ci: add deadcode check (#3)

* ci: add deadcode check

* ci: enforce deadcode gate

Author: vincentkoc

.github/workflows/ci.yml

@@ -37,13 +37,23 @@ jobs:
           go install honnef.co/go/tools/cmd/staticcheck@v0.7.0
           go install mvdan.cc/gofumpt@v0.9.2
           go install github.com/securego/gosec/v2/cmd/gosec@v2.26.1
+          go install golang.org/x/tools/cmd/deadcode@v0.45.0
 
       - name: Vet
         run: go vet ./...
 
       - name: Staticcheck
         run: '"$(go env GOPATH)/bin/staticcheck" ./...'
 
+      - name: Deadcode
+        run: |
+          output_file=$(mktemp)
+          "$(go env GOPATH)/bin/deadcode" -test ./... > "$output_file"
+          if [ -s "$output_file" ]; then
+            cat "$output_file"
+            exit 1
+          fi
+
       - name: Gofumpt
         run: |
           changed="$("$(go env GOPATH)/bin/gofumpt" -l .)"