Fail if no valid lstmf file was written (fix issue tesseract-ocr#2741)

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/api/baseapi.cpp

@@ -855,7 +855,9 @@ int TessBaseAPI::Recognize(ETEXT_DESC* monitor) {
   }
 
   if (tesseract_->tessedit_train_line_recognizer) {
-    tesseract_->TrainLineRecognizer(*input_file_, *output_file_, block_list_);
+    if (!tesseract_->TrainLineRecognizer(*input_file_, *output_file_, block_list_)) {
+      return -1;
+    }
     tesseract_->CorrectClassifyWords(page_res_);
     return 0;
   }

src/ccmain/linerec.cpp

@@ -39,7 +39,8 @@ const float kWorstDictCertainty = -25.0f;
 // Generates training data for training a line recognizer, eg LSTM.
 // Breaks the page into lines, according to the boxes, and writes them to a
 // serialized DocumentData based on output_basename.
-void Tesseract::TrainLineRecognizer(const STRING& input_imagename,
+// Return true if successful, false if an error occurred.
+bool Tesseract::TrainLineRecognizer(const STRING& input_imagename,
                                     const STRING& output_basename,
                                     BLOCK_LIST *block_list) {
   STRING lstmf_name = output_basename + ".lstmf";
@@ -48,7 +49,7 @@ void Tesseract::TrainLineRecognizer(const STRING& input_imagename,
     // Load existing document for the previous pages.
     if (!images.LoadDocument(lstmf_name.c_str(), 0, 0, nullptr)) {
       tprintf("Failed to read training data from %s!\n", lstmf_name.c_str());
-      return;
+      return false;
     }
   }
   GenericVector<TBOX> boxes;
@@ -58,17 +59,19 @@ void Tesseract::TrainLineRecognizer(const STRING& input_imagename,
                     nullptr) ||
       boxes.empty()) {
     tprintf("Failed to read boxes from %s\n", input_imagename.c_str());
-    return;
+    return false;
   }
   TrainFromBoxes(boxes, texts, block_list, &images);
   if (images.NumPages() <= 0) {
     tprintf("Failed to read pages from %s\n", input_imagename.c_str());
-    return;
+    return false;
   }
   images.Shuffle();
   if (!images.SaveDocument(lstmf_name.c_str(), nullptr)) {
     tprintf("Failed to write training data to %s!\n", lstmf_name.c_str());
+    return false;
   }
+  return true;
 }
 
 // Generates training data for training a line recognizer, eg LSTM.

src/ccmain/tesseractclass.h

@@ -334,7 +334,8 @@ class Tesseract : public Wordrec {
   // Generates training data for training a line recognizer, eg LSTM.
   // Breaks the page into lines, according to the boxes, and writes them to a
   // serialized DocumentData based on output_basename.
-  void TrainLineRecognizer(const STRING& input_imagename,
+  // Return true if successful, false if an error occurred.
+  bool TrainLineRecognizer(const STRING& input_imagename,
                            const STRING& output_basename,
                            BLOCK_LIST* block_list);
   // Generates training data for training a line recognizer, eg LSTM.