From 47db835e58de4a4fbdc89e79ee07247709096cbe Mon Sep 17 00:00:00 2001
From: Lillian Zhang <lillian.zhang@shopify.com>
Date: Wed, 11 Nov 2020 17:51:01 -0500
Subject: [PATCH] Implement and untag Enumerator#produce

---
 CHANGELOG.md                                 |  1 +
 spec/tags/core/enumerator/produce_tags.txt   |  4 ----
 src/main/ruby/truffleruby/core/enumerator.rb | 13 +++++++++++++
 3 files changed, 14 insertions(+), 4 deletions(-)
 delete mode 100644 spec/tags/core/enumerator/produce_tags.txt

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d822a6743ca1..7a45fe8d1b98 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ Compatibility:
 * Implement `Enumerable#tally` and `Enumerable#filter_map` (#2144 and #2152, @LillianZ).
 * Implement `Range#minmax`.
 * Pass more `Enumerator::Lazy#uniq` and `Enumerator::Lazy#chunk` specs (#2146, @LillianZ).
+* Implement `Enumerator#produce` (#2160, @zverok)
 
 Performance:
 
diff --git a/spec/tags/core/enumerator/produce_tags.txt b/spec/tags/core/enumerator/produce_tags.txt
deleted file mode 100644
index a4382b33ed24..000000000000
--- a/spec/tags/core/enumerator/produce_tags.txt
+++ /dev/null
@@ -1,4 +0,0 @@
-fails:Enumerator.produce creates an infinite enumerator
-fails:Enumerator.produce terminates iteration when block raises StopIteration exception
-fails:Enumerator.produce when initial value skipped uses nil instead
-fails:Enumerator.produce when initial value skipped starts enumerable from result of first block call
diff --git a/src/main/ruby/truffleruby/core/enumerator.rb b/src/main/ruby/truffleruby/core/enumerator.rb
index 46d3b78722b8..9d4c8ed430de 100644
--- a/src/main/ruby/truffleruby/core/enumerator.rb
+++ b/src/main/ruby/truffleruby/core/enumerator.rb
@@ -216,6 +216,19 @@ def +(other)
     Enumerator::Chain.new(self, other)
   end
 
+  def self.produce(initial = nil)
+    # Taken from https://github.com/zverok/enumerator_generate
+    raise ArgumentError, 'No block given' unless block_given?
+    Enumerator.new(Float::INFINITY) do |y|
+      val = initial == nil ? yield() : initial
+
+      loop do
+        y << val
+        val = yield(val)
+      end
+    end
+  end
+
   class Yielder
     def initialize(&block)
       raise LocalJumpError, 'Expected a block to be given' unless block_given?