ci: detect and prevent empty case statements in Go code (#11593)

One of the security patches released 2026-03-09 [fixed a vulnerability](https://codeberg.org/forgejo/forgejo/pulls/11513/commits/d1c7b04d09f6a13896eaa1322ac690b2021539da) 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>

.semgrep/config/go.yaml

@@ -0,0 +1,18 @@
+rules:
+  - id: forgejo-switch-empty-case
+    pattern-either:
+      - pattern: |-
+          switch $_ {
+            case $_:
+          }
+      - patterns:
+        - pattern: |-
+            switch {
+              case $_:
+            }
+    languages:
+      - go
+    severity: ERROR
+    message: >
+      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".

.semgrep/tests/go.go

@@ -0,0 +1,44 @@
+// Copyright 2014 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cmd
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	_ "net/http/pprof" // Used for debugging if enabled and a web server is running
+
+	"forgejo.org/modules/setting"
+)
+
+func setPortEmptyCaseBad(port string) error {
+	setting.AppURL = strings.Replace(setting.AppURL, setting.HTTPPort, port, 1)
+	setting.HTTPPort = port
+
+	// ruleid:forgejo-switch-empty-case
+	switch setting.Protocol {
+	case setting.HTTPUnix:
+	case setting.FCGI:
+	case setting.FCGIUnix:
+	default:
+		defaultLocalURL := string(setting.Protocol) + "://"
+	}
+
+	// ok:forgejo-switch-empty-case
+	switch setting.Protocol {
+	case setting.HTTPUnix:
+		break
+	case setting.FCGI:
+		break
+	case setting.FCGIUnix:
+		break
+	default:
+		defaultLocalURL := string(setting.Protocol) + "://"
+	}
+
+	return nil
+}

cmd/forgejo/forgejo.go

@@ -126,7 +126,9 @@ func installSignals(ctx context.Context) (context.Context, context.CancelFunc) {
 		)
 		select {
 		case <-signalChannel:
+			break
 		case <-ctx.Done():
+			break
 		}
 		cancel()
 		signal.Reset()

cmd/web.go

@@ -278,8 +278,11 @@ func setPort(port string) error {
 
 	switch setting.Protocol {
 	case setting.HTTPUnix:
+		break
 	case setting.FCGI:
+		break
 	case setting.FCGIUnix:
+		break
 	default:
 		defaultLocalURL := string(setting.Protocol) + "://"
 		if setting.HTTPAddr == "0.0.0.0" {

models/gitea_migrations/v1_13/v151.go

@@ -25,6 +25,7 @@ func SetDefaultPasswordToArgon2(x *xorm.Engine) error {
 		return err
 	case setting.Database.Type.IsSQLite3():
 		// drop through
+		break
 	default:
 		log.Fatal("Unrecognized DB")
 	}

models/packages/descriptor.go

@@ -174,8 +174,10 @@ func GetPackageDescriptor(ctx context.Context, pv *PackageVersion) (*PackageDesc
 		metadata = &debian.Metadata{}
 	case TypeGeneric:
 		// generic packages have no metadata
+		break
 	case TypeGo:
 		// go packages have no metadata
+		break
 	case TypeHelm:
 		metadata = &helm.Metadata{}
 	case TypeNuGet:

modules/eventsource/manager.go

@@ -39,7 +39,9 @@ func (m *Manager) Register(uid int64) <-chan *Event {
 	}
 	select {
 	case m.connection <- struct{}{}:
+		break
 	default:
+		break
 	}
 	m.mutex.Unlock()
 	return messenger.Register()

modules/eventsource/manager_run.go

@@ -47,7 +47,9 @@ loop:
 				// empty the connection channel
 				select {
 				case <-m.connection:
+					break
 				default:
+					break
 				}
 			}
 			m.mutex.Unlock()
@@ -63,7 +65,9 @@ loop:
 					// We won't change the "then" time because there could be concurrency issues
 					select {
 					case <-timer.C:
+						break
 					default:
+						break
 					}
 					continue
 				}

modules/eventsource/messenger.go

@@ -62,7 +62,9 @@ func (m *Messenger) SendMessage(message *Event) {
 		channel := m.channels[i]
 		select {
 		case channel <- message:
+			break
 		default:
+			break
 		}
 	}
 }

modules/git/diff.go

@@ -221,6 +221,7 @@ func CutDiffAroundLine(originalDiff io.Reader, line int64, old bool, numbersOfLi
 				}
 			case '\\':
 				// FIXME: handle `\ No newline at end of file`
+				break
 			default:
 				currentLine++
 				otherLine++

modules/git/pushoptions/pushoptions.go

@@ -65,12 +65,8 @@ func (o *gitPushOptions) Parse(data string) bool {
 		value = "true"
 	}
 	switch Key(key) {
-	case RepoPrivate:
-	case RepoTemplate:
-	case AgitTopic:
-	case AgitForcePush:
-	case AgitTitle:
-	case AgitDescription:
+	case RepoPrivate, RepoTemplate, AgitTopic, AgitForcePush, AgitTitle, AgitDescription:
+		break
 	default:
 		return false
 	}

modules/git/repo_stats.go

@@ -98,6 +98,7 @@ func (repo *Repository) GetCodeActivityStats(fromTime time.Time, branch string)
 				}
 				switch p {
 				case 1: // Separator
+					break
 				case 2: // Commit sha-1
 					stats.CommitCount++
 				case 3: // Author

modules/graceful/manager.go

@@ -164,6 +164,7 @@ func (g *Manager) doHammerTime(d time.Duration) {
 	g.lock.Lock()
 	select {
 	case <-g.hammerCtx.Done():
+		break
 	default:
 		log.Warn("Setting Hammer condition")
 		g.hammerCtxCancel()
@@ -180,6 +181,7 @@ func (g *Manager) doTerminate() {
 	g.lock.Lock()
 	select {
 	case <-g.terminateCtx.Done():
+		break
 	default:
 		log.Warn("Terminating")
 		g.terminateCtxCancel()

modules/graceful/manager_common.go

@@ -86,6 +86,7 @@ func (g *Manager) DoGracefulShutdown() {
 	g.lock.Lock()
 	select {
 	case <-g.shutdownRequested:
+		break
 	default:
 		close(g.shutdownRequested)
 	}

modules/indexer/code/indexer.go

@@ -215,7 +215,9 @@ func Init() {
 		}
 		select {
 		case waitChannel <- time.Since(start):
+			break
 		case <-graceful.GetManager().IsShutdown():
+			break
 		}
 
 		close(waitChannel)

modules/indexer/issues/indexer.go

@@ -141,7 +141,9 @@ func InitIssueIndexer(syncReindex bool) {
 	if syncReindex {
 		select {
 		case <-indexerInitWaitChannel:
+			break
 		case <-graceful.GetManager().IsShutdown():
+			break
 		}
 	} else if setting.Indexer.StartupTimeout > 0 {
 		go func() {

modules/log/event_writer_base.go

@@ -80,7 +80,9 @@ func (b *EventWriterBaseImpl) Run(ctx context.Context) {
 		if pause := b.GetPauseChan(); pause != nil {
 			select {
 			case <-pause:
+				break
 			case <-ctx.Done():
+				break
 			}
 		}
 	}
@@ -178,6 +180,7 @@ func eventWriterStopWait(w EventWriter) {
 	close(w.Base().Queue)
 	select {
 	case <-w.Base().stopped:
+		break
 	case <-time.After(2 * time.Second):
 		FallbackErrorf("unable to stop log writer %q in time, skip", w.GetWriterName())
 	}

modules/log/logger_impl.go

@@ -58,6 +58,7 @@ func (l *LoggerImpl) SendLogEvent(event *Event) {
 		}
 		select {
 		case w.Base().Queue <- formatted:
+			break
 		default:
 			bs, _ := json.Marshal(event)
 			FallbackErrorf("log writer %q queue is full, event: %v", w.GetWriterName(), string(bs))

modules/markup/html.go

@@ -742,6 +742,7 @@ func shortLinkProcessor(ctx *RenderContext, node *html.Node) {
 		// fast path: empty string, ignore
 		case "":
 			// leave image as false
+			break
 		case ".jpg", ".jpeg", ".png", ".tif", ".tiff", ".webp", ".gif", ".bmp", ".ico", ".svg":
 			image = true
 		}

modules/migration/retry_downloader.go

@@ -44,6 +44,7 @@ func (d *RetryDownloader) retry(work func() error) error {
 		case <-d.ctx.Done():
 			return d.ctx.Err()
 		case <-time.After(time.Second * time.Duration(d.RetryDelay)):
+			break
 		}
 	}
 	return err

modules/proxyprotocol/conn.go

@@ -262,6 +262,7 @@ func (p *Conn) readV2ProxyHeader() error {
 		// - \x1 : PROXY : the connection was established on behalf of another node,
 		//   and reflects the original connection endpoints. The receiver must then use
 		//   the information provided in the protocol block to get original the address.
+		break
 	default:
 		// - other values are unassigned and must not be emitted by senders. Receivers
 		//   must drop connections presenting unexpected values here.
@@ -466,7 +467,9 @@ func (p *Conn) readV1ProxyHeader() error {
 		p.localAddr = p.conn.RemoteAddr()
 		return nil
 	case "TCP4":
+		break
 	case "TCP6":
+		break
 	default:
 		p.conn.Close()
 		return &ErrBadAddressType{parts[1]}

modules/queue/workergroup.go

@@ -56,6 +56,7 @@ func (q *WorkerPoolQueue[T]) doDispatchBatchToWorker(wg *workerGroup[T], flushCh
 	full := false
 	select {
 	case q.batchChan <- batch:
+		break
 	default:
 		full = true
 	}
@@ -76,6 +77,7 @@ func (q *WorkerPoolQueue[T]) doDispatchBatchToWorker(wg *workerGroup[T], flushCh
 	if full {
 		select {
 		case q.batchChan <- batch:
+			break
 		case flush := <-flushChan:
 			q.doWorkerHandle(batch)
 			q.doFlush(wg, flush)
@@ -105,7 +107,9 @@ func (q *WorkerPoolQueue[T]) doWorkerHandle(batch []T) {
 		log.Error("Queue %q failed to handle batch of %d items, backoff for a few seconds", q.GetName(), len(batch))
 		select {
 		case <-q.ctxRun.Done():
+			break
 		case <-time.After(time.Duration(unhandledItemRequeueDuration.Load())):
+			break
 		}
 	}
 	for _, item := range unhandled {
@@ -170,7 +174,9 @@ func (q *WorkerPoolQueue[T]) doStartNewWorker(wp *workerGroup[T]) {
 				t.Reset(workerIdleDuration)
 				select {
 				case <-t.C:
+					break
 				default:
+					break
 				}
 			case <-t.C:
 				q.workerNumMu.Lock()
@@ -296,6 +302,7 @@ func (q *WorkerPoolQueue[T]) doRun() {
 			go func() { wg.wg.Wait(); close(workerDone) }()
 			select {
 			case <-workerDone:
+				break
 			case <-time.After(shutdownTimeout):
 				log.Error("Queue %q is shutting down, but workers are still running after timeout", q.GetName())
 			}

modules/queue/workerqueue.go

@@ -110,6 +110,7 @@ func (q *WorkerPoolQueue[T]) FlushWithContext(ctx context.Context, timeout time.
 	// if it blocks, it means that there is a flush in progress or the queue hasn't been started yet
 	select {
 	case q.flushChan <- c:
+		break
 	case <-ctx.Done():
 		return ctx.Err()
 	case <-q.ctxRun.Done():

modules/setting/cache.go

@@ -53,6 +53,7 @@ func loadCacheFrom(rootCfg ConfigProvider) {
 	CacheService.Adapter = sec.Key("ADAPTER").In("memory", []string{"memory", "redis", "memcache", "twoqueue"})
 	switch CacheService.Adapter {
 	case "memory":
+		break
 	case "redis", "memcache":
 		CacheService.Conn = strings.Trim(sec.Key("HOST").String(), "\" ")
 	case "twoqueue":

modules/setting/incoming_email.go

@@ -82,6 +82,7 @@ func checkReplyToAddress() error {
 	case 0:
 		return fmt.Errorf("%s must appear in the user part of the address (before the @)", IncomingEmail.TokenPlaceholder)
 	case 1:
+		break
 	default:
 		return fmt.Errorf("%s must appear only once", IncomingEmail.TokenPlaceholder)
 	}

modules/setting/mailer.go

@@ -235,6 +235,7 @@ func loadMailerFrom(rootCfg ConfigProvider) {
 			}
 		}
 	case "dummy": // just mention and do nothing
+		break
 	}
 
 	if MailService.From != "" {

modules/templates/helper.go

@@ -229,6 +229,7 @@ func HTMLFormat(s string, rawArgs ...any) template.HTML {
 		switch v := v.(type) {
 		case nil, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, template.HTML:
 			// for most basic types (including template.HTML which is safe), just do nothing and use it
+			break
 		case string:
 			args[i] = template.HTMLEscapeString(v)
 		case fmt.Stringer:

modules/templates/util_date.go

@@ -75,6 +75,7 @@ func anyToTime(any any) (t time.Time, isZero bool) {
 	switch v := any.(type) {
 	case nil:
 		// it is zero
+		break
 	case *time.Time:
 		if v != nil {
 			t = *v

modules/translation/i18n/localestore.go

@@ -145,6 +145,7 @@ func (l *locale) LookupPluralByForm(trKey string, pluralForm PluralFormIndex) st
 		suffix = PluralFormSeparator + "many"
 	case PluralFormOther:
 		// No suffix for the "other" string.
+		break
 	default:
 		log.Error("Invalid plural form index %d", pluralForm)
 		return ""
@@ -248,6 +249,7 @@ func PrepareArgsForHTML(trArgs ...any) []any {
 		switch v := v.(type) {
 		case nil, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, template.HTML:
 			// for most basic types (including template.HTML which is safe), just do nothing and use it
+			break
 		case string:
 			args[i] = template.HTMLEscapeString(v)
 		case fmt.Stringer:

modules/translation/localeiter/utils.go

@@ -56,6 +56,7 @@ func iterateMessagesNextInner(onMsgid func(string, string, string) error, data m
 				pluralSuffix = key
 			case "other":
 				// do nothing
+				break
 			default:
 				realKey = fullKey
 			}
@@ -71,6 +72,7 @@ func iterateMessagesNextInner(onMsgid func(string, string, string) error, data m
 
 		case nil:
 			// do nothing
+			break
 
 		default:
 			return fmt.Errorf("Unexpected JSON type: %s - %T", fullKey, value)

routers/api/packages/chef/auth.go

@@ -141,6 +141,7 @@ func getSignVersion(req *http.Request) (string, error) {
 
 	switch m[1] {
 	case "1.0", "1.1", "1.2", "1.3":
+		break
 	default:
 		return "", util.NewInvalidArgumentErrorf("unsupported version")
 	}

routers/api/v1/repo/repo.go

@@ -176,6 +176,7 @@ func Search(ctx *context.APIContext) {
 		opts.Mirror = optional.Some(false)
 		opts.Collaborate = optional.Some(true)
 	case "":
+		break
 	default:
 		ctx.Error(http.StatusUnprocessableEntity, "", fmt.Errorf("Invalid search mode: \"%s\"", mode))
 		return

routers/web/admin/diagnosis.go

@@ -54,7 +54,9 @@ func MonitorDiagnosis(ctx *context.Context) {
 
 	select {
 	case <-time.After(time.Duration(seconds) * time.Second):
+		break
 	case <-ctx.Done():
+		break
 	}
 	pprof.StopCPUProfile()
 	trace.Stop()

routers/web/admin/queue_tester.go

@@ -34,7 +34,9 @@ func initTestQueueOnce() {
 			for range t {
 				select {
 				case <-graceful.GetManager().ShutdownContext().Done():
+					break
 				case <-time.After(5 * time.Second):
+					break
 				}
 			}
 			return nil
@@ -56,6 +58,7 @@ func initTestQueueOnce() {
 			for {
 				select {
 				case <-ctx.Done():
+					break
 				case <-time.After(500 * time.Millisecond):
 					if adding {
 						if testQueue.GetQueueItemNumber() == qs.Length {

routers/web/auth/oauth.go

@@ -1418,6 +1418,7 @@ func generateCodeChallenge(ctx *context.Context, provider string) (codeChallenge
 	case *openidConnect.Provider, *fitbit.Provider, *zoom.Provider:
 		// those providers forward the `code_verifier`
 		// a code_challenge can be generated
+		break
 	}
 
 	codeVerifier := util.CryptoRandomString(util.RandomStringHigh)

routers/web/repo/repo.go

@@ -634,6 +634,7 @@ func SearchRepo(ctx *context.Context) {
 		opts.Mirror = optional.Some(false)
 		opts.Collaborate = optional.Some(true)
 	case "":
+		break
 	default:
 		ctx.Error(http.StatusUnprocessableEntity, fmt.Sprintf("Invalid search mode: \"%s\"", mode))
 		return

routers/web/user/home.go

@@ -511,8 +511,6 @@ func buildIssueOverview(ctx *context.Context, unitType unit.Type) {
 	}
 
 	switch filterMode {
-	case issues_model.FilterModeAll:
-	case issues_model.FilterModeYourRepositories:
 	case issues_model.FilterModeAssign:
 		opts.AssigneeID = ctx.Doer.ID
 	case issues_model.FilterModeCreate:
@@ -846,7 +844,7 @@ func getUserIssueStats(ctx *context.Context, ctxUser *user_model.User, filterMod
 		openClosedOpts := opts.Copy()
 		switch filterMode {
 		case issues_model.FilterModeAll:
-			// no-op
+			break
 		case issues_model.FilterModeYourRepositories:
 			openClosedOpts.AllPublic = false
 		case issues_model.FilterModeAssign:

routers/web/user/package.go

@@ -180,8 +180,6 @@ func ViewPackageVersion(ctx *context.Context) {
 	ctx.Data["PackageRegistryHost"] = setting.Packages.RegistryHost
 
 	switch pd.Package.Type {
-	case packages_model.TypeContainer:
-
 	case packages_model.TypeAlpine:
 		branches := make(container.Set[string])
 		repositories := make(container.Set[string])

services/actions/job_emitter.go

@@ -85,6 +85,7 @@ func checkJobsOfRun(ctx context.Context, runID int64, recursionCount int) error
 
 					case behaviourExecuteJob:
 						// Intentional blank case -- proceed with updating the status of the job to waiting.
+						break
 
 					case behaviourIgnoreJob:
 						// Skip updating this job's status to waiting, continue with other jobs in the run.

services/convert/activitypub_user_action.go

@@ -164,13 +164,6 @@ func ActionToForgeUserActivity(ctx context.Context, action *activities_model.Act
 			renderIssue(action.Comment.Issue),
 			renderedComment,
 		)
-	case activities_model.ActionMirrorSyncPush:
-	case activities_model.ActionMirrorSyncCreate:
-	case activities_model.ActionMirrorSyncDelete:
-	case activities_model.ActionPublishRelease:
-	case activities_model.ActionPullReviewDismissed:
-	case activities_model.ActionPullRequestReadyForReview:
-	case activities_model.ActionAutoMergePullRequest:
 	}
 
 	return makeUserActivity("performed an unrecognised action: %s", action.OpType.String())

services/mailer/incoming/incoming.go

@@ -69,6 +69,7 @@ func Init(ctx context.Context) error {
 				case <-ctx.Done():
 					return
 				case <-time.NewTimer(10 * time.Second).C:
+					break
 				}
 			}
 		}
@@ -123,6 +124,7 @@ func processIncomingEmails(ctx context.Context) error {
 			case <-ctx.Done():
 				return nil
 			case <-time.NewTimer(time.Second).C:
+				break
 			}
 		}
 	}

services/migrations/github.go

@@ -182,6 +182,7 @@ func (g *GithubDownloaderV3) waitAndPickClient() {
 			timer.Stop()
 			return
 		case <-timer.C:
+			break
 		}
 
 		err := g.RefreshRate()

services/pull/patch_unmerged.go

@@ -170,6 +170,7 @@ func unmergedFiles(ctx context.Context, tmpBasePath string, unmerged chan *unmer
 		switch line.stage {
 		case 0:
 			// Should not happen as this represents successfully merged file - we will tolerate and ignore though
+			break
 		case 1:
 			if next.stage1 != nil || next.stage2 != nil || next.stage3 != nil {
 				// We need to handle the unstaged file stage1,stage2,stage3

services/repository/gitgraph/parser.go

@@ -184,7 +184,7 @@ func (parser *Parser) ParseGlyphs(glyphs []byte) {
 		case '-':
 			parser.setLeftFlow(i)
 		case ' ':
-			// no-op
+			break
 		default:
 			parser.newFlow(i)
 		}

services/task/migrate.go

@@ -108,6 +108,7 @@ func runMigrateTask(ctx context.Context, t *admin_model.Task) (err error) {
 		for {
 			select {
 			case <-time.After(2 * time.Second):
+				break
 			case <-ctx.Done():
 				return
 			}