func writeDSTFileWithDebug()

in tools/go-agent/tools/dst.go [316:369]
50 lines of code
12 McCabe index (conditional complexity)

func writeDSTFileWithDebug(fset *token.FileSet, file *ast.File, debug *DebugInfo, output io.Writer) error {
	var changeInfo *dstFilePathChangeInfo
	if !debug.CheckOldLine {
		changeInfo = &dstFilePathChangeInfo{
			oldDebugPath: debug.FilePath,
			oldDebugLine: 1,
			newDebugLine: 1,
		}
		if _, err := fmt.Fprintf(output, "//line %s:%d\n", debug.FilePath, debug.Line); err != nil {
			return err
		}
		if err := printer.Fprint(output, fset, file); err != nil {
			return err
		}
		return nil
	}
	var buffer bytes.Buffer
	if err := printer.Fprint(&buffer, fset, file); err != nil {
		return err
	}
	newPosition, err := findFirstNoImportLocation(fset, file, bytes.NewBuffer(buffer.Bytes()))
	if err != nil {
		return err
	}
	changeInfo = &dstFilePathChangeInfo{
		oldDebugPath: debug.FilePath,
		oldDebugLine: debug.Line,
		newDebugLine: newPosition,
	}

	lineCount := 1
	alreadyChange := false
	for {
		line, err := buffer.ReadBytes('\n')
		if err != nil {
			if err == io.EOF && !alreadyChange {
				return fmt.Errorf("rewrite file line number failure: %v", err)
			}
			break
		}

		if lineCount == changeInfo.newDebugLine {
			line = []byte(fmt.Sprintf("//line %s:%d\n%s", debug.FilePath, changeInfo.oldDebugLine, line))
			alreadyChange = true
		}

		if _, e := output.Write(line); e != nil {
			return err
		}

		lineCount++
	}
	return nil
}