fix: kube-core::Schema hoisting logic

[NickLarsenNZ]

Fixes #1821

This updates the kube Schema hoisting since schemars Schema's have changed.

• Add tests for a variety of enum use-cases:
  • Tagged vs Untagged
  • Unit vs Tuple vs Structural variants
  • With and without doc-comments (descriptions)
• Rewrite the hoisting logic
  • This is annotated with dev-comments to help understand intend and to ease future schemars changes.

This also fixes other issues that appeared along the way:

• Untagged enum variant doc-comments were being applied to field descriptions.
• Additional null entry added to enums.

See also: stackabletech#1, where this work was originally done.

---

Motivation

Since kube 1.0.0, schemas became invalid when optional enums contained comments on the variants.

Solution

• Break out the hoisting logic into separate modules with scoped tests.
  • Heavily document the steps to help developers with future schemars Schema generation changes.
• Add tests to try and catch this in future.

[codecov]

Codecov Report

❌ Patch coverage is 96.65272% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.0%. Comparing base (7c63f56) to head (cfdfcd1).

Files with missing lines	Patch %	Lines
kube-core/src/schema/transform_any_of.rs	91.7%	3 Missing ⚠️
kube-core/src/schema/transform_one_of.rs	90.4%	3 Missing ⚠️
kube-core/src/schema/transform_properties.rs	97.4%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1839     +/-   ##
=======================================
+ Coverage   74.5%   75.0%   +0.6%     
=======================================
  Files         84      90      +6     
  Lines       7877    8050    +173     
=======================================
+ Hits        5867    6037    +170     
- Misses      2010    2013      +3     

Files with missing lines	Coverage Δ
kube-core/src/schema/mod.rs	100.0% <100.0%> (ø)
...re/src/schema/transform_optional_enum_with_null.rs	100.0% <100.0%> (ø)
kube-derive/src/custom_resource.rs	83.9% <100.0%> (-<0.1%)	⬇️
kube-derive/tests/crd_complex_enum_tests.rs	100.0% <100.0%> (ø)
kube-derive/tests/crd_mixed_enum_test.rs	100.0% <100.0%> (ø)
kube-derive/tests/crd_schema_test.rs	100.0% <100.0%> (ø)
kube-derive/tests/crd_top_level_enum_test.rs	100.0% <ø> (ø)
kube-core/src/schema/transform_properties.rs	97.4% <97.4%> (ø)
kube-core/src/schema/transform_any_of.rs	91.7% <91.7%> (ø)
kube-core/src/schema/transform_one_of.rs	90.4% <90.4%> (ø)

... and 4 files with indirect coverage changes

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[NickLarsenNZ]

I'm unsure what to do about the CI error:

error: rustc 1.86.0 is not supported by the following package:
  home@0.5.12 requires rustc 1.88

For me, I get home@0.5.9. Should I pin the dependency?

kube/Cargo.toml

Line 50 in 7c63f56

home = "0.5.4"

[sbernauer]

Created #1840 to address the home CI failures