CliRunner prompt input echos twice on Python 2

[davidism]

import click
from click.testing import CliRunner

@click.command()
def cli():
    prompt("value")
    click.echo("done")

runner = CliRunner(echo_stdin=True)
result = runner.invoke(cli, input="test")
print(result.output)

Python 3 output (correct):

value: test
done

Python 2 output:

value: testtest
done

I went back and this appears to be the case in every version since 1.x. The issue seems to be with the visible_input function in CliRunner.isolation. It uses input after that has been wrapped in EchoingStdin. It appears to work in Python 3 due to some weird lookup behavior, but that appears to be an accident. There are no tests for echo_stdin and prompt at the same time.

It didn't show up in the docs because the docs runner overrode isolation with different code that had visible_input pull from the original input and only replaced sys.stdin with the EchoingStdin wrapper, rather than both with the wrapper. While porting the docs runner to pallets-sphinx-themes, I removed that code in favor of simpler subclassing, and noticed that the docs had double input, which led me to discover the full issue.

[bporter125]

Taking a look at this

[bporter125]

So this feature has proven to be a little more complex than it would seem. The reason behind this bug is that the EchoingStdin was not being set up properly for Python 3 as it's intended functionality of printing anything being read is being overrode by io.TextIOWrapper:

if self.echo_stdin:
    input = EchoingStdin(input, bytes_output)	
input = io.TextIOWrapper(input, encoding=self.charset)

So some re-ordering of this can reproduce the double print for 3.7 as well:

input = io.TextIOWrapper(input, encoding=self.charset)
output = io.TextIOWrapper(
    bytes_output, encoding=self.charset)
if self.echo_stdin:
    input = EchoingStdin(input, output)
sys.stdout = output

Then removing the forced print will lead to what I would believe to the the expected functionality:

def visible_input(prompt=None):
    sys.stdout.write(prompt or '')
    val = input.readline().rstrip('\r\n')
-     sys.stdout.write(val + '\n')
+     sys.stdout.write('\n')
    sys.stdout.flush()
    return val

With echo_stdin=True both Python 2 and Python 3 output:

value: test
done

and echo_stdin=False outputs:

value: 
done

Assuming this is the desired functionality, this causes some breaks in unit tests, which to be honest are a little confusing as to what their intentions are based on how they are structured. Further investigation leads to a question of the actual purpose to the echo_stdin flag is, as there are also a hide_input and prompt options available to commands.

[ssbarnea]

This can be closed, support for py2 was removed.

[davidism]

It revealed another issue with the Python 3 implementation.