Handle empty files

pkg/yqlib/all_at_once_evaluator.go

@@ -68,6 +68,17 @@ func (e *allAtOnceEvaluator) EvaluateFiles(expression string, filenames []string
 		allDocuments.PushBackList(fileDocuments)
 		fileIndex = fileIndex + 1
 	}
+
+	if allDocuments.Len() == 0 {
+		candidateNode := &CandidateNode{
+			Document:  0,
+			Filename:  "",
+			Node:      &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode},
+			FileIndex: 0,
+		}
+		allDocuments.PushBack(candidateNode)
+	}
+
 	matches, err := e.EvaluateCandidateNodes(expression, allDocuments)
 	if err != nil {
 		return err

pkg/yqlib/operators_test.go

@@ -114,7 +114,7 @@ func formatYaml(yaml string, filename string) string {
 		panic(err)
 	}
 	streamEvaluator := NewStreamEvaluator()
-	err = streamEvaluator.Evaluate(filename, strings.NewReader(yaml), node, printer)
+	_, err = streamEvaluator.Evaluate(filename, strings.NewReader(yaml), node, printer)
 	if err != nil {
 		panic(err)
 	}

pkg/yqlib/stream_evaluator.go

@@ -12,7 +12,7 @@ import (
 // Uses less memory than loading all documents and running the expression once, but this cannot process
 // cross document expressions.
 type StreamEvaluator interface {
-	Evaluate(filename string, reader io.Reader, node *ExpressionNode, printer Printer) error
+	Evaluate(filename string, reader io.Reader, node *ExpressionNode, printer Printer) (uint, error)
 	EvaluateFiles(expression string, filenames []string, printer Printer) error
 	EvaluateNew(expression string, printer Printer) error
 }
@@ -49,7 +49,7 @@ func (s *streamEvaluator) EvaluateNew(expression string, printer Printer) error
 }
 
 func (s *streamEvaluator) EvaluateFiles(expression string, filenames []string, printer Printer) error {
-
+	var totalProcessDocs uint = 0
 	node, err := s.treeCreator.ParseExpression(expression)
 	if err != nil {
 		return err
@@ -63,23 +63,28 @@ func (s *streamEvaluator) EvaluateFiles(expression string, filenames []string, p
 		if err != nil {
 			return err
 		}
-		err = s.Evaluate(filename, reader, node, printer)
+		processedDocs, err := s.Evaluate(filename, reader, node, printer)
 		if err != nil {
 			return err
 		}
+		totalProcessDocs = totalProcessDocs + processedDocs
 
 		switch reader := reader.(type) {
 		case *os.File:
 			safelyCloseFile(reader)
 		}
 	}
+
+	if totalProcessDocs == 0 {
+		return s.EvaluateNew(expression, printer)
+	}
+
 	return nil
 }
 
-func (s *streamEvaluator) Evaluate(filename string, reader io.Reader, node *ExpressionNode, printer Printer) error {
+func (s *streamEvaluator) Evaluate(filename string, reader io.Reader, node *ExpressionNode, printer Printer) (uint, error) {
 
 	var currentIndex uint
-
 	decoder := yaml.NewDecoder(reader)
 	for {
 		var dataBucket yaml.Node
@@ -87,9 +92,9 @@ func (s *streamEvaluator) Evaluate(filename string, reader io.Reader, node *Expr
 
 		if errorReading == io.EOF {
 			s.fileIndex = s.fileIndex + 1
-			return nil
+			return currentIndex, nil
 		} else if errorReading != nil {
-			return errorReading
+			return currentIndex, errorReading
 		}
 		candidateNode := &CandidateNode{
 			Document:  currentIndex,
@@ -102,11 +107,11 @@ func (s *streamEvaluator) Evaluate(filename string, reader io.Reader, node *Expr
 
 		result, errorParsing := s.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputList}, node)
 		if errorParsing != nil {
-			return errorParsing
+			return currentIndex, errorParsing
 		}
 		err := printer.PrintResults(result.MatchingNodes)
 		if err != nil {
-			return err
+			return currentIndex, err
 		}
 		currentIndex = currentIndex + 1
 	}

scripts/acceptance.sh

@@ -55,7 +55,7 @@ if [[ $? != 1 ]]; then
   exit 1
 fi
 
-# Test leading seperator logic
+echo "Test: leading seperator logic"
 expected=$(cat examples/leading-seperator.yaml)
 
 X=$(cat examples/leading-seperator.yaml | ./yq e '.' -)
@@ -113,7 +113,7 @@ if [[ $X != $expected ]]; then
   exit 1
 fi
 
-# handle empty files
+echo "Test: handle empty files"
 ./yq e '.' examples/empty.yaml
 if [[ $? != 0 ]]; then
   echo "Expected no error when processing empty file but got one"
@@ -126,6 +126,29 @@ if [[ $? != 0 ]]; then
   exit 1
 fi
 
+# run expression against empty file
+touch temp.yaml
+expected="apple: tree"
+
+./yq e '.apple = "tree"' temp.yaml -i
+X=$(cat temp.yaml)
+rm temp.yaml
+if [[ $X != $expected ]]; then
+  echo "Write empty doc"
+  echo "Expected $expected but was $X"
+  exit 1
+fi
+
+touch temp.yaml
+
+./yq ea '.apple = "tree"' temp.yaml -i
+X=$(cat temp.yaml)
+rm temp.yaml
+if [[ $X != $expected ]]; then
+  echo "Write all empty doc"
+  echo "Expected $expected but was $X"
+  exit 1
+fi
 
 echo "--success"