Bug: Syntax error handling in console.html

[hoodmane]

Syntax errors in console.html are not printed immediately, only after the next command is submitted. E.g., type 1+<ENTER> into console.html.

I think this was introduced in #1125. I investigated but I can't figure out why it's happening. Any ideas @casatir?

[casatir]

Thanks @hoodmane for catching this. I'll investigate.

[casatir]

I am pretty sure it was working after #1155.

[hoodmane]

I will check (unfortunately, #1155 was before the emscripten update was merged so I have to rebuild everything).

[casatir]

Doing

pyconsole.stderr_callback = $.terminal.active().error

in JS console makes it work (with newline of course).

[casatir]

So it seems related to newline stuff since it works with

pyconsole.stderr_callback = $.terminal.active().echo

but not with

pyconsole.stderr_callback = (s) => $.terminal.active().echo(s, {newline : false})

[hoodmane]

pyconsole.stderr_callback = $.terminal.active().error

Does that prevent sys.except_hook from happening? I would guess that doing that would cause most errors to be printed twice?

[casatir]

This is code.py 's InteractiveConsole that manage this. sys.exepthook seems to not be called in our case since https://github.com/python/cpython/blob/f82578ace103ec977cec3424b20e0b5f19cf720e/Lib/code.py#L123

[casatir]

I suspect something like syntax error occurs when terminal is paused which echo_newline.js may dislike.

[hoodmane]

Okay it definitely does work after #1155.

[casatir]

I think I got it. In console.html, we continuously set the prompt:

async function interpreter(command) {
    // multiline should be splitted (usefull when pasting)
    term.pause();
    for( const c of command.split('\n') ) {
        const prompt = pyconsole.push(c) ? ps2 : ps1;
        term.set_prompt(prompt);
        await pyconsole.run_complete;
    }
    term.resume();
}

which disturb echo_newline.js since it also set the prompt...

[hoodmane]

echo_newline.js uses a really awful hack. I might try to make an improvement upstream.

[casatir]

Commenting our set_prompt makes it work (but disable ps2...) showing that this might be this.

[hoodmane]

It's weird actually: echo_newline.js makes a copy of the original term.set_prompt as if it's planning to monkey patch it:

        term.__set_prompt = term.set_prompt;

https://github.com/jcubic/jquery.terminal/blob/9c28d597e8295a5bd282030256a9fe1b50a371c1/js/echo_newline.js#L96

but then it never does the monkey patch. It would work much better if it monkey patched set_prompt.

[casatir]

I remember I've seen this when trying to make echo_newline.js work for #1141.

[casatir]

Partially reverting #1274 restoring my term.echo_no_newline function plus

pyconsole.stdout_callback = term.echo_no_newline;
pyconsole.stderr_callback = (s) => term.echo_no_newline(`[[;red;]${$.terminal.escape_brackets(s)}\u200B]`);

makes it work without loading echo_newline.js.

[casatir]

I can submit a PR with this correction or we can wait for an upstream fix. WDYT?

[hoodmane]

I opened a PR: jcubic/jquery.terminal#652

[casatir]

The why it happens only for syntax errors (and not runtime errors) can be understood with this three lines:

    const prompt = pyconsole.push(c) ? ps2 : ps1;
    term.set_prompt(prompt);
    await pyconsole.run_complete;

Execution steps for runtime errors (or even code exec without any error) are:

1. pyconsole.push(c) returns false (code is not yet executed)
2. prompt is set to >>>
3. code is executed (via the run_complete promise), error is printed to stderr
4. JQuery Terminal shows it by setting the prompt.

While for syntax error, we have:

1. pyconsole.push(c) prints syntax error to stderr (and return false)
2. JQuery Terminal shows it by setting the prompt
3. prompt is erased by our call to set_prompt
4. run_complete is a dummy promise so the await has no effect.

[hoodmane]

So as an update, my jquery terminal PR has been reviewed and has received positive feedback so it will probably be merged soon.
It should make the behavior of echo / error with newline : false completely consistent with the behavior with newline : true and fix the various issues we've had with it (any interaction with set_prompt has been removed, term.error will get the color right, etc).
jcubic/jquery.terminal#654

It looks like releases of jquery.terminal are fairly frequent (about one every two weeks recently) and the most recent release was 14 days ago so it probably won't be too long before this change is included into a release.

[hoodmane]

Closed by #1480. jquery.terminal just released a version with my PR included today!