The Difference
Since Ruby1.9, the keyword arguments were emulated by Ruby using the hash
object at the bottom of the arguments. But we have gradually moved toward
keyword arguments separated from normal (positinal) arguments.
At the same time, we value compatibility, so that Ruby3.0 keyword
arguments are somewhat compromise. Basically, keyword arguments are
separated from positional arguments, except when the method does not
take any formal keyword arguments, given keyword arguments (packed
in the hash object) are considered as the last argument.
And we also allow non symbol keys in the keyword arguments. In that
case, those keys are just passed in the `**` hash (or raise
`ArgumentError` for unknown keys).
The Instruction Changes
We have changed `OP_SEND` instruction. `OP_SEND` instruction used to
take 3 operands, the register, the symbol, the number of (positional)
arguments. The meaning of the third operand has been changed. It is now
considered as `n|(nk<<4)`, where `n` is the number of positional
arguments, and `nk` is the number of keyword arguments, both occupies
4 bits in the operand.
The number `15` in both `n` and `nk` means variable sized arguments are
packed in the object. Positional arguments will be packed in the array,
and keyword arguments will be packed in the hash object. That means
arguments more than 14 values are always packed in the object.
Arguments information for other instructions (`OP_SENDB` and `OP_SUPER`)
are also changed. It works as the third operand of `OP_SEND`. the
difference between `OP_SEND` and `OP_SENDB` is just trivial. It assigns
`nil` to the block hidden arguments (right after arguments).
The instruction `OP_SENDV` and `OP_SENDVB` are removed. Those
instructions are replaced by `OP_SEND` and `OP_SENDB` respectively with
the `15` (variable sized) argument information.
Calling Convention
When calling a method, the stack elements shall be in the order of the
receiver of the method, positional arguments, keyword arguments and the
block argument. If the number of positional or keyword arugument (`n` or
`nk`) is zero, corresponding arguments will be empty. So when `n=0` and
`nk=0` the stack layout (from bottom to top) will be:
+-----------------------+
| recv | block (or nil) |
+-----------------------+
The last elements `block` should be explicitly filled before `OP_SEND`
or assigned to `nil` by `OP_SENDB` internally. In other words, the
following have exactly same behavior:
OP_SENDB clears `block` implicitly:
```
OP_SENDB reg sym 0
```
OP_SEND clears `block` implicitly:
```
OP_LOADNIL R2
OP_SEND R2 sym 0
```
When calling a method with only positional arguments (n=0..14) without
keyword arguments, the stack layout will be like following:
+--------------------------------------------+
| recv | arg1 | ... | arg_n | block (or nil) |
+--------------------------------------------+
When calling a method with arguments packed in the array (n=15) which
means argument splat (*) is used in the actual arguments, or more than
14 arguments are passed the stack layout will be like following:
+-------------------------------+
| recv | array | block (or nil) |
+-------------------------------+
The number of the actual arguments is determined by the length of the
argument array.
When keyword arguments are given (nk>0), keyword arguments are passed
between positional arguments and the block argument. For example, when
we pass one positional argument `1` and one keyword argument `a: 2`,
the stack layout will be like:
+------------------------------------+
| recv | 1 | :a | 2 | block (or nil) |
+------------------------------------+
Note that keyword arguments consume `2*nk` elements in the stack when
`nk=0..14` (unpacked).
When calling a method with keyword arguments packed in the hash object
(nk=15) which means keyword argument splat (**) is used or more than
14 keyword arguments in the actual arguments, the stack layout will
be like:
+------------------------------+
| recv | hash | block (or nil) |
+------------------------------+
Note for mruby/c
When mruby/c authors try to support new keyword arguments, they need
to handle the new meaning of the argument information operand. If they
choose not to support keyword arguments in mruby/c, it just raise
error when `nk` (taken by `(c>>4)&0xf`) is not zero. And combine
`OP_SENDV` behavior with `OP_SEND` when `n` is `15`.
If they want to support keyword arguments seriously, contact me at
<matz@ruby.or.jp> or `@yukihiro_matz`. I can help you.
It used to be return the default value if available, but it should
ignore the default value for behavior consistency. CRuby will adopt
this behavior too in the future. [ruby-bugs:16908]
In `h_check_modified()`, in the case of `MRB_NO_BOXING`, `ht_ea()` or
`ht_ea_capa()` for AR may read uninitialized area. Therefore, do not use
those macros for AR in `MRB_NO_BOXING` (but in the case of `MRB_64BIT`,
`ht_ea_capa()` is the same as `ar_ea_capa()`, so use it).
fix#5332
### Example
##### example.rb
```ruby
h = {}
(1..17).each{h[_1] = _1}
(1..16).each{h.delete(_1)}
h.rehash
```
##### ASAN report
```console
$ bin/mruby example.rb
==52587==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000006998 at pc 0x55a29cddf96b bp 0x7fff7b1b1720 sp 0x7fff7b1b1710
READ of size 4 at 0x602000006998 thread T0
#0 0x55a29cddf96a in ib_it_next /mruby/src/hash.c:639
#1 0x55a29cde2ca2 in ht_rehash /mruby/src/hash.c:900
#2 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
#3 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
#4 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
#5 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
#6 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
#7 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
#8 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
#9 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
#10 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
#11 0x55a29cdb4a6d in _start (/mruby/bin/mruby+0x2a3a6d)
0x602000006998 is located 0 bytes to the right of 8-byte region [0x602000006990,0x602000006998)
allocated by thread T0 here:
#0 0x7f24f01cfffe in __interceptor_realloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dffe)
#1 0x55a29ceb9440 in mrb_default_allocf /mruby/src/state.c:68
#2 0x55a29cdba747 in mrb_realloc_simple /mruby/src/gc.c:228
#3 0x55a29cdba928 in mrb_realloc /mruby/src/gc.c:242
#4 0x55a29cde12e5 in ht_init /mruby/src/hash.c:749
#5 0x55a29cde2b8e in ht_rehash /mruby/src/hash.c:897
#6 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
#7 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
#8 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
#9 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
#10 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
#11 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
#12 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
#13 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
#14 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
```
Instead of including `mruby/presym.h` everywhere, we provided the
fallback `mruby/presym.inc` under `include/mruby` directory, and specify
`-I<build-dir>/include` before `-I<top-dir>/include` in `presym.rake`.
So even when someone drops `-I<build-dir>/include` in compiler options,
it just compiles without failure.
The Hash implementation assumed that there were always empty buckets, but
sometimes there were only active or deleted buckets (no empty buckets).
Therefore, fix it so that this situation does not occur.
### Example
```ruby
# example.rb
class A
attr_reader :v
def initialize(v) @v = v end
def ==(o) @v == o.v end
def hash; @v end
def to_s; "#{self.class}[#{@v}]" end
alias eql? ==
alias inspect to_s
end
keys = (0..31).map{A.new(_1)}
h = {}
(0..16).each{h[keys[_1]] = _1}
(17..31).each do
k = keys[_1]
h[k] = _1
h.delete(k)
end
p h.keys
```
#### Before this patch:
```console
$ bin/mruby example.rb
[A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[8], A[9], A[10], A[11], A[12], A[13], A[14], A[15], A[16], A[30], A[31]]
```
#### After this patch:
```console
$ bin/mruby example.rb
[A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[8], A[9], A[10], A[11], A[12], A[13], A[14], A[15], A[16]]
```
* The term `hash_table` can be misleading because the return value of this
function includes memory usage of entire `Hash` object, including not only
hash table part but also entry list part, etc.
* This function takes a `Hash` object as a receiver and is defined in
`src/hash.c`, so it is natural to have a `mrb_hash_` prefix.
- Integrate `Fixnum` and `Integer`
- Remove `Integral`
- `int / int -> int`
- Replace `mrb_fixnum()` to `mrb_int()`
- Replace `mrb_fixnum_value()` to `mrb_int_value()`.
- Use `mrb_integer_p()` instead of `mrb_fixnum_p()`
- `MRB_WITHOUT_FLOAT` => `MRB_NO_FLOAT`
- `MRB_USE_FLOAT` => `MRB_USE_FLOAT32`
The former is to use `USE_XXX` naming convention. The latter is to make
sure `float` is 32bit float and not floating point number in general.
The function corresponding to `ht_hash_func()` was as follows in the days of
khash implementation (before d78acc7a).
```c
mrb_hash_ht_hash_func(mrb_state *mrb, mrb_value key)
{
enum mrb_vtype t = mrb_type(key);
...
switch (t) {
...
default:
hv = mrb_funcall(mrb, key, "hash", 0);
h = (khint_t)t ^ (khint_t)mrb_fixnum(hv);
break;
}
...
}
```
When switched to the segmented list implementation (d78acc7a), this function
was changed as follows.
```c
sg_hash_func(mrb_state *mrb, seglist *t, mrb_value key)
{
enum mrb_vtype tt = mrb_type(key);
...
switch (tt) {
...
default:
hv = mrb_funcall(mrb, key, "hash", 0);
h = (size_t)t ^ (size_t)mrb_fixnum(hv);
break;
}
...
}
```
Since the argument `t` was added, the variable for type tag was changed from
`t` to `tt`, but the variable used in the expression of `h` remained `t`.
Probably this is an omission of change, so fixed it.
`mrb_get_arg1()` raises `ArgumentError` if the method does not receive one
argument.
And replaces all `mrb_get_args(mrb, "o", &arg)` by the new function.
### Example
```ruby
# example.rb
class A
def eql?(o)
p self.class
super
end
def hash
1
end
end
class B < A; end
h = {A.new => 1}
h[B.new]
```
#### Before this patch:
```console
$ bin/mruby example.rb
A
```
#### After this patch (same as Ruby)
```console
$ bin/mruby example.rb
B
```
Yukihiro "Matz" Matsumoto