Fix an issue when parsing empty input documents

CHANGELOG.md

@@ -7,8 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
 - Add `man` that generates manpages for all dasel subcommands.
 
+### Fixed
+
+- Fixed an issue when [parsing empty input documents](https://github.com/TomWright/dasel/issues/374).
+
 ## [v2.4.1] - 2023-10-18
 
 ### Fixed

internal/command/options.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"github.com/spf13/cobra"
 	"github.com/tomwright/dasel/v2"
+	"github.com/tomwright/dasel/v2/dencoding"
 	"github.com/tomwright/dasel/v2/storage"
 	"io"
 	"os"
@@ -75,7 +76,20 @@ func (o *readOptions) rootValue(cmd *cobra.Command) (dasel.Value, error) {
 		}
 	}
 
-	return storage.Load(parser, reader, options...)
+	rootNode, err := storage.Load(parser, reader, options...)
+	if err != nil {
+		return rootNode, err
+	}
+
+	if !rootNode.Value.IsValid() {
+		var defaultValue any = dencoding.NewMap()
+		if _, ok := parser.(*storage.CSVParser); ok {
+			defaultValue = []any{}
+		}
+		rootNode = dasel.ValueOf(defaultValue)
+	}
+
+	return rootNode, nil
 }
 
 type writeOptions struct {

internal/command/select.go

@@ -103,11 +103,4 @@ func runSelectCommand(opts *selectOptions, cmd *cobra.Command) error {
 	}
 
 	return nil
-
-	// todo : check if this is still needed.
-	// if !rootNode.Value.IsValid() {
-	// 	rootNode = dasel.New(&storage.BasicSingleDocument{
-	// 		Value: map[string]interface{}{},
-	// 	})
-	// }
 }

internal/command/select_test.go

@@ -378,4 +378,43 @@ d.e.f`)),
 		nil,
 	))
 
+	t.Run("Issue 374 empty input", func(t *testing.T) {
+		tests := []struct {
+			format string
+			exp    []byte
+		}{
+			{
+				format: "json",
+				exp:    []byte("{}\n"),
+			},
+			{
+				format: "toml",
+				exp:    []byte("\n"),
+			},
+			{
+				format: "yaml",
+				exp:    []byte("{}\n"),
+			},
+			{
+				format: "xml",
+				exp:    []byte("<doc/>\n"),
+			},
+			{
+				format: "csv",
+				exp:    []byte(""),
+			},
+		}
+
+		for _, test := range tests {
+			tc := test
+			t.Run(tc.format, runTest(
+				[]string{"-r", tc.format},
+				[]byte(``),
+				tc.exp,
+				nil,
+				nil,
+			))
+		}
+	})
+
 }