One of the security patches released 2026-03-09 [fixed a vulnerability](d1c7b04d09) caused by a misapplication of Go `case` statements, where the implementation would have been correct if Go `case` statements automatically fall through to the next case block, but they do not. This PR adds a semgrep rule which detects any empty `case` statement and raises an error, in order to prevent this coding mistake in the future.
For example, code like this will now trigger a build error:
```go
switch setting.Protocol {
case setting.HTTPUnix:
case setting.FCGI:
case setting.FCGIUnix:
default:
defaultLocalURL := string(setting.Protocol) + "://"
}
```
Example error:
```
cmd/web.go
❯❯❱ semgrep.config.forgejo-switch-empty-case
switch has a case block with no content. This is treated as "break" by Go, but developers may
confuse it for "fallthrough". To fix this error, disambiguate by using "break" or
"fallthrough".
279┆ switch setting.Protocol {
280┆ case setting.HTTPUnix:
281┆ case setting.FCGI:
282┆ case setting.FCGIUnix:
283┆ default:
284┆ defaultLocalURL := string(setting.Protocol) + "://"
285┆ if setting.HTTPAddr == "0.0.0.0" {
286┆ defaultLocalURL += "localhost"
287┆ } else {
288┆ defaultLocalURL += setting.HTTPAddr
```
As described in the error output, this error can be fixed by explicitly listing `break` (the real Go behaviour, to do nothing in the block), or by listing `fallthrough` (if the intent was to fall through).
All existing code triggering this detection has been changed to `break` (or, rarely, irrelevant cases have been removed), which should maintain the same code functionality. While performing this fixup, a light analysis was performed on each case and they *appeared* correct, but with ~65 cases I haven't gone into extreme depth.
Tests are present for the semgrep rule in `.semgrep/tests/go.go`.
## Checklist
The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).
### Documentation
- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.
### Release notes
- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11593
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>
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