bpo-42246: Don't forget the entry block when ensuring that all exits have a line number

Lib/test/test_compile.py

@@ -809,6 +809,24 @@ def save_caller_frame():
                 func(save_caller_frame)
                 self.assertEqual(frame.f_lineno-frame.f_code.co_firstlineno, lastline)
 
+    def test_lineno_after_no_code(self):
+        def no_code1():
+            "doc string"
+
+        def no_code2():
+            a: int
+
+        for func in (no_code1, no_code2):
+            with self.subTest(func=func):
+                code = func.__code__
+                lines = list(code.co_lines())
+                self.assertEqual(len(lines), 1)
+                start, end, line = lines[0]
+                self.assertEqual(start, 0)
+                self.assertEqual(end, len(code.co_code))
+                self.assertEqual(line, code.co_firstlineno)
+
+
     def test_big_dict_literal(self):
         # The compiler has a flushing point in "compiler_dict" that calls compiles
         # a portion of the dictionary literal when the loop that iterates over the items

Python/compile.c

@@ -6514,6 +6514,7 @@ is_exit_without_lineno(basicblock *b) {
 static int
 ensure_exits_have_lineno(struct compiler *c)
 {
+    basicblock *entry = NULL;
     /* Copy all exit blocks without line number that are targets of a jump.
      */
     for (basicblock *b = c->u->u_blocks; b != NULL; b = b->b_list) {
@@ -6535,6 +6536,11 @@ ensure_exits_have_lineno(struct compiler *c)
                 b->b_instr[b->b_iused-1].i_target = new_target;
             }
         }
+        entry = b;
+    }
+    assert(entry != NULL);
+    if (is_exit_without_lineno(entry)) {
+        entry->b_instr[0].i_lineno = c->u->u_firstlineno;
     }
     /* Any remaining reachable exit blocks without line number can only be reached by
      * fall through, and thus can only have a single predecessor */