fix(crosslink): correct pruning logic to ensure all replace statement…

[Abhay349]

Description:

In continuation with PR #1593, this PR fixes a bug in the prune command where some replace statements were not being removed correctly.

Changes:

Pointer usage for in-place modification: Changed modContents to use a pointer. Previously, it was creating a value copy of the module struct, so DropReplace calls were modifying a local copy that was discarded, leaving the original module unchanged.

Safe iteration: Implemented a two-pass approach for pruning. We now collect all replace statements to be pruned into a toPrune slice first, and then iterate over that slice to remove them. This prevents index-shifting bugs that occur when modifying a slice (removing elements) while iterating over it, which previously caused some statements to be skipped.

[codecov]

Codecov Report

❌ Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.16%. Comparing base (963233d) to head (23aaa19).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
crosslink/internal/prune.go	61.53%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1597      +/-   ##
==========================================
+ Coverage   64.08%   64.16%   +0.08%     
==========================================
  Files          66       66              
  Lines        3408     3427      +19     
==========================================
+ Hits         2184     2199      +15     
- Misses        988      990       +2     
- Partials      236      238       +2     

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[Abhay349]

Hi @dmathieu @mx-psi I attempted to add a specific unit test, however I encountered flaky behavior related to modfile.File internal state management. Since the existing test suite covers the general pruning functionality and passes with these changes, I have omitted the flaky test case for now to maintain CI stability.

Let me know if there are issues, happy to iterate on feedback.
Thanks :)

[mx-psi]

I am not supportive of adding this without a unit test

[Abhay349]

@mx-psi Totally understand your concern. I’ll revisit this and make another attempt at adding a proper unit test. If I run into issues while stabilizing it, I’ll reach out for guidance.
Thanks for the feedback!

[Abhay349]

Hi @mx-psi @dmathieu,
I’ve added the missing test case. I was getting flaky behaviour in earlier attempts because I was comparing the whole modfile.File, and DropReplace tweaks thing internally in ways that made that unreliable.
Now I’m just adding a few dummy replace entries, running Cleanup(), and checking that the Replace slice ends up empty. If the bug were still there, some entries would remain.

[Abhay349]

Let me know if this approach looks good, happy to iterate on further feedback.
Thanks :)

[mx-psi]

The test you added does not seem to fail if I revert your changes on crosslink/internal/prune.go. I would want a test that is able to reproduce the issue you are fixing before you change the code, and that it passes after your changes are applied

[Abhay349]

@mx-psi @dmathieu I have tried a lot to add test but feeling stuck at this pont, could you pls help me with some hints and all to proceed further.