prevent targeting for unsupported API versions

backend/remote/backend_apply.go

@@ -8,6 +8,7 @@ import (
 	"log"
 
 	tfe "github.com/hashicorp/go-tfe"
+	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/hashicorp/terraform/tfdiags"
@@ -94,6 +95,26 @@ func (b *Remote) opApply(stopCtx, cancelCtx context.Context, op *backend.Operati
 		))
 	}
 
+	if len(op.Targets) != 0 {
+		// For API versions prior to 2.3, RemoteAPIVersion will return an empty string,
+		// so if there's an error when parsing the RemoteAPIVersion, it's handled as
+		// equivalent to an API version < 2.3.
+		currentAPIVersion, parseErr := version.NewVersion(b.client.RemoteAPIVersion())
+		desiredAPIVersion, _ := version.NewVersion("2.3")
+
+		if parseErr != nil || currentAPIVersion.LessThan(desiredAPIVersion) {
+			diags = diags.Append(tfdiags.Sourceless(
+				tfdiags.Error,
+				"Resource targeting is not supported",
+				fmt.Sprintf(
+					`The host %s does not support the -target option for `+
+						`remote plans.`,
+					b.hostname,
+				),
+			))
+		}
+	}
+
 	// Return if there are any errors.
 	if diags.HasErrors() {
 		return nil, diags.Err()

backend/remote/backend_plan.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	tfe "github.com/hashicorp/go-tfe"
+	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/tfdiags"
 )
@@ -98,6 +99,26 @@ func (b *Remote) opPlan(stopCtx, cancelCtx context.Context, op *backend.Operatio
 		))
 	}
 
+	if len(op.Targets) != 0 {
+		// For API versions prior to 2.3, RemoteAPIVersion will return an empty string,
+		// so if there's an error when parsing the RemoteAPIVersion, it's handled as
+		// equivalent to an API version < 2.3.
+		currentAPIVersion, parseErr := version.NewVersion(b.client.RemoteAPIVersion())
+		desiredAPIVersion, _ := version.NewVersion("2.3")
+
+		if parseErr != nil || currentAPIVersion.LessThan(desiredAPIVersion) {
+			diags = diags.Append(tfdiags.Sourceless(
+				tfdiags.Error,
+				"Resource targeting is not supported",
+				fmt.Sprintf(
+					`The host %s does not support the -target option for `+
+						`remote plans.`,
+					b.hostname,
+				),
+			))
+		}
+	}
+
 	// Return if there are any errors.
 	if diags.HasErrors() {
 		return nil, diags.Err()

backend/remote/testing.go

@@ -207,6 +207,12 @@ func testServer(t *testing.T) *httptest.Server {
 }`, path.Base(r.URL.Path)))
 	})
 
+	// Respond to pings to get the API version header.
+	mux.HandleFunc("/api/v2/ping", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("TFP-API-Version", "2.3")
+	})
+
 	// Respond to the initial query to read the hashicorp org entitlements.
 	mux.HandleFunc("/api/v2/organizations/hashicorp/entitlement-set", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/vnd.api+json")