Hide shell functions from _G using upvalues on the main chunk

Store __command, __interactive, __getenv, __setenv as upvalues
populated by lua_load() from the registry, keeping them invisible
to user code while accessible to the parser's codegen.

lparser.c

@@ -27,6 +27,7 @@
 #include "lstate.h"
 #include "lstring.h"
 #include "ltable.h"
+#include "lcmd.h"
 
 
 
@@ -499,6 +500,19 @@ static void singlevaraux (FuncState *fs, TString *n, expdesc *var, int base) {
 }
 
 
+/*
+** Look up a lush shell function (e.g. __command) that is registered
+** as an upvalue on the main chunk. singlevaraux will find it directly
+** as VUPVAL, emitting OP_GETUPVAL instead of OP_GETTABUP.
+*/
+static void buildlushvar (LexState *ls, TString *varname, expdesc *var) {
+  FuncState *fs = ls->fs;
+  init_exp(var, VGLOBAL, -1);
+  singlevaraux(fs, varname, var, 1);
+  lua_assert(var->k == VUPVAL);  /* must be found as upvalue */
+}
+
+
 static void buildglobal (LexState *ls, TString *varname, expdesc *var) {
   FuncState *fs = ls->fs;
   expdesc key;
@@ -552,8 +566,8 @@ static void codecommand (LexState *ls, expdesc *v, expdesc *cmdstr) {
   expdesc func;
   TString *cmdname = luaX_newstring(ls, "__command", 9);
   line = ls->linenumber;
-  /* look up __command as _ENV["__command"] */
-  buildglobal(ls, cmdname, &func);
+  /* look up __command as upvalue */
+  buildlushvar(ls, cmdname, &func);
   luaK_exp2nextreg(fs, &func);
   base = func.u.info;
   /* push the command string argument */
@@ -1243,7 +1257,7 @@ static void commandexp (LexState *ls, expdesc *v) {
     TString *cmdname = luaX_newstring(ls, "__command", 9);
     TString *tsname = luaX_newstring(ls, "tostring", 8);
     /* load __command function first so it occupies the base register */
-    buildglobal(ls, cmdname, &func);
+    buildlushvar(ls, cmdname, &func);
     luaK_exp2nextreg(fs, &func);
     base = func.u.info;
     /* load the first fragment */
@@ -1308,7 +1322,7 @@ static void codeenvget (LexState *ls, expdesc *v, TString *name) {
   expdesc func, arg;
   TString *fname = luaX_newstring(ls, "__getenv", 8);
   line = ls->linenumber;
-  buildglobal(ls, fname, &func);
+  buildlushvar(ls, fname, &func);
   luaK_exp2nextreg(fs, &func);
   base = func.u.info;
   codestring(&arg, name);
@@ -2193,7 +2207,7 @@ static void envstat (LexState *ls) {
   luaX_next(ls);  /* skip TK_ENVVAR */
   checknext(ls, '=');
   fname = luaX_newstring(ls, "__setenv", 8);
-  buildglobal(ls, fname, &func);
+  buildlushvar(ls, fname, &func);
   luaK_exp2nextreg(fs, &func);
   base = func.u.info;
   codestring(&arg, name);
@@ -2219,7 +2233,7 @@ static void interactivestat (LexState *ls) {
     expdesc func, cmdstr, v;
     TString *fname = luaX_newstring(ls, "__interactive", 13);
     line = ls->linenumber;
-    buildglobal(ls, fname, &func);
+    buildlushvar(ls, fname, &func);
     luaK_exp2nextreg(fs, &func);
     base = func.u.info;
     codestring(&cmdstr, ls->t.seminfo.ts);
@@ -2236,7 +2250,7 @@ static void interactivestat (LexState *ls) {
     int line = ls->linenumber;
     TString *fname = luaX_newstring(ls, "__interactive", 13);
     TString *tsname = luaX_newstring(ls, "tostring", 8);
-    buildglobal(ls, fname, &func);
+    buildlushvar(ls, fname, &func);
     luaK_exp2nextreg(fs, &func);
     base = func.u.info;
     /* load the first fragment */
@@ -2396,8 +2410,12 @@ static void statement (LexState *ls) {
 ** upvalue named LUA_ENV
 */
 static void mainfunc (LexState *ls, FuncState *fs) {
+  static const char *const lush_upval_names[] = {
+    "__command", "__interactive", "__getenv", "__setenv"
+  };
   BlockCnt bl;
   Upvaldesc *env;
+  int i;
   open_func(ls, fs, &bl);
   setvararg(fs, PF_ISVARARG);  /* main function is always vararg */
   env = allocupvalue(fs);  /* ...set environment upvalue */
@@ -2406,6 +2424,15 @@ static void mainfunc (LexState *ls, FuncState *fs) {
   env->kind = VDKREG;
   env->name = ls->envn;
   luaC_objbarrier(ls->L, fs->f, env->name);
+  /* allocate upvalues for lush shell functions */
+  for (i = 0; i < 4; i++) {
+    Upvaldesc *uv = allocupvalue(fs);
+    uv->instack = 1;
+    uv->idx = 0;
+    uv->kind = VDKREG;
+    uv->name = luaS_new(ls->L, lush_upval_names[i]);
+    luaC_objbarrier(ls->L, fs->f, uv->name);
+  }
   luaX_next(ls);  /* read first token */
   statlist(ls);  /* parse main body */
   check(ls, TK_EOS);
@@ -2417,7 +2444,7 @@ LClosure *luaY_parser (lua_State *L, ZIO *z, Mbuffer *buff,
                        Dyndata *dyd, const char *name, int firstchar) {
   LexState lexstate;
   FuncState funcstate;
-  LClosure *cl = luaF_newLclosure(L, 1);  /* create main closure */
+  LClosure *cl = luaF_newLclosure(L, LUSH_NUM_UPVALS);  /* create main closure */
   setclLvalue2s(L, L->top.p, cl);  /* anchor it (to avoid being collected) */
   luaD_inctop(L);
   lexstate.h = luaH_new(L);  /* create table for scanner */
@@ -2432,7 +2459,7 @@ LClosure *luaY_parser (lua_State *L, ZIO *z, Mbuffer *buff,
   dyd->actvar.n = dyd->gt.n = dyd->label.n = 0;
   luaX_setinput(L, &lexstate, z, funcstate.f->source, firstchar);
   mainfunc(&lexstate, &funcstate);
-  lua_assert(!funcstate.prev && funcstate.nups == 1 && !lexstate.fs);
+  lua_assert(!funcstate.prev && funcstate.nups == LUSH_NUM_UPVALS && !lexstate.fs);
   /* all scopes should be correctly finished */
   lua_assert(dyd->actvar.n == 0 && dyd->gt.n == 0 && dyd->label.n == 0);
   L->top.p--;  /* remove scanner's table */