Ractor.shareable_proc

call-seq:
  Ractor.sharable_proc(self: nil){} -> sharable proc

It returns shareable Proc object. The Proc object is
shareable and the self in a block will be replaced with
the value passed via `self:` keyword.

In a shareable Proc, the outer variables should
* (1) refer shareable objects
* (2) be not be overwritten

```ruby
  a = 42
  Ractor.shareable_proc{ p a }
  #=> OK

  b = 43
  Ractor.shareable_proc{ p b; b = 44 }
  #=> Ractor::IsolationError because 'b' is reassigned in the block.

  c = 44
  Ractor.shareable_proc{ p c }
  #=> Ractor::IsolationError because 'c' will be reassigned outside of the block.
  c = 45

  d = 45
  d = 46 if cond
  Ractor.shareable_proc{ p d }
  #=> Ractor::IsolationError because 'd' was reassigned outside of the block.
```

The last `d`'s case can be relaxed in a future version.

The above check will be done in a static analysis at compile time,
so the reflection feature such as `Binding#local_varaible_set`
can not be detected.

```ruby
  e = 42
  shpr = Ractor.shareable_proc{ p e } #=> OK
  binding.local_variable_set(:e, 43)
  shpr.call #=> 42 (returns captured timing value)
```

Ractor.sharaeble_lambda is also introduced.
[Feature #21550]
[Feature #21557]

Author: ko1

NEWS.md

@@ -117,6 +117,10 @@ Note: We're only listing outstanding class updates.
 
     * `Ractor#close_incoming` and `Ractor#close_outgoing` were removed.
 
+    * `Ractor.sharealbe_proc` and `Ractor.shareable_lambda` is introduced
+      to make shareable Proc or lambda.
+      [[Feature #21550]], [[Feature #21557]]
+
 * `Set`
 
     * `Set` is now a core class, instead of an autoloaded stdlib class.
@@ -316,3 +320,5 @@ A lot of work has gone into making Ractors more stable, performant, and usable.
 [Feature #21347]: https://bugs.ruby-lang.org/issues/21347
 [Feature #21360]: https://bugs.ruby-lang.org/issues/21360
 [Feature #21527]: https://bugs.ruby-lang.org/issues/21527
+[Feature #21550]: https://bugs.ruby-lang.org/issues/21550
+[Feature #21557]: https://bugs.ruby-lang.org/issues/21557

bootstraptest/test_ractor.rb

@@ -145,28 +145,47 @@
   }.map(&:value)
 }
 
+assert_equal "42", %q{
+  a = 42
+  Ractor.shareable_lambda{ a }.call
+}
+
 # Ractor.make_shareable issue for locals in proc [Bug #18023]
 assert_equal '[:a, :b, :c, :d, :e]', %q{
   v1, v2, v3, v4, v5 = :a, :b, :c, :d, :e
-  closure = Ractor.current.instance_eval{ Proc.new { [v1, v2, v3, v4, v5] } }
-
-  Ractor.make_shareable(closure).call
+  closure = Proc.new { [v1, v2, v3, v4, v5] }
+  Ractor.shareable_proc(&closure).call
 }
 
-# Ractor.make_shareable issue for locals in proc [Bug #18023]
-assert_equal '[:a, :b, :c, :d, :e, :f, :g]', %q{
-  a = :a
-  closure = Ractor.current.instance_eval do
-    -> {
-      b, c, d = :b, :c, :d
-      -> {
-        e, f, g = :e, :f, :g
-        -> { [a, b, c, d, e, f, g] }
-      }.call
-    }.call
+# Ractor::IsolationError cases
+assert_equal '3', %q{
+  ok = 0
+
+  begin
+    a = 1
+    Ractor.shareable_proc{a}
+    a = 2
+  rescue Ractor::IsolationError => e
+    ok += 1
   end
 
-  Ractor.make_shareable(closure).call
+  begin
+    cond = false
+    a = 1
+    a = 2 if cond
+    Ractor.shareable_proc{a}
+  rescue Ractor::IsolationError => e
+    ok += 1
+  end
+
+  begin
+    1.times{|i|
+      i = 2
+      Ractor.shareable_proc{i}
+    }
+  rescue Ractor::IsolationError => e
+    ok += 1
+  end
 }
 
 ###
@@ -967,7 +986,7 @@ class C
   end
   RUBY
 
-# Constant cache should care about non-sharable constants
+# Constant cache should care about non-shareable constants
 assert_equal "can not access non-shareable objects in constant Object::STR by non-main Ractor.", <<~'RUBY', frozen_string_literal: false
   STR = "hello"
   def str; STR; end
@@ -1137,41 +1156,17 @@ def /(other)
   [a.frozen?, a[0].frozen?] == [true, false]
 }
 
-# Ractor.make_shareable(a_proc) makes a proc shareable.
+# Ractor.make_shareable(a_proc) is not supported now.
 assert_equal 'true', %q{
-  a = [1, [2, 3], {a: "4"}]
-
-  pr = Ractor.current.instance_eval do
-    Proc.new do
-      a
-    end
-  end
+  pr = Proc.new{}
 
-  Ractor.make_shareable(a) # referred value should be shareable
-  Ractor.make_shareable(pr)
-  Ractor.shareable?(pr)
-}
-
-# Ractor.make_shareable(a_proc) makes inner structure shareable and freezes it
-assert_equal 'true,true,true,true', %q{
-  class Proc
-    attr_reader :obj
-    def initialize
-      @obj = Object.new
-    end
-  end
-
-  pr = Ractor.current.instance_eval do
-    Proc.new {}
+  begin
+    Ractor.make_shareable(pr)
+  rescue Ractor::Error
+    true
+  else
+    false
   end
-
-  results = []
-  Ractor.make_shareable(pr)
-  results << Ractor.shareable?(pr)
-  results << pr.frozen?
-  results << Ractor.shareable?(pr.obj)
-  results << pr.obj.frozen?
-  results.map(&:to_s).join(',')
 }
 
 # Ractor.shareable?(recursive_objects)
@@ -1202,50 +1197,16 @@ module M; end
   Ractor.make_shareable(ary = [C, M])
 }
 
-# Ractor.make_shareable with curried proc checks isolation of original proc
-assert_equal 'isolation error', %q{
-  a = Object.new
-  orig = proc { a }
-  curried = orig.curry
-
-  begin
-    Ractor.make_shareable(curried)
-  rescue Ractor::IsolationError
-    'isolation error'
-  else
-    'no error'
-  end
-}
-
 # define_method() can invoke different Ractor's proc if the proc is shareable.
 assert_equal '1', %q{
   class C
     a = 1
-    define_method "foo", Ractor.make_shareable(Proc.new{ a })
-    a = 2
+    define_method "foo", Ractor.shareable_proc{ a }
   end
 
   Ractor.new{ C.new.foo }.value
 }
 
-# Ractor.make_shareable(a_proc) makes a proc shareable.
-assert_equal 'can not make a Proc shareable because it accesses outer variables (a).', %q{
-  a = b = nil
-  pr = Ractor.current.instance_eval do
-    Proc.new do
-      c = b # assign to a is okay because c is block local variable
-      # reading b is okay
-      a = b # assign to a is not allowed #=> Ractor::Error
-    end
-  end
-
-  begin
-    Ractor.make_shareable(pr)
-  rescue => e
-    e.message
-  end
-}
-
 # Ractor.make_shareable(obj, copy: true) makes copied shareable object.
 assert_equal '[false, false, true, true]', %q{
   r = []
@@ -1471,42 +1432,6 @@ class C
   "ok"
 } if !yjit_enabled? && ENV['GITHUB_WORKFLOW'] != 'ModGC' # flaky
 
-assert_equal "ok", %q{
-  def foo(*); ->{ super }; end
-  begin
-    Ractor.make_shareable(foo)
-  rescue Ractor::IsolationError
-    "ok"
-  end
-}
-
-assert_equal "ok", %q{
-  def foo(**); ->{ super }; end
-  begin
-    Ractor.make_shareable(foo)
-  rescue Ractor::IsolationError
-    "ok"
-  end
-}
-
-assert_equal "ok", %q{
-  def foo(...); ->{ super }; end
-  begin
-    Ractor.make_shareable(foo)
-  rescue Ractor::IsolationError
-    "ok"
-  end
-}
-
-assert_equal "ok", %q{
-  def foo((x), (y)); ->{ super }; end
-  begin
-    Ractor.make_shareable(foo([], []))
-  rescue Ractor::IsolationError
-    "ok"
-  end
-}
-
 # check method cache invalidation
 assert_equal "ok", %q{
   module M