hash.c: Do not use the fast path (rb_yield_values) for lambda blocks

As a semantics, Hash#each yields a 2-element array (pairs of keys and
values).  So, `{ a: 1 }.each(&->(k, v) { })` should raise an exception
due to lambda's arity check.
However, the optimization that avoids Array allocation by using
rb_yield_values for blocks whose arity is more than 1 (introduced at
b9d29603375d17c3d1d609d9662f50beaec61fa1 and some commits), seemed to
overlook the lambda case, and wrongly allowed the code above to work.

This change experimentally attempts to make it strict; now the code
above raises an ArgumentError.  This is an incompatible change; if the
compatibility issue is bigger than our expectation, it may be reverted
(until Ruby 3.0 release).

[Bug #12706]

1 files changed, 1 insertions, 0 deletions

diff --git a/internal/proc.h b/internal/proc.h
index 864392906b..35bc43a4ee 100644
--- a/internal/proc.h
+++ b/internal/proc.h
@@ -17,6 +17,7 @@ struct rb_iseq_struct;          /* in vm_core.h */
 /* proc.c */
 VALUE rb_proc_location(VALUE self);
 st_index_t rb_hash_proc(st_index_t hash, VALUE proc);
+int rb_block_pair_yield_optimizable(void);
 int rb_block_arity(void);
 int rb_block_min_max_arity(int *max);
 VALUE rb_block_to_s(VALUE self, const struct rb_block *block, const char *additional_info);