Hash.new: print a deprecation warning when receiving keyword arguments (#7828)

[Feature #19236]

In Ruby 3.3, `Hash.new` shall print a deprecation warning if keyword arguments
are passed instead of treating them as an implicit positional Hash.

This will allow to safely introduce a `capacity` keyword argument in 3.4

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>

5 files changed, 27 insertions, 10 deletions

diff --git a/hash.c b/hash.c
index 63a51f54c4..323e0ad512 100644
--- a/hash.c
+++ b/hash.c
@@ -1714,17 +1714,21 @@ set_proc_default(VALUE hash, VALUE proc)
 static VALUE
 rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
 {
-    VALUE ifnone;
-
     rb_hash_modify(hash);
+
     if (rb_block_given_p()) {
         rb_check_arity(argc, 0, 0);
-        ifnone = rb_block_proc();
-        SET_PROC_DEFAULT(hash, ifnone);
+        SET_PROC_DEFAULT(hash, rb_block_proc());
     }
     else {
         rb_check_arity(argc, 0, 1);
-        ifnone = argc == 0 ? Qnil : argv[0];
+
+        VALUE options, ifnone;
+        rb_scan_args(argc, argv, "01:", &ifnone, &options);
+        if (NIL_P(ifnone) && !NIL_P(options)) {
+            ifnone = options;
+            rb_warn_deprecated_to_remove("3.4", "Calling Hash.new with keyword arguments", "Hash.new({ key: value })");
+        }
         RHASH_SET_IFNONE(hash, ifnone);
     }
 
diff --git a/spec/ruby/core/hash/fetch_spec.rb b/spec/ruby/core/hash/fetch_spec.rb
index 753167f709..6e0d207224 100644
--- a/spec/ruby/core/hash/fetch_spec.rb
+++ b/spec/ruby/core/hash/fetch_spec.rb
@@ -4,7 +4,7 @@ require_relative '../../shared/hash/key_error'
 
 describe "Hash#fetch" do
   context "when the key is not found" do
-    it_behaves_like :key_error, -> obj, key { obj.fetch(key) }, Hash.new(a: 5)
+    it_behaves_like :key_error, -> obj, key { obj.fetch(key) }, Hash.new({ a: 5 })
     it_behaves_like :key_error, -> obj, key { obj.fetch(key) }, {}
     it_behaves_like :key_error, -> obj, key { obj.fetch(key) }, Hash.new { 5 }
     it_behaves_like :key_error, -> obj, key { obj.fetch(key) }, Hash.new(5)
diff --git a/spec/ruby/core/hash/fetch_values_spec.rb b/spec/ruby/core/hash/fetch_values_spec.rb
index af3673f6ef..0cd48565af 100644
--- a/spec/ruby/core/hash/fetch_values_spec.rb
+++ b/spec/ruby/core/hash/fetch_values_spec.rb
@@ -19,7 +19,7 @@ describe "Hash#fetch_values" do
   end
 
   describe "with unmatched keys" do
-    it_behaves_like :key_error, -> obj, key { obj.fetch_values(key) }, Hash.new(a: 5)
+    it_behaves_like :key_error, -> obj, key { obj.fetch_values(key) }, Hash.new({ a: 5 })
 
     it "returns the default value from block" do
       @hash.fetch_values(:z) { |key| "`#{key}' is not found" }.should == ["`z' is not found"]
diff --git a/spec/ruby/core/hash/new_spec.rb b/spec/ruby/core/hash/new_spec.rb
index 6054b69bdd..6279815fd6 100644
--- a/spec/ruby/core/hash/new_spec.rb
+++ b/spec/ruby/core/hash/new_spec.rb
@@ -33,4 +33,17 @@ describe "Hash.new" do
     -> { Hash.new(5) { 0 }   }.should raise_error(ArgumentError)
     -> { Hash.new(nil) { 0 } }.should raise_error(ArgumentError)
   end
+
+  ruby_version_is "3.3" do
+    it "emits a deprecation warning if keyword arguments are passed" do
+      -> { Hash.new(unknown: true) }.should complain(
+        Regexp.new(Regexp.escape("Calling Hash.new with keyword arguments is deprecated and will be removed in Ruby 3.4; use Hash.new({ key: value }) instead"))
+      )
+
+      -> { Hash.new(1, unknown: true) }.should raise_error(ArgumentError)
+      -> { Hash.new(unknown: true) { 0 } }.should raise_error(ArgumentError)
+
+      Hash.new({ unknown: true }).default.should == { unknown: true }
+    end
+  end
 end
diff --git a/spec/ruby/core/marshal/shared/load.rb b/spec/ruby/core/marshal/shared/load.rb
index 57cd6b0d26..bc094f28f2 100644
--- a/spec/ruby/core/marshal/shared/load.rb
+++ b/spec/ruby/core/marshal/shared/load.rb
@@ -539,19 +539,19 @@ describe :marshal_load, shared: true do
       end
 
       it "preserves compare_by_identity behaviour for a Hash subclass" do
-        h = UserHash.new(a: 1)
+        h = UserHash.new({ a: 1 })
         h.compare_by_identity
         unmarshalled = Marshal.send(@method, Marshal.dump(h))
         unmarshalled.should.compare_by_identity?
 
-        h = UserHash.new(a: 1)
+        h = UserHash.new({ a: 1 })
         unmarshalled = Marshal.send(@method, Marshal.dump(h))
         unmarshalled.should_not.compare_by_identity?
       end
     end
 
     it "allocates an instance of the proper class when Hash subclass with compare_by_identity behaviour" do
-      h = UserHash.new(a: 1)
+      h = UserHash.new({ a: 1 })
       h.compare_by_identity
 
       unmarshalled = Marshal.send(@method, Marshal.dump(h))