fix(uv): fix evaluation of PEP 508 specs involving nested parentheses

[acozzette]

This change fixes two bugs in pep508_evaluate.bzl:

• _new_expr used _current[0] (outermost) instead of _current[-1] (innermost) when resolving the active sub-expression, causing values inside nested parens to land in the wrong expression node
• There was a typo of current.tree._append(value) instead of current.tree.append(value).

This change also adds a Starlark unit test suite for the evaluate function.

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Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• New test cases added

[aspect-workflows]

Bazel 8 (Test)

All tests were cache hits

112 tests (100.0%) were fully cached saving 56s.

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Bazel 9 (Test)

All tests were cache hits

112 tests (100.0%) were fully cached saving 1m.

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Bazel 8 (Test)

e2e

All tests were cache hits

51 tests (100.0%) were fully cached saving 42s.

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Bazel 9 (Test)

e2e

All tests were cache hits

51 tests (100.0%) were fully cached saving 1m 8s.

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Bazel 8 (Test)

examples/uv_pip_compile

All tests were cache hits

1 test (100.0%) was fully cached saving 444ms.

[acozzette]

@xangcastle I was wondering if you could take a look at this PR when you have a chance? I'm not sure what the CI error is about but it looks like it's not related to my change.

[gregmagolan]

🌮

[jbedard]

If you rebase the CI error should be gone now

[acozzette]

If you rebase the CI error should be gone now

I gave that a try but it's still not working unfortunately. I see it's trying to fetch something involving refs/remotes/origin/pep508*, and I think that's probably failing because origin points to aspect-build/rules_py rather than my personal fork.