Restore API version checking, with internal usage accounted for

internal/cloud/backend.go

@@ -85,6 +85,8 @@ type Cloud struct {
 	// version. This will also cause VerifyWorkspaceTerraformVersion to return
 	// a warning diagnostic instead of an error.
 	ignoreVersionConflict bool
+
+	runningInAutomation bool
 }
 
 var _ backend.Backend = (*Cloud)(nil)
@@ -296,15 +298,25 @@ func (b *Cloud) Configure(obj cty.Value) tfdiags.Diagnostics {
 
 	if parseErr != nil || currentAPIVersion.LessThan(desiredAPIVersion) {
 		log.Printf("[TRACE] API version check failed; want: >= %s, got: %s", desiredAPIVersion.Original(), currentAPIVersion)
-		// FIXME: Skip version checking temporarily.
-		// diags = diags.Append(tfdiags.Sourceless(
-		// 	tfdiags.Error,
-		// 	"Unsupported Terraform Enterprise version",
-		// 	fmt.Sprintf(
-		// 		`The 'cloud' option requires Terraform Enterprise %s or later.`,
-		// 		apiToMinimumTFEVersion["2.5"],
-		// 	),
-		// ))
+		if b.runningInAutomation {
+			// It should never be possible for this Terraform process to be mistakenly
+			// used internally within an unsupported Terraform Enterprise install - but
+			// just in case it happens, give an actionable error.
+			diags = diags.Append(
+				tfdiags.Sourceless(
+					tfdiags.Error,
+					"Unsupported Terraform Enterprise version",
+					cloudIntegrationUsedInUnsupportedTFE,
+				),
+			)
+		} else {
+			diags = diags.Append(tfdiags.Sourceless(
+				tfdiags.Error,
+				"Unsupported Terraform Enterprise version",
+				`The 'cloud' option is not supported with this version of Terraform Enterprise.`,
+			),
+			)
+		}
 	}
 
 	// Configure a local backend for when we need to run operations locally.
@@ -967,8 +979,13 @@ const refreshToApplyRefresh = `[bold][yellow]Proceeding with 'terraform apply -r
 const unavailableTerraformVersion = `
 [reset][yellow]The local Terraform version (%s) is not available in Terraform Cloud, or your
 organization does not have access to it. The new workspace will use %s. You can
-change this later in the workspace settings.[reset]
-`
+change this later in the workspace settings.[reset]`
+
+const cloudIntegrationUsedInUnsupportedTFE = `
+This version of Terraform Cloud/Enterprise does not support the state mechanism
+attempting to be used by the platform. This should never happen.
+
+Please reach out to HashiCorp Support to resolve this issue.`
 
 var (
 	workspaceConfigurationHelp = fmt.Sprintf(

internal/cloud/backend_cli.go

@@ -15,6 +15,7 @@ func (b *Cloud) CLIInit(opts *backend.CLIOpts) error {
 	b.CLI = opts.CLI
 	b.CLIColor = opts.CLIColor
 	b.ContextOpts = opts.ContextOpts
+	b.runningInAutomation = opts.RunningInAutomation
 
 	return nil
 }

internal/cloud/backend_test.go

@@ -269,7 +269,6 @@ func TestCloud_config(t *testing.T) {
 }
 
 func TestCloud_configVerifyMinimumTFEVersion(t *testing.T) {
-	t.Skip("skipping, as TFE version checking has been temporarily disabled")
 	config := cty.ObjectVal(map[string]cty.Value{
 		"hostname":     cty.NullVal(cty.String),
 		"organization": cty.StringVal("hashicorp"),
@@ -299,7 +298,45 @@ func TestCloud_configVerifyMinimumTFEVersion(t *testing.T) {
 		t.Fatalf("expected configure to error")
 	}
 
-	expected := "The 'cloud' option requires Terraform Enterprise v202201-1 or later."
+	expected := `The 'cloud' option is not supported with this version of Terraform Enterprise.`
+	if !strings.Contains(confDiags.Err().Error(), expected) {
+		t.Fatalf("expected configure to error with %q, got %q", expected, confDiags.Err().Error())
+	}
+}
+
+func TestCloud_configVerifyMinimumTFEVersionInAutomation(t *testing.T) {
+	config := cty.ObjectVal(map[string]cty.Value{
+		"hostname":     cty.NullVal(cty.String),
+		"organization": cty.StringVal("hashicorp"),
+		"token":        cty.NullVal(cty.String),
+		"workspaces": cty.ObjectVal(map[string]cty.Value{
+			"name": cty.NullVal(cty.String),
+			"tags": cty.SetVal(
+				[]cty.Value{
+					cty.StringVal("billing"),
+				},
+			),
+		}),
+	})
+
+	handlers := map[string]func(http.ResponseWriter, *http.Request){
+		"/api/v2/ping": func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			w.Header().Set("TFP-API-Version", "2.4")
+		},
+	}
+	s := testServerWithHandlers(handlers)
+
+	b := New(testDisco(s))
+	b.runningInAutomation = true
+
+	confDiags := b.Configure(config)
+	if confDiags.Err() == nil {
+		t.Fatalf("expected configure to error")
+	}
+
+	expected := `This version of Terraform Cloud/Enterprise does not support the state mechanism
+attempting to be used by the platform. This should never happen.`
 	if !strings.Contains(confDiags.Err().Error(), expected) {
 		t.Fatalf("expected configure to error with %q, got %q", expected, confDiags.Err().Error())
 	}

internal/cloud/versioning.go

@@ -1,12 +0,0 @@
-package cloud
-
-// This simple map exists to translate TFP-API-Version strings to the TFE release where it was
-// introduced, to provide actionable feedback on features that may be unsupported by the TFE
-// installation but present in this version of Terraform.
-//
-// The cloud package here, introduced in Terraform 1.1.0, requires a minimum of 2.5 (v202201-1)
-// The TFP-API-Version header that this refers to was introduced in 2.3 (v202006-1), so an absent
-// header can be considered < 2.3.
-// var apiToMinimumTFEVersion = map[string]string{
-// 	"2.5": "v202201-1",
-// }