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Improve echo_via_pager behaviour in face of errors #2775

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merged 1 commit into from
Nov 9, 2024

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stefreak
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@stefreak stefreak commented Sep 7, 2024

fixes #2674 (echo_via_pager with generators leaves terminal in broken state).

  • Add tests that demonstrate the correct behavior of the change. Tests
    should fail without the change.
  • Add or update relevant docs, in the docs folder and in code.
  • Add an entry in CHANGES.rst summarizing the change and linking to the issue.
  • Add .. versionchanged:: entries in any relevant code docs.

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stefreak commented Sep 7, 2024

I've had a look at #350 and the new behaviour sounds like what @amjith describes in the comment #350 (comment)

The fix by @untitaker is still in place (https://github.com/pallets/click/commits/e71f0a040a81e03276b25ab1d1b0671822ab331b) – now in the finally block, which should be even better.

For me this works really well in all the situations I was able to come up with so far.

src/click/_termui_impl.py Outdated Show resolved Hide resolved
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I don't have rights to approve, but this looks like it will do the trick.

@AndreasBackx AndreasBackx added this to the 8.2.0 milestone Oct 26, 2024
@AndreasBackx AndreasBackx mentioned this pull request Oct 26, 2024
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…cho in the generator

This commit fixes pallets#2674 (echo_via_pager with generators leaves terminal in broken state).

When running the program to reproduce the issue (thanks to @0xDEC0DE for providing it in the issue mentioned above!)

```
import click

def output_generator():
    counter = 0
    while True:
        yield "this is a line of output\n"
        if counter == 1024:
            click.echo("kaboom", err=True)
            click.get_current_context().exit(0)
        counter += 1

@click.command
def kaboom():
    click.echo_via_pager(output_generator)

if __name__ == "__main__":
    kaboom()
```

The "kaboom" message will now be visible immediately (the error will cause click to terminate the pager). ZSH and bash will not be in a broken state (tested using bash and zsh on macos).

Further changes:
- Error handling: terminate the pager and close the file descriptors in a finally block
- KeyboardInterrupt: the pager code will not ignore KeyboardInterrupt anymore. This allows the user to
  search for future output of the generator when using less and then aborting the program using ctrl-c.
- tests: improved the echo_via_pager tests by using a named tuple and separate assertions for pager
  output, stderr and stdout. Added additional test cases.
@AndreasBackx AndreasBackx merged commit 3b06e0b into pallets:main Nov 9, 2024
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echo_via_pager with generators leaves terminal in broken state
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