fix(applicationset): Git generator: Don't append default object to literal empty json array (#23500)

[ChristianCiach]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

This is basically an improved version of #15661. That PR fixed the case where an empty yaml file wasn't distinguished from a missing file, which could easily lead to deleted applications when a user commented out all entries from their yaml file.

Unfortunately, that PR didn't distinguish between an empty yaml file from yaml files containing a literal empty json array ([]) as the root element. Using arrays as the top-level structure for yaml files has long been supported by the git generator, but it seems to be an undocumented feature (or at least I couldn't find any documentation).

If a yaml file contains an array as the top level element, the Git generator outputs a separate params-object for each element of the array. In other words, this feature can be used to easily template multiple applications from a single yaml file without the use of a matrix generator, as a user does this here:

• Git Generator with empty config.json file not working #23500

Since this is a supported use-case, it stands to reason that an empty array ([]) should result in an empty slice of objects returned by the git generator. But this has been broken since v2.10 due to #15661 failing to distinguish between an empty file (or {}) from an empty array, because the code previously tried to unmarshal the data into a slice, which even succeeds for empty files.

To fix this I've just reversed the order of parsing attempts: This PR first tries to unmarshal the data into a map, which even succeeds for empty files! This also makes the code a bit cleaner, since there is no need for constructing a dummy slice entry anymore. Only if parsing as a map fails (which is also the case for []) we fall back to trying to unmarshal the data into a slice.

I think it's also nice that the most common use case (yaml containing an object) is now tried first, while arrays are only attempted as a fallback. This slightly changed the returned error messsages, but no tests needed to be adjusted aside from that. I've added a unit test that fails with the previous implementation.

Kindly pinging @agaudreault because this builds on his previous PR.

Please see the comments of the linked issue for more details about the use-case and the cause of this issue.

Closes #23500

[bunnyshell]

❌ Preview Environment deleted from Bunnyshell

Available commands (reply to this comment):

• 🚀 /bns:deploy to deploy the environment

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.25%. Comparing base (5c9a5ef) to head (7935218).
⚠️ Report is 431 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #23513      +/-   ##
==========================================
- Coverage   60.25%   60.25%   -0.01%     
==========================================
  Files         344      344              
  Lines       59084    59082       -2     
==========================================
- Hits        35604    35597       -7     
+ Misses      20611    20610       -1     
- Partials     2869     2875       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[rumstead]

LGTM

[nitishfy]

LGTM!