From 6f9e3731acf9952ad3f242974c22ead4659d6239 Mon Sep 17 00:00:00 2001
From: Elijah Duffy <elijah@thatoneguy.ca>
Date: Tue, 3 Jun 2025 16:58:59 -0700
Subject: [PATCH] add Lifecycle.RequireUnique methods for load-once deps

---
 lifecycle.go      | 23 +++++++++++++++++++
 lifecycle_test.go | 57 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/lifecycle.go b/lifecycle.go
index 9c7de38..e609ced 100644
--- a/lifecycle.go
+++ b/lifecycle.go
@@ -123,6 +123,12 @@ func (app *Lifecycle) Require(modules ...*Module) error {
 	return app.RequireL(app.logger, modules...)
 }
 
+// RequireUnique is the same as Require, but it returns an error if any requested
+// module is already set up--rather than ignoring it.
+func (app *Lifecycle) RequireUnique(modules ...*Module) error {
+	return app.RequireUniqueL(app.logger, modules...)
+}
+
 // RequireL adds module(s) to the lifecycle with a specific logger and
 // immediately runs any setup functions. See Require for more details.
 // This variation is useful when you need to set up modules with a non-
@@ -163,6 +169,23 @@ func (app *Lifecycle) RequireL(logger *slog.Logger, modules ...*Module) error {
 	return nil
 }
 
+// RequireUniqueL is the same as RequireL, but it returns an error if any requested
+// module is already set up--rather than ignoring it.
+func (app *Lifecycle) RequireUniqueL(logger *slog.Logger, modules ...*Module) error {
+	// Check if any module is already set up
+	for _, mod := range modules {
+		if mod == nil {
+			return fmt.Errorf("module is nil")
+		}
+
+		if _, ok := app.setupTracker[mod.name]; ok {
+			return fmt.Errorf("module '%s' is already set up, cannot require it again", mod.name)
+		}
+	}
+
+	return app.RequireL(logger, modules...)
+}
+
 // setupSingle is a helper function to set up a single module. Returns an error
 // if the module cannot be set up or if dependencies are not satisfied.
 func (app *Lifecycle) setupSingle(mod *Module, logger *slog.Logger) error {
diff --git a/lifecycle_test.go b/lifecycle_test.go
index 0d381e2..ba5b2b3 100644
--- a/lifecycle_test.go
+++ b/lifecycle_test.go
@@ -222,6 +222,14 @@ func TestLifecycle_Require(t *testing.T) {
 	assert.Equal(t, lc.logger, mod.logger, "expected module logger to match lifecycle logger")
 }
 
+func TestLifecycle_RequireUnique(t *testing.T) {
+	lc := NewLifecycle()
+	mod := NewModule("module1", ModuleOpts{})
+	err := lc.RequireUnique(mod)
+	assert.NoError(t, err, "expected RequireL to succeed")
+	assert.Equal(t, lc.logger, mod.logger, "expected module logger to match lifecycle logger")
+}
+
 func TestLifecycle_RequireL(t *testing.T) {
 	cases := []struct {
 		name            string
@@ -324,7 +332,56 @@ func TestLifecycle_RequireL(t *testing.T) {
 			}
 		})
 	}
+}
 
+func TestLifecycle_RequireUniqueL(t *testing.T) {
+	cases := []struct {
+		name            string
+		modules         []*Module
+		existingModules []string
+		expectedErr     string
+	}{
+		{
+			name: "no existing modules",
+			modules: []*Module{
+				NewModule("module1", ModuleOpts{}),
+			},
+		},
+		{
+			name: "module already set up",
+			modules: []*Module{
+				NewModule("module1", ModuleOpts{}),
+				NewModule("module2", ModuleOpts{}),
+			},
+			existingModules: []string{"module1"},
+			expectedErr:     "module 'module1' is already set up, cannot require it again",
+		},
+		{
+			name:        "nil module",
+			modules:     []*Module{nil},
+			expectedErr: "module is nil",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			assert := assert.New(t)
+			lc := NewLifecycle()
+
+			// Fake existing modules
+			for _, modName := range tc.existingModules {
+				lc.setupTracker[modName] = 0 // Mark as set up
+			}
+
+			err := lc.RequireUniqueL(lc.logger, tc.modules...)
+			if tc.expectedErr == "" {
+				assert.NoError(err, "expected RequireUniqueL to succeed")
+			} else {
+				assert.Error(err, "expected RequireUniqueL to fail")
+				assert.Contains(err.Error(), tc.expectedErr, "expected error message to match")
+			}
+		})
+	}
 }
 
 func TestLifecycle_setupSingle(t *testing.T) {