feat: fitness function & CI workflow

.github/workflows/fitness.yml

@@ -0,0 +1,17 @@
+name: Fitness Functions
+
+on:
+  pull_request:
+
+jobs:
+  fitness:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Run fitness tests
+        run: go test ./fitness/...

fitness/dependency_test.go

@@ -0,0 +1,39 @@
+package fitness
+
+import (
+	"encoding/json"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+func TestDependencyDirection(t *testing.T) {
+	hierarchy := []string{
+		"listener",
+		"proxy",
+		"router",
+		"backend",
+	}
+
+	for i, pkg := range hierarchy {
+		imports := getImports("load-balancer/" + pkg)
+		for _, imp := range imports {
+			for j := 0; j < i; j++ {
+				if strings.Contains(imp, "load-balancer/"+hierarchy[j]) {
+					t.Errorf(
+						"%s imports %s — violates downward dependency rule",
+						pkg, hierarchy[j],
+					)
+				}
+			}
+		}
+	}
+}
+
+func getImports(pkg string) []string {
+	cmd := exec.Command("go", "list", "-json", pkg)
+	out, _ := cmd.Output()
+	var info struct{ Imports []string }
+	json.Unmarshal(out, &info)
+	return info.Imports
+}

fitness/interface_size_test.go

@@ -0,0 +1,66 @@
+package fitness
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestInterfaceSizes(t *testing.T) {
+	maxMethods := 5
+	projectRoot := ".."
+
+	filepath.Walk(projectRoot, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return nil
+		}
+		if info.IsDir() {
+			name := info.Name()
+			if name == "vendor" || name == "fitness" || name == ".git" {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if !strings.HasSuffix(path, ".go") {
+			return nil
+		}
+		if strings.HasSuffix(path, "_test.go") {
+			return nil
+		}
+
+		fset := token.NewFileSet()
+		file, err := parser.ParseFile(fset, path, nil, 0)
+		if err != nil {
+			return nil
+		}
+
+		for _, decl := range file.Decls {
+			gd, ok := decl.(*ast.GenDecl)
+			if !ok || gd.Tok != token.TYPE {
+				continue
+			}
+			for _, spec := range gd.Specs {
+				ts := spec.(*ast.TypeSpec)
+				iface, ok := ts.Type.(*ast.InterfaceType)
+				if !ok {
+					continue
+				}
+
+				methodCount := len(iface.Methods.List)
+				name := file.Name.Name + "." + ts.Name.Name
+
+				if methodCount > maxMethods {
+					t.Errorf(
+						"%s (%s) has %d methods (max %d)",
+						name, path, methodCount, maxMethods,
+					)
+				}
+			}
+		}
+		return nil
+	})
+}