Overview
--------
I forget the exact name of this feature, but when you declare a function or a member function in a header file and then partially type it in an implementation file, the editor will "magically" produce suggestions for autocompleting the declared function. In the old parser, this would replace the text you had already typed with the new completion. In the new parser, it ignores any text you have typed and just fills in the function, which in a lot of cases is just wrong.

Steps to Reproduce
------------------
1) Create a header file with the following content

  void Foo(int thing);
  struct Bar
  {
      void Method(int thing);
  };

2) Create a .cpp file and type: "void Foo"
3) Wait, because the parser is now really slow
4) Finally, a suggestion for completing the "Foo" function pops up. Accept it.
5) Do the same for "Method" by typing "void Method" and accepting the completion.

Actual Results
--------------
The resulting completions ignore the already typed "void" keyword and simply insert the signatures, such that "void" now appears twice:

  void void Foo(int thing)
  {
  }

  void void Bar::Method(int thing)
  {
  }

If a project wishes to format the return type such that it appears on a new line, then typing "void <new line> Foo" and accepting the suggestion produces this incorrect completion:

  void 
  void Foo(int thing)
  {
  }

An even worse example of this: 
1) Begin typing "void Foo(int "
2) Press ctrl+space
3) Select "implement method Foo"
4) The completion creates this terrible snippet:

  Foo(int void Foo(int thing)
  {
  }
  )

Expected Results
----------------
The parser should be aware of the code that has already been typed and remove/adjust it as necessary.

For the first example I expect the code to look like this after completion:

  void Foo(int thing)
  {
  }

  void Bar::Method(int thing)
  {
  }

For the second example:

  void 
  Foo(int thing)
  {
  }

And for the third example:

  void Foo(int thing)
  {
  }

Build Date & Platform
---------------------
Ever since the clang based parser was introduced.