Avoid raising OverflowError in truncate() if possible

[serhiy-storchaka]

BPO	29819
Nosy	@vstinner, @benjaminp, @serhiy-storchaka, @orenmn, @nanjekyejoannah
Dependencies	bpo-29852: Argument Clinic: add common converter to Py_ssize_t that accepts None

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-03-15.15:11:06.614>
labels = ['3.7', 'type-feature', 'library', 'expert-IO']
title = 'Avoid raising OverflowError in truncate() if possible'
updated_at = <Date 2019-05-27.16:44:36.338>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2019-05-27.16:44:36.338>
actor = 'nanjekyejoannah'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'IO']
creation = <Date 2017-03-15.15:11:06.614>
creator = 'serhiy.storchaka'
dependencies = ['29852']
files = []
hgrepos = []
issue_num = 29819
keywords = []
message_count = 2.0
messages = ['289677', '289848']
nosy_count = 6.0
nosy_names = ['vstinner', 'benjamin.peterson', 'stutzbach', 'serhiy.storchaka', 'Oren Milman', 'nanjekyejoannah']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29819'
versions = ['Python 3.7']

[serhiy-storchaka]

os.truncate(), os.ftruncate() and truncate() methods of file-like objects raise OverflowError when the argument is out of ranger of certain C type. It would be better to extend the behavior of small integers to large integers. ValueError is raised for negative integers and it should be raised for negative integers out of range. Values larger than the current size should be ignored in BytesIO.truncate() and StringIO.truncate(). BytesIO.truncate() and StringIO.truncate() should never raise OverflowError. Since the behavior of underlying OS functions is OS and FS depended, OverflowError can be raised for large integers in os.truncate(), os.ftruncate() and FileIO.truncate().

[serhiy-storchaka]

bpo-29852 is not strict dependency, but it may make the solution of this issue simpler.