GR-9831: format the message for Syntax error to add more context akin to how cpython does it

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/PythonErrorStrategy.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates.
+ *
+ * The Universal Permissive License (UPL), Version 1.0
+ *
+ * Subject to the condition set forth below, permission is hereby granted to any
+ * person obtaining a copy of this software, associated documentation and/or data
+ * (collectively the "Software"), free of charge and under any and all copyright
+ * rights in the Software, and any and all patent rights owned or freely
+ * licensable by each licensor hereunder covering either (i) the unmodified
+ * Software as contributed to or provided by such licensor, or (ii) the Larger
+ * Works (as defined below), to deal in both
+ *
+ * (a) the Software, and
+ * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
+ *     one is included with the Software (each a "Larger Work" to which the
+ *     Software is contributed by such licensors),
+ *
+ * without restriction, including without limitation the rights to copy, create
+ * derivative works of, display, perform, and distribute the Software and make,
+ * use, sell, offer for sale, import, export, have made, and have sold the
+ * Software and the Larger Work(s), and to sublicense the foregoing rights on
+ * either these or other terms.
+ *
+ * This license is subject to the following condition:
+ *
+ * The above copyright notice and either this complete permission notice or at a
+ * minimum a reference to the UPL must be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.oracle.graal.python.parser;
+
+import org.antlr.v4.runtime.DefaultErrorStrategy;
+import org.antlr.v4.runtime.InputMismatchException;
+import org.antlr.v4.runtime.Parser;
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.antlr.v4.runtime.RecognitionException;
+import org.antlr.v4.runtime.Token;
+import org.antlr.v4.runtime.TokenStream;
+import org.antlr.v4.runtime.misc.Interval;
+
+public class PythonErrorStrategy extends DefaultErrorStrategy {
+    private static final String LINE_PADDING = "  ";
+
+    @Override
+    public void recover(Parser recognizer, RecognitionException e) {
+        super.recover(recognizer, e);
+    }
+
+    private String getTokeLineText(Parser recognizer, Token token) {
+        TokenStream tokenStream = recognizer.getTokenStream();
+        int index = token.getTokenIndex();
+        // search for line start
+        int tokenIndex = index - 1;
+        int start = -1;
+        while (tokenIndex >= 0) {
+            Token t = tokenStream.get(tokenIndex);
+            if (t.getText().equals("\n")) {
+                break;
+            }
+            start = t.getStartIndex();
+            tokenIndex--;
+        }
+
+        // search for line stop
+        tokenIndex = index + 1;
+        int stop = -1;
+        while (tokenIndex < tokenStream.size()) {
+            Token t = tokenStream.get(tokenIndex);
+            stop = t.getStopIndex();
+            if (t.getText().equals("\n")) {
+                break;
+            }
+            tokenIndex++;
+        }
+
+        return token.getInputStream().getText(Interval.of(start, stop));
+    }
+
+    @Override
+    protected void reportInputMismatch(Parser recognizer, InputMismatchException e) {
+        Token offendingToken = e.getOffendingToken();
+        String lineText = getTokeLineText(recognizer, offendingToken);
+        String errorMarker = new String(new char[offendingToken.getCharPositionInLine() + 1]).replace('\0', ' ') + "^";
+        String pythonSyntaxErrorMessage = "\n" + LINE_PADDING + lineText + "\n" + LINE_PADDING + errorMarker;
+
+        RecognitionException re = e;
+        // the error message in some cases is not set properly producing an annoying "null" in the
+        // final message, we replace the error with a copy of itself but, no message
+        if (re.getMessage() == null) {
+            re = new RecognitionException("", e.getRecognizer(), e.getInputStream(), (ParserRuleContext) e.getCtx());
+        }
+        recognizer.notifyErrorListeners(offendingToken, pythonSyntaxErrorMessage, re);
+    }
+}

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/PythonParserImpl.java

@@ -28,6 +28,7 @@
 import static com.oracle.graal.python.runtime.exception.PythonErrorType.SyntaxError;
 
 import java.util.HashMap;
+import java.util.InputMismatchException;
 import java.util.Map;
 import java.util.regex.Pattern;
 
@@ -63,6 +64,7 @@ private static ParserRuleContext preParseWithAntlr(PythonCore core, Source sourc
         String fileDirAndName = pathParts[pathParts.length - 2] + PythonCore.FILE_SEPARATOR + pathParts[pathParts.length - 1];
         CodePointCharStream fromString = CharStreams.fromString(source.getCharacters().toString(), fileDirAndName);
         Python3Parser parser = new com.oracle.graal.python.parser.antlr.Builder.Parser(fromString).build();
+        parser.setErrorHandler(new PythonErrorStrategy());
         ParserRuleContext input;
         if (!core.isInitialized()) {
             input = cachedParseTrees.get(fileDirAndName);