From ae5b5ba529753c7a653901ffc29b5ea24c3fdf3a Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 27 Jul 2020 13:23:05 -0300
Subject: [PATCH] Fixed bug: line hooks in stripped functions

Line-hook handling was accessing debug info. without checking whether
it was present.
---
 ldebug.c      |  4 +++-
 testes/db.lua | 19 ++++++++++++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/ldebug.c b/ldebug.c
index 9ff7edeb..8cb00e51 100644
--- a/ldebug.c
+++ b/ldebug.c
@@ -783,11 +783,13 @@ l_noret luaG_runerror (lua_State *L, const char *fmt, ...) {
 ** previous instruction 'oldpc'.
 */
 static int changedline (const Proto *p, int oldpc, int newpc) {
+  if (p->lineinfo == NULL)  /* no debug information? */
+    return 0;
   while (oldpc++ < newpc) {
     if (p->lineinfo[oldpc] != 0)
       return (luaG_getfuncline(p, oldpc - 1) != luaG_getfuncline(p, newpc));
   }
-  return 0;  /* no line changes in the way */
+  return 0;  /* no line changes between positions */
 }
 
 
diff --git a/testes/db.lua b/testes/db.lua
index 941283f7..5377f6ec 100644
--- a/testes/db.lua
+++ b/testes/db.lua
@@ -884,7 +884,7 @@ end
 
 
 print("testing debug functions on chunk without debug info")
-prog = [[-- program to be loaded without debug information
+prog = [[-- program to be loaded without debug information (strip)
 local debug = require'debug'
 local a = 12  -- a local variable
 
@@ -927,6 +927,23 @@ local f = assert(load(string.dump(load(prog), true)))
 
 assert(f() == 13)
 
+do   -- bug in 5.4.0: line hooks in stripped code
+  local function foo ()
+    local a = 1
+    local b = 2
+    return b
+  end
+
+  local s = load(string.dump(foo, true))
+  local line = true
+  debug.sethook(function (e, l)
+    assert(e == "line")
+    line = l
+  end, "l")
+  assert(s() == 2); debug.sethook(nil)
+  assert(line == nil)  -- hook called withoug debug info for 1st instruction
+end
+
 do   -- tests for 'source' in binary dumps
   local prog = [[
     return function (x)