Huge performance gap due to reading unnecessary metadata

[Bananeweizen]

#242 introduced some eclipse-metadata.yml. To my understanding that is not needed at all. AFAIK only the sevntu checks have that yaml file in their jar (because it was introduced with that PR). And even there it's not needed, because the sevntu modules are perfectly found and displayed by the normal checkstyle-metadata. Deleting that yaml related code doesn't make any difference for me. (I've debugged the entire metadata loading with the sevntu eclipse plugin in my workspace, and I can configure and execute them as before).

At the same time, scanning all classes on the classpath for those yaml files takes an eternity and is the main responsible for the slow initialization of metadata on first access to any rule (remember #375). Below image shows this taking 27.8 seconds of CPU time on my performance laptop.

Am I missing anything about those yaml files or can we really just get rid of this?

[rnveach]

the sevntu checks have that yaml file in their jar
even there it's not needed, because the sevntu modules are perfectly found
Am I missing anything about those yaml files

I believe the purpose of the YAML was to provide extra data about the checks being presented in the metadata. I was not really involved in it's planning and development, but @romani should be able to confirm.

https://github.com/sevntu-checkstyle/sevntu.checkstyle/blob/master/eclipsecs-sevntu-plugin/src/com/github/sevntu/eclipse-metadata.yml
For example, eclipse-cs puts all the checks under categories. What category name to use for example is not provided in the other metadata. The YML has the name and descriptions to be used for this.
Sonar needs similar things. https://github.com/checkstyle/sonar-checkstyle/blob/eef33ccf76f73a35bb8579137ab003592dba722b/src/main/java/org/sonar/plugins/checkstyle/metadata/CheckstyleMetadata.java#L91-L92

the sevntu modules are perfectly found and displayed by the normal checkstyle-metadata

There are issues with sevntu since 8.36.1 and an issue has been sitting for a while. I tried providing fixes for the issue, but I believe my PRs were reverted because of some issues with the changes.
#316
sevntu-checkstyle/sevntu.checkstyle#857

scanning all classes on the classpath

Just so your aware, main Checkstyle does the same scanning when it needs to find a module that is not the FQCP and is not one of Checkstyle's main modules (shorthand or full name) ( https://checkstyle.org/checks.html ).

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Your picture cuts off on how far down specifically the slowdown goes. I am curious if the specific call is something from CS or is connected to the YML.

If it is XmlMetaReader#readAllModulesIncludingThirdPartyIfAny (https://github.com/checkstyle/checkstyle/blob/54616f662130aa0ca5afe45f72d36cdefb78a781/src/main/java/com/puppycrawl/tools/checkstyle/meta/XmlMetaReader.java) then this doesn't read the YML, but all the metadata of the checks.
Example: https://github.com/checkstyle/checkstyle/blob/54616f662130aa0ca5afe45f72d36cdefb78a781/src/main/resources/com/puppycrawl/tools/checkstyle/meta/checks/annotation/AnnotationLocationCheck.xml

[romani]

I though that all thirparty providers need to provide such details for eclipse-cs:
https://github.com/sevntu-checkstyle/sevntu.checkstyle/blob/7c5e2b668d191ff727687e9e381a08b044940aeb/eclipsecs-sevntu-plugin/src/com/github/sevntu/eclipse-metadata.yml#L1-L6

If we can optimize something wihtout loosing functionality - I am agree.

Looks like this yml was only for decaration purposes - sevntu-checkstyle/sevntu.checkstyle#822
previosly such data was in some other file(s). It might still there (I remember we discussed not removing old files for compatibility for some period of time), there is why it might works.

If we see way to improve, lets do this.