From a4f0e5141ad384fb86960f35edf5c0717c465483 Mon Sep 17 00:00:00 2001
From: Samuel Williams <samuel.williams@oriontransfer.co.nz>
Date: Fri, 24 Nov 2023 13:44:08 +1300
Subject: [PATCH] Add support for passing a block to `IO#readlines` and
 `IO.readlines`.

---
 io.c                                | 19 ++++++++++++++-----
 spec/ruby/core/io/readlines_spec.rb | 18 ++++++++++++++++++
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/io.c b/io.c
index 590e8d11d7..ca5e27c41f 100644
--- a/io.c
+++ b/io.c
@@ -4472,15 +4472,24 @@ rb_io_readlines(int argc, VALUE *argv, VALUE io)
 static VALUE
 io_readlines(const struct getline_arg *arg, VALUE io)
 {
-    VALUE line, ary;
+    VALUE line;
 
     if (arg->limit == 0)
         rb_raise(rb_eArgError, "invalid limit: 0 for readlines");
-    ary = rb_ary_new();
-    while (!NIL_P(line = rb_io_getline_1(arg->rs, arg->limit, arg->chomp, io))) {
-        rb_ary_push(ary, line);
+
+    // If a block is provided, yield lines.
+    if (rb_block_given_p()) {
+        while (!NIL_P(line = rb_io_getline_1(arg->rs, arg->limit, arg->chomp, io))) {
+            rb_yield(line);
+        }
+        return Qnil;
+    } else {
+        VALUE ary = rb_ary_new();
+        while (!NIL_P(line = rb_io_getline_1(arg->rs, arg->limit, arg->chomp, io))) {
+            rb_ary_push(ary, line);
+        }
+        return ary;
     }
-    return ary;
 }
 
 /*
diff --git a/spec/ruby/core/io/readlines_spec.rb b/spec/ruby/core/io/readlines_spec.rb
index 3a6ff3d0f3..2cf930746c 100644
--- a/spec/ruby/core/io/readlines_spec.rb
+++ b/spec/ruby/core/io/readlines_spec.rb
@@ -20,6 +20,16 @@ describe "IO#readlines" do
     -> { @io.readlines }.should raise_error(IOError)
   end
 
+  ruby_version_is "3.3" do
+    describe "when invoked with a block" do
+      it "yields each line to the block" do
+        lines = []
+        @io.readlines { |line| lines << line }
+        lines.should == IOSpecs.lines
+      end
+    end
+  end
+
   describe "when passed no arguments" do
     before :each do
       suppress_warning {@sep, $/ = $/, " "}
@@ -214,6 +224,14 @@ describe "IO.readlines" do
         IO.readlines(cmd)
       }.should complain(/IO process creation with a leading '\|'/)
     end
+
+    describe "when invoked with a block" do
+      it "yields each line to the block" do
+        lines = []
+        IO.readlines(@name) { |line| lines << line }
+        lines.should == IOSpecs.lines
+      end
+    end
   end
 
   it_behaves_like :io_readlines, :readlines