command: Auto-select single workspace if necessary

When initializing a backend, if the currently selected workspace does
not exist, the user is prompted to select from the list of workspaces
the backend provides.

Instead, we should automatically select the only workspace available
_if_ that's all that's there.

Although with being a nice bit of polish, this enables future
improvments with Terraform Cloud in potentially removing the implicit
depenency on always using the 'default' workspace when the current
configuration is mapped to a single TFC workspace.

internal/command/meta_backend.go

@@ -196,13 +196,19 @@ func (m *Meta) selectWorkspace(b backend.Backend) error {
 	var list strings.Builder
 	for i, w := range workspaces {
 		if w == workspace {
+			log.Printf("[TRACE] Meta.selectWorkspace: the currently selected workspace is present in the configured backend (%s)", workspace)
 			return nil
 		}
 		fmt.Fprintf(&list, "%d. %s\n", i+1, w)
 	}
 
-	// If the selected workspace doesn't exist, ask the user to select
-	// a workspace from the list of existing workspaces.
+	// If the backend only has a single workspace, select that as the current workspace
+	if len(workspaces) == 1 {
+		log.Printf("[TRACE] Meta.selectWorkspace: automatically selecting the single workspace provided by the backend (%s)", workspaces[0])
+		return m.SetWorkspace(workspaces[0])
+	}
+
+	// Otherwise, ask the user to select a workspace from the list of existing workspaces.
 	v, err := m.UIInput().Input(context.Background(), &terraform.InputOpts{
 		Id: "select-workspace",
 		Query: fmt.Sprintf(
@@ -220,7 +226,9 @@ func (m *Meta) selectWorkspace(b backend.Backend) error {
 		return fmt.Errorf("Failed to select workspace: input not a valid number")
 	}
 
-	return m.SetWorkspace(workspaces[idx-1])
+	workspace = workspaces[idx-1]
+	log.Printf("[TRACE] Meta.selectWorkspace: setting the current workpace according to user selection (%s)", workspace)
+	return m.SetWorkspace(workspace)
 }
 
 // BackendForPlan is similar to Backend, but uses backend settings that were

internal/command/meta_backend_test.go

@@ -789,6 +789,84 @@ func TestMetaBackend_reconfigureChange(t *testing.T) {
 	}
 }
 
+// Initializing a backend which supports workspaces and does *not* have
+// the currently selected workspace should prompt the user with a list of
+// workspaces to choose from to select a valid one, if more than one workspace
+// is available.
+func TestMetaBackend_initSelectedWorkspaceDoesNotExist(t *testing.T) {
+	// Create a temporary working directory that is empty
+	td := tempDir(t)
+	testCopyDir(t, testFixturePath("init-backend-selected-workspace-doesnt-exist-multi"), td)
+	defer os.RemoveAll(td)
+	defer testChdir(t, td)()
+
+	// Setup the meta
+	m := testMetaBackend(t, nil)
+
+	defer testInputMap(t, map[string]string{
+		"select-workspace": "2",
+	})()
+
+	// Get the backend
+	_, diags := m.Backend(&BackendOpts{Init: true})
+	if diags.HasErrors() {
+		t.Fatal(diags.Err())
+	}
+
+	expected := "foo"
+	actual, err := m.Workspace()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if actual != expected {
+		t.Fatalf("expected selected workspace to be %q, but was %q", expected, actual)
+	}
+}
+
+// Initializing a backend which supports workspaces and does *not* have the
+// currently selected workspace - and which only has a single workspace - should
+// automatically select that single workspace.
+func TestMetaBackend_initSelectedWorkspaceDoesNotExistAutoSelect(t *testing.T) {
+	// Create a temporary working directory that is empty
+	td := tempDir(t)
+	testCopyDir(t, testFixturePath("init-backend-selected-workspace-doesnt-exist-single"), td)
+	defer os.RemoveAll(td)
+	defer testChdir(t, td)()
+
+	// Setup the meta
+	m := testMetaBackend(t, nil)
+
+	// this should not ask for input
+	m.input = false
+
+	// Assert test precondition: The current selected workspace is "bar"
+	previousName, err := m.Workspace()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if previousName != "bar" {
+		t.Fatalf("expected test fixture to start with 'bar' as the current selected workspace")
+	}
+
+	// Get the backend
+	_, diags := m.Backend(&BackendOpts{Init: true})
+	if diags.HasErrors() {
+		t.Fatal(diags.Err())
+	}
+
+	expected := "default"
+	actual, err := m.Workspace()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if actual != expected {
+		t.Fatalf("expected selected workspace to be %q, but was %q", expected, actual)
+	}
+}
+
 // Changing a configured backend, copying state
 func TestMetaBackend_configuredChangeCopy(t *testing.T) {
 	// Create a temporary working directory that is empty
@@ -1267,7 +1345,6 @@ func TestMetaBackend_configuredChangeCopy_multiToNoDefaultWithoutDefault(t *test
 	// Ask input
 	defer testInputMap(t, map[string]string{
 		"backend-migrate-multistate-to-multistate": "yes",
-		"select-workspace":                         "1",
 	})()
 
 	// Setup the meta

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-multi/.terraform/environment

@@ -0,0 +1 @@
+bar

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-multi/.terraform/terraform.tfstate

@@ -0,0 +1,23 @@
+{
+    "version": 3,
+    "serial": 2,
+    "lineage": "2f3864a6-1d3e-1999-0f84-36cdb61179d3",
+    "backend": {
+        "type": "local",
+        "config": {
+            "path": null,
+            "workspace_dir": null
+        },
+        "hash": 666019178
+    },
+    "modules": [
+        {
+            "path": [
+                "root"
+            ],
+            "outputs": {},
+            "resources": {},
+            "depends_on": []
+        }
+    ]
+}

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-multi/main.tf

@@ -0,0 +1,7 @@
+terraform {
+    backend "local" {}
+}
+
+output "foo" {
+  value = "bar"
+}

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-multi/terraform.tfstate

@@ -0,0 +1,13 @@
+{
+  "version": 4,
+  "terraform_version": "1.1.0",
+  "serial": 1,
+  "lineage": "cc4bb587-aa35-87ad-b3b7-7abdb574f2a1",
+  "outputs": {
+    "foo": {
+      "value": "bar",
+      "type": "string"
+    }
+  },
+  "resources": []
+}

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-multi/terraform.tfstate.d/foo/terraform.tfstate

@@ -0,0 +1,13 @@
+{
+  "version": 4,
+  "terraform_version": "1.1.0",
+  "serial": 1,
+  "lineage": "8ad3c77d-51aa-d90a-4f12-176f538b6e8b",
+  "outputs": {
+    "foo": {
+      "value": "bar",
+      "type": "string"
+    }
+  },
+  "resources": []
+}

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-single/.terraform/environment

@@ -0,0 +1 @@
+bar

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-single/.terraform/terraform.tfstate

@@ -0,0 +1,23 @@
+{
+    "version": 3,
+    "serial": 2,
+    "lineage": "2f3864a6-1d3e-1999-0f84-36cdb61179d3",
+    "backend": {
+        "type": "local",
+        "config": {
+            "path": null,
+            "workspace_dir": null
+        },
+        "hash": 666019178
+    },
+    "modules": [
+        {
+            "path": [
+                "root"
+            ],
+            "outputs": {},
+            "resources": {},
+            "depends_on": []
+        }
+    ]
+}

internal/command/testdata/init-backend-selected-workspace-doesnt-exist-single/main.tf

@@ -0,0 +1,7 @@
+terraform {
+    backend "local" {}
+}
+
+output "foo" {
+  value = "bar"
+}