Add and use new EnvironDict class

[cottsay]

On Win32, the os.environ mapping behaves in many case-insensitive ways. When we copy os.environ to a typical dict instance, we lose those behaviors.

This new class preserves the case insensitivity on Windows and behaves like a normal OrderedDict on non-Windows platforms.

In draft for now, because I'm still trying to understand the exact behaviors that Windows exhibits. In particular, it might be closer in behavior to just convert all keys to UPPERCASE before accessing the underlying dict.

Okay, from what I can tell, Python converts all keys in os.environ to UPPERCASE on Windows, but since colcon is capturing the environment variables using set, we don't see the same treatment. If the goal was to align EnvironDict with os.environ on Windows precisely, we'd want to convert everything to UPPERCASE as it seems to implicitly do. However, given that we want this class to be used on the variables we capture with set as well, I think we should just preserve the original case but make access case-insensitive.

Assisted-by: Gemini 3.5 Flash

Note

The Windows implementation of EnvironDict is a lot bigger than it should be. Implementing Mapping was a lot simpler, but the public colcon API specifically returns an instance of dict, so we need the new class to also inherit from dict to maintain compatibility.

[codecov]

Codecov Report

❌ Patch coverage is 71.17117% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.23%. Comparing base (6428dca) to head (c589bee).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
colcon_core/environment_variable.py	70.00%	23 Missing and 7 partials ⚠️
colcon_core/task/python/test/__init__.py	50.00%	1 Missing ⚠️
colcon_core/task/python/test/pytest.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #744      +/-   ##
==========================================
- Coverage   87.66%   87.23%   -0.43%     
==========================================
  Files          74       75       +1     
  Lines        4442     4686     +244     
  Branches      771      816      +45     
==========================================
+ Hits         3894     4088     +194     
- Misses        433      468      +35     
- Partials      115      130      +15     

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[cottsay]

Tapping Pepper for review here (via @claraberendsen)

[knmcguire]

lgtm! and your explanation makes sense

The one thing perhaps to mention is that 'move_to_end()' from OrderedDict is not changed and can't handle the case-sensitive cases. It's not used anywhere though... so... I don't think it has consequences now?

fyi, did you use any agents here? It's not mentioned in the commits

[cottsay]

'move_to_end()' from OrderedDict is not changed

An oversight, addressed in the latest change.

did you use any agents here? It's not mentioned in the commits

I did and I definitely forgot to mention it. Good call out.