Remove distracted red bar from IDLE for some SyntaxErrors

[aroberge]

Bug report

This may be more an distracting cosmetic issue than a true bug, but it is something that can be fixed easily.

As Raymond Hettinger mentioned a while ago on Twitter (https://twitter.com/raymondh/status/1501700903870468099), when a SyntaxError is raised and the location corresponds to the "\n" at the end of a line, a huge red highlighted region is shown at the end of the invalid line.

For example, type

from math

followed by enter. This red highlighted line will remain on the screen until another SyntaxError occurs.
Unlike cases where a SyntaxError highlights just a few characters pointing at a specific problem, this adds really no informative value, once the user starts entering some new code.

Your environment

I have reproduced this will IDLE on Windows 10 on all Python versions I have installed, from 3.6 to 3.11 inclusively.

Proposed fix

I have been able to fix this on a custom version of IDLE (friendly_idle) by doing the following:

In pyshell.ModifiedInterpreter.transfer_path which sets up some values at the beginning of a new process,
define the following:

self.error_at_end_of_line = False

In pyshell.ModifiedInterpreter.showsyntaxerror, add the last line shown below:

        if lineno == 1:
            pos = "iomark + %d chars" % (offset - 1)
        else:
            pos = "iomark linestart + %d lines + %d chars" % (lineno - 1, offset - 1)
        self.error_at_end_of_line = text.get(pos) == "\n"  # <-- add this

At the beginning of pyshell.ModifiedInterpreter.runsource, add the following:

        if self.error_at_end_of_line:
            self.error_at_end_of_line = False
            self.tkconsole.text.tag_remove("ERROR", "1.0", "end")

If desired, I could do a pull request that would include these changes.

Linked PRs

• gh-93966: Remove the syntax error highlighting in the IDLE Shell on the next statement #157595

[terryjreedy]

The bar is what tk does when one tags '\n'. I don't know of anyway to tag just one space.

In the editor, any edit to the line with the SyntaxError tag dismisses the tag. In Shell, I think waiting until one submits a new statement is fine, but I see no reason not to then dismiss any such tag. So adding the new flag is not needed and the only addition needed is the tag_ remove() without the condition.

I believe that adding the line to def runsource() should make the existing tag_remove in def showsyntaxerror. Try commenting out the latter and testing with a repeat of the syntax error to make sure before removing it.

[aroberge]

Yes, simply adding self.tkconsole.text.tag_remove("ERROR", "1.0", "end") at the beginning of runsource is sufficient. Then, text.tag_remove("ERROR", "1.0", "end") can be removed from showsyntaxerror as it becomes superfluous.

I did not suggest this simpler change as I thought that the original thinking was there was some value in keeping the highlighting when there is only one, or perhaps a few characters highlighted.

[serhiy-storchaka]

#157595 does what was agreed above: the highlighting is removed when the next statement is entered.