feat: add support to json marshal the module output (#143)

Author: Emyrk

preview.go

@@ -11,6 +11,7 @@ import (
 	"github.com/aquasecurity/trivy/pkg/iac/scanners/terraform/parser"
 	"github.com/hashicorp/hcl/v2"
 	"github.com/zclconf/go-cty/cty"
+	ctyjson "github.com/zclconf/go-cty/cty/json"
 
 	"github.com/coder/preview/hclext"
 	"github.com/coder/preview/types"
@@ -31,14 +32,35 @@ type Output struct {
 	// ModuleOutput is any 'output' values from the terraform files. This has 0
 	// effect on the parameters, tags, etc. It can be helpful for debugging, as it
 	// allows exporting some terraform values to the caller to review.
-	ModuleOutput cty.Value
+	//
+	// JSON marshalling is handled in the custom methods.
+	ModuleOutput cty.Value `json:"-"`
 
-	Parameters    []types.Parameter
-	WorkspaceTags types.TagBlocks
+	Parameters    []types.Parameter `json:"parameters"`
+	WorkspaceTags types.TagBlocks   `json:"workspace_tags"`
 	// Files is included for printing diagnostics.
-	// TODO: Is the memory impact of this too much? Should we render diagnostic source code
-	// into the diagnostics up front? and remove this?
-	Files map[string]*hcl.File
+	// They can be marshalled, but not unmarshalled. This is a limitation
+	// of the HCL library.
+	Files map[string]*hcl.File `json:"-"`
+}
+
+// MarshalJSON includes the ModuleOutput and files in the JSON output. Output
+// should never be unmarshalled. Marshalling to JSON is strictly useful for
+// debugging information.
+func (o Output) MarshalJSON() ([]byte, error) {
+	// Do not make this a fatal error, as it is supplementary information.
+	modOutput, _ := ctyjson.Marshal(o.ModuleOutput, o.ModuleOutput.Type())
+
+	type Alias Output
+	return json.Marshal(&struct {
+		ModuleOutput json.RawMessage      `json:"module_output"`
+		Files        map[string]*hcl.File `json:"files"`
+		Alias
+	}{
+		ModuleOutput: modOutput,
+		Files:        o.Files,
+		Alias:        (Alias)(o),
+	})
 }
 
 func Preview(ctx context.Context, input Input, dir fs.FS) (output *Output, diagnostics hcl.Diagnostics) {