bug#66363: gdb-control-commands-regexp issues

[Mattias Engdegård]

The variable `gdb-control-commands-regexp` in gdb-mi.el cannot work as 
currently defined and used. Only group 3 is of  interest, but that group hasn't 
referred to anything useful for several years.

Group 3 probably refers to a part of the regex's tail where the command 
argument is matched:

   "\\([[:blank:]]+\\([^[:blank:]]*\\)\\)*$"

However, this seems to be broken as well, because all groups here are inside 
repetitions. This part of the regexp is also exponential in form if not in 
practice but we'd better simplify it anyway.

Attached is a suggested patch which makes explicit the command abbreviations 
matched, and leaves only a single submatch. It also changes the tail to 
assuming that the command argument doesn't contain non-newlines (or the final 
eol anchor wouldn't make sense) but that it can contain spaces (which seems 
reasonable). However, right now the argument is only checked for being 
non-empty or not.

I don't have a working gdb setup at the moment so if someone would be kind to 
test it, I would be very grateful for it.

gdb-control-commands-regexp.diff
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