refactor(env): Add a WithCancel option to the Env context (#43)

Author: dmcilvaney

internal/app/azldev/env.go

@@ -211,6 +211,20 @@ func (env *Env) Context() context.Context {
 	return env.ctx
 }
 
+// WithCancel returns a shallow copy of the [Env] with a child [context.Context]
+// derived from [context.WithCancel]. The returned [Env] shares all features
+// (FS, config, event listener, cmd factory, etc.) with the original but has an
+// independently cancellable context. The caller must call the returned
+// [context.CancelFunc] when done. Useful when performing parallel operations
+// that benefit from early cancellation on error.
+func (env *Env) WithCancel() (*Env, context.CancelFunc) {
+	childCtx, cancel := context.WithCancel(env.ctx)
+	childEnv := *env
+	childEnv.ctx = childCtx
+
+	return &childEnv, cancel
+}
+
 // ConfirmAutoResolution prompts the user to confirm auto-resolution of a problem. The provided
 // text is displayed to the user as explanation.
 func (env *Env) ConfirmAutoResolution(text string) bool {

internal/app/azldev/env_test.go

@@ -115,3 +115,20 @@ func TestEnvConstructionTime(t *testing.T) {
 	// Make sure it appears to be a valid time that's before or at *now*.
 	assert.LessOrEqual(t, testEnv.Env.ConstructionTime(), time.Now())
 }
+
+func TestEnvWithCancel(t *testing.T) {
+	testEnv := testutils.NewTestEnv(t)
+	original := testEnv.Env
+
+	child, cancel := original.WithCancel()
+	defer cancel()
+
+	// Child should share config and project dir with original.
+	assert.Equal(t, original.ProjectDir(), child.ProjectDir())
+	assert.Equal(t, original.Config(), child.Config())
+
+	// Cancelling the child should not cancel the original.
+	cancel()
+	require.Error(t, child.Err())
+	assert.NoError(t, original.Err())
+}