Add Try node

[cdce8p]

Description

Replaces both #1388 and #1389. I first tried implementing the migration plan laid out in #1388 (comment). However, the new Try node not being part of the "official" tree caused a lot of issues.

• The most difficult part would have been to set the parent attributes on all child nodes correctly. Since it needs to point to the immediate parent, it would have been different depending if a child was part of the "old" TryExcept or the new Try node. That would basically mean that we couldn't reuse the child nodes and instead need to create new ones.
• With that, it's not clear how we can resolve inference to (only) use the new ones while they are effectively still hidden behind the special try_node attribute.
• All tree visitors in pylint would still use the old child nodes or might even emit all errors twice if both the old and new ones are visited.

I reached the conclusion that it might be better to do a breaking change now, instead of trying to work around a solution which would likely create new issues and would still lead to a breaking change down the line.

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This PR replaces the old TryExcept and TryFinally nodes with the new Try node. Python replaced the old nodes a long time ago in 3.3. The new node simplifies things a bit and even helps generate better line numbers for pylint errors in try-except blocks. It will also make it much easier to add support for TryStar nodes which would just need to inherit from Try. pylint-dev/pylint#7703

--
As this PR is a (major) breaking change, I suggest it should be the start for astroid 3.0 once merged. I'm going to create a planning issue for 3.0. However, even with the breaking change, the work required to update is manageable. I'll also open a pylint PR to update our code base.

• Use Try node pylint#7767
• Planning for astroid 3.0 #1868

--

What's left to do

I'll also mention it in the 3.0 issue, but I think we should create a separate docs page just describing the breaking changes and how to update plugins. That can probably be done separately. If someone else would like to take the lead on this, I would appreciate any help. Some notes

• TryExcept and TryFinally removed
• Update visit_* and leave_* methods

[coveralls]

Pull Request Test Coverage Report for Build 3463412808

• 35 of 35 (100.0%) changed or added relevant lines in 4 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.07%) to 92.222%

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Files with Coverage Reduction	New Missed Lines	%
astroid/nodes/_base_nodes.py	6	92.66%

Totals
Change from base Build 3463322631:	-0.07%
Covered Lines:	9841
Relevant Lines:	10671

---

💛 - Coveralls

[DanielNoord]

@cdce8p Should this be reviewed? Or should we wait until we are sure we can start merging 3.0 PRs?

[cdce8p]

@cdce8p Should this be reviewed? Or should we wait until we are sure we can start merging 3.0 PRs?

The change itself is done. Might only need to resolve merge conflicts and update the changelog when we start with 3.0. If you have some spare time, feel free to take a look. Just don't merge it quite yet.

[codecov]

Codecov Report

Merging #1867 (04ba8ca) into main (a7ab088) will decrease coverage by 0.07%.
The diff coverage is 97.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1867      +/-   ##
==========================================
- Coverage   92.84%   92.77%   -0.07%     
==========================================
  Files          94       94              
  Lines       10964    10941      -23     
==========================================
- Hits        10179    10151      -28     
- Misses        785      790       +5     

Flag	Coverage Δ
linux	92.58% <97.72%> (-0.07%)	⬇️
pypy	90.89% <97.72%> (-0.07%)	⬇️
windows	92.34% <97.72%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
astroid/__init__.py	100.00% <ø> (ø)
astroid/nodes/__init__.py	100.00% <ø> (ø)
astroid/nodes/node_ng.py	93.67% <ø> (ø)
astroid/nodes/scoped_nodes/scoped_nodes.py	92.38% <ø> (ø)
astroid/nodes/node_classes.py	94.82% <97.43%> (-0.02%)	⬇️
astroid/nodes/as_string.py	97.01% <100.00%> (ø)
astroid/rebuilder.py	98.44% <100.00%> (+0.13%)	⬆️

... and 1 file with indirect coverage changes

[Pierre-Sassoulas]

It's not a work in progress anymore, right ? I think it's going to simplify a lot of checks in pylint 👍

[cdce8p]

It's not a work in progress anymore, right ? I think it's going to simplify a lot of checks in pylint 👍

The PR is basically ready at this point. We could merge it as is.
The real work will be to update pylint after that. I do already have a PR with most of the required changes but we'll definitely need to double check these pylint-dev/pylint#7767.

Once we merge it, I'll create another alpha release just for it.

[jacobtylerwalls]

Great! Eager to merge this after we release 3.0.0a7 and can devote an alpha release to just this change.

[Pierre-Sassoulas]

Let's do it ! :)