fix(manager/gradle): preserve next token for parsing in case dependency interpolation fails

[Churro]

Changes

Return {} instead of null for errors in processDepInterpolation. tryMatch() won't try other matchers but assume it was the correct one and that only handling failed.

Currently, token.shift() removes the next token if a) no matching sequence was found or b) it was found but an error occurred during processing. This is problematic if there is another potential match following directly afterwards, as it will miss the first token for matching.

This PR addresses this only for processDepInterpolation, although there are other spots in the code where the same behavior could show up (processLongFormDep, processDepString). Switching to {} everywhere seems risky to me as it could mean that other relevant matching sequences are simply skipped. In this case, I think this should be no issue since with the current order no other matching sequence follows that would begin with TokenType.StringInterpolation. Subsequent matching sequences including TokenType.StringInterpolation don't use it for the first token, so all other occurrences should still match fine with the token lookahead done in matchTokens.

More details also here.

To get rid of this problem overall, I'd prefer to address it in the parser refactoring (work ongoing).

Context

Closes #18317

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

Test repository: renovate-demo/18317-renovate-gradle-variable-interpolate-reproduction#4

[viceice]

needs deconfliction

[renovate-release]

🎉 This PR is included in version 34.2.2 🎉

The release is available on:

• GitHub release
• 34.2.2

Your semantic-release bot 📦🚀