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qapi: Prefer explicit relative imports

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All of the QAPI include statements are changed to be package-aware, as
explicit relative imports.

A quirk of Python packages is that the name of the package exists only
*outside* of the package. This means that to a module inside of the qapi
folder, there is inherently no such thing as the "qapi" package. The
reason these imports work is because the "qapi" package exists in the
context of the caller -- the execution shim, where sys.path includes a
directory that has a 'qapi' folder in it.

When we write "from qapi import sibling", we are NOT referencing the folder
'qapi', but rather "any package named qapi in sys.path". If you should
so happen to have a 'qapi' package in your path, it will use *that*
package.

When we write "from .sibling import foo", we always reference explicitly
our sibling module; guaranteeing consistency in *where* we are importing
these modules from.

This can be useful when working with virtual environments and packages
in development mode. In development mode, a package is installed as a
series of symlinks that forwards to your same source files. The problem
arises because code quality checkers will follow "import qapi.x" to the
"installed" version instead of the sibling file and -- even though they
are the same file -- they have different module paths, and this causes
cyclic import problems, false positive type mismatch errors, and more.

It can also be useful when dealing with hierarchical packages, e.g. if
we allow qemu.core.qmp, qemu.qapi.parser, etc.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201009161558.107041-6-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
John Snow 2020-10-09 12:15:27 -04:00 • committed by Markus Armbruster
parent a76ab215ec
commit 7137a96099
10 changed files with 33 additions and 33 deletions
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14
scripts/qapi/main.py
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@ -12,13 +12,13 @@ import re
import sys
from typing import Optional
from qapi.commands import gen_commands
from qapi.error import QAPIError
from qapi.events import gen_events
from qapi.introspect import gen_introspect
from qapi.schema import QAPISchema
from qapi.types import gen_types
from qapi.visit import gen_visit
from .commands import gen_commands
from .error import QAPIError
from .events import gen_events
from .introspect import gen_introspect
from .schema import QAPISchema
from .types import gen_types
from .visit import gen_visit
def invalid_prefix_char(prefix: str) -> Optional[str]: