feat: adding support for defining the backend file content

apis/v1beta1/types.go

@@ -34,6 +34,13 @@ type ProviderConfigSpec struct {
 	// +optional
 	Configuration *string `json:"configuration,omitempty"`
 
+	// Terraform backend file configuration content,
+	// it has the contents of the backend block as top-level attributes,
+	// without the need to wrap it in another terraform or backend block.
+	// More details at https://developer.hashicorp.com/terraform/language/settings/backends/configuration#file.
+	// +optional
+	BackendFile *string `json:"backendFile,omitempty"`
+
 	// PluginCache enables terraform provider plugin caching mechanism
 	// https://developer.hashicorp.com/terraform/cli/config/config-file#provider-plugin-cache
 	// +optional

examples/providerconfig-backend-file.yaml

@@ -0,0 +1,36 @@
+apiVersion: tf.upbound.io/v1beta1
+kind: ProviderConfig
+metadata:
+  name: default
+spec:
+  # Note that unlike most provider configs this one supports an array of
+  # credentials. This is because each Terraform workspace uses a single
+  # Crossplane provider config, but could use multiple Terraform providers each
+  # with their own credentials.
+  credentials:
+  - filename: gcp-credentials.json
+    source: Secret
+    secretRef:
+      namespace: upbound-system
+      name: gcp-creds
+      key: credentials
+  # This optional configuration block can be used to inject HCL into any
+  # workspace that uses this provider config, for example to setup Terraform
+  # providers.
+  configuration: |
+      provider "google" {
+        credentials = "gcp-credentials.json"
+        project     = "official-provider-testing"
+      }
+
+      // Defining partial backend configuration as documented at 
+      // https://developer.hashicorp.com/terraform/language/settings/backends/configuration#partial-configuration
+      terraform {
+        backend "kubernetes" {}
+      }
+  # Using backend configuration file as documented at
+  # https://developer.hashicorp.com/terraform/language/settings/backends/configuration#file
+  backendFile: |
+    secret_suffix     = "providerconfig-default"
+    namespace         = "upbound-system"
+    in_cluster_config = true

internal/controller/workspace/workspace.go

@@ -63,6 +63,7 @@ const (
 	errWriteGitCreds   = "cannot write .git-credentials to /tmp dir"
 	errWriteConfig     = "cannot write Terraform configuration " + tfConfig
 	errWriteMain       = "cannot write Terraform configuration " + tfMain
+	errWriteBackend    = "cannot write Terraform configuration " + tfBackendFile
 	errInit            = "cannot initialize Terraform configuration"
 	errWorkspace       = "cannot select Terraform workspace"
 	errResources       = "cannot list Terraform resources"
@@ -81,9 +82,10 @@ const (
 
 const (
 	// TODO(negz): Make the Terraform binary path and work dir configurable.
-	tfPath   = "terraform"
-	tfMain   = "main.tf"
-	tfConfig = "crossplane-provider-config.tf"
+	tfPath        = "terraform"
+	tfMain        = "main.tf"
+	tfConfig      = "crossplane-provider-config.tf"
+	tfBackendFile = "crossplane.remote.tfbackend"
 )
 
 func envVarFallback(envvar string, fallback string) string {
@@ -259,6 +261,12 @@ func (c *connector) Connect(ctx context.Context, mg resource.Managed) (managed.E
 		}
 	}
 
+	if pc.Spec.BackendFile != nil {
+		if err := c.fs.WriteFile(filepath.Join(dir, tfBackendFile), []byte(*pc.Spec.BackendFile), 0600); err != nil {
+			return nil, errors.Wrap(err, errWriteBackend)
+		}
+	}
+
 	// NOTE(ytsarev): user tf provider cache mechanism to speed up
 	// reconciliation, see https://developer.hashicorp.com/terraform/cli/config/config-file#provider-plugin-cache
 	if pc.Spec.PluginCache == nil {
@@ -279,6 +287,9 @@ func (c *connector) Connect(ctx context.Context, mg resource.Managed) (managed.E
 	}
 
 	o := make([]terraform.InitOption, 0, len(cr.Spec.ForProvider.InitArgs))
+	if pc.Spec.BackendFile != nil {
+		o = append(o, terraform.WithInitArgs([]string{"-backend-config=" + filepath.Join(dir, tfBackendFile)}))
+	}
 	o = append(o, terraform.WithInitArgs(cr.Spec.ForProvider.InitArgs))
 	if err := tf.Init(ctx, *pc.Spec.PluginCache, o...); err != nil {
 		return nil, errors.Wrap(err, errInit)

internal/controller/workspace/workspace_test.go

@@ -672,6 +672,53 @@ func TestConnect(t *testing.T) {
 			},
 			want: nil,
 		},
+		"SuccessUsingBackendFile": {
+			reason: "We should not return an error when we successfully 'connect' to Terraform using a Backend file",
+			fields: fields{
+				kube: &test.MockClient{
+					MockGet: test.NewMockGetFn(nil, func(obj client.Object) error {
+						if pc, ok := obj.(*v1beta1.ProviderConfig); ok {
+							cfg := "I'm HCL!"
+							backendFile := "I'm a backend!"
+							pc.Spec.Configuration = &cfg
+							pc.Spec.BackendFile = &backendFile
+						}
+						return nil
+					}),
+				},
+				usage: resource.TrackerFn(func(_ context.Context, _ resource.Managed) error { return nil }),
+				fs:    afero.Afero{Fs: afero.NewMemMapFs()},
+				terraform: func(_ string) tfclient {
+					return &MockTf{
+						MockInit: func(ctx context.Context, cache bool, o ...terraform.InitOption) error {
+							args := terraform.InitArgsToString(o)
+							if len(args) != 2 {
+								return errors.New("two init args are expected")
+							} else if args[0] != "-backend-config=/tf/no-you-id/crossplane.remote.tfbackend" {
+								return errors.Errorf("backend config arg has invalid value: %s", args[0])
+							}
+							return nil
+						},
+						MockGenerateChecksum: func(ctx context.Context) (string, error) { return tfChecksum, nil },
+						MockWorkspace:        func(_ context.Context, _ string) error { return nil },
+					}
+				},
+			},
+			args: args{
+				mg: &v1beta1.Workspace{
+					ObjectMeta: metav1.ObjectMeta{UID: uid},
+					Spec: v1beta1.WorkspaceSpec{
+						ForProvider: v1beta1.WorkspaceParameters{
+							InitArgs: []string{"-upgrade=true"},
+						},
+						ResourceSpec: xpv1.ResourceSpec{
+							ProviderConfigReference: &xpv1.Reference{},
+						},
+					},
+				},
+			},
+			want: nil,
+		},
 	}
 
 	for name, tc := range cases {

internal/terraform/terraform.go

@@ -148,6 +148,15 @@ func WithInitArgs(v []string) InitOption {
 	}
 }
 
+// InitArgsToString converts Terraform init arguments to a list of strings.
+func InitArgsToString(o []InitOption) []string {
+	io := &initOptions{}
+	for _, fn := range o {
+		fn(io)
+	}
+	return io.args
+}
+
 // RWMutex protects the terraform shared cache from corruption. If an init is
 // performed, it requires a write lock. Only one write lock at a time. If another
 // action is performed, a read lock is acquired. More than one read locks can be acquired.
@@ -157,12 +166,7 @@ var rwmutex = &sync.RWMutex{}
 
 // Init initializes a Terraform configuration.
 func (h Harness) Init(ctx context.Context, cache bool, o ...InitOption) error {
-	io := &initOptions{}
-	for _, fn := range o {
-		fn(io)
-	}
-
-	args := append([]string{"init", "-input=false", "-no-color"}, io.args...)
+	args := append([]string{"init", "-input=false", "-no-color"}, InitArgsToString(o)...)
 	cmd := exec.CommandContext(ctx, h.Path, args...) //nolint:gosec
 	cmd.Dir = h.Dir
 	for _, e := range os.Environ() {

package/crds/tf.upbound.io_providerconfigs.yaml

@@ -46,6 +46,12 @@ spec:
           spec:
             description: A ProviderConfigSpec defines the desired state of a ProviderConfig.
             properties:
+              backendFile:
+                description: Terraform backend file configuration content, it has
+                  the contents of the backend block as top-level attributes, without
+                  the need to wrap it in another terraform or backend block. More
+                  details at https://developer.hashicorp.com/terraform/language/settings/backends/configuration#file.
+                type: string
               configuration:
                 description: Configuration that should be injected into all workspaces
                   that use this provider config, expressed as inline HCL. This can