Add snapshot-related test for the new graph-based config loader

This ensures we test snapshot related configuration loading. These tests
previously lived in the `configload` package.

internal/terraform/config_graph_build_test.go

@@ -0,0 +1,166 @@
+// Copyright IBM Corp. 2014, 2026
+// SPDX-License-Identifier: BUSL-1.1
+
+package terraform
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	"github.com/davecgh/go-spew/spew"
+	"github.com/go-test/deep"
+	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/terraform/internal/configs"
+	"github.com/hashicorp/terraform/internal/configs/configload"
+	"github.com/hashicorp/terraform/internal/tfdiags"
+)
+
+func TestLoadConfigWithSnapshot(t *testing.T) {
+	fixtureDir := filepath.Clean("testdata/config-graph/already-installed")
+	loader, err := configload.NewLoader(&configload.Config{
+		ModulesDir: filepath.Join(fixtureDir, ".terraform/modules"),
+	})
+	if err != nil {
+		t.Fatalf("unexpected error from NewLoader: %s", err)
+	}
+
+	_, got, diags := testLoadWithSnapshot(fixtureDir, loader, nil)
+	assertNoDiagnostics(t, diags)
+	if got == nil {
+		t.Fatalf("snapshot is nil; want non-nil")
+	}
+
+	t.Log(spew.Sdump(got))
+
+	{
+		gotModuleDirs := map[string]string{}
+		for k, m := range got.Modules {
+			gotModuleDirs[k] = m.Dir
+		}
+		wantModuleDirs := map[string]string{
+			"":                "testdata/config-graph/already-installed",
+			"child_a":         "testdata/config-graph/already-installed/.terraform/modules/child_a",
+			"child_a.child_c": "testdata/config-graph/already-installed/.terraform/modules/child_a/child_c",
+			"child_b":         "testdata/config-graph/already-installed/.terraform/modules/child_b",
+			"child_b.child_d": "testdata/config-graph/already-installed/.terraform/modules/child_b.child_d",
+		}
+
+		problems := deep.Equal(wantModuleDirs, gotModuleDirs)
+		for _, problem := range problems {
+			t.Error(problem)
+		}
+		if len(problems) > 0 {
+			return
+		}
+	}
+
+	gotRoot := got.Modules[""]
+	wantRoot := &configload.SnapshotModule{
+		Dir: "testdata/config-graph/already-installed",
+		Files: map[string][]byte{
+			"root.tf": []byte(`
+module "child_a" {
+  source  = "example.com/foo/bar_a/baz"
+  version = ">= 1.0.0"
+}
+
+module "child_b" {
+  source = "example.com/foo/bar_b/baz"
+  version = ">= 1.0.0"
+}
+`),
+		},
+	}
+	if !reflect.DeepEqual(gotRoot, wantRoot) {
+		t.Errorf("wrong root module snapshot\ngot: %swant: %s", spew.Sdump(gotRoot), spew.Sdump(wantRoot))
+	}
+
+}
+
+func TestLoadConfigWithSnapshot_invalidSource(t *testing.T) {
+	fixtureDir := filepath.Clean("testdata/config-graph/already-installed-now-invalid")
+
+	old, _ := os.Getwd()
+	os.Chdir(fixtureDir)
+	defer os.Chdir(old)
+
+	loader, err := configload.NewLoader(&configload.Config{
+		ModulesDir: ".terraform/modules",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error from NewLoader: %s", err)
+	}
+
+	_, _, diags := testLoadWithSnapshot(".", loader, nil)
+	if !diags.HasErrors() {
+		t.Error("LoadConfigWithSnapshot succeeded; want errors")
+	}
+}
+
+func TestSnapshotRoundtrip(t *testing.T) {
+	fixtureDir := filepath.Clean("testdata/config-graph/already-installed")
+	loader, err := configload.NewLoader(&configload.Config{
+		ModulesDir: filepath.Join(fixtureDir, ".terraform/modules"),
+	})
+	if err != nil {
+		t.Fatalf("unexpected error from NewLoader: %s", err)
+	}
+
+	_, snap, diags := testLoadWithSnapshot(fixtureDir, loader, nil)
+	assertNoDiagnostics(t, diags)
+	if snap == nil {
+		t.Fatalf("snapshot is nil; want non-nil")
+	}
+
+	snapLoader := configload.NewLoaderFromSnapshot(snap)
+	if loader == nil {
+		t.Fatalf("loader is nil; want non-nil")
+	}
+	rootMod, rootDiags := snapLoader.LoadRootModule(snap.Modules[""].Dir)
+	assertNoDiagnostics(t, rootDiags)
+
+	config, diags := BuildConfigWithGraph(
+		rootMod,
+		snapLoader.ModuleWalker(),
+		nil,
+		configs.MockDataLoaderFunc(snapLoader.LoadExternalMockData),
+	)
+	assertNoDiagnostics(t, diags)
+	if config == nil {
+		t.Fatalf("config is nil; want non-nil")
+	}
+	if config.Module == nil {
+		t.Fatalf("config has no root module")
+	}
+	if got, want := config.Module.SourceDir, "testdata/config-graph/already-installed"; got != want {
+		t.Errorf("wrong root module sourcedir %q; want %q", got, want)
+	}
+	if got, want := len(config.Module.ModuleCalls), 2; got != want {
+		t.Errorf("wrong number of module calls in root module %d; want %d", got, want)
+	}
+	childA := config.Children["child_a"]
+	if childA == nil {
+		t.Fatalf("child_a config is nil; want non-nil")
+	}
+	if childA.Module == nil {
+		t.Fatalf("child_a config has no module")
+	}
+	if got, want := childA.Module.SourceDir, "testdata/config-graph/already-installed/.terraform/modules/child_a"; got != want {
+		t.Errorf("wrong child_a sourcedir %q; want %q", got, want)
+	}
+	if got, want := len(childA.Module.ModuleCalls), 1; got != want {
+		t.Errorf("wrong number of module calls in child_a %d; want %d", got, want)
+	}
+}
+
+func assertNoDiagnostics[D hcl.Diagnostics | tfdiags.Diagnostics](t *testing.T, diags D) bool {
+	t.Helper()
+
+	if len(diags) != 0 {
+		t.Errorf("wrong number of diagnostics %d; want %d", len(diags), 0)
+		return true
+	}
+	return false
+}

internal/terraform/testdata/config-graph/already-installed-now-invalid/.terraform/modules/modules.json

@@ -0,0 +1,7 @@
+{
+  "Modules": [
+    { "Key": "", "Source": "", "Dir": "." },
+    { "Key": "foo", "Source": "./foo", "Dir": "foo" },
+    { "Key": "foo.bar", "Source": "./bar", "Dir": "foo/bar" }
+  ]
+}

internal/terraform/testdata/config-graph/already-installed-now-invalid/foo/bar/main.tf

@@ -0,0 +1,3 @@
+output "hello" {
+  value = "Hello from foo/bar"
+}

internal/terraform/testdata/config-graph/already-installed-now-invalid/foo/main.tf

@@ -0,0 +1,3 @@
+module "bar" {
+  source = "${path.module}/bar"
+}

internal/terraform/testdata/config-graph/already-installed-now-invalid/root.tf

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

internal/terraform/testdata/config-graph/already-installed/.terraform/modules/child_a/child_a.tf

@@ -0,0 +1,4 @@
+
+module "child_c" {
+  source  = "./child_c"
+}

internal/terraform/testdata/config-graph/already-installed/.terraform/modules/child_a/child_c/child_c.tf

@@ -0,0 +1,4 @@
+
+output "hello" {
+  value = "Hello from child_c"
+}

internal/terraform/testdata/config-graph/already-installed/.terraform/modules/child_b.child_d/child_d.tf

@@ -0,0 +1,4 @@
+
+output "hello" {
+  value = "Hello from child_d"
+}

internal/terraform/testdata/config-graph/already-installed/.terraform/modules/child_b/child_b.tf

@@ -0,0 +1,5 @@
+
+module "child_d" {
+  source  = "example.com/foo/bar_d/baz"
+  # Intentionally no version here
+}

internal/terraform/testdata/config-graph/already-installed/.terraform/modules/modules.json

@@ -0,0 +1,32 @@
+{
+  "Modules": [
+    {
+      "Key": "",
+      "Source": "",
+      "Dir": "testdata/config-graph/already-installed"
+    },
+    {
+      "Key": "child_a",
+      "Source": "example.com/foo/bar_a/baz",
+      "Version": "1.0.1",
+      "Dir": "testdata/config-graph/already-installed/.terraform/modules/child_a"
+    },
+    {
+      "Key": "child_b",
+      "Source": "example.com/foo/bar_b/baz",
+      "Version": "1.0.0",
+      "Dir": "testdata/config-graph/already-installed/.terraform/modules/child_b"
+    },
+    {
+      "Key": "child_a.child_c",
+      "Source": "./child_c",
+      "Dir": "testdata/config-graph/already-installed/.terraform/modules/child_a/child_c"
+    },
+    {
+      "Key": "child_b.child_d",
+      "Source": "example.com/foo/bar_d/baz",
+      "Version": "1.2.0",
+      "Dir": "testdata/config-graph/already-installed/.terraform/modules/child_b.child_d"
+    }
+  ]
+}

internal/terraform/testdata/config-graph/already-installed/root.tf

@@ -0,0 +1,10 @@
+
+module "child_a" {
+  source  = "example.com/foo/bar_a/baz"
+  version = ">= 1.0.0"
+}
+
+module "child_b" {
+  source = "example.com/foo/bar_b/baz"
+  version = ">= 1.0.0"
+}