Move checking for duplicated keywords to the compiler

[pablogsal]

BPO	40147
Nosy	@lysnikolaou, @ZackerySpytz, @pablogsal
PRs	bpo-40147: Move the check for duplicate keywords to the compiler #19289 bpo-40147: Fix a compiler warning on Windows in Python/compile.c #19389

^{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 = <Date 2020-04-03.19:42:15.142>
created_at = <Date 2020-04-02.00:22:24.878>
labels = []
title = 'Move checking for duplicated keywords to the compiler'
updated_at = <Date 2020-04-06.06:48:03.533>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2020-04-06.06:48:03.533>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2020-04-03.19:42:15.142>
closer = 'pablogsal'
components = []
creation = <Date 2020-04-02.00:22:24.878>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 40147
keywords = ['patch']
message_count = 3.0
messages = ['365537', '365719', '365841']
nosy_count = 3.0
nosy_names = ['lys.nikolaou', 'ZackerySpytz', 'pablogsal']
pr_nums = ['19289', '19389']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue40147'
versions = []

[pablogsal]

When a keyword is repeated in a call for instance:

'f(1, x=2, *(3, 4), x=5)'

we raise a SyntaxError:

File "lel.py", line 1
f(1, x=2, *(3, 4), x=5)
^
SyntaxError: keyword argument repeated

This error is raised from the AST but there is nothing technically wrong with that code from the grammar perspective. Indeed, the grammar must accepts that code, but the check must fail later (in the compiler for instance) because the code is semantically invalid. When working on the new PEG parser we have encountered this situation and changing the parser would remove the check as it is right now. For these reasons, the check should be moved from the AST to the compiler.

[pablogsal]

New changeset 254ec78 by Pablo Galindo in branch 'master':
bpo-40147: Move the check for duplicate keywords to the compiler (GH-19289)
254ec78

[pablogsal]

New changeset 08050e9 by Zackery Spytz in branch 'master':
bpo-40147: Fix a compiler warning on Windows in Python/compile.c (GH-19389)
08050e9