failing test for changing intermediate modules

This test highlights how changing an intermediate source path prevents
reloading of submodules. While this is somewhat of an edge case now, it
becomes quite common in the cacse where module versions are updated.

config/module/test-fixtures/change-intermediate-source/a/b/main.tf

@@ -0,0 +1 @@
+resource "test_resource" "a-b" {}

config/module/test-fixtures/change-intermediate-source/a/main.tf

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

config/module/test-fixtures/change-intermediate-source/c/b/main.tf

@@ -0,0 +1 @@
+resource "test_resource" "c-b" {}

config/module/test-fixtures/change-intermediate-source/c/main.tf

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

config/module/test-fixtures/change-intermediate-source/main.tf

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

config/module/test-fixtures/change-intermediate-source/main.tf.disabled

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

config/module/tree_test.go

@@ -724,7 +724,71 @@ func TestTreeLoad_conflictingSubmoduleNames(t *testing.T) {
 					t.Fatal("found wrong resource in b/c:", res.Name)
 				}
 			}
+		}
+	}
+}
+
+// changing the source for a module but not the module "path"
+func TestTreeLoad_changeIntermediateSource(t *testing.T) {
+	// copy the config to our tempdir this time, since we're going to edit it
+	td, err := ioutil.TempDir("", "tf")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	defer os.RemoveAll(td)
+
+	if err := copyDir(td, filepath.Join(fixtureDir, "change-intermediate-source")); err != nil {
+		t.Fatal(err)
+	}
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chdir(td); err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chdir(wd)
+
+	if err := os.MkdirAll(".terraform/modules", 0777); err != nil {
+		t.Fatal(err)
+	}
+	storage := &getter.FolderStorage{StorageDir: ".terraform/modules"}
+	cfg, err := config.LoadDir("./")
+	if err != nil {
+		t.Fatal(err)
+	}
+	tree := NewTree("", cfg)
+	if err := tree.Load(storage, GetModeGet); err != nil {
+		t.Fatalf("load failed: %s", err)
+	}
+
+	// now we change the source of our module, without changing its path
+	if err := os.Rename("main.tf.disabled", "main.tf"); err != nil {
+		t.Fatal(err)
+	}
+
+	// reload the tree
+	cfg, err = config.LoadDir("./")
+	if err != nil {
+		t.Fatal(err)
+	}
+	tree = NewTree("", cfg)
+	if err := tree.Load(storage, GetModeGet); err != nil {
+		t.Fatalf("load failed: %s", err)
+	}
 
+	// check for our resource in b
+	for _, c := range tree.Children() {
+		for _, gc := range c.Children() {
+			if len(gc.config.Resources) != 1 {
+				t.Fatalf("expected 1 resource in %s, got %d", gc.name, len(gc.config.Resources))
+			}
+			res := gc.config.Resources[0]
+			expected := "c-b"
+			if res.Name != expected {
+				t.Fatalf("expexted resource %q, got %q", expected, res.Name)
+			}
 		}
 	}
 }