I've attached the "configure --help" output for MPFR.
I'm using:

  zstyle ':completion:*' format 'Completing %d'

With zsh 5.2, I get the following, which doesn't make sense:

zira:~/software/mpfr> ./configure --enable-decimal-float[Tab]
Completing option
--enable-decimal-float  -- build conversion functions from/to decimal floats
--enable-decimal-float  -- explicitly disable decimal floats support

One has from the "configure --help" output:

  --disable-decimal-float explicitly disable decimal floats support
  --enable-decimal-float  build conversion functions from/to decimal floats
                          [default=autodetect]

And there is an inconsistency:

zira:~/software/mpfr> ./configure --enable-log[Tab]

gives

./configure --enable-logging []

where [] is the cursor. But

zira:~/software/mpfr> ./configure --enable-gmp-int[Tab]

gives:

zira:~/software/mpfr> ./configure --enable-gmp-internals=[]

and

zira:~/software/mpfr> ./configure --enable-gmp-internals --[Tab]

gives:

zira:~/software/mpfr> ./configure --enable-gmp-internals --[]
Completing --enable-gmp-internals

instead of completing a new option.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)