accept empty json object

Author: Emyrk

plan.go

@@ -22,7 +22,9 @@ import (
 
 func PlanJSONHook(dfs fs.FS, input Input) (func(ctx *tfcontext.Context, blocks terraform.Blocks, inputVars map[string]cty.Value), error) {
 	var contents io.Reader = bytes.NewReader(input.PlanJSON)
-	if len(input.PlanJSON) == 0 {
+	// Also accept `{}` as an empty plan. If this is stored in postgres or another json
+	// type, then `{}` is the "empty" value.
+	if len(input.PlanJSON) == 0 || bytes.Compare(input.PlanJSON, []byte("{}")) == 0 {
 		if input.PlanJSONPath == "" {
 			return func(ctx *tfcontext.Context, blocks terraform.Blocks, inputVars map[string]cty.Value) {}, nil
 		}

plan_test.go

@@ -0,0 +1,26 @@
+package preview_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/preview"
+	"github.com/coder/preview/types"
+)
+
+func TestPlanJSONHook(t *testing.T) {
+	t.Parallel()
+
+	t.Run("Empty plan", func(t *testing.T) {
+		dirFS := os.DirFS("testdata/static")
+		_, diags := preview.Preview(t.Context(), preview.Input{
+			PlanJSONPath:    "",
+			PlanJSON:        []byte("{}"),
+			ParameterValues: nil,
+			Owner:           types.WorkspaceOwner{},
+		}, dirFS)
+		require.False(t, diags.HasErrors())
+	})
+}