Prevent future deadlocks

When a (1) capped channel has more than one consumer, one of them will
effectively remain blocking as the other consumes the message from
the channel. Closing the channel unblocks any/all consumers.

Here we also unpublish previously public ModuleOperation.Done()
to further prevent deadlocks in the future, i.e. effectively
to prevent any place that schedules tasks to wait.

The only reason we keep the channel there for now is to make testing
*within the package* easier.

internal/terraform/module/module_loader_test.go

@@ -46,7 +46,7 @@ func TestModuleLoader_referenceCollection(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	<-modOp.doneCh
+	<-modOp.done()
 
 	manifestOp := NewModuleOperation(modPath, op.OpTypeLoadModuleMetadata)
 	err = ml.EnqueueModuleOp(manifestOp)
@@ -66,17 +66,12 @@ func TestModuleLoader_referenceCollection(t *testing.T) {
 	}
 
 	t.Log("waiting for all operations to finish")
-	for i := 0; i <= 2; i++ {
-		select {
-		case <-manifestOp.doneCh:
-			t.Log("manifest parsed")
-		case <-originsOp.doneCh:
-			t.Log("origins collected")
-		case <-targetsOp.doneCh:
-			t.Log("targets collected")
-		case <-ctx.Done():
-		}
-	}
+	<-manifestOp.done()
+	t.Log("manifest parsed")
+	<-originsOp.done()
+	t.Log("origins collected")
+	<-targetsOp.done()
+	t.Log("targets collected")
 
 	mod, err := ss.Modules.ModuleByPath(modPath)
 	if err != nil {

internal/terraform/module/module_manager.go

@@ -86,7 +86,7 @@ func (mm *moduleManager) EnqueueModuleOp(modPath string, opType op.OpType, defer
 	modOp.Defer = deferFunc
 	mm.loader.EnqueueModuleOp(modOp)
 	if mm.syncLoading {
-		<-modOp.Done()
+		<-modOp.done()
 	}
 	return nil
 }

internal/terraform/module/module_ops.go

@@ -39,9 +39,10 @@ func NewModuleOperation(modPath string, typ op.OpType) ModuleOperation {
 
 func (mo ModuleOperation) markAsDone() {
 	mo.doneCh <- struct{}{}
+	close(mo.doneCh)
 }
 
-func (mo ModuleOperation) Done() <-chan struct{} {
+func (mo ModuleOperation) done() <-chan struct{} {
 	return mo.doneCh
 }