fix(report): handle empty OPA result sets in findReports

Adds a check for empty result sets from OPA evaluation to prevent panics when no documents are returned. Includes a regression test.

Author: apeabody

cli/report/report.go

@@ -90,8 +90,12 @@ func findReports(paths []string) (results interface{}, err error) {
 	if err != nil {
 		return nil, err
 	}
+	if len(rs) == 0 || len(rs[0].Expressions) == 0 {
+		// Return an empty map to prevent panics in calling functions.
+		return make(map[string]interface{}), nil
+	}
 	results = rs[0].Expressions[0].Value
-	return results, err
+	return results, nil
 }
 
 func generateReportData(rawAssetFileName string, queryPath string, outputPath string) (results interface{}, err error) {

cli/report/report_test.go

@@ -0,0 +1,47 @@
+package report
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFindReports_EmptyResults(t *testing.T) {
+	// Create a temporary directory for test files
+	tempDir, err := os.MkdirTemp("", "report_test")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	// Create a dummy rego file that produces no results for data.reports
+	regoContent := `package not_reports
+# No rules defined
+`
+	regoFile := filepath.Join(tempDir, "empty.rego")
+	if err := os.WriteFile(regoFile, []byte(regoContent), 0644); err != nil {
+		t.Fatalf("Failed to write rego file: %v", err)
+	}
+
+	// Create a dummy data file (can be empty json object)
+	dataContent := `{}`
+	dataFile := filepath.Join(tempDir, "data.json")
+	if err := os.WriteFile(dataFile, []byte(dataContent), 0644); err != nil {
+		t.Fatalf("Failed to write data file: %v", err)
+	}
+
+	// Call findReports
+	results, err := findReports([]string{regoFile, dataFile})
+	if err != nil {
+		t.Fatalf("findReports returned error: %v", err)
+	}
+
+	// Check if results is a map (expected empty map)
+	resultsMap, ok := results.(map[string]interface{})
+	if !ok {
+		t.Errorf("Expected results to be map[string]interface{}, got %T", results)
+	}
+	if len(resultsMap) != 0 {
+		t.Errorf("Expected empty results map, got length %d", len(resultsMap))
+	}
+}