config/module: validate that required parameters are passed through

config/module/test-fixtures/validate-required-var/child/main.tf

@@ -0,0 +1 @@
+variable "memory" {}

config/module/test-fixtures/validate-required-var/main.tf

@@ -0,0 +1,3 @@
+module "child" {
+    source = "./child"
+}

config/module/tree.go

@@ -257,9 +257,14 @@ func (t *Tree) Validate() error {
 		}
 
 		// Build the variables that the module defines
+		requiredMap := make(map[string]struct{})
 		varMap := make(map[string]struct{})
 		for _, v := range tree.config.Variables {
 			varMap[v.Name] = struct{}{}
+
+			if v.Required() {
+				requiredMap[v.Name] = struct{}{}
+			}
 		}
 
 		// Compare to the keys in our raw config for the module
@@ -270,6 +275,17 @@ func (t *Tree) Validate() error {
 					m.Name, k)
 				return newErr
 			}
+
+			// Remove the required
+			delete(requiredMap, k)
+		}
+
+		// If we have any required left over, they aren't set.
+		for k, _ := range requiredMap {
+			newErr.Err = fmt.Errorf(
+				"module %s: required variable %s not set",
+				m.Name, k)
+			return newErr
 		}
 	}
 

config/module/tree_test.go

@@ -148,6 +148,17 @@ func TestTreeValidate_notLoaded(t *testing.T) {
 	}
 }
 
+func TestTreeValidate_requiredChildVar(t *testing.T) {
+	tree := NewTree("", testConfig(t, "validate-required-var"))
+
+	if err := tree.Load(testStorage(t), GetModeGet); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if err := tree.Validate(); err == nil {
+		t.Fatal("should error")
+	}
+}
 
 const treeLoadStr = `
 root