Removed comma support for -i (-i=a,b becomes -i=a -i=b)

[marler8997]

@WalterBright has suggested that supporting multiple arguments for a single option using the comma character is "a lot of effort". He also mentions other command-line options already support multiple arguments because they can be given multiple times. This PR removes comma support for -i so the following

-i=foo,-foo.bar,baz

must now be specified via:

-i=foo i=-foo.bar -i=baz

[dlang-bot]

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[wilzbach]

(If we go with this, changelog and documentation should be updated too.)
Luckily everything is now in this repo.

[marler8997]

I've modified the changelog, and we can delay integrating the documentation PR until this PR is settled.

[JinShil]

Comma or no comma is fine with me.

[thewilsonator]

@WalterBright has suggested that supporting multiple arguments for a single option using the comma character is "a lot of effort".

Really? It shouldn't be hard to do what we have in LDC, namely a generic comma separated command line option parser.

[timotheecour]

totally agree and strongly support comma separated list of arguments for this flag and others. I planned to add one for Comma separated linker flags to ease adapting these from, say, clang or gcc -Wl,-lfoo1,-lfoo2

ldc, clang and others do it for good reason. Some push back desirable here. Original cmdline design had a number of issues (eg flags without = separator eg -ofbar is just bad). Allowing comma separated flags improve things a bit. If parsing for all comma separated flags was reusing some common code, maybe it would ease some of walters concerns.

[marler8997]

If parsing for all comma separated flags was reusing some common code, maybe it would ease some of walters concerns.

I'll create a PR to see how complex this would be and we can see what Walter thinks.

[marler8997]

Ok, PR is here: https://github.com/dlang/dmd/pull/7863/files

The implementation creates a struct called OptionRange that takes care of splitting an option's arguments into a range of null-terminated strings, so then when you parse the option all you have to do is pass the argument to this OptionRange and iterate over all the values.

[PetarKirov]

I thought this syntax was removed with this PR.

[timotheecour]

indeed, unless #7863 gets merged before we release

[marler8997]

Shoot, missed that one

[marler8997]

@ZombineDev do you want to make a PR for that one or shall I? I think at this point it's gotta be merged to the stable branch