It is not clear why test reports cannot be parsed

Summary

There is very little information available when test reports cannot be parsed by GitLab for some reason.

For example, https://gitlab.com/camilstaps/rgx/pipelines/125654920/test_report.json just says "error parsing report". (This means the XML is syntactically valid; otherwise another error is given.) You can only find this error message by going to that URL; the test report page (or the test summary on an MR) provide no information at all: https://gitlab.com/camilstaps/rgx/pipelines/125654920/test_report.

Steps to reproduce

Here is a JUnit XML that I believe should be fine but fails to parse: junit.xml

Example Project

https://gitlab.com/camilstaps/rgx, see last commit to master.

What is the current bug behavior?

Very little information is given about what is wrong with the test report.

What is the expected correct behavior?

Some informative error message, preferably with line and column number (column no. because these files are automatically generated; lines may be long).

Relevant logs and/or screenshots

N/A.

Output of checks

This bug happens on GitLab.com.

Results of GitLab environment info

N/A.

Results of GitLab application Check

N/A.

Possible fixes

No idea, sorry. Thanks for looking into this!