gh-123123: Fix display of syntax errors covering multiple lines

Author: pablogsal

Lib/test/test_traceback.py

@@ -699,6 +699,35 @@ def f_with_multiline():
         result_lines = self.get_exception(f_with_multiline)
         self.assertEqual(result_lines, expected_f.splitlines())
 
+        # Check custom error messages covering multiple lines
+        code = textwrap.dedent("""
+        dummy_call(
+            "dummy value"
+            foo="bar",
+        )
+        """)
+
+        def f_with_multiline():
+            # Need to defer the compilation until in self.get_exception(..)
+            return compile(code, "?", "exec")
+
+        lineno_f = f_with_multiline.__code__.co_firstlineno
+
+        expected_f = (
+            'Traceback (most recent call last):\n'
+            f'  File "{__file__}", line {self.callable_line}, in get_exception\n'
+            '    callable()\n'
+            '    ~~~~~~~~^^\n'
+            f'  File "{__file__}", line {lineno_f+2}, in f_with_multiline\n'
+            '    return compile(code, "?", "exec")\n'
+            '  File "?", line 3\n'
+            '    "dummy value"\n'
+            '    ^^^^^^^^^^^^'
+            )
+
+        result_lines = self.get_exception(f_with_multiline)
+        self.assertEqual(result_lines, expected_f.splitlines())
+
     def test_caret_multiline_expression_bin_op(self):
         # Make sure no carets are printed for expressions spanning multiple
         # lines.

Lib/traceback.py

@@ -1292,7 +1292,10 @@ def _format_syntax_error(self, stype, **kwargs):
                 yield '    {}\n'.format(ltext)
             else:
                 offset = self.offset
-                end_offset = self.end_offset if self.end_offset not in {None, 0} else offset
+                if self.lineno == self.end_lineno:
+                    end_offset = self.end_offset if self.end_offset not in {None, 0} else offset
+                else:
+                    end_offset = len(self.text)
                 if self.text and offset > len(self.text):
                     offset = len(self.text) + 1
                 if self.text and end_offset > len(self.text):

Misc/NEWS.d/next/Core and Builtins/2024-08-18-18-25-54.gh-issue-123123.0ZcaEB.rst

@@ -0,0 +1,2 @@
+Fix displaying :exc:`SyntaxError` exceptions covering multiple lines. Patch
+by Pablo Galindo