bpo-40985: Show correct SyntaxError text when last line has a LINECONT (GH-20888)


When a file ends with a line that contains a line continuation character
the text of the emitted SyntaxError is empty, contrary to the old
parser, where the error text contained the text of the last line.
(cherry picked from commit 113e2b0a07c72c0d5e3489076afb14f6b3ad1049)

Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>
diff --git a/Lib/test/test_eof.py b/Lib/test/test_eof.py
index bebad31..51cbbd8 100644
--- a/Lib/test/test_eof.py
+++ b/Lib/test/test_eof.py
@@ -52,10 +52,14 @@
             file_name = script_helper.make_script(temp_dir, 'foo', '\\')
             rc, out, err = script_helper.assert_python_failure(file_name)
             self.assertIn(b'unexpected EOF while parsing', err)
+            self.assertIn(b'line 2', err)
+            self.assertIn(b'\\', err)
 
             file_name = script_helper.make_script(temp_dir, 'foo', 'y = 6\\')
             rc, out, err = script_helper.assert_python_failure(file_name)
             self.assertIn(b'unexpected EOF while parsing', err)
+            self.assertIn(b'line 2', err)
+            self.assertIn(b'y = 6\\', err)
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-06-15-16-29-55.bpo-40985.IIN_xX.rst b/Misc/NEWS.d/next/Core and Builtins/2020-06-15-16-29-55.bpo-40985.IIN_xX.rst
new file mode 100644
index 0000000..e07134c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-06-15-16-29-55.bpo-40985.IIN_xX.rst
@@ -0,0 +1 @@
+Fix a bug that caused the :exc:`SyntaxError` text to be empty when a file ends with a line ending in a line continuation character (i.e. backslash). The error text should contain the text of the last line.
diff --git a/Python/errors.c b/Python/errors.c
index 5d17256..87af39d 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -1648,16 +1648,18 @@
 {
     int i;
     char linebuf[1000];
-
-    if (fp == NULL)
+    if (fp == NULL) {
         return NULL;
+    }
+
     for (i = 0; i < lineno; i++) {
         char *pLastChar = &linebuf[sizeof(linebuf) - 2];
         do {
             *pLastChar = '\0';
             if (Py_UniversalNewlineFgets(linebuf, sizeof linebuf,
-                                         fp, NULL) == NULL)
-                break;
+                                         fp, NULL) == NULL) {
+                goto after_loop;
+            }
             /* fgets read *something*; if it didn't get as
                far as pLastChar, it must have found a newline
                or hit the end of the file; if pLastChar is \n,
@@ -1665,6 +1667,8 @@
                yet seen a newline, so must continue */
         } while (*pLastChar != '\0' && *pLastChar != '\n');
     }
+
+after_loop:
     fclose(fp);
     if (i == lineno) {
         PyObject *res;