lua4jvm: Fix Antlr 4 syntax error handling

lua4jvm/src/main/java/fi/benjami/code4jvm/lua/LuaVm.java

@@ -1,18 +1,29 @@
 package fi.benjami.code4jvm.lua;
 
+import java.util.ArrayList;
 import java.util.List;
 
+import org.antlr.v4.runtime.BailErrorStrategy;
+import org.antlr.v4.runtime.BaseErrorListener;
 import org.antlr.v4.runtime.CharStreams;
 import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.DefaultErrorStrategy;import org.antlr.v4.runtime.Parser;
+import org.antlr.v4.runtime.RecognitionException;
+import org.antlr.v4.runtime.Recognizer;
+import org.antlr.v4.runtime.atn.ATNConfigSet;
+import org.antlr.v4.runtime.dfa.DFA;
+import org.antlr.v4.runtime.misc.ParseCancellationException;
 
 import fi.benjami.code4jvm.lua.compiler.IrCompiler;
 import fi.benjami.code4jvm.lua.compiler.LuaScope;
+import fi.benjami.code4jvm.lua.compiler.LuaSyntaxException;
 import fi.benjami.code4jvm.lua.ir.LuaLocalVar;
 import fi.benjami.code4jvm.lua.ir.LuaModule;
 import fi.benjami.code4jvm.lua.ir.LuaType;
 import fi.benjami.code4jvm.lua.ir.UpvalueTemplate;
 import fi.benjami.code4jvm.lua.parser.LuaLexer;
 import fi.benjami.code4jvm.lua.parser.LuaParser;
+import fi.benjami.code4jvm.lua.parser.LuaParser.ChunkContext;
 import fi.benjami.code4jvm.lua.runtime.LuaFunction;
 import fi.benjami.code4jvm.lua.runtime.LuaTable;
 
@@ -49,7 +60,32 @@ public LuaModule compile(String name, String chunk) {
 		// Tokenize and parse the chunk
 		var lexer = new LuaLexer(CharStreams.fromString(chunk));
 		var parser = new LuaParser(new CommonTokenStream(lexer));
-		var tree = parser.chunk();
+		parser.setErrorHandler(new BailErrorStrategy());
+
+		ChunkContext tree;
+		try {			
+			tree = parser.chunk();
+		} catch (ParseCancellationException e) {
+			// Parse error; try again, this time with error recovery and no IR generation
+			lexer = new LuaLexer(CharStreams.fromString(chunk));
+			parser = new LuaParser(new CommonTokenStream(lexer));
+			parser.removeErrorListeners();
+
+			var errors = new ArrayList<LuaSyntaxException.Error>();
+			parser.addErrorListener(new BaseErrorListener() {
+				@Override
+				public void syntaxError(Recognizer<?, ?> recognizer,
+						Object offendingSymbol,
+						int line,
+						int charPositionInLine,
+						String msg,
+						RecognitionException e) {
+					errors.add(new LuaSyntaxException.Error(name, line, charPositionInLine, msg));
+				}
+			});
+			tree = parser.chunk();
+			throw new LuaSyntaxException(errors);
+		}
 
 		// Perform semantic analysis and compile to IR
 		var rootScope = LuaScope.chunkRoot();

lua4jvm/src/main/java/fi/benjami/code4jvm/lua/compiler/LuaSyntaxException.java

@@ -0,0 +1,45 @@
+package fi.benjami.code4jvm.lua.compiler;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import fi.benjami.code4jvm.lua.LuaVm;
+
+/**
+ * Thrown by the {@link LuaVm Lua VM} when source code given to it contains
+ * syntax errors. Although the VM will refuse to load such code, it will
+ * attempt to parse through the entire chunk and report all identified syntax
+ * errors.
+ *
+ */
+public class LuaSyntaxException extends RuntimeException {
+
+	private static final long serialVersionUID = 1L;
+
+	private final List<Error> errors;
+
+	public LuaSyntaxException(List<Error> errors) {
+		super(makeMsg(errors));
+		if (errors.isEmpty()) {
+			throw new IllegalArgumentException("cannot to create syntax error without errors");
+		}
+		this.errors = errors;
+	}
+
+	private static String makeMsg(List<Error> errors) {
+		return errors.stream()
+				.map(error -> error.chunkName + ":" + error.line + ":" + error.posInLine + " " + error.message)
+				.collect(Collectors.joining("\n"));
+	}
+
+	public record Error(
+			String chunkName,
+			int line,
+			int posInLine,
+			String message
+	) {}
+
+	public List<Error> errors() {
+		return errors;
+	}
+}

lua4jvm/src/test/java/fi/benjami/code4jvm/lua/test/CompilerErrorTest.java

@@ -0,0 +1,56 @@
+package fi.benjami.code4jvm.lua.test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+import fi.benjami.code4jvm.lua.LuaVm;
+import fi.benjami.code4jvm.lua.compiler.LuaSyntaxException;
+
+public class CompilerErrorTest {
+
+	private final LuaVm vm = new LuaVm();
+
+	@Test
+	public void syntaxError() {
+		try {
+			vm.compile("\nfunction #() end");
+		} catch (LuaSyntaxException e) {
+			var errors = e.errors();
+			assertEquals(1, errors.size());
+			var err = errors.get(0);
+			assertEquals("unknown", err.chunkName());
+			assertEquals(2, err.line());
+			assertEquals(9, err.posInLine());
+			// Don't check the message; it is currently whatever antlr 4 sees fit
+			return;
+		}
+		fail();
+	}
+
+	@Test
+	public void multipleErrors() {
+		try {
+			vm.compile("""
+					function #() end
+					
+					function #() end
+					""");
+		} catch (LuaSyntaxException e) {
+			var errors = e.errors();
+			assertEquals(2, errors.size());
+			var first = errors.get(0);
+			assertEquals("unknown", first.chunkName());
+			assertEquals(1, first.line());
+			assertEquals(9, first.posInLine());
+
+			var second = errors.get(1);
+			assertEquals("unknown", second.chunkName());
+			assertEquals(3, second.line());
+			assertEquals(9, second.posInLine());
+			return;
+		}
+		fail();
+	}
+}