Bug #1512814, Fix incorrect lineno's when code at module scope

started after line 256.

Lib/test/test_compile.py

@@ -166,6 +166,16 @@ if 1:
         pass"""
         compile(s, "<string>", "exec")
 
+    # This test is probably specific to CPython and may not generalize
+    # to other implementations.  We are trying to ensure that when
+    # the first line of code starts after 256, correct line numbers
+    # in tracebacks are still produced.
+    def test_leading_newlines(self):
+        s256 = "".join(["\n"] * 256 + ["spam"])
+        co = compile(s256, 'fn', 'exec')
+        self.assertEqual(co.co_firstlineno, 257)
+        self.assertEqual(co.co_lnotab, '')
+
     def test_literals_with_leading_zeroes(self):
         for arg in ["077787", "0xj", "0x.", "0e",  "090000000000000",
                     "080000000000000", "000000000000009", "000000000000008"]:

Misc/NEWS

@@ -33,6 +33,9 @@ Core and builtins
 - On 64 bit systems, int literals that use less than 64 bits are
   now ints rather than longs.
 
+- Bug #1512814, Fix incorrect lineno's when code at module scope
+  started after line 256.
+
 Library
 -------
 

Python/compile.c

@@ -1776,7 +1776,8 @@ compiler_mod(struct compiler *c, mod_ty mod)
 		if (!module)
 			return NULL;
 	}
-	if (!compiler_enter_scope(c, module, mod, 1))
+	/* Use 0 for firstlineno initially, will fixup in assemble(). */
+	if (!compiler_enter_scope(c, module, mod, 0))
 		return NULL;
 	switch (mod->kind) {
 	case Module_kind: 
@@ -4446,6 +4447,13 @@ assemble(struct compiler *c, int addNone)
 		entryblock = b; 
 	}
 
+	/* Set firstlineno if it wasn't explicitly set. */
+	if (!c->u->u_firstlineno) {
+		if (entryblock && entryblock->b_instr)
+			c->u->u_firstlineno = entryblock->b_instr->i_lineno;
+		else
+			c->u->u_firstlineno = 1;
+	}
 	if (!assemble_init(&a, nblocks, c->u->u_firstlineno))
 		goto error;
 	dfs(c, entryblock, &a);