Refactor error messages in symtable.c

[ilevkivskyi]

BPO	28100
Nosy	@tiran, @ilevkivskyi
Files	refactor-error-msg.diff refactor-error-msg-v2.diff

^{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 2016-10-07.22:28:59.790>
created_at = <Date 2016-09-12.11:43:04.186>
labels = ['interpreter-core']
title = 'Refactor error messages in symtable.c'
updated_at = <Date 2016-10-07.22:28:59.789>
user = 'https://github.com/ilevkivskyi'

bugs.python.org fields:

activity = <Date 2016-10-07.22:28:59.789>
actor = 'levkivskyi'
assignee = 'none'
closed = True
closed_date = <Date 2016-10-07.22:28:59.790>
closer = 'levkivskyi'
components = ['Interpreter Core']
creation = <Date 2016-09-12.11:43:04.186>
creator = 'levkivskyi'
dependencies = []
files = ['44592', '44782']
hgrepos = []
issue_num = 28100
keywords = ['patch']
message_count = 4.0
messages = ['276024', '277150', '277164', '277291']
nosy_count = 3.0
nosy_names = ['christian.heimes', 'python-dev', 'levkivskyi']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue28100'
versions = ['Python 3.6']

[ilevkivskyi]

Patch with added comment and a minor refactoring to error messages in symtable.c

Now the error message is simply always overwritten by any more "severe" SyntaxError found in the same block.

[tiran]

Please rewrite the patch to use if / else if / else, e.g.

 if (cur & (DEF_LOCAL | USE | DEF_ANNOT)) {
    ...
    if (cur & USE) {
        msg = GLOBAL_AFTER_USE;
    } else if (cur & DEF_LOCAL) {
        msg = GLOBAL_AFTER_ASSIGN;
    } else {  /* DEF_ANNOT */
        msg = GLOBAL_ANNOT;
    }
    ...
}

[ilevkivskyi]

Here is the patch for 3.6 with requested changes.

While playing with this a bit more, I discovered that the error message in this case (if no value is actually assigned):

def f():
    x: int
    global x

could be misleading. Therefore I changed the order of DEF_LOCAL and DEF_ANNOT to get a more clear error message for such cases (this does not spoil error messages in other cases).

[python-dev]

New changeset 966b57281536 by Christian Heimes in branch '3.6':
Issue bpo-28100: Refactor error messages, patch by Ivan Levkivskyi
https://hg.python.org/cpython/rev/966b57281536

New changeset a953112116ac by Christian Heimes in branch 'default':
Issue bpo-28100: Refactor error messages, patch by Ivan Levkivskyi
https://hg.python.org/cpython/rev/a953112116ac