Ractor.make_shareable(a_proc)

Ractor.make_shareable() supports Proc object if
(1) a Proc only read outer local variables (no assignments)
(2) read outer local variables are shareable.

Read local variables are stored in a snapshot, so after making
shareable Proc, any assignments are not affeect like that:

```ruby
a = 1
pr = Ractor.make_shareable(Proc.new{p a})
pr.call #=> 1
a = 2
pr.call #=> 1 # `a = 2` doesn't affect
```

[Feature #17284]

1 files changed, 27 insertions, 0 deletions

diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index 6e006b246c..a61e741b54 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -922,6 +922,33 @@ assert_equal 'true', %q{
   [a.frozen?, a[0].frozen?] == [true, false]
 }
 
+# Ractor.make_shareable(a_proc) makes a proc shareable.
+assert_equal 'true', %q{
+  a = [1, [2, 3], {a: "4"}]
+  pr = Proc.new do
+    a
+  end
+  Ractor.make_shareable(a) # referred value should be shareable
+  Ractor.make_shareable(pr)
+  Ractor.shareable?(pr)
+}
+
+# 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 = 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
+
+  begin
+    Ractor.make_shareable(pr)
+  rescue => e
+    e.message
+  end
+}
+
 ###
 ### Synchronization tests
 ###