core: Don't return error on RegisterModule() and RegisterAdapter()

These functions are called at init-time, and their inputs are hard-coded
so there are no environmental or user factors that could make it fail
or succeed; the error return values are often ignored, and when they're
not, they are usually a fatal error anyway. To ensure that a programmer
mistake is not missed, we now panic instead.

Last breaking change 🤞

Author: mholt

caddyconfig/configadapters.go

@@ -101,13 +101,14 @@ func JSONIndent(val interface{}) ([]byte, error) {
 }
 
 // RegisterAdapter registers a config adapter with the given name.
-// This should usually be done at init-time.
-func RegisterAdapter(name string, adapter Adapter) error {
+// This should usually be done at init-time. It panics if the
+// adapter cannot be registered successfully.
+func RegisterAdapter(name string, adapter Adapter) {
 	if _, ok := configAdapters[name]; ok {
-		return fmt.Errorf("%s: already registered", name)
+		panic(fmt.Errorf("%s: already registered", name))
 	}
 	configAdapters[name] = adapter
-	return caddy.RegisterModule(adapterModule{name, adapter})
+	caddy.RegisterModule(adapterModule{name, adapter})
 }
 
 // GetAdapter returns the adapter with the given name,

modules.go

@@ -125,33 +125,32 @@ type ModuleMap map[string]json.RawMessage
 // be properly recorded, this should be called in the
 // init phase of runtime. Typically, the module package
 // will do this as a side-effect of being imported.
-// This function returns an error if the module's info
-// is incomplete or invalid, or if the module is
-// already registered.
-func RegisterModule(instance Module) error {
+// This function panics if the module's info is
+// incomplete or invalid, or if the module is already
+// registered.
+func RegisterModule(instance Module) {
 	mod := instance.CaddyModule()
 
 	if mod.ID == "" {
-		return fmt.Errorf("module ID missing")
+		panic("module ID missing")
 	}
 	if mod.ID == "caddy" || mod.ID == "admin" {
-		return fmt.Errorf("module ID '%s' is reserved", mod.ID)
+		panic(fmt.Sprintf("module ID '%s' is reserved", mod.ID))
 	}
 	if mod.New == nil {
-		return fmt.Errorf("missing ModuleInfo.New")
+		panic("missing ModuleInfo.New")
 	}
 	if val := mod.New(); val == nil {
-		return fmt.Errorf("ModuleInfo.New must return a non-nil module instance")
+		panic("ModuleInfo.New must return a non-nil module instance")
 	}
 
 	modulesMu.Lock()
 	defer modulesMu.Unlock()
 
 	if _, ok := modules[string(mod.ID)]; ok {
-		return fmt.Errorf("module already registered: %s", mod.ID)
+		panic(fmt.Sprintf("module already registered: %s", mod.ID))
 	}
 	modules[string(mod.ID)] = mod
-	return nil
 }
 
 // GetModule returns module information from its ID (full name).

modules/caddyhttp/app.go

@@ -30,10 +30,7 @@ import (
 )
 
 func init() {
-	err := caddy.RegisterModule(App{})
-	if err != nil {
-		caddy.Log().Fatal(err.Error())
-	}
+	caddy.RegisterModule(App{})
 }
 
 // App is a robust, production-ready HTTP server.

modules/caddyhttp/caddyhttp.go

@@ -30,10 +30,7 @@ import (
 func init() {
 	weakrand.Seed(time.Now().UnixNano())
 
-	err := caddy.RegisterModule(tlsPlaceholderWrapper{})
-	if err != nil {
-		caddy.Log().Fatal(err.Error())
-	}
+	caddy.RegisterModule(tlsPlaceholderWrapper{})
 }
 
 // RequestMatcher is a type that can match to a request.