -> required by
     ("build-alias", { dir = In_build_dir "default/lib/test"; name = "all" })
  -> required by ("<unnamed>", ())
  -> required by
     ("build-alias", { dir = In_build_dir "default"; name = "default" })
  -> required by ("toplevel", ())

[rgrinberg]

Hmm, i think we need to go to the old approach of shoving the backtrace inside the Action_builder.fail

[anmonteiro]

Pushed a new version that exposes Report_error.format_memo_stack and uses it to format the error stack trace.

[anmonteiro]

@rgrinberg could you give this one a look when you have a chance?