Fix issue with lua_loadfile and require. (#2317)

Fixes an regression introduced in
afcbbb2.

`require` actually follows a different code path in Lua with a different
stack layout expectation than the other code paths.

Fix the code to deal with this case, and also clean up some other
tidbits around cleaning up stack values. The new approach is simpler to
understand and should fix a potential issue that could happen in the
error case.

Fixes #2314.

Author: tritao

src/host/lua_auxlib.c

@@ -5,6 +5,7 @@
  */
 
 #include "premake.h"
+#include <assert.h>
 
 
 static int chunk_wrapper(lua_State* L);
@@ -29,11 +30,15 @@ LUALIB_API int luaL_loadfilex (lua_State* L, const char* filename, const char* m
 	const char* script_dir;
 	const char* test_name;
 
-	/* this function can be called with from 1 to 3 arguments on the stack,
+	/* this function is usually called with from 1 to 3 arguments on the stack,
 	 * the filename, the mode and an environment table */
 
-  	int env = (!lua_isnone(L, 3) ? 1 : 0);  /* 1 if there is an env or 0 if no 'env' */
+	/* however, in the case of require, we end up being called from searcher_Lua,
+	   which sets up extra values on the stack */
 	int bottom = lua_gettop(L);
+	int is_require = bottom >= 4;
+
+  	int env = (!is_require && !lua_isnone(L, 3)) ? 1 : 0;  /* 1 if there is an env or 0 if no 'env' */
 	int z = !OKAY;
 
 	/* If filename starts with "$/" then we want to load the version that
@@ -50,6 +55,7 @@ LUALIB_API int luaL_loadfilex (lua_State* L, const char* filename, const char* m
 	if (z != OKAY) {
 		lua_getglobal(L, "_SCRIPT_DIR");
 		script_dir = lua_tostring(L, -1);
+		int script_dir_index = lua_gettop(L);
 
 		if (script_dir && script_dir[0] == '$') {
 			/* Call `path.getabsolute(filename, _SCRIPT_DIR)` to resolve any
@@ -59,16 +65,17 @@ LUALIB_API int luaL_loadfilex (lua_State* L, const char* filename, const char* m
 			lua_pushvalue(L, -3);
 			lua_call(L, 2, 1);
 			test_name = lua_tostring(L, -1);
+			int test_name_index = lua_gettop(L);
 
 			/* if successful, filename and chunk will be on top of stack */
 			z = premake_load_embedded_script(L, test_name + 2); /* Skip over leading "$/" */
 
 			/* remove test_name */
-			lua_remove(L, -3);
+			lua_remove(L, test_name_index);
 		}
 
 		/* remove _SCRIPT_DIR */
-		lua_remove(L, bottom + env);
+		lua_remove(L, script_dir_index);
 	}
 
 	/* Try to locate the script on the filesystem */
@@ -103,6 +110,9 @@ LUALIB_API int luaL_loadfilex (lua_State* L, const char* filename, const char* m
 	/* Either way I should have ended up with the file name followed by the
 	 * script chunk on the stack. Turn these into a closure that will call my
 	 * wrapper below when the loaded script needs to be executed. */
+
+	assert(lua_gettop(L) == bottom + 2);
+
 	if (z == OKAY) {
 		/* if we are called with an env, then our caller, luaB_loadfile, will
 		 * call load_aux, which sets up our env as the first up value via

tests/folder/init.lua

@@ -0,0 +1 @@
+-- empty file used by loadfile_with_require test

tests/test_lua.lua

@@ -35,3 +35,13 @@ end
 		test.isequal(10, value)
 	end
 
+
+--
+-- loadfile via require with init.lua
+--
+
+function suite.loadfile_with_require()
+	os.chdir(_SCRIPT_DIR)
+	assert(require("folder"))
+end
+