bpo-44297: Fix missing line number in generator expressions (GH-26801)

* Make sure that line number is set when entering comprehension scope in compiler.

Lib/test/test_compile.py

@@ -895,6 +895,21 @@ if 1:
                               for (_, _, line) in func.__code__.co_lines() ]
                 self.assertEqual(lines, code_lines)
 
+    def test_line_number_genexp(self):
+
+        def return_genexp():
+            return (1
+                    for
+                    x
+                    in
+                    y)
+        genexp_lines = [None, 1, 3, 1]
+
+        genexp_code = return_genexp.__code__.co_consts[1]
+        code_lines = [None if line is None else line-return_genexp.__code__.co_firstlineno
+                      for (_, _, line) in genexp_code.co_lines() ]
+        self.assertEqual(genexp_lines, code_lines)
+
 
     def test_big_dict_literal(self):
         # The compiler has a flushing point in "compiler_dict" that calls compiles

Misc/NEWS.d/next/Core and Builtins/2021-06-19-12-41-13.bpo-44297.F53vHj.rst

@@ -0,0 +1,3 @@
+Make sure that the line number is set when entering a comprehension scope.
+Ensures that backtraces inclusing generator expressions show the correct
+line number.

Python/compile.c

@@ -4900,6 +4900,7 @@ compiler_comprehension(struct compiler *c, expr_ty e, int type,
     {
         goto error;
     }
+    SET_LOC(c, e);
 
     is_async_generator = c->u->u_ste->ste_coroutine;