Docs: Aggregate AppSec troubleshooting

Support is seeing many tickets about these errors and warnings.
This adds basic advice about where to find more specific messages
and how to enable logging to find even more details.

The idea behind updating both `application_security/index.md` and
`job_artifacts.md` with almost similar advice is that the latter
is probably the "last resort".

More details and review discussion:
https://gitlab.com/gitlab-org/gitlab/merge_requests/42486

doc/ci/pipelines/job_artifacts.md

@@ -431,6 +431,17 @@ To erase a job:
 
 In order to retrieve a job artifact of a different project, you might need to use a private token in order to [authenticate and download](../../api/job_artifacts.md#get-job-artifacts) the artifacts.
 
+## Troubleshooting
+
+### Error message `No files to upload`
+
+This is often preceded by other errors or warnings that specify the filename and why it wasn't
+generated in the first place. Please check the entire job log for such messages.
+
+If you find no helpful messages, please retry the failed job after activating
+[CI debug logging](../variables/README.md#debug-logging).
+This provides useful information to investigate further.
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues

doc/user/application_security/container_scanning/index.md

@@ -433,3 +433,7 @@ This is a result of a bug in Docker which is now [fixed](https://github.com/cont
 To prevent the error, ensure the Docker version that the runner is using is
 `18.09.03` or higher. For more information, see
 [issue #10241](https://gitlab.com/gitlab-org/gitlab/-/issues/10241 "Investigate why Container Scanning is not working with NFS mounts").
+
+### Getting warning message `gl-container-scanning-report.json: no matching files`
+
+For information on this, see the [general Application Security troubleshooting section](../../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload).

doc/user/application_security/dast/index.md

@@ -897,6 +897,10 @@ Change the number after `-Xmx` to the required memory amount.
 
 If your DAST job exceeds the job timeout and you need to reduce the scan duration, we shared some tips for optimizing DAST scans in a [blog post](https://about.gitlab.com/blog/2020/08/31/how-to-configure-dast-full-scans-for-complex-web-applications/).
 
+### Getting warning message `gl-dast-report.json: no matching files`
+
+For information on this, see the [general Application Security troubleshooting section](../../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload).
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues

doc/user/application_security/dependency_scanning/index.md

@@ -485,6 +485,10 @@ Consider updating to Docker `19.03.1` or greater. Older versions are not
 affected. Read more in
 [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/13830#note_211354992 "Current SAST container fails").
 
+### Getting warning message `gl-dependency-scanning-report.json: no matching files`
+
+For information on this, see the [general Application Security troubleshooting section](../../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload).
+
 ### Limitation when using rules:exists
 
 The [dependency scanning CI template](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/ci/templates/Security/Dependency-Scanning.gitlab-ci.yml)

doc/user/application_security/index.md

@@ -458,6 +458,15 @@ To fix this issue, you can either:
 [Learn more on overriding SAST jobs](sast/index.md#overriding-sast-jobs).
 All the security scanning tools define their stage, so this error can occur with all of them.
 
+### Getting warning messages `… report.json: no matching files`
+
+This is often followed by the [error `No files to upload`](../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload),
+and preceded by other errors or warnings that indicate why the JSON report wasn't generated. Please
+check the entire job log for such messages. If you don't find these messages, retry the failed job
+after setting `SECURE_LOG_LEVEL: "debug"` as a
+[custom environment variable](../../ci/variables/README.md#custom-environment-variables).
+This provides useful information to investigate further.
+
 ### Getting error message `sast job: config key may not be used with 'rules': only/except`
 
 When [including](../../ci/yaml/README.md#includetemplate) a `.gitlab-ci.yml` template

doc/user/application_security/sast/index.md

@@ -547,3 +547,7 @@ This error occurs when the Docker version that runs the SAST job is `19.03.0`.
 Consider updating to Docker `19.03.1` or greater. Older versions are not
 affected. Read more in
 [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/13830#note_211354992 "Current SAST container fails").
+
+### Getting warning message `gl-sast-report.json: no matching files`
+
+For information on this, see the [general Application Security troubleshooting section](../../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload).

doc/user/application_security/secret_detection/index.md

@@ -197,3 +197,9 @@ We have created a [short video walkthrough](https://youtu.be/wDtc_K00Y0A) showca
 <figure class="video-container">
   <iframe src="https://www.youtube.com/embed/wDtc_K00Y0A" frameborder="0" allowfullscreen="true"> </iframe>
 </figure>
+
+## Troubleshooting
+
+### Getting warning message `gl-secret-detection-report.json: no matching files`
+
+For information on this, see the [general Application Security troubleshooting section](../../../ci/pipelines/job_artifacts.md#error-message-no-files-to-upload).