Do not respect ruby2_keywords on method/proc with post arguments

Previously, ruby2_keywords could be used on a method or proc with
post arguments, but I don't think the behavior is desired:

```ruby
def a(*c, **kw) [c, kw] end
def b(*a, b) a(*a, b) end
ruby2_keywords(:b)

b({foo: 1}, bar: 1)
```

This changes ruby2_keywords to emit a warning and not set the
flag on a method/proc with post arguments.

While here, fix the ruby2_keywords specs for warnings, since they
weren't testing what they should be testing.  They all warned
because the method didn't accept a rest argument, not because it
accepted a keyword or keyword rest argument.

[Backport #21402]

Author: jeremyevans

proc.c

@@ -3958,12 +3958,13 @@ proc_ruby2_keywords(VALUE procval)
     switch (proc->block.type) {
       case block_type_iseq:
         if (ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_rest &&
+                !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_post &&
                 !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_kw &&
                 !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_kwrest) {
             ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.ruby2_keywords = 1;
         }
         else {
-            rb_warn("Skipping set of ruby2_keywords flag for proc (proc accepts keywords or proc does not accept argument splat)");
+            rb_warn("Skipping set of ruby2_keywords flag for proc (proc accepts keywords or post arguments or proc does not accept argument splat)");
         }
         break;
       default:

spec/ruby/core/module/ruby2_keywords_spec.rb

@@ -275,7 +275,7 @@ def obj.foo(a, b, c) end
 
   it "prints warning when a method accepts keywords" do
     obj = Object.new
-    def obj.foo(a:, b:) end
+    def obj.foo(*a, b:) end
 
     -> {
       obj.singleton_class.class_exec do
@@ -286,12 +286,25 @@ def obj.foo(a:, b:) end
 
   it "prints warning when a method accepts keyword splat" do
     obj = Object.new
-    def obj.foo(**a) end
+    def obj.foo(*a, **b) end
 
     -> {
       obj.singleton_class.class_exec do
         ruby2_keywords :foo
       end
     }.should complain(/Skipping set of ruby2_keywords flag for/)
   end
+
+  ruby_version_is "3.5" do
+    it "prints warning when a method accepts post arguments" do
+      obj = Object.new
+      def obj.foo(*a, b) end
+
+      -> {
+        obj.singleton_class.class_exec do
+          ruby2_keywords :foo
+        end
+      }.should complain(/Skipping set of ruby2_keywords flag for/)
+    end
+  end
 end

spec/ruby/core/proc/ruby2_keywords_spec.rb

@@ -39,18 +39,28 @@
   end
 
   it "prints warning when a proc accepts keywords" do
-    f = -> a:, b: { }
+    f = -> *a, b: { }
 
     -> {
       f.ruby2_keywords
     }.should complain(/Skipping set of ruby2_keywords flag for/)
   end
 
   it "prints warning when a proc accepts keyword splat" do
-    f = -> **a { }
+    f = -> *a, **b { }
 
     -> {
       f.ruby2_keywords
     }.should complain(/Skipping set of ruby2_keywords flag for/)
   end
+
+  ruby_version_is "3.5" do
+    it "prints warning when a proc accepts post arguments" do
+      f = -> *a, b { }
+
+      -> {
+        f.ruby2_keywords
+      }.should complain(/Skipping set of ruby2_keywords flag for/)
+    end
+  end
 end

test/ruby/test_keyword.rb

@@ -2424,6 +2424,21 @@ class << c
     assert_raise(ArgumentError) { m.call(42, a: 1, **h2) }
   end
 
+  def test_ruby2_keywords_post_arg
+    def self.a(*c, **kw) [c, kw] end
+    def self.b(*a, b) a(*a, b) end
+    assert_warn(/Skipping set of ruby2_keywords flag for b \(method accepts keywords or post arguments or method does not accept argument splat\)/) do
+      assert_nil(singleton_class.send(:ruby2_keywords, :b))
+    end
+    assert_equal([[{foo: 1}, {bar: 1}], {}], b({foo: 1}, bar: 1))
+
+    b = ->(*a, b){a(*a, b)}
+    assert_warn(/Skipping set of ruby2_keywords flag for proc \(proc accepts keywords or post arguments or proc does not accept argument splat\)/) do
+      b.ruby2_keywords
+    end
+    assert_equal([[{foo: 1}, {bar: 1}], {}], b.({foo: 1}, bar: 1))
+  end
+
   def test_proc_ruby2_keywords
     h1 = {:a=>1}
     foo = ->(*args, &block){block.call(*args)}
@@ -2436,8 +2451,8 @@ def test_proc_ruby2_keywords
     assert_raise(ArgumentError) { foo.call(:a=>1, &->(arg, **kw){[arg, kw]}) }
     assert_equal(h1, foo.call(:a=>1, &->(arg){arg}))
 
-    [->(){}, ->(arg){}, ->(*args, **kw){}, ->(*args, k: 1){}, ->(*args, k: ){}].each do |pr|
-      assert_warn(/Skipping set of ruby2_keywords flag for proc \(proc accepts keywords or proc does not accept argument splat\)/) do
+    [->(){}, ->(arg){}, ->(*args, x){}, ->(*args, **kw){}, ->(*args, k: 1){}, ->(*args, k: ){}].each do |pr|
+      assert_warn(/Skipping set of ruby2_keywords flag for proc \(proc accepts keywords or post arguments or proc does not accept argument splat\)/) do
         pr.ruby2_keywords
       end
     end
@@ -2790,10 +2805,21 @@ def method_missing(*args)
     assert_equal(:opt, o.clear_last_opt(a: 1))
     assert_nothing_raised(ArgumentError) { o.clear_last_empty_method(a: 1) }
 
-    assert_warn(/Skipping set of ruby2_keywords flag for bar \(method accepts keywords or method does not accept argument splat\)/) do
+    assert_warn(/Skipping set of ruby2_keywords flag for bar \(method accepts keywords or post arguments or method does not accept argument splat\)/) do
       assert_nil(c.send(:ruby2_keywords, :bar))
     end
 
+    c.class_eval do
+      def bar_post(*a, x) = nil
+      define_method(:bar_post_bmethod) { |*a, x| }
+    end
+    assert_warn(/Skipping set of ruby2_keywords flag for bar_post \(method accepts keywords or post arguments or method does not accept argument splat\)/) do
+      assert_nil(c.send(:ruby2_keywords, :bar_post))
+    end
+    assert_warn(/Skipping set of ruby2_keywords flag for bar_post_bmethod \(method accepts keywords or post arguments or method does not accept argument splat\)/) do
+      assert_nil(c.send(:ruby2_keywords, :bar_post_bmethod))
+    end
+
     utf16_sym = "abcdef".encode("UTF-16LE").to_sym
     c.send(:define_method, utf16_sym, c.instance_method(:itself))
     assert_warn(/abcdef/) do

vm_method.c

@@ -2599,13 +2599,14 @@ rb_mod_ruby2_keywords(int argc, VALUE *argv, VALUE module)
             switch (me->def->type) {
               case VM_METHOD_TYPE_ISEQ:
                 if (ISEQ_BODY(me->def->body.iseq.iseqptr)->param.flags.has_rest &&
+                        !ISEQ_BODY(me->def->body.iseq.iseqptr)->param.flags.has_post &&
                         !ISEQ_BODY(me->def->body.iseq.iseqptr)->param.flags.has_kw &&
                         !ISEQ_BODY(me->def->body.iseq.iseqptr)->param.flags.has_kwrest) {
                     ISEQ_BODY(me->def->body.iseq.iseqptr)->param.flags.ruby2_keywords = 1;
                     rb_clear_method_cache(module, name);
                 }
                 else {
-                    rb_warn("Skipping set of ruby2_keywords flag for %"PRIsVALUE" (method accepts keywords or method does not accept argument splat)", QUOTE_ID(name));
+                    rb_warn("Skipping set of ruby2_keywords flag for %"PRIsVALUE" (method accepts keywords or post arguments or method does not accept argument splat)", QUOTE_ID(name));
                 }
                 break;
               case VM_METHOD_TYPE_BMETHOD: {
@@ -2618,13 +2619,14 @@ rb_mod_ruby2_keywords(int argc, VALUE *argv, VALUE module)
                     const struct rb_captured_block *captured = VM_BH_TO_ISEQ_BLOCK(procval);
                     const rb_iseq_t *iseq = rb_iseq_check(captured->code.iseq);
                     if (ISEQ_BODY(iseq)->param.flags.has_rest &&
+                            !ISEQ_BODY(iseq)->param.flags.has_post &&
                             !ISEQ_BODY(iseq)->param.flags.has_kw &&
                             !ISEQ_BODY(iseq)->param.flags.has_kwrest) {
                         ISEQ_BODY(iseq)->param.flags.ruby2_keywords = 1;
                         rb_clear_method_cache(module, name);
                     }
                     else {
-                        rb_warn("Skipping set of ruby2_keywords flag for %"PRIsVALUE" (method accepts keywords or method does not accept argument splat)", QUOTE_ID(name));
+                        rb_warn("Skipping set of ruby2_keywords flag for %"PRIsVALUE" (method accepts keywords or post arguments or method does not accept argument splat)", QUOTE_ID(name));
                     }
                     break;
                 }