cabal-install cmd line parser: silently accepts ambiguous prefixes

[jwaldmann]

I was getting strange behaviour from

cabal install --with-hc-pkg=ghc-pkg-7.8.4 --with-hc=ghc-7.8.4

until I realized that one option is a prefix of the other, and was ignored. (The second option should be --with-compiler, I think)

I think this is wrong behaviour, instead cabal-install should complain loudly, and refuse to start.

This is for

cabal-install version 1.22.7.0
using version 1.22.4.0 of the Cabal library 

[23Skidoo]

This is standard behaviour for GNU-style long options (1, 2, 3), and a lot of people rely on it.

[jwaldmann]

Really?

tar --list --use-compress-program=bzip2 --use-compress=gzip something.tgz
tar: Conflicting compression options

[23Skidoo]

OK, so you don't suggest removing abbreviations. Maybe we can do something.

[jwaldmann]

Yes, abbreviations are fine. I guess my "complaint" is: the options parser views

cabal --foo=bar1 --foo=bar2

as equivalent to

cabal --foo=bar1 

it silently ignores the value on the right, prefix-abbreviated or not. I think this is non-standard. It should complain and halt.

[23Skidoo]

I'm not sure how non-standard this is, gcc -O2 -O3 is the same as gcc -O3, for example. But for stuff like --with-hc-pkg it probably does make sense.

/cc @dcoutts