Issue #27594: Prevent assertion error when running test_ast with coverage

enabled: ensure code object has a valid first line number.
Patch suggested by Ivan Levkivskyi.

Misc/NEWS

@@ -167,6 +167,10 @@ Tests
 - Issue #27369: In test_pyexpat, avoid testing an error message detail that
   changed in Expat 2.2.0.
 
+- Issue #27594: Prevent assertion error when running test_ast with coverage
+  enabled: ensure code object has a valid first line number.
+  Patch suggested by Ivan Levkivskyi.
+
 Windows
 -------
 

Python/compile.c

@@ -4963,7 +4963,7 @@ assemble(struct compiler *c, int addNone)
 
     /* Set firstlineno if it wasn't explicitly set. */
     if (!c->u->u_firstlineno) {
-        if (entryblock && entryblock->b_instr)
+        if (entryblock && entryblock->b_instr && entryblock->b_instr->i_lineno)
             c->u->u_firstlineno = entryblock->b_instr->i_lineno;
         else
             c->u->u_firstlineno = 1;