Fix SyntaxError indicator printing too many spaces for multi-line strings (GH-14433)

(cherry picked from commit 5b94f35)

Co-authored-by: Anthony Sottile <asottile@umich.edu>

Author: miss-islington

Lib/test/test_cmd_line_script.py

@@ -601,6 +601,20 @@ def test_syntaxerror_indented_caret_position(self):
             self.assertNotIn("\f", text)
             self.assertIn("\n    1 + 1 = 2\n    ^", text)
 
+    def test_syntaxerror_multi_line_fstring(self):
+        script = 'foo = f"""{}\nfoo"""\n'
+        with support.temp_dir() as script_dir:
+            script_name = _make_test_script(script_dir, 'script', script)
+            exitcode, stdout, stderr = assert_python_failure(script_name)
+            self.assertEqual(
+                stderr.splitlines()[-3:],
+                [
+                    b'    foo = f"""{}',
+                    b'          ^',
+                    b'SyntaxError: f-string: empty expression not allowed',
+                ],
+            )
+
     def test_consistent_sys_path_for_direct_execution(self):
         # This test case ensures that the following all give the same
         # sys.path configuration:

Misc/NEWS.d/next/Core and Builtins/2019-06-27-15-01-14.bpo-37433.amNGqr.rst

@@ -0,0 +1 @@
+Fix ``SyntaxError`` indicator printing too many spaces for multi-line strings - by Anthony Sottile.

Parser/tokenizer.c

@@ -956,6 +956,7 @@ tok_nextc(struct tok_state *tok)
             while (!done) {
                 Py_ssize_t curstart = tok->start == NULL ? -1 :
                           tok->start - tok->buf;
+                Py_ssize_t cur_multi_line_start = tok->multi_line_start - tok->buf;
                 Py_ssize_t curvalid = tok->inp - tok->buf;
                 Py_ssize_t newsize = curvalid + BUFSIZ;
                 char *newbuf = tok->buf;
@@ -968,6 +969,7 @@ tok_nextc(struct tok_state *tok)
                 }
                 tok->buf = newbuf;
                 tok->cur = tok->buf + cur;
+                tok->multi_line_start = tok->buf + cur_multi_line_start;
                 tok->line_start = tok->cur;
                 tok->inp = tok->buf + curvalid;
                 tok->end = tok->buf + newsize;