Instead of changing the visibility of this particular method, what about calling it adjustMaxSteps or updateMaxSteps? This would imply the max steps gets adjusted or updated instead of merely setting it, could in theory even add some hooks in there if needed.

Instead of doing this change, I think this problem could be solved in two different ways as explained in https://symfony.com/doc/current/components/console/helpers/progressbar.html:

1. Don't use a progress bar with a defined number of steps:

If you don't know the number of steps in advance, just omit the
steps argument when creating the ProgressBar instance:

$progress = new ProgressBar($output);

2. Regress the progress bar when more work is found, passing a negative number to advance():

$progress->advance(-2);

@javiereguiluz what i know (last tried) you have to put the number at __construct or at start. And if the Progress does not know the max amount at the current time, its very hard to know the aprox. time left.

@dominikzogg I'm not sure I follow you. The number of steps in an optional argument in the ProgressBar constructor: https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Console/Helper/ProgressBar.php#L57

@javiereguiluz yes, also on https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Console/Helper/ProgressBar.php#L339, but if its missing on both you get an Exception on a advance, at least in my tries. But even if it would work, you explanation would not solve the issue that i want a max, but a changeable onces.

Agree with @javiereguiluz here. Calling advance() while omitting the $maxSteps argument in both constructor and start() call should work. Please retry and, if it doesn't work for you, consider providing enough code to reproduce the issue.

@chalasr even if it does i would have no calculation, or wrong if set initial, if there is no max set

I'm not completely sure, but in some Symfony apps I've seen those kind of progress bars "overflow" and start over from the beginning. This is the same behavior as most operating systems when displaying what they call "Indeterminate Progress Indicators".

We should check if this is indeed working like that.

Outside a class we can not access any private function.
But we can change the access specifier in the following way.

$class = new \ReflectionClass('\Symfony\Component\Console\Helper\ProgressBar');
$method = $class->getMethod('setMaxSteps');
$method->setAccessible(true);
$progress = new ProgressBar($output, 50);
$method->invokeArgs($progress, array(100));

Please let me know if it helps you or not.

Yes, but the main question here I think is whether we want to support this feature or not. I'm 👎 because it's uncommon/unused in other software applications, such as operating systems. Usually you only have two kinds of progress bars: 1) you know the total in advance; 2) you don't know the total.

In the 2) case, the progress bar simply cycles or shows an undetermined animation. But this proposal asks for a third case: "I know the total in advance, but it can change, so I want to update it".

@javiereguiluz Yes you can update the max steps when it is needed to be changed due to any situation. This can be done by change of accessibility outside the class.
Based on this logic we can write test cases of private methods.

I also have a case for that. I'm downloading and repackaging some data. I know the upper bound beforehand, however the real max is known after some status files are downloaded and compared against the locally cached ones. Having a totally borked ETA and max count doesn't look nice.

Please see #26449

Issue with overflowing/starting over of a bar is moot when you realize you can set custom format for ProgressBar. In my case I don't show %bar% at all, but other information, like percentage, time left, etc