Improve AST validation for Constant nodes

[isidentical]

BPO	40000
Nosy	@vstinner, @serhiy-storchaka, @pablogsal, @isidentical
PRs	bpo-40000: Improve AST validation for invalid constant nodes #19055

^{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 = 'https://github.com/isidentical'
closed_at = <Date 2020-03-19.12:01:11.736>
created_at = <Date 2020-03-18.09:46:11.962>
labels = ['type-feature', 'library', '3.9']
title = 'Improve AST validation for Constant nodes'
updated_at = <Date 2020-03-19.18:43:55.107>
user = 'https://github.com/isidentical'

bugs.python.org fields:

activity = <Date 2020-03-19.18:43:55.107>
actor = 'vstinner'
assignee = 'BTaskaya'
closed = True
closed_date = <Date 2020-03-19.12:01:11.736>
closer = 'BTaskaya'
components = ['Library (Lib)']
creation = <Date 2020-03-18.09:46:11.962>
creator = 'BTaskaya'
dependencies = []
files = []
hgrepos = []
issue_num = 40000
keywords = ['patch']
message_count = 6.0
messages = ['364505', '364509', '364529', '364530', '364599', '364626']
nosy_count = 4.0
nosy_names = ['vstinner', 'serhiy.storchaka', 'pablogsal', 'BTaskaya']
pr_nums = ['19055']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40000'
versions = ['Python 3.9']

[isidentical]

When something that isn't constant found in a ast.Constant node's body, python reports errors like this

>>> e = ast.Expression(body=ast.Constant(value=type))
>>> ast.fix_missing_locations(e)
<_ast.Expression object at 0x7fc2c23981c0>
>>> compile(e, "<test>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: got an invalid type in Constant: type

But if something is part of constant tuple and frozenset isn't constant, the error reporting is wrong

>>> e = ast.Expression(body=ast.Constant(value=(1,2,type)))
>>> compile(e, "<test>", "eval")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: got an invalid type in Constant: tuple

This should've been

TypeError: got an invalid type in Constant: type

[serhiy-storchaka]

You got an anniversary issue!

[vstinner]

Congratulations Batuhan! You win with the bug number 40000! A nice number ;-) To be honest, I wanted to get it, but I didn't want to cheat by opening a stupid issue.

[isidentical]

sorry to take it Victor, maybe you can get the perfect issue number when we migrate to github?

[pablogsal]

New changeset 0ac59f9 by Batuhan Taşkaya in branch 'master':
bpo-40000: Improve error messages when validating invalid ast.Constant nodes (GH-19055)
0ac59f9

[vstinner]

_PyType_Name(Py_TYPE(value)))

Why truncating the type name in the error message? The qualified name (don't call _PyType_Name()) should provide more information, no?