lua: fix compilation with lua 5.2

Commit e2e450f9 started making use of luaL_register(), but OF COURSE
this function disappeared in Lua 5.2, and was replaced with a 5.2-only
alternative, slightly different mechanism.

So just NIH our own function. This is actually slightly more correct,
since it forces the user to call "require" to actually make the module
visible for builtin C-only modules other than "mp". Fix autoload.lua
accordingly.

3 files changed, 47 insertions, 11 deletions

diff --git a/DOCS/man/en/lua.rst b/DOCS/man/en/lua.rst
index fca158cad7..80467f8f8c 100644
--- a/DOCS/man/en/lua.rst
+++ b/DOCS/man/en/lua.rst
@@ -437,7 +437,7 @@ Example implementation::
         optionB = -0.5,
         optionC = true,
     }
-    read_options(options, "myscript")
+    options.read_options(options, "myscript")
     print(option.optionA)
 
 
diff --git a/TOOLS/lua/autoload.lua b/TOOLS/lua/autoload.lua
index 1fe1aec49c..f6e9313f9a 100644
--- a/TOOLS/lua/autoload.lua
+++ b/TOOLS/lua/autoload.lua
@@ -7,6 +7,8 @@
 -- Add at most 5 * 2 files when starting a file (before + after).
 MAXENTRIES = 5
 
+mputils = require 'mp.utils'
+
 function add_files_at(index, files)
     index = index - 1
     local oldcount = mp.get_property_number("playlist-count", 1)
@@ -18,11 +20,11 @@ end
 
 function find_and_add_entries()
     local path = mp.get_property("path", "")
-    local dir, filename = mp.utils.split_path(path)
+    local dir, filename = mputils.split_path(path)
     if #dir == 0 then
         return
     end
-    local files = mp.utils.readdir(dir, "files")
+    local files = mputils.readdir(dir, "files")
     table.sort(files)
     local pl = mp.get_property_native("playlist", {})
     local pl_current = mp.get_property_number("playlist-pos", 0) + 1
diff --git a/player/lua.c b/player/lua.c
index 60e380b554..efbd21b18e 100644
--- a/player/lua.c
+++ b/player/lua.c
@@ -187,6 +187,23 @@ static bool require(lua_State *L, const char *name)
     return true;
 }
 
+// Push the table of a module. If it doesn't exist, it's created.
+// The Lua script can call "require(module)" to "load" it.
+static void push_module_table(lua_State *L, const char *module)
+{
+    lua_getglobal(L, "package"); // package
+    lua_getfield(L, -1, "loaded"); // package loaded
+    lua_remove(L, -2); // loaded
+    lua_getfield(L, -1, module); // loaded module
+    if (lua_isnil(L, -1)) {
+        lua_pop(L, 1); // loaded
+        lua_newtable(L); // loaded module
+        lua_pushvalue(L, -1); // loaded module module
+        lua_setfield(L, -3, module); // loaded module
+    }
+    lua_remove(L, -2); // module
+}
+
 static int load_lua(struct mpv_handle *client, const char *fname)
 {
     struct MPContext *mpctx = mp_client_get_core(client);
@@ -212,13 +229,14 @@ static int load_lua(struct mpv_handle *client, const char *fname)
     lua_setfield(L, LUA_REGISTRYINDEX, "wrap_cpcall"); // -
 
     luaL_openlibs(L);
+    add_functions(ctx); // mp
+
+    push_module_table(L, "mp"); // mp
 
-    lua_newtable(L); // mp
+    // "mp" is available by default, and no "require 'mp'" is needed
     lua_pushvalue(L, -1); // mp mp
     lua_setglobal(L, "mp"); // mp
 
-    add_functions(ctx); // mp
-
     lua_pushstring(L, ctx->name); // mp name
     lua_setfield(L, -2, "script_name"); // mp
 
@@ -1044,8 +1062,12 @@ static int script_join_path(lua_State *L)
 }
 
 #define FN_ENTRY(name) {#name, script_ ## name}
+struct fn_entry {
+    const char *name;
+    int (*fn)(lua_State *L);
+};
 
-static struct luaL_Reg main_fns[] = {
+static const struct fn_entry main_fns[] = {
     FN_ENTRY(log),
     FN_ENTRY(suspend),
     FN_ENTRY(resume),
@@ -1080,18 +1102,31 @@ static struct luaL_Reg main_fns[] = {
     {0}
 };
 
-static struct luaL_Reg utils_fns[] = {
+static struct fn_entry utils_fns[] = {
     FN_ENTRY(readdir),
     FN_ENTRY(split_path),
     FN_ENTRY(join_path),
     {0}
 };
 
+static void register_package_fns(lua_State *L, char *module,
+                                 const struct fn_entry *e)
+{
+    push_module_table(L, module); // modtable
+    for (int n = 0; e[n].name; n++) {
+        lua_pushcclosure(L, e[n].fn, 0); // modtable fn
+        lua_setfield(L, -2, e[n].name); // modtable
+    }
+    lua_pop(L, 1); // -
+}
+
 static void add_functions(struct script_ctx *ctx)
 {
     lua_State *L = ctx->state;
 
-    luaL_register(L, "mp", main_fns); // mp
+    register_package_fns(L, "mp", main_fns);
+
+    push_module_table(L, "mp"); // mp
 
     lua_pushinteger(L, 0);
     lua_pushcclosure(L, script_get_property, 1);
@@ -1103,8 +1138,7 @@ static void add_functions(struct script_ctx *ctx)
 
     lua_pop(L, 1); // -
 
-    luaL_register(L, "mp.utils", utils_fns);
-    lua_pop(L, 1);
+    register_package_fns(L, "mp.utils", utils_fns);
 }
 
 const struct mp_scripting mp_scripting_lua = {