backend/remote: Support -target on plan and apply

Previously we did not allow -target to be used with the remote backend
because there was no way to send the targets to Terraform Cloud/Enterprise
via the API.

There is now an attribute in the request for creating a plan that allows
us to send target addresses, so we'll remove that restriction and copy
the given target addresses into the API request.

backend/remote/backend_apply.go

@@ -67,14 +67,6 @@ func (b *Remote) opApply(stopCtx, cancelCtx context.Context, op *backend.Operati
 		))
 	}
 
-	if op.Targets != nil {
-		diags = diags.Append(tfdiags.Sourceless(
-			tfdiags.Error,
-			"Resource targeting is currently not supported",
-			`The "remote" backend does not support resource targeting at this time.`,
-		))
-	}
-
 	if b.hasExplicitVariableValues(op) {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,

backend/remote/backend_apply_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
 	tfe "github.com/hashicorp/go-tfe"
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/backend"
@@ -278,16 +279,23 @@ func TestRemote_applyWithTarget(t *testing.T) {
 	}
 
 	<-run.Done()
-	if run.Result == backend.OperationSuccess {
-		t.Fatal("expected apply operation to fail")
+	if run.Result != backend.OperationSuccess {
+		t.Fatal("expected apply operation to succeed")
 	}
-	if !run.PlanEmpty {
-		t.Fatalf("expected plan to be empty")
+	if run.PlanEmpty {
+		t.Fatalf("expected plan to be non-empty")
 	}
 
-	errOutput := b.CLI.(*cli.MockUi).ErrorWriter.String()
-	if !strings.Contains(errOutput, "targeting is currently not supported") {
-		t.Fatalf("expected a targeting error, got: %v", errOutput)
+	// We should find a run inside the mock client that has the same
+	// target address we requested above.
+	runsAPI := b.client.Runs.(*mockRuns)
+	if got, want := len(runsAPI.runs), 1; got != want {
+		t.Fatalf("wrong number of runs in the mock client %d; want %d", got, want)
+	}
+	for _, run := range runsAPI.runs {
+		if diff := cmp.Diff([]string{"null_resource.foo"}, run.TargetAddrs); diff != "" {
+			t.Errorf("wrong TargetAddrs in the created run\n%s", diff)
+		}
 	}
 }
 

backend/remote/backend_mock.go

@@ -757,6 +757,7 @@ func (m *mockRuns) Create(ctx context.Context, options tfe.RunCreateOptions) (*t
 		Permissions:  &tfe.RunPermissions{},
 		Plan:         p,
 		Status:       tfe.RunPending,
+		TargetAddrs:  options.TargetAddrs,
 	}
 
 	if pc != nil {

backend/remote/backend_plan.go

@@ -70,14 +70,6 @@ func (b *Remote) opPlan(stopCtx, cancelCtx context.Context, op *backend.Operatio
 		))
 	}
 
-	if op.Targets != nil {
-		diags = diags.Append(tfdiags.Sourceless(
-			tfdiags.Error,
-			"Resource targeting is currently not supported",
-			`The "remote" backend does not support resource targeting at this time.`,
-		))
-	}
-
 	if b.hasExplicitVariableValues(op) {
 		diags = diags.Append(tfdiags.Sourceless(
 			tfdiags.Error,
@@ -224,6 +216,17 @@ in order to capture the filesystem context the remote workspace expects:
 		Workspace:            w,
 	}
 
+	if len(op.Targets) != 0 {
+		runOptions.TargetAddrs = make([]string, 0, len(op.Targets))
+		for _, addr := range op.Targets {
+			// The API client wants the normal string representation of a
+			// target address, which will ultimately get inserted into a
+			// -target option when Terraform CLI is launched in the
+			// Cloud/Enterprise execution environment.
+			runOptions.TargetAddrs = append(runOptions.TargetAddrs, addr.String())
+		}
+	}
+
 	r, err := b.client.Runs.Create(stopCtx, runOptions)
 	if err != nil {
 		return r, generalError("Failed to create run", err)

backend/remote/backend_plan_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
 	tfe "github.com/hashicorp/go-tfe"
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/backend"
@@ -283,16 +284,23 @@ func TestRemote_planWithTarget(t *testing.T) {
 	}
 
 	<-run.Done()
-	if run.Result == backend.OperationSuccess {
-		t.Fatal("expected plan operation to fail")
+	if run.Result != backend.OperationSuccess {
+		t.Fatal("expected plan operation to succeed")
 	}
-	if !run.PlanEmpty {
-		t.Fatalf("expected plan to be empty")
+	if run.PlanEmpty {
+		t.Fatalf("expected plan to be non-empty")
 	}
 
-	errOutput := b.CLI.(*cli.MockUi).ErrorWriter.String()
-	if !strings.Contains(errOutput, "targeting is currently not supported") {
-		t.Fatalf("expected a targeting error, got: %v", errOutput)
+	// We should find a run inside the mock client that has the same
+	// target address we requested above.
+	runsAPI := b.client.Runs.(*mockRuns)
+	if got, want := len(runsAPI.runs), 1; got != want {
+		t.Fatalf("wrong number of runs in the mock client %d; want %d", got, want)
+	}
+	for _, run := range runsAPI.runs {
+		if diff := cmp.Diff([]string{"null_resource.foo"}, run.TargetAddrs); diff != "" {
+			t.Errorf("wrong TargetAddrs in the created run\n%s", diff)
+		}
 	}
 }