How can I assign a vim syntax group to a 'Foo( ... )'? For arbitrary ... including contained parenthesis - vim

Question

I am trying to give my debug macros a different color, not just the macro names, but at least the opening and closing parenthesis in the same color.
As a test I'm current using the following line:
,--- Uncolored paren!?
v
int foobar; Dout( (( ) ) ( ) ); f((char*)x);
^^^^^^^^^^^^^^^^^^
\__ all of this should be colored.
If I try the following syntax rule:
syn region Debug matchgroup=DebugDelim start=/Dout(/ end=/)/ contains=cParen
then this isn't working: the first closing parenthesis that should be part of cParen isn't part of any highlighting group anymore and remains therefore uncolored.
Is this a bug in vim or am I doing something wrong?
Note: cParen here is defined as 'usual' (in the vim's c.vim syntax file).
EDIT: After figuring out the answer to my previous question (namely that contained groups match inside the start and end pattern unless you use a matchgroup argument), I changed my question to what remains a question to me.

Answer 1

After more than a week of research and trying things; the main conclusion is that vim's syntax system needs a redesign. It is flawed.
Having said that, the best answer would be 'it can not be done', because the system is just too broken; but -- with lots and lots of efforts a sort of horrible work around can be forged (for THIS case -- not for what I really needed) that looks as follows:
" Highlight my debug macros.
" A group with things that are normally already excluded from cParen.
syn cluster cwNotInParen contains=#cParenGroup,cCppParen,cErrInBracket,cCppBracket,#cStringGroup,#Spell
" Create a new cParen syntax group that will have Debug highlighting.
syn region cwDebugParen transparent matchgroup=cwDebugParenDelim contains=ALLBUT,#cwNotInParen
\ start='(' end=")\#="
" Define cParen last, so it will overrule the previous one.
syn clear cParen
syn region cParen transparent contains=ALLBUT,#cwNotInParen,cwDebugParen
\ start='(' end=')'
" Redefine cCppParen to also exclude cwDebugParen
syn clear cCppParen
syn region cCppParen transparent contained contains=ALLBUT,#cParenGroup,cErrInBracket,cParen,cwDebugParen,cBracket,cString,#Spell
\ start='(' skip='\\$' excludenl end=')' end='$'
" Redefine cCppBracket to also exclude cwDebugParen.
syn clear cCppBracket
syn region cCppBracket transparent contained contains=ALLBUT,#cParenGroup,cErrInParen,cParen,cwDebugParen,cBracket,cString,#Spell
\ start='\[\|<::\#!' skip='\\$' excludenl end=']\|:>' end='$'
" Add a syntax group for "Debug( ... );".
syn region cwDebugMacros transparent matchgroup=cwDebugMacrosDelim contains=cwDebugParen
\ start="\v\W(Debug|DoutFatal|DoutEntering|Dout|ASSERT|assert)\(#="hs=s+1
\ start="\v^(Debug|DoutFatal|DoutEntering|Dout|ASSERT|assert)\(#="
\ end="\v\);?"
hi link cwDebugMacrosDelim Debug " Highlight 'Debug' and the close paren of that macro.
hi link cwDebugParenDelim Debug " Highlight the open paren of the Debug macro.
This works as follows:
A new syntax group is created called cwDebugParen. It is basically the same as cParen but will have highlighting for the parenthesis. Because the syntax definition is containing ALLBUT in many places, this new group will now be accepted everywhere. It is possible - but not very convenient - to just replace the whole syntax file with your own and then add the new cwDebugParen to all ALLBUT,... lists, but in this case it is easier to remove cParen and redefine it after the definition of cwDebugParen, effectively hiding that because the last rule that matches will be used. Unfortunately the definition of cParen depends on some conditionals so the whole would get pretty complex still; therefore I just picked the one cParen definition that is used based on my .vimrc.
Because cParen doesn't have a matchgroup I found that its start pattern is still also matched by cwDebugParen?! -- this seems a bug to me but at least can be avoided by adding cwDebugParen to the ALLBUT list of cParen.
cwDebugParen itself does have a matchgroup, which is necessary for the syntax highlighting of the parens of course. Note that although it ends on the closing paren ')', I use a zero-match (:help \#=) because the same paren is needed to end the enclosing cwDebugMacros region. Note that using end=')'me=s-1 would have the same effect here.
Finally a new region is added, cwDebugMacros, that starts at a pattern like Debug( and ends on );. The two start= arguments are necessary because they use a different highlight start (hs) since one starts at the beginning of the line while the other demands that there is a non-word character in front of Debug. Also the opening paren here is a zero-match because we need it to start the cwDebugParen region that we contain in this region (fortunately we can use a zero-match here; because me=s-1 isn't support for start!?). That then will gobble up all input up till the closing paren, so we don't have to be afraid that our end will match a closing paren that isn't the closing paren of our debug macro. Note that I used end="\v\);?" with a question mark after the semi-colon so that IF the semi-colon directly follows the closing paren then it is also colored the same color (I like that) while if for whatever reason there is white-space (including comments) in between then things aren't broken - only the semi-colon isn't colored anymore then.
Edit: Added a redefine for cCppParen and cCppBracket which use the construct ALLBUT=...,cParen,... and therefore now also need to exclude cwDebugParen.