Branch analysis is available as part of Developer Edition.
Status vs Quality Gate
For short-lived branches, there is a kind of hard-coded quality gate focusing only on new issues. Its status is reflected by the green|red signal associated with each short-lived branch:
status: green / OK or red / ERROR
new open bugs > 0
new open vulnerabilities > 0
new open code smells > 0
It is possible to change the status of a short-lived branch from ERROR to OK (red to green), i.e. mergable, by manually confirming the issues. The same is true for the False-Positive and Won't Fix statuses. It means the status of a short-lived branch will be red only when there are Open issues in the branch.
Issue Creation and Synchronization
The issues visible on the short-lived branch are the new issues corresponding to files modified in the branch.
Modified files are determined based on the checksum of each file on the sonar.branch.target and the short-lived branch.
The ephemeral nature of short-lived branches means no explicit Leak Period is necessary; it's all new code. Thus, no "new code" data is available for a short-lived branch.
Settings and Quality Profiles on Branches
Branch settings and quality profiles default to those set for the master branch, and by design, it's not possible to configure other values.
Only the number of bugs, code smells, vulnerabilities and files are computed. As a consequence, you have no way to get a Quality Gate status as such on short-lived branch.
You cannot connect SonarLint to a short-lived branch.
Analysis of a short-lived branch based on another short-lived branch is not supported.