The behavior of flag arguments differs depending on whether a default is specified

[kzrnm]

When a task argument has type set to "boolean", I expect default=false and leaving the default unset to behave the same way. However, when the default is not specified, None is passed instead of false.

Setting the type to "boolean" makes the resulting argument a flag that if provided will set the value to the boolean opposite of the default value – i.e. true if no default value is given, or false if default = true.

https://poethepoet.natn.io/guides/args_guide.html#task-argument-options

This is inconvenient when performing variable expansion in a cmd task.
When default=true, I would expect the argument to become an empty string when the flag is provided.

https://poethepoet.natn.io/tasks/task_types/cmd.html#parameter-expansion-operators

example

[tool.poe.tasks.boolean]
cmd = """echo \\
var_default=${var} var_plus=${var:+plus} var_minus=${var:-minus} \\
pos_default=${pos} pos_plus=${pos:+plus} pos_minus=${pos:-minus} \\
neg_default=${neg} neg_plus=${neg:+plus} neg_minus=${neg:-minus}
"""
args = [
    { name = "var", type = "boolean" },
    { name = "pos", type = "boolean", default = true },
    { name = "neg", type = "boolean", default = false },
]

$ poe boolean 
Poe => echo '
var_default=' var_plus= var_minus=minus '
pos_default=True' pos_plus=plus pos_minus=True '
neg_default=False' neg_plus=plus neg_minus=False

var_default= var_plus= var_minus=minus 
pos_default=True pos_plus=plus pos_minus=True 
neg_default=False neg_plus=plus neg_minus=False

$ poe boolean --var --pos --neg 
Poe => echo '
var_default=True' var_plus=plus var_minus=True '
pos_default=False' pos_plus=plus pos_minus=False '
neg_default=True' neg_plus=plus neg_minus=True

var_default=True var_plus=plus var_minus=True 
pos_default=False pos_plus=plus pos_minus=False 
neg_default=True neg_plus=plus neg_minus=True

[nat-n]

I see your point that maybe the existing behavior isn't quite right, but since this would be a breaking change I need to take some time to think this through. I think there's some complexity in making sure whatever the solution is makes sense for all scenarios. For example in a script or expr task I would think the default value should normally be False in the python runtime.

[kzrnm]

Added tests for cmd, shell, script, expr, and switch tasks.

I skipped ref tasks for now, as their current behavior does not seem to be clearly defined.