Catch parser errors. (#38)

This should resolve:
#36

CMakeLists.txt

@@ -105,6 +105,11 @@ configure_file(
 add_library(diagon_base STATIC
   src/translator/Translator.cpp
   src/translator/Translator.h
+  src/translator/antlr_error_listener.cpp
+  src/translator/antlr_error_listener.h
+)
+target_link_libraries(diagon_base
+  PRIVATE antlr4_static
 )
 target_set_common(diagon_base)
 

src/translator/antlr_error_listener.cpp

@@ -0,0 +1,13 @@
+#include "translator/antlr_error_listener.h"
+#include <sstream>
+
+void AntlrErrorListener::syntaxError(antlr4::Recognizer* recognizer,
+                                     antlr4::Token* offendingSymbol,
+                                     size_t line,
+                                     size_t charPositionInLine,
+                                     const std::string& msg,
+                                     std::exception_ptr e) {
+  std::stringstream s;
+  s << "Line(" << line << ":" << charPositionInLine << ") Error(" << msg << ")";
+  throw std::invalid_argument(s.str());
+}

src/translator/antlr_error_listener.h

@@ -0,0 +1,15 @@
+#ifndef TRANSLATOR_ANTLR_ERROR_LISTENER_HPP
+#define TRANSLATOR_ANTLR_ERROR_LISTENER_HPP
+
+#include <antlr4-runtime.h>
+
+class AntlrErrorListener : public antlr4::BaseErrorListener {
+  void syntaxError(antlr4::Recognizer* recognizer,
+                   antlr4::Token* offendingSymbol,
+                   size_t line,
+                   size_t charPositionInLine,
+                   const std::string& msg,
+                   std::exception_ptr e) final;
+};
+
+#endif  // TRANSLATOR_ANTLR_ERROR_LISTENER_HPP

src/translator/flowchart/Flowchart.cpp

@@ -7,8 +7,8 @@
 #include <string_view>
 #include <vector>
 #include "screen/Screen.h"
-
 #include "translator/Translator.h"
+#include "translator/antlr_error_listener.h"
 #include "translator/flowchart/FlowchartLexer.h"
 #include "translator/flowchart/FlowchartParser.h"
 #include "util.hpp"
@@ -636,8 +636,20 @@ std::string Flowchart::Translate(const std::string& input,
   antlr4::CommonTokenStream tokens(&lexer);
   tokens.fill();
 
+  // Parser:
   FlowchartParser parser(&tokens);
-  return Parse(parser.program(), true).screen.ToString();
+
+  AntlrErrorListener error_listener;
+  parser.addErrorListener(&error_listener);
+
+  FlowchartParser::ProgramContext* context = nullptr;
+  try {
+    context = parser.program();
+  } catch (...) {
+    return "";
+  }
+
+  return Parse(context, true).screen.ToString();
 }
 
 }  // namespace

src/translator/graph_planar/GraphPlanar.cpp

@@ -10,6 +10,7 @@
 #include <vector>
 #include "screen/Screen.h"
 #include "translator/Translator.h"
+#include "translator/antlr_error_listener.h"
 #include "translator/graph_planar/GraphPlanarLexer.h"
 #include "translator/graph_planar/GraphPlanarParser.h"
 
@@ -201,8 +202,18 @@ void GraphPlanar::Read(const std::string& input) {
   antlr4::CommonTokenStream tokens(&lexer);
   tokens.fill();
 
+  // Parser:
+  AntlrErrorListener error_listener;
   GraphPlanarParser parser(&tokens);
-  ReadGraph(parser.graph());
+  parser.addErrorListener(&error_listener);
+  GraphPlanarParser::GraphContext* context = nullptr;
+  try {
+    context = parser.graph();
+  } catch (...) {
+    return;
+  }
+
+  ReadGraph(context);
 }
 
 void GraphPlanar::ReadGraph(GraphPlanarParser::GraphContext* graph) {

src/translator/math/Math.cpp

@@ -8,6 +8,7 @@
 #include "translator/Translator.h"
 #include "translator/math/MathLexer.h"
 #include "translator/math/MathParser.h"
+#include "translator/antlr_error_listener.h"
 
 class Screen;
 
@@ -1291,7 +1292,6 @@ class Math : public Translator {
       };
     }
 
-    //
     antlr4::ANTLRInputStream input_stream(input);
 
     // Lexer.
@@ -1300,8 +1300,16 @@ class Math : public Translator {
     tokens.fill();
 
     // Parser.
+    AntlrErrorListener error_listener;
     MathParser parser(&tokens);
-    auto* content = parser.multilineEquation();
+    parser.addErrorListener(&error_listener);
+
+    MathParser::MultilineEquationContext* content = nullptr;
+    try {
+      content = parser.multilineEquation();
+    } catch (...) {
+      return "";
+    }
 
     if (options["style"] == "Latex")
       return to_string(ParseLatex(content, &style)) + '\n';

src/translator/sequence/Sequence.cpp

@@ -11,6 +11,7 @@
 #include <string>
 #include <vector>
 #include "screen/Screen.h"
+#include "translator/antlr_error_listener.h"
 #include "translator/sequence/Graph.hpp"
 
 void Actor::Draw(Screen& screen, int height) {
@@ -269,10 +270,16 @@ void Sequence::ComputeInternalRepresentation(const std::string& input) {
   tokens.fill();
 
   // Parser.
+  AntlrErrorListener error_listener;
   SequenceParser parser(&tokens);
+  parser.addErrorListener(&error_listener);
 
-  // Print the tree.
-  auto program = parser.program();
+  SequenceParser::ProgramContext* program = nullptr;
+  try {
+    program = parser.program();
+  } catch (...) {
+    return;
+  }
 
   for (SequenceParser::CommandContext* command : program->command()) {
     AddCommand(command);