GROOVY-12188: accept covariant override of abstract method regardless…

[paulk-asert]

… of classgen order

Since GROOVY-10687, a top-level class whose inner classes contain a closure is generated after its nest members, which can place it after its own subclass in the classgen order. The abstract-method check in ClassCompletionVerifier relied on the covariant bridge method that Verifier adds to the declaring class, so verifying a subclass first raised a spurious "same name but different return type" error. Recognise a covariant override directly instead; genuinely incompatible return types are still rejected by Verifier's covariant-method check.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.2743%. Comparing base (3240fcf) to head (3334e37).

Files with missing lines	Patch %	Lines
...ehaus/groovy/classgen/ClassCompletionVerifier.java	0.0000%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##               master      #2733        +/-   ##
==================================================
+ Coverage     69.2732%   69.2743%   +0.0012%     
- Complexity      34769      34771         +2     
==================================================
  Files            1542       1542                
  Lines          130456     130461         +5     
  Branches        23786      23790         +4     
==================================================
+ Hits            90371      90376         +5     
  Misses          31962      31962                
  Partials         8123       8123                

Files with missing lines	Coverage Δ
...ehaus/groovy/classgen/ClassCompletionVerifier.java	84.2199% <0.0000%> (-0.7533%)	⬇️

... and 7 files with indirect coverage changes

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[testlens-app]

✅ All tests passed ✅

🏷️ Commit: 3334e37
▶️ Tests: 105866 executed
⚪️ Checks: 31/31 completed

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[paulk-asert]

Cherry-picked manually onto the GROOVY_5_0_X branch as the minimal fix. For master, see #2734 which should be a better long-term fix. If no impacts from the long-term fix are noticed on master, it would be a candidate for back-porting to GROOVY_5_0_X.

GROOVY_5_0_X: 09a2d2f
Master: 361a02e