Warn when passing a non-literal block to Kernel#lambda

Implements [Feature #15973]

basictest/test.rb

@@ -1425,9 +1425,6 @@ marity_test(:test_ok)
 marity_test(:marity_test)
 marity_test(:p)
 
-lambda(&method(:test_ok)).call(true)
-lambda(&block_get{|a,n| test_ok(a,n)}).call(true, 2)
-
 class ITER_TEST1
    def a
      block_given?

proc.c

@@ -855,6 +855,19 @@ rb_block_lambda(void)
 static VALUE
 f_lambda(VALUE _)
 {
+    VALUE block_handler = rb_vm_frame_block_handler(GET_EC()->cfp);
+
+    if (block_handler != VM_BLOCK_HANDLER_NONE) {
+        switch (vm_block_handler_type(block_handler)) {
+          case block_handler_type_proc:
+          case block_handler_type_symbol:
+          case block_handler_type_ifunc:
+            rb_warn_deprecated("lambda without a literal block", "the proc without lambda");
+          default:
+            break;
+        }
+    }
+
     return rb_block_lambda();
 }
 

test/ruby/test_iterator.rb

@@ -339,8 +339,7 @@ class TestIterator < Test::Unit::TestCase
     marity_test(:marity_test)
     marity_test(:p)
 
-    lambda(&method(:assert)).call(true)
-    lambda(&get_block{|a,n| assert(a,n)}).call(true, "marity")
+    get_block{|a,n| assert(a,n)}.call(true, "marity")
   end
 
   def foo

test/ruby/test_lambda.rb

@@ -74,6 +74,12 @@ class TestLambdaParameters < Test::Unit::TestCase
     assert_raise(ArgumentError, bug9605) {proc(&plus).call [1,2]}
   end
 
+  def test_warning_for_non_literal_blocks
+    assert_warn(/lambda without a literal block/, '[ruby-core:93482] [Feature #15973]') do
+      lambda(&:symbol)
+    end
+  end
+
   def pass_along(&block)
     lambda(&block)
   end