Syntax warnings are duplicated in zipimport

[serhiy-storchaka]

When importing a not precompiled module from a ZIP archive, syntax warnings are emitted twice.

Discovered during adding tests for #139652.

[typenoob]

The warnings are emitted both in _frozen_importlib._find_spec and _frozen_importlib._load_unlocked.

I think warnings are not supposed to be emitted in _frozen_importlib._find_spec.

cpython/Lib/importlib/_bootstrap_external.py

Lines 576 to 586 in 92741c5

	if location is None:
	# The caller may simply want a partially populated location-
	# oriented spec. So we set the location to a bogus value and
	# fill in as much as we can.
	location = '<unknown>'
	if hasattr(loader, 'get_filename'):
	# ExecutionLoader
	try:
	location = loader.get_filename(name)
	except ImportError:
	pass

_frozen_importlib._find_spec acquired the filename by get_filename

cpython/Lib/zipimport.py

Lines 158 to 167 in 92741c5

	def get_filename(self, fullname):
	"""get_filename(fullname) -> filename string.
	Return the filename for the specified module or raise ZipImportError
	if it couldn't be imported.
	"""
	# Deciding the filename requires working out where the code
	# would come from if the module was actually loaded
	code, ispackage, modpath = _get_module_code(self, fullname)
	return modpath

however it triggered the compile action which may be not intended?

cpython/Lib/zipimport.py

Lines 809 to 824 in 92741c5

	modpath = toc_entry[0]
	data = _get_data(self.archive, toc_entry)
	code = None
	if isbytecode:
	try:
	code = _unmarshal_code(self, modpath, fullpath, fullname, data)
	except ImportError as exc:
	import_error = exc
	else:
	code = _compile_source(modpath, data)
	if code is None:
	# bad magic number or non-matching mtime
	# in byte code, try next
	continue
	modpath = toc_entry[0]
	return code, ispackage, modpath

If all we want is just the filename, there's no need to compile the code right?

[typenoob]

@serhiy-storchaka Sorry to bother you. I has found the root cause, but don't know whether to fix it or the best approach to fix it. Could you take a look at it?

[itamaro]

I happened to stumble across this when noticing that modules loaded from pyc's with zipimport go through lookup and unmarshalling twice (once though get_filename and once through get_code).
There's a comment in get_filename about needing to get the code for the filename, so this seems intentional, but I'm not sure whether it is intentional to do the entire dance twice instead of some caching.
@serhiy-storchaka let me know if this should be a separate issue (or isn't an issue at all).