[ruby-cvs:78381] 191ce5344e (master): Reduce duplicated warnings for the change of Ruby 3 keyword arguments

Yusuke Endoh	2019-09-13 17:02:08 +0900 (Fri, 13 Sep 2019)

  New Revision: 191ce5344e

  https://github.com/ruby/ruby/commit/191ce5344e

  Log:
    Reduce duplicated warnings for the change of Ruby 3 keyword arguments
    
    By this change, the following code prints only one warning.
    
    ```
    def foo(**opt); end
    100.times { foo({kw:1}) }
    ```
    
    A global variable `st_table *caller_to_callees` is a map from caller to
    a set of callee methods.  It remembers that a warning is already printed
    for each pair of caller and callee.
    
    [Feature #16289]

  Modified files:
    test/ruby/test_keyword.rb
    test/ruby/test_struct.rb
    vm_args.c
    vm_insnhelper.c