Print out warnings associated with local variables

[JaroslavTulach]

Pull Request Description

Fixes #9749 by:

• Adding fn option to enso-debug-server instrument - eb3b76e
• Print warnings (if any) to stderr - 4fda04b
• Improving output of :list to print out warnings - dbe3c45
• Print errors to stderr - 1312546
• Exiting on DataflowError - 2cc7ef5 and e6fbf73
• Using all of that inside of runner/*Main - 7df58ef

The core of the change is in instrumentation that wraps the main method and at its end checks for warnings or errors among local variables. When an error is found, it wraps the original return value of main with a proxy that delegates to the original value, but also pretends to be exit exception with exit code 173. That one is detected in Main launcher to exit the process with exit code 173.

Important Notes

As a side-effect of this change, one can request an invocation of REPL at the end of any method just by providing a property to the VM:

$ enso --vm.D=polyglot.enso-debug-server.method-break-point=err_test.main --run err_test.enso --repl

stops at the end of main method of err_test.enso file.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[JaroslavTulach]

After 63d1560 one can create following warn_test.enso file:

from Standard.Base import all

main =
    j = 1
    d = Warning.attach "Doubled number" 2
    t = j + d
    v = [j, d, t]
    v

and then execute:

$ ./built-distribution/enso-engine-*/enso-*/bin/enso \
  --run warn_test.enso \
  -vm.D=polyglot.enso-debug-server.fn=warn_test.main \
  --repl
> :list
d = WithWarnings{2 has 1 warnings}
t = WithWarnings{3 has 1 warnings}
v = [1, 2, 3]
j = 1

e.g. by using the polyglot.enso-debug-server.fn one can trigger the standard REPL without having to specify Debug.breakpoint in the source code and some of the warnings are somehow displayed.

[JaroslavTulach]

With dbe3c45 the output of the :list command for the previously shown warn_test.enso program is:

> :list
d = 2
  ! Doubled number
t = 3
  ! Doubled number
v = [1, 2, 3]
  ! Error 1 Doubled number
  ! Error 2 Doubled number
j = 1
> 

OK, @jdunkerley?

[JaroslavTulach]

The last improvement to startup we got was because of disabling the debug server by default:

this PR basically enables the same debug server instrument (but without the message transfer), so let's check what is the affect on startup with followin bench run. Probably there is some slowdown in _Startup_ benchmark - verifying with another run.

[radeusgd]

The warnings printed upon :list look great, I think that will be quite helpful.

In the REPL, we also print the value returned from a function. Will the warnings show up there as well??? If not, could we please make them?

E.g.

> Warning.attach 2+2 3+3
>>> 6
    ! 4

That would be super helpful and would give immediate feedback for the warnings in REPL without having to check :list every time.

---

I'm a bit concerned about the changes to semantics of error propagation - I need to understand it further.

[JaroslavTulach]

APIs being introduced by this PR:

• exit code 173
• property to select method to stop at
• format of the printed (to stderr) out warnings and error

Changing these APIs will have a visible effect on users of Enso. Please review with care.

[radeusgd]

Looks good, thanks for addressing the comments

[radeusgd]

In the REPL, we also print the value returned from a function. Will the warnings show up there as well??? If not, could we please make them?

E.g.

> Warning.attach 2+2 3+3
>>> 6
    ! 4

That would be super helpful and would give immediate feedback for the warnings in REPL without having to check :list every time.

Just checked and the warnings are not printed on REPL values. Any chance we could get that? Not necessarily as part of this PR. Shall I create a ticket?

[radeusgd]

Just checked and the warnings are not printed on REPL values. Any chance we could get that? Not necessarily as part of this PR. Shall I create a ticket?

Ah, I guess the problem is that = actually return Nothing and not the assigned value, and the warning is associated with that value. So hmm, maybe it's more problematic than I thought. So maybe ignore my suggestion for now, as the REPL isn't a big priority anywhere.

[JaroslavTulach]

In the REPL, we also print the value returned from a function. Will the warnings show up there as well??? If not, could we please make them?
E.g.

> Warning.attach 2+2 3+3
>>> 6
    ! 4

Just checked and the warnings are not printed on REPL values. Any chance we could get that? Not necessarily as part of this PR. Shall I create a ticket?

I am just too sloooow this afternoon. Done in 49d535b

[hubertp]

Looks alright but please rename FN

[hubertp]

shouldn't this print to stderr?

[JaroslavTulach]

Good question. However the code has been there before this PR - so the answer doesn't need to be provided by this PR.

[JaroslavTulach]

Looks alright but please rename FN

Renamed to METHOD_BREAKPOINT.