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.

lapi.c

@@ -29,6 +29,7 @@
 #include "ltm.h"
 #include "lundump.h"
 #include "lvm.h"
+#include "lcmd.h"
 
 
 
@@ -1135,6 +1136,27 @@ LUA_API int lua_load (lua_State *L, lua_Reader reader, void *data,
       setobj(L, f->upvals[0]->v.p, &gt);
       luaC_barrier(L, f->upvals[0], &gt);
     }
+    if (f->nupvalues >= LUSH_NUM_UPVALS) {  /* has lush upvalues? */
+      /* populate shell function upvalues from registry */
+      Table *regt = hvalue(&G(L)->l_registry);
+      TValue lushtv;
+      lu_byte tag = luaH_getint(regt, LUA_RIDX_LUSH, &lushtv);
+      if (novariant(tag) == LUA_TTABLE) {
+        static const char *const fields[] = {
+          "command", "interactive", "getenv", "setenv"
+        };
+        Table *lusht = hvalue(&lushtv);
+        int i;
+        for (i = 0; i < 4; i++) {
+          TValue val;
+          TString *key = luaS_new(L, fields[i]);
+          if (luaH_getstr(lusht, key, &val) != LUA_TNIL) {
+            setobj(L, f->upvals[i + 1]->v.p, &val);
+            luaC_barrier(L, f->upvals[i + 1], &val);
+          }
+        }
+      }
+    }
   }
   lua_unlock(L);
   return APIstatus(status);

lbuiltin.c

@@ -155,5 +155,9 @@ void luaopen_builtins (lua_State *L) {
   lua_setfield(L, -2, "exec");
   lua_pushcfunction(L, builtin_umask);
   lua_setfield(L, -2, "umask");
-  lua_setglobal(L, "__builtins");
+  /* Store as __lush.builtins in registry */
+  lua_rawgeti(L, LUA_REGISTRYINDEX, LUA_RIDX_LUSH);
+  lua_insert(L, -2);
+  lua_setfield(L, -2, "builtins");
+  lua_pop(L, 1);
 }

lcmd.c

@@ -874,15 +874,21 @@ static int exec_pipeline (lua_State *L, char **stages, int nstages,
 */
 static int try_builtin (lua_State *L, ParsedArgs *pa) {
   int i;
-  if (lua_getglobal(L, "__builtins") != LUA_TTABLE) {
+  lua_rawgeti(L, LUA_REGISTRYINDEX, LUA_RIDX_LUSH);
+  if (!lua_istable(L, -1)) {
     lua_pop(L, 1);
     return 0;
   }
-  if (lua_getfield(L, -1, pa->argv[0]) != LUA_TFUNCTION) {
+  if (lua_getfield(L, -1, "builtins") != LUA_TTABLE) {
     lua_pop(L, 2);
     return 0;
   }
-  lua_remove(L, -2);  /* remove __builtins, keep function */
+  if (lua_getfield(L, -1, pa->argv[0]) != LUA_TFUNCTION) {
+    lua_pop(L, 3);
+    return 0;
+  }
+  lua_remove(L, -2);  /* remove builtins table */
+  lua_remove(L, -2);  /* remove lush table */
   for (i = 0; i < pa->argc; i++)
     lua_pushstring(L, pa->argv[i]);
   lua_call(L, pa->argc, 1);
@@ -890,9 +896,9 @@ static int try_builtin (lua_State *L, ParsedArgs *pa) {
 }
 
 
-/* ===== luaB_command ===== */
+/* ===== lushCmd_command ===== */
 
-int luaB_command (lua_State *L) {
+int lushCmd_command (lua_State *L) {
   const char *cmd = luaL_checkstring(L, 1);
   char *stages[MAX_PIPELINE_STAGES];
   int nstages;
@@ -1033,9 +1039,9 @@ int luaB_command (lua_State *L) {
 }
 
 
-/* ===== luaB_interactive ===== */
+/* ===== lushCmd_interactive ===== */
 
-int luaB_interactive (lua_State *L) {
+int lushCmd_interactive (lua_State *L) {
   const char *cmd = luaL_checkstring(L, 1);
   char *stages[MAX_PIPELINE_STAGES];
   int nstages;
@@ -1142,3 +1148,30 @@ int luaB_interactive (lua_State *L) {
 
   return 0;  /* void — no Lua return values */
 }
+
+
+/* ===== lushCmd_getenv ===== */
+
+int lushCmd_getenv (lua_State *L) {
+  const char *name = luaL_checkstring(L, 1);
+  const char *val = getenv(name);
+  if (val == NULL)
+    lua_pushnil(L);
+  else
+    lua_pushstring(L, val);
+  return 1;
+}
+
+
+/* ===== lushCmd_setenv ===== */
+
+int lushCmd_setenv (lua_State *L) {
+  const char *name = luaL_checkstring(L, 1);
+  if (lua_isnoneornil(L, 2))
+    unsetenv(name);
+  else {
+    const char *val = luaL_tolstring(L, 2, NULL);
+    setenv(name, val, 1);
+  }
+  return 0;
+}

lcmd.h

@@ -9,7 +9,17 @@
 
 #include "lua.h"
 
-int luaB_command (lua_State *L);
-int luaB_interactive (lua_State *L);
+/* Upvalue indices for shell functions on the main chunk.
+** Index 0 is _ENV (standard). Indices 1-4 are lush shell functions. */
+#define LUSH_UPVAL_COMMAND      1
+#define LUSH_UPVAL_INTERACTIVE  2
+#define LUSH_UPVAL_GETENV       3
+#define LUSH_UPVAL_SETENV       4
+#define LUSH_NUM_UPVALS         5  /* total: _ENV(0) + 4 shell functions */
+
+int lushCmd_command (lua_State *L);
+int lushCmd_interactive (lua_State *L);
+int lushCmd_getenv (lua_State *L);
+int lushCmd_setenv (lua_State *L);
 
 #endif

linit.c

@@ -43,41 +43,21 @@ static const luaL_Reg stdlibs[] = {
 };
 
 
-static int luaB_getenv (lua_State *L) {
-  const char *name = luaL_checkstring(L, 1);
-  const char *val = getenv(name);
-  if (val == NULL)
-    lua_pushnil(L);
-  else
-    lua_pushstring(L, val);
-  return 1;
-}
-
-
-static int luaB_setenv (lua_State *L) {
-  const char *name = luaL_checkstring(L, 1);
-  if (lua_isnoneornil(L, 2))
-    unsetenv(name);
-  else {
-    const char *val = luaL_tolstring(L, 2, NULL);
-    setenv(name, val, 1);
-  }
-  return 0;
-}
-
-
 /*
-** Register shell built-in globals (called after standard libraries).
+** Store shell functions in a registry table at LUA_RIDX_LUSH.
+** These are populated as upvalues on the main chunk by lua_load().
 */
 static void opencommand (lua_State *L) {
-  lua_pushcfunction(L, luaB_command);
-  lua_setglobal(L, "__command");
-  lua_pushcfunction(L, luaB_interactive);
-  lua_setglobal(L, "__interactive");
-  lua_pushcfunction(L, luaB_getenv);
-  lua_setglobal(L, "__getenv");
-  lua_pushcfunction(L, luaB_setenv);
-  lua_setglobal(L, "__setenv");
+  lua_createtable(L, 0, 5);
+  lua_pushcfunction(L, lushCmd_command);
+  lua_setfield(L, -2, "command");
+  lua_pushcfunction(L, lushCmd_interactive);
+  lua_setfield(L, -2, "interactive");
+  lua_pushcfunction(L, lushCmd_getenv);
+  lua_setfield(L, -2, "getenv");
+  lua_pushcfunction(L, lushCmd_setenv);
+  lua_setfield(L, -2, "setenv");
+  lua_rawseti(L, LUA_REGISTRYINDEX, LUA_RIDX_LUSH);
 }
 
 

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 */

lua.h

@@ -83,7 +83,8 @@ typedef struct lua_State lua_State;
 /* index 1 is reserved for the reference mechanism */
 #define LUA_RIDX_GLOBALS	2
 #define LUA_RIDX_MAINTHREAD	3
-#define LUA_RIDX_LAST		3
+#define LUA_RIDX_LUSH		4
+#define LUA_RIDX_LAST		LUA_RIDX_LUSH
 
 
 /* type of numbers in Lua */

testes/lush/builtins.lua

@@ -3,13 +3,10 @@
 
 print "testing shell builtins"
 
--- === __builtins table ===
+-- === __builtins is NOT in _G (internal, stored in registry) ===
 
 do
-  assert(type(__builtins) == "table")
-  assert(type(__builtins.cd) == "function")
-  assert(type(__builtins.exec) == "function")
-  assert(type(__builtins.umask) == "function")
+  assert(__builtins == nil, "__builtins should not be in _G")
 end
 
 
@@ -117,9 +114,9 @@ end
 
 -- === exec ===
 
--- exec with no command returns error
+-- exec with no command returns error (tested via backtick)
 do
-  local r = __builtins.exec("exec")
+  local r = `exec`
   assert(r.code == 1)
   assert(r.stderr:find("command required"),
          "expected 'command required', got: " .. r.stderr)
@@ -127,7 +124,7 @@ end
 
 -- exec nonexistent command returns error
 do
-  local r = __builtins.exec("exec", "nonexistent_cmd_xyz_999")
+  local r = `exec nonexistent_cmd_xyz_999`
   assert(r.code == 1)
   assert(r.stderr:find("exec:"),
          "expected exec error, got: " .. r.stderr)
@@ -140,21 +137,4 @@ do
 end
 
 
--- === builtins are overridable ===
-
-do
-  local old_cd = __builtins.cd
-  local called = false
-  __builtins.cd = function(...)
-    called = true
-    return old_cd(...)
-  end
-  local before = `pwd`.stdout:gsub("\n$", "")
-  `cd /tmp`
-  assert(called, "custom cd was not called")
-  __builtins.cd = old_cd
-  `cd ${before}`
-end
-
-
 print "OK"