gh-130775: Allow negative locations in ast (#130795)

Co-authored-by: Victor Stinner <[email protected]>

Author: sobolevn

Lib/test/test_ast/test_ast.py

@@ -189,6 +189,26 @@ def test_compilation_of_ast_nodes_with_default_end_position_values(self):
         # Check that compilation doesn't crash. Note: this may crash explicitly only on debug mode.
         compile(tree, "<string>", "exec")
 
+    def test_negative_locations_for_compile(self):
+        # See https://github.com/python/cpython/issues/130775
+        alias = ast.alias(name='traceback', lineno=0, col_offset=0)
+        for attrs in (
+            {'lineno': -2, 'col_offset': 0},
+            {'lineno': 0, 'col_offset': -2},
+            {'lineno': 0, 'col_offset': -2, 'end_col_offset': -2},
+            {'lineno': -2, 'end_lineno': -2, 'col_offset': 0},
+        ):
+            with self.subTest(attrs=attrs):
+                tree = ast.Module(body=[
+                    ast.Import(names=[alias], **attrs)
+                ], type_ignores=[])
+
+                # It used to crash on this step:
+                compile(tree, "<string>", "exec")
+
+                # This also must not crash:
+                ast.parse(tree, optimize=2)
+
     def test_slice(self):
         slc = ast.parse("x[::]").body[0].value.slice
         self.assertIsNone(slc.upper)

Misc/NEWS.d/next/Core_and_Builtins/2025-03-03-20-02-45.gh-issue-130775.fEM6T-.rst

@@ -0,0 +1 @@
+Do not crash on negative ``column`` and ``end_column`` in :mod:`ast` locations.

Python/assemble.c

@@ -290,18 +290,15 @@ write_location_info_entry(struct assembler* a, location loc, int isize)
         assert(len > THEORETICAL_MAX_ENTRY_SIZE);
         RETURN_IF_ERROR(_PyBytes_Resize(&a->a_linetable, len*2));
     }
-    if (loc.lineno < 0) {
-        assert(loc.lineno == NO_LOCATION.lineno);
+    if (loc.lineno == NO_LOCATION.lineno) {
         write_location_info_none(a, isize);
         return SUCCESS;
     }
     int line_delta = loc.lineno - a->a_lineno;
     int column = loc.col_offset;
     int end_column = loc.end_col_offset;
-    assert(column >= -1);
-    assert(end_column >= -1);
     if (column < 0 || end_column < 0) {
-        if (loc.end_lineno == loc.lineno || loc.end_lineno == -1) {
+        if (loc.end_lineno == loc.lineno || loc.end_lineno < 0) {
             write_location_info_no_column(a, isize, line_delta);
             a->a_lineno = loc.lineno;
             return SUCCESS;