refactor: Add attributes to dmd.common.{outbuffer,file}

[PetarKirov]

• refactor(dmd/common/file): Add function attributes
• refactor(dmd/common/outbuffer): Add @nogc and harmonize attributes

[dlang-bot]

Thanks for your pull request, @PetarKirov!

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Testing this PR locally

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dub run digger -- build "master + dmd#15531"

[PetarKirov]

This is part of a bigger branch, where I was able to add nothrow and/or @nogc (with no casts or try/catch workarounds) to various parts of hdrgen and mtype, but the changeset was starting to become big, so I decided to publish what I have so far.

[PetarKirov]

------------
src/dmd/common/outbuffer.d(543): Error: `@nogc` function `dmd.common.outbuffer.OutBuffer.vprintf` cannot call non-@nogc function `core.stdc.stdarg.va_copy`
...

This must be happening because the CI is using an older version of bootstrap dmd.

Perhaps I should redefine the stdarg functions in the pureMalloc? In addition to nothrow, I wonder if I should also add pure.

[thewilsonator]

do we not have a mallocNew!(T)(Args...) that we could have be @trusted instead?

[WalterBright]

While in general I like @nogc, it doesn't serve much purpose in the dmd source code because dmd uses the gc here and there.

[WalterBright]

I tried adding nothrow to the code base, but it turned out to be clumsy because of all the circular control paths. @ibuclaw suggested adding a nothrow compiler switch, and I implemented that.

[PetarKirov]

@WalterBright, yes I followed the progress on the -nothrow switch, nice work 👍

That said, I still find value in explicit attributes for the use case of using dmd as a library. I plan to continue work on this PR once I have time.

[RazvanN7]

@PetarKirov Any updates on this?