Add a note on reloading from declarative pipelines #1227

[fugkco]

If JCasC is reloaded from a declarative pipeline, Jenkins throws an error due to permission issues. Subsequent reloads of JCasC fail regardless of the mechanisms used to do so, and regardless of user permissions.

This issue probably needs to be addressed correctly so that Jenkins isn't put in an invalid state, as it could potentially have other side effects that hasn't been noticed yet.

Your checklist for this pull request

🚨 Please review the guidelines for contributing to this repository.

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side) and not your master branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or in Jenkins JIRA
• Link to relevant pull requests, esp. upstream and downstream changes
• Did you provide a test-case? That demonstrates feature works or fixes the issue.

Relates to #1227

[timja]

is it better to just remove the above from the docs?

[fugkco]

Ultimately that is something for CloudBees/CJCasC maintainers to decide, but I don't believe so. So far we've been using this successfully as per the workaround posted in #1227, and this works as long as a) the script approvals allow it, b) it's a freestyle job, and c) it is run using systemGroovyCommand. The issue of course is when this is run through pipelineJob. Mind you, even if the above three predicates aren't met and the code is run in a freestyle job, Jenkins is still in a good state and the code above can be run e.g. within the script console fine.

[fugkco]

@timja will this get approved/merged? If not, I'll close this PR. Thanks

[codecov]

Codecov Report

Merging #1675 (18d01ff) into master (d77a466) will increase coverage by 0.16%.
The diff coverage is n/a.

❗ Current head 18d01ff differs from pull request most recent head 5367924. Consider uploading reports for the commit 5367924 to get more accurate results

@@             Coverage Diff              @@
##             master    #1675      +/-   ##
============================================
+ Coverage     80.64%   80.80%   +0.16%     
- Complexity      820      835      +15     
============================================
  Files            66       71       +5     
  Lines          2402     2464      +62     
  Branches        340      345       +5     
============================================
+ Hits           1937     1991      +54     
- Misses          356      363       +7     
- Partials        109      110       +1     

Impacted Files	Coverage Δ
...ators/GlobalConfigurationCategoryConfigurator.java	87.80% <0.00%> (-0.57%)	⬇️
...plugins/casc/impl/DefaultConfiguratorRegistry.java	74.00% <0.00%> (-0.51%)	⬇️
...casc/impl/configurators/DataBoundConfigurator.java	82.80% <0.00%> (-0.11%)	⬇️
...java/io/jenkins/plugins/casc/SchemaGeneration.java	93.90% <0.00%> (-0.08%)	⬇️
...ain/java/io/jenkins/plugins/casc/Configurator.java	79.06% <0.00%> (ø)
...ain/java/io/jenkins/plugins/casc/model/Scalar.java	88.67% <0.00%> (ø)
...java/io/jenkins/plugins/casc/BaseConfigurator.java	85.35% <0.00%> (ø)
...a/io/jenkins/plugins/casc/ConfigurationAsCode.java	80.31% <0.00%> (ø)
...kins/plugins/casc/yaml/StreamReaderWithSource.java	85.71% <0.00%> (ø)
...nkins/plugins/casc/misc/RoundTripAbstractTest.java	98.33% <0.00%> (ø)
... and 8 more