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

[Markus Armbruster]

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.

> ---
>  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.

> +        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('''
>      }
>  ''')