coder · aslilac · May 7, 2025 · May 7, 2025 · May 8, 2025 · May 8, 2025
diff --git a/coderd/files/overlay.go b/coderd/files/overlay.go
@@ -0,0 +1,56 @@
+package files
+
+import (
+	"io/fs"
+	"path"
+	"strings"
+)
+
+// withModulesFS allows you to "join" together the template files tar file fs.FS
+// with the Terraform modules tar file fs.FS. We could potentially turn this
+// into something more parameterized/configurable, but the requirements here are
+// a _bit_ odd, because every file in the modulesFS includes the
+// .terraform/modules/ folder at the beginning of it's path.
+type overlayFS struct {
+	baseFS   fs.FS
+	overlays []Overlay
+}
+
+type Overlay struct {
+	Path string
+	fs.FS
+}
+
+func NewOverlayFS(baseFS fs.FS, overlays []Overlay) fs.FS {
+	return overlayFS{
+		baseFS:   baseFS,
+		overlays: overlays,
+	}
+}
+
+func (f overlayFS) Open(p string) (fs.File, error) {
+	for _, overlay := range f.overlays {
+		if strings.HasPrefix(path.Clean(p), overlay.Path) {
+			return overlay.FS.Open(p)
+		}
+	}
+	return f.baseFS.Open(p)
+}
+
+func (f overlayFS) ReadDir(p string) ([]fs.DirEntry, error) {
+	for _, overlay := range f.overlays {
+		if strings.HasPrefix(path.Clean(p), overlay.Path) {
+			return overlay.FS.(fs.ReadDirFS).ReadDir(p)
+		}
+	}
+	return f.baseFS.(fs.ReadDirFS).ReadDir(p)
+}
+
+func (f overlayFS) ReadFile(p string) ([]byte, error) {
+	for _, overlay := range f.overlays {
+		if strings.HasPrefix(path.Clean(p), overlay.Path) {
+			return overlay.FS.(fs.ReadFileFS).ReadFile(p)
+		}
+	}
+	return f.baseFS.(fs.ReadFileFS).ReadFile(p)
+}
diff --git a/coderd/files/overlay_test.go b/coderd/files/overlay_test.go
@@ -0,0 +1,40 @@
+package files_test
+
+import (
+	"io/fs"
+	"testing"
+
+	"github.com/coder/coder/v2/coderd/files"
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/require"
+)
+
+func TestOverlayFS(t *testing.T) {
+	a := afero.NewMemMapFs()
+	afero.WriteFile(a, "main.tf", []byte("terraform {}"), 0o644)
+	afero.WriteFile(a, ".terraform/modules/example_module/main.tf", []byte("inaccessible"), 0o644)
+	afero.WriteFile(a, ".terraform/modules/other_module/main.tf", []byte("inaccessible"), 0o644)
+	b := afero.NewMemMapFs()
+	afero.WriteFile(b, ".terraform/modules/modules.json", []byte("{}"), 0o644)
+	afero.WriteFile(b, ".terraform/modules/example_module/main.tf", []byte("terraform {}"), 0o644)
+
+	it := files.NewOverlayFS(afero.NewIOFS(a), []files.Overlay{{
+		Path: ".terraform/modules",
+		FS:   afero.NewIOFS(b),
+	}})
+
+	content, err := fs.ReadFile(it, "main.tf")
+	require.NoError(t, err)
+	require.Equal(t, "terraform {}", string(content))
+
+	_, err = fs.ReadFile(it, ".terraform/modules/other_module/main.tf")
+	require.Error(t, err)
+
+	content, err = fs.ReadFile(it, ".terraform/modules/modules.json")
+	require.NoError(t, err)
+	require.Equal(t, "{}", string(content))
+
+	content, err = fs.ReadFile(it, ".terraform/modules/example_module/main.tf")
+	require.NoError(t, err)
+	require.Equal(t, "terraform {}", string(content))
+}
diff --git a/coderd/parameters.go b/coderd/parameters.go
@@ -13,6 +13,7 @@ import (
 
 	"github.com/coder/coder/v2/coderd/database"
 	"github.com/coder/coder/v2/coderd/database/dbauthz"
+	"github.com/coder/coder/v2/coderd/files"
 	"github.com/coder/coder/v2/coderd/httpapi"
 	"github.com/coder/coder/v2/coderd/httpmw"
 	"github.com/coder/coder/v2/codersdk"
@@ -68,7 +69,7 @@ func (api *API) templateVersionDynamicParameters(rw http.ResponseWriter, r *http
 		return
 	}
 
-	fs, err := api.FileCache.Acquire(fileCtx, fileID)
+	templateFS, err := api.FileCache.Acquire(fileCtx, fileID)
 	defer api.FileCache.Release(fileID)
 	if err != nil {
 		httpapi.Write(ctx, rw, http.StatusNotFound, codersdk.Response{
@@ -85,6 +86,19 @@ func (api *API) templateVersionDynamicParameters(rw http.ResponseWriter, r *http
 	tf, err := api.Database.GetTemplateVersionTerraformValues(ctx, templateVersion.ID)
 	if err == nil {
 		plan = tf.CachedPlan
+
+		if tf.CachedModuleFiles.Valid {
+			moduleFilesFS, err := api.FileCache.Acquire(fileCtx, tf.CachedModuleFiles.UUID)
+			defer api.FileCache.Release(tf.CachedModuleFiles.UUID)
+			if err != nil {
+				httpapi.Write(ctx, rw, http.StatusNotFound, codersdk.Response{
+					Message: "Internal error fetching Terraform modules.",
+					Detail:  err.Error(),
+				})
+				return
+			}
+			templateFS = files.NewOverlayFS(templateFS, []files.Overlay{{Path: ".terraform/modules", FS: moduleFilesFS}})
+		}
 	} else if !xerrors.Is(err, sql.ErrNoRows) {
 		httpapi.Write(ctx, rw, http.StatusInternalServerError, codersdk.Response{
 			Message: "Failed to retrieve Terraform values for template version",
@@ -124,7 +138,7 @@ func (api *API) templateVersionDynamicParameters(rw http.ResponseWriter, r *http
 	)
 
 	// Send an initial form state, computed without any user input.
-	result, diagnostics := preview.Preview(ctx, input, fs)
+	result, diagnostics := preview.Preview(ctx, input, templateFS)
 	response := codersdk.DynamicParametersResponse{
 		ID:          -1,
 		Diagnostics: previewtypes.Diagnostics(diagnostics),
@@ -152,7 +166,7 @@ func (api *API) templateVersionDynamicParameters(rw http.ResponseWriter, r *http
 				return
 			}
 			input.ParameterValues = update.Inputs
-			result, diagnostics := preview.Preview(ctx, input, fs)
+			result, diagnostics := preview.Preview(ctx, input, templateFS)
 			response := codersdk.DynamicParametersResponse{
 				ID:          update.ID,
 				Diagnostics: previewtypes.Diagnostics(diagnostics),

diff --git a/provisioner/terraform/modules_internal_test.go b/provisioner/terraform/modules_internal_test.go
@@ -42,6 +42,6 @@ func TestGetModulesArchive(t *testing.T) {
 	if runtime.GOOS != "windows" {
 		require.Equal(t, "05d2994c1a50ce573fe2c2b29507e5131ba004d15812d8bb0a46dc732f3211f5", hash)
 	} else {
-		require.Equal(t, "0001fc95ac0ac18188931db2ef28c42f51919ee24bc18482fab38d1ea9c7a4e8", hash)
+		require.Equal(t, "09a30ffc30138f9a411b280ef4581dcf22ffab8f0ca9de982329226400ec8520", hash)
 	}
 }