Re: [PATCH v5 11/36] qapi/common.py: Add indent manager

[John Snow <jsnow@redhat.com>]

On 10/7/20 4:50 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
> 
>> Code style tools really dislike the use of global keywords, because it
>> generally involves re-binding the name at runtime which can have strange
>> effects depending on when and how that global name is referenced in
>> other modules.
>>
>> Make a little indent level manager instead.
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
>> Reviewed-by: Cleber Rosa <crosa@redhat.com>
> 
> Intentation is a job for QAPIGen (and its subtypes).  But if this patch
> is easier to achieve this series' goal, I don't mind.
> 

I agree, but refactoring it properly is beyond my capacity right now.

This was the dumbest thing I could do to get pylint/mypy passing, which 
required the elimination (or suppression) of the global keyword.

Creating a stateful object was the fastest way from A to B.

>> ---
>>   scripts/qapi/common.py | 49 ++++++++++++++++++++++++++++--------------
>>   scripts/qapi/visit.py  |  7 +++---
>>   2 files changed, 36 insertions(+), 20 deletions(-)
>>
>> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
>> index cee63eb95c7..b35318b72cf 100644
>> --- a/scripts/qapi/common.py
>> +++ b/scripts/qapi/common.py
>> @@ -93,33 +93,50 @@ def c_name(name, protect=True):
>>   pointer_suffix = ' *' + eatspace
>>   
>>   
>> -def genindent(count):
>> -    ret = ''
>> -    for _ in range(count):
>> -        ret += ' '
>> -    return ret
>> +class Indentation:
>> +    """
>> +    Indentation level management.
>>   
>> +    :param initial: Initial number of spaces, default 0.
>> +    """
>> +    def __init__(self, initial: int = 0) -> None:
>> +        self._level = initial
>>   
>> -indent_level = 0
>> +    def __int__(self) -> int:
>> +        return self._level
>>   
>> +    def __repr__(self) -> str:
>> +        return "{}({:d})".format(type(self).__name__, self._level)
>>   
>> -def push_indent(indent_amount=4):
>> -    global indent_level
>> -    indent_level += indent_amount
>> +    def __str__(self) -> str:
>> +        """Return the current indentation as a string of spaces."""
>> +        return ' ' * self._level
>>   
>> +    def __bool__(self) -> bool:
>> +        """True when there is a non-zero indentation."""
>> +        return bool(self._level)
>>   
>> -def pop_indent(indent_amount=4):
>> -    global indent_level
>> -    indent_level -= indent_amount
>> +    def increase(self, amount: int = 4) -> None:
>> +        """Increase the indentation level by ``amount``, default 4."""
>> +        self._level += amount
>> +
>> +    def decrease(self, amount: int = 4) -> None:
>> +        """Decrease the indentation level by ``amount``, default 4."""
>> +        if self._level < amount:
>> +            raise ArithmeticError(
>> +                f"Can't remove {amount:d} spaces from {self!r}")
> 
> Raise a fancy error when there's an actual need for it.  You're not
> coding a framework thousands of people you never heard of will put to
> uses you cannot imagine.
> 

It's not fancy, it's just a normal built-in exception, like 
AssertionError or any other:

Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
ArithmeticError: Can't remove 4 spaces from Indent(0)

vs

Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
AssertionError: Can't remove 4 spaces from Indent(0)


I feel like it's kind of a lateral move? I realize you feel this is an 
overfancy class doing what we hope is a temporary job, and that I have 
overengineered the hell out of a tiny do-nothing class... but I suppose 
that's also why I feel weird changing it around so much to accomplish so 
little.

Differences in style, I suppose.

Feel free to change it around to suit your tastes, I don't think it's 
worth spending a lot of ping-pong time on this paintsink in particular.

--js

>> +        self._level -= amount
>> +
>> +
>> +indent = Indentation()
>>   
>>   
>>   # Generate @code with @kwds interpolated.
>> -# Obey indent_level, and strip eatspace.
>> +# Obey indent, and strip eatspace.
>>   def cgen(code, **kwds):
>>       raw = code % kwds
>> -    if indent_level:
>> -        indent = genindent(indent_level)
>> -        raw = re.sub(r'^(?!(#|$))', indent, raw, flags=re.MULTILINE)
>> +    if indent:
>> +        raw = re.sub(r'^(?!(#|$))', str(indent), raw, flags=re.MULTILINE)
>>       return re.sub(re.escape(eatspace) + r' *', '', raw)
>>   
>>   
>> diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
>> index 808410d6f1b..14f30c228b7 100644
>> --- a/scripts/qapi/visit.py
>> +++ b/scripts/qapi/visit.py
>> @@ -18,9 +18,8 @@
>>       c_name,
>>       gen_endif,
>>       gen_if,
>> +    indent,
>>       mcgen,
>> -    pop_indent,
>> -    push_indent,
>>   )
>>   from .gen import QAPISchemaModularCVisitor, ifcontext
>>   from .schema import QAPISchemaObjectType
>> @@ -69,7 +68,7 @@ def gen_visit_object_members(name, base, members, variants):
>>       if (visit_optional(v, "%(name)s", &obj->has_%(c_name)s)) {
>>   ''',
>>                            name=memb.name, c_name=c_name(memb.name))
>> -            push_indent()
>> +            indent.increase()
>>           ret += mcgen('''
>>       if (!visit_type_%(c_type)s(v, "%(name)s", &obj->%(c_name)s, errp)) {
>>           return false;
>> @@ -78,7 +77,7 @@ def gen_visit_object_members(name, base, members, variants):
>>                        c_type=memb.type.c_name(), name=memb.name,
>>                        c_name=c_name(memb.name))
>>           if memb.optional:
>> -            pop_indent()
>> +            indent.decrease()
>>               ret += mcgen('''
>>       }
>>   ''')