Add stack pack and unpack methods

crates/luajit/src/lib.rs

@@ -851,6 +851,85 @@ impl Stack {
         unsafe { lua_rawseti(self.as_ptr(), table.index(), n) }
     }
 
+    /// Packs the array-part of the table at index `idx` from the stack.
+    ///
+    /// This pops `n` values at the top of the stack, sets them as the fields of the table at index
+    /// `idx` at indices `1` to `n` inclusive, then sets the field `"n"` to `n`. Any existing values
+    /// in the table are overwritten. If the table already has more than `n` values in its
+    /// array-part, these values are **not** cleared. The number of values popped is returned, which
+    /// is always equal to `n`.
+    ///
+    /// This method does not invoke any metamethods.
+    ///
+    /// Equivalent to `table.pack(...)`.
+    ///
+    /// # Panic
+    ///
+    /// Panics if `n` is negative, there are not enough values on the stack, or the value at index
+    /// `idx` is not a table.
+    pub fn pack(&mut self, idx: c_int, n: c_int) -> c_int {
+        assert!(n >= 0, "n must be nonnegative");
+        let size = self.size();
+        let table = self.slot(idx);
+        assert!(
+            table.type_of() == Type::Table,
+            "expected table at index {idx}: {self:?}"
+        );
+        assert!(n <= size, "expected {n} values: {self:?}");
+        assert!(idx <= size - n, "cannot pack a table into itself: {self:?}");
+        unsafe {
+            (0..n).for_each(|i| lua_rawseti(self.as_ptr(), table.index(), n - i));
+            self.ensure(2);
+            lua_pushliteral(self.as_ptr(), "n");
+            lua_pushinteger(self.as_ptr(), n as lua_Integer);
+            lua_rawset(self.as_ptr(), table.index());
+            n
+        }
+    }
+
+    /// Unpacks the array-part of the table at index `idx` onto the stack.
+    ///
+    /// If `j` is [`None`], then it is set to be the value of the field `"n"` interpreted as an
+    /// integer. If this field does not exist, then it is set to the be length of the table as
+    /// defined by the Lua `#` length operator. All values in indices `i` to `j` inclusive are
+    /// pushed at the top of the stack in ascending order. If `i > j`, then nothing is pushed.
+    /// Otherwise, `j - i + 1` values are pushed, and the number of values pushed is returned.
+    ///
+    /// This method does not invoke any metamethods.
+    ///
+    /// Equivalent to `table.unpack(list, i, j)`.
+    ///
+    /// # Panic
+    ///
+    /// Panics if the value at index `idx` is not a table.
+    pub fn unpack(&mut self, idx: c_int, i: c_int, j: Option<c_int>) -> c_int {
+        let table = self.slot(idx);
+        assert!(
+            table.type_of() == Type::Table,
+            "expected table at index {idx}: {self:?}"
+        );
+        let j = match j {
+            Some(j) => j,
+            None => unsafe {
+                self.ensure(1);
+                lua_pushliteral(self.as_ptr(), "n");
+                lua_rawget(self.as_ptr(), table.index());
+                let mut isnum = 0;
+                let n = lua_tointegerx(self.as_ptr(), -1, &raw mut isnum);
+                lua_pop(self.as_ptr(), 1);
+                (isnum != 0)
+                    .then_some(n as c_int)
+                    .unwrap_or_else(|| lua_objlen(self.as_ptr(), table.index()) as c_int)
+            },
+        };
+        let n = (j - i + 1).max(0);
+        if n > 0 {
+            self.ensure(n);
+            (0..n).for_each(|n| unsafe { lua_rawgeti(self.as_ptr(), table.index(), i + n) });
+        }
+        n
+    }
+
     /// Pushes the given chunk as a function at the top of the stack.
     ///
     /// Equivalent to [`lua_loadx`].
@@ -1144,7 +1223,7 @@ impl Stack {
     ///
     /// Equivalent to [`luaL_traceback`].
     pub fn backtrace(&self, level: c_int) -> Option<BString> {
-        assert!(level >= 0, "backtrace level must be nonnegative");
+        assert!(level >= 0, "level must be nonnegative");
         self.ensure(LUA_MINSTACK);
         unsafe {
             luaL_traceback(self.as_ptr(), self.as_ptr(), ptr::null(), 0);
@@ -1590,8 +1669,8 @@ impl NewTable {
 impl Push for NewTable {
     fn push(&self, stack: &mut Stack) {
         let Self { narr, nrec } = *self;
-        assert!(0 <= narr, "size of table array part must be nonnegative");
-        assert!(0 <= nrec, "size of table hash part must be nonnegative");
+        assert!(0 <= narr, "narr must be nonnegative");
+        assert!(0 <= nrec, "nrec must be nonnegative");
         stack.ensure(1);
         unsafe { lua_createtable(stack.as_ptr(), narr, nrec) }
     }