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Implement chilled strings

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[Feature #20205]

As a path toward enabling frozen string literals by default in the future,
this commit introduce "chilled strings". From a user perspective chilled
strings pretend to be frozen, but on the first attempt to mutate them,
they lose their frozen status and emit a warning rather than to raise a
`FrozenError`.

Implementation wise, `rb_compile_option_struct.frozen_string_literal` is
no longer a boolean but a tri-state of `enabled/disabled/unset`.

When code is compiled with frozen string literals neither explictly enabled
or disabled, string literals are compiled with a new `putchilledstring`
instruction. This instruction is identical to `putstring` except it marks
the String with the `STR_CHILLED (FL_USER3)` and `FL_FREEZE` flags.

Chilled strings have the `FL_FREEZE` flag as to minimize the need to check
for chilled strings across the codebase, and to improve compatibility with
C extensions.

Notes:
  - `String#freeze`: clears the chilled flag.
  - `String#-@`: acts as if the string was mutable.
  - `String#+@`: acts as if the string was mutable.
  - `String#clone`: copies the chilled flag.

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>
This commit is contained in:
Étienne Barrié 2023-12-01 11:33:00 +01:00 • committed by Jean Boussier
parent 86b15316a7
commit 12be40ae6b
36 changed files with 714 additions and 282 deletions
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5
object.c
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@ -502,7 +502,10 @@ rb_obj_clone_setup(VALUE obj, VALUE clone, VALUE kwfreeze)
case Qnil:
rb_funcall(clone, id_init_clone, 1, obj);
RBASIC(clone)->flags |= RBASIC(obj)->flags & FL_FREEZE;
if (RB_OBJ_FROZEN(obj)) {
if (CHILLED_STRING_P(obj)) {
STR_CHILL_RAW(clone);
}
else if (RB_OBJ_FROZEN(obj)) {
rb_shape_t * next_shape = rb_shape_transition_shape_frozen(clone);
if (!rb_shape_obj_too_complex(clone) && next_shape->type == SHAPE_OBJ_TOO_COMPLEX) {
rb_evict_ivars_to_hash(clone);