plans/planfile: Create takes most arguments via a struct type

Previously the planfile.Create function had accumulated probably already
too many positional arguments, and I'm intending to add another one in
a subsequent commit and so this is preparation to make the callsites more
readable (subjectively) and make it clearer how we can extend this
function's arguments to include further components in a plan file.

There's no difference in observable functionality here. This is just
passing the same set of arguments in a slightly different way.

internal/backend/local/backend_local_test.go

@@ -132,7 +132,13 @@ func TestLocalRun_stalePlan(t *testing.T) {
 	outDir := t.TempDir()
 	defer os.RemoveAll(outDir)
 	planPath := filepath.Join(outDir, "plan.tfplan")
-	if err := planfile.Create(planPath, configload.NewEmptySnapshot(), prevStateFile, stateFile, plan); err != nil {
+	planfileArgs := planfile.CreateArgs{
+		ConfigSnapshot:       configload.NewEmptySnapshot(),
+		PreviousRunStateFile: prevStateFile,
+		StateFile:            stateFile,
+		Plan:                 plan,
+	}
+	if err := planfile.Create(planPath, planfileArgs); err != nil {
 		t.Fatalf("unexpected error writing planfile: %s", err)
 	}
 	planFile, err := planfile.Open(planPath)

internal/backend/local/backend_plan.go

@@ -133,7 +133,12 @@ func (b *Local) opPlan(
 		}
 
 		log.Printf("[INFO] backend/local: writing plan output to: %s", path)
-		err := planfile.Create(path, configSnap, prevStateFile, plannedStateFile, plan)
+		err := planfile.Create(path, planfile.CreateArgs{
+			ConfigSnapshot:       configSnap,
+			PreviousRunStateFile: prevStateFile,
+			StateFile:            plannedStateFile,
+			Plan:                 plan,
+		})
 		if err != nil {
 			diags = diags.Append(tfdiags.Sourceless(
 				tfdiags.Error,

internal/command/command_test.go

@@ -242,7 +242,12 @@ func testPlanFile(t *testing.T, configSnap *configload.Snapshot, state *states.S
 	}
 
 	path := testTempFile(t)
-	err := planfile.Create(path, configSnap, prevStateFile, stateFile, plan)
+	err := planfile.Create(path, planfile.CreateArgs{
+		ConfigSnapshot:       configSnap,
+		PreviousRunStateFile: prevStateFile,
+		StateFile:            stateFile,
+		Plan:                 plan,
+	})
 	if err != nil {
 		t.Fatalf("failed to create temporary plan file: %s", err)
 	}

internal/plans/planfile/planfile_test.go

@@ -77,7 +77,12 @@ func TestRoundtrip(t *testing.T) {
 	}
 	planFn := filepath.Join(workDir, "tfplan")
 
-	err = Create(planFn, snapIn, prevStateFileIn, stateFileIn, planIn)
+	err = Create(planFn, CreateArgs{
+		ConfigSnapshot:       snapIn,
+		PreviousRunStateFile: prevStateFileIn,
+		StateFile:            stateFileIn,
+		Plan:                 planIn,
+	})
 	if err != nil {
 		t.Fatalf("failed to create plan file: %s", err)
 	}

internal/plans/planfile/writer.go

@@ -11,6 +11,30 @@ import (
 	"github.com/hashicorp/terraform/internal/states/statefile"
 )
 
+type CreateArgs struct {
+	// ConfigSnapshot is a snapshot of the configuration that the plan
+	// was created from.
+	ConfigSnapshot *configload.Snapshot
+
+	// PreviousRunStateFile is a representation of the state snapshot we used
+	// as the original input when creating this plan, containing the same
+	// information as recorded at the end of the previous apply except for
+	// upgrading managed resource instance data to the provider's latest
+	// schema versions.
+	PreviousRunStateFile *statefile.File
+
+	// BaseStateFile is a representation of the state snapshot we used to
+	// create the plan, which is the result of asking the providers to refresh
+	// all previously-stored objects to match the current situation in the
+	// remote system. (If this plan was created with refreshing disabled,
+	// this should be the same as PreviousRunStateFile.)
+	StateFile *statefile.File
+
+	// Plan records the plan itself, which is the main artifact inside a
+	// saved plan file.
+	Plan *plans.Plan
+}
+
 // Create creates a new plan file with the given filename, overwriting any
 // file that might already exist there.
 //
@@ -18,7 +42,7 @@ import (
 // state file in addition to the plan itself, so that Terraform can detect
 // if the world has changed since the plan was created and thus refuse to
 // apply it.
-func Create(filename string, configSnap *configload.Snapshot, prevStateFile, stateFile *statefile.File, plan *plans.Plan) error {
+func Create(filename string, args CreateArgs) error {
 	f, err := os.Create(filename)
 	if err != nil {
 		return err
@@ -38,7 +62,7 @@ func Create(filename string, configSnap *configload.Snapshot, prevStateFile, sta
 		if err != nil {
 			return fmt.Errorf("failed to create tfplan file: %s", err)
 		}
-		err = writeTfplan(plan, w)
+		err = writeTfplan(args.Plan, w)
 		if err != nil {
 			return fmt.Errorf("failed to write plan: %s", err)
 		}
@@ -54,7 +78,7 @@ func Create(filename string, configSnap *configload.Snapshot, prevStateFile, sta
 		if err != nil {
 			return fmt.Errorf("failed to create embedded tfstate file: %s", err)
 		}
-		err = statefile.Write(stateFile, w)
+		err = statefile.Write(args.StateFile, w)
 		if err != nil {
 			return fmt.Errorf("failed to write state snapshot: %s", err)
 		}
@@ -70,7 +94,7 @@ func Create(filename string, configSnap *configload.Snapshot, prevStateFile, sta
 		if err != nil {
 			return fmt.Errorf("failed to create embedded tfstate-prev file: %s", err)
 		}
-		err = statefile.Write(prevStateFile, w)
+		err = statefile.Write(args.PreviousRunStateFile, w)
 		if err != nil {
 			return fmt.Errorf("failed to write previous state snapshot: %s", err)
 		}
@@ -78,7 +102,7 @@ func Create(filename string, configSnap *configload.Snapshot, prevStateFile, sta
 
 	// tfconfig directory
 	{
-		err := writeConfigSnapshot(configSnap, zw)
+		err := writeConfigSnapshot(args.ConfigSnapshot, zw)
 		if err != nil {
 			return fmt.Errorf("failed to write config snapshot: %s", err)
 		}

internal/terraform/context_test.go

@@ -655,7 +655,12 @@ func contextOptsForPlanViaFile(configSnap *configload.Snapshot, plan *plans.Plan
 	}
 
 	filename := filepath.Join(dir, "tfplan")
-	err = planfile.Create(filename, configSnap, prevStateFile, stateFile, plan)
+	err = planfile.Create(filename, planfile.CreateArgs{
+		ConfigSnapshot:       configSnap,
+		PreviousRunStateFile: prevStateFile,
+		StateFile:            stateFile,
+		Plan:                 plan,
+	})
 	if err != nil {
 		return nil, nil, nil, err
 	}