Error range of "duplicate argument" SyntaxErrors is too big

[cfbolz]

BPO	46042
Nosy	@cfbolz, @aroberge, @pablogsal, @miss-islington
PRs	bpo-46042: Improve SyntaxError locations in the symbol table #30059 [3.10] bpo-46042: Improve SyntaxError locations in the symbol table (GH-30059) #30064

^{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 2021-12-11.21:29:46.835>
created_at = <Date 2021-12-10.21:24:21.180>
labels = []
title = 'Error range of "duplicate argument" SyntaxErrors is too big'
updated_at = <Date 2021-12-12.05:24:58.584>
user = 'https://github.com/cfbolz'

bugs.python.org fields:

activity = <Date 2021-12-12.05:24:58.584>
actor = 'Carl.Friedrich.Bolz'
assignee = 'none'
closed = True
closed_date = <Date 2021-12-11.21:29:46.835>
closer = 'pablogsal'
components = []
creation = <Date 2021-12-10.21:24:21.180>
creator = 'Carl.Friedrich.Bolz'
dependencies = []
files = []
hgrepos = []
issue_num = 46042
keywords = ['patch']
message_count = 10.0
messages = ['408248', '408250', '408298', '408322', '408323', '408324', '408343', '408344', '408356', '408360']
nosy_count = 4.0
nosy_names = ['Carl.Friedrich.Bolz', 'aroberge', 'pablogsal', 'miss-islington']
pr_nums = ['30059', '30064']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46042'
versions = []

[cfbolz]

The error range for the "duplicate argument in function definition" SyntaxError is too large:

$ cat x.py 
def f(a, b, c, d, e, f, g, a): pass
$ python x.py
  File "/home/cfbolz/projects/cpython/x.py", line 1
    def f(a, b, c, d, e, f, g, a): pass
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: duplicate argument 'a' in function definition

I would expect only the second 'a' to be underlined.

I can try to fix this.

[pablogsal]

Thanks for the catch Carl!

I can try to fix this.

Awesome, I will wait for the PR!

[cfbolz]

let's see whether I promised too much, I don't know CPython's symtable.c too well yet ;-). Will shout for help when I get stuck.

Anyway, here is a related bug, coming from the same symtable function symtable_add_def_helper, also with an imprecise error location:

$ cat x.py 
{i for i in range(5)
        if (j := 0)
            for j in range(5)}

$ ./python x.py 
  File "/home/cfbolz/projects/cpython/x.py", line 1
    {i for i in range(5)
    ^^^^^^^^^^^^^^^^^^^^
SyntaxError: comprehension inner loop cannot rebind assignment expression target 'j'

[pablogsal]

Don't worry, turns out it was a bit messier than I thought, so I prepared the PR. If you have some time, it would be great if you can take a quick look.

[cfbolz]

Oh no, I was about to open mine ;-)

https://github.com/python/cpython/compare/main...cfbolz:bpo-46042-syntax-error-range-duplicate-argument?expand=1

Basically equivalent, but I fixed the second bug too (would be very easy to add to yours)

[cfbolz]

ah, confused, seems you fixed them both too. will take a closer look!

[pablogsal]

New changeset 59435ee by Pablo Galindo Salgado in branch 'main':
bpo-46042: Improve SyntaxError locations in the symbol table (GH-30059)
59435ee

[pablogsal]

Oh no, I was about to open mine ;-)

Sorry, Carl, I apologize. I hope it was not too disruptive to do the work. I was taking a look and I felt bad that the issue was probably messier than I thought and I didn't want you to have to iterate many times :(

Thanks a lot for helping review the PR and for pointing out the extra cases!!

[pablogsal]

New changeset 438817f by Miss Islington (bot) in branch '3.10':
bpo-46042: Improve SyntaxError locations in the symbol table (GH-30059) (GH-30064)
438817f

[cfbolz]

Oh, don't worry, it's all good! It got fixed and I learned something.