Support .json target files

[RalfJung]

We currently don't support .json target files. At least I assume that to be the case since I never tested them. I also know absolutely nothing about how they work, so some help would be appreciated here. :)

[berkus]

It's basically the LLVM target configuration dumped in a file via rustc command.

Here's a longer section with more details on intended use-case.

[RalfJung]

That would be helpful if I knew anything at all about LLVM target configurations. ;)

[RalfJung]

What would be useful for testing is to have a reasonably standard JSON file target. Is there something that can be relied upon to keep working, or all these all prone to breakage from rustc/LLVM changes?

[berkus]

Basically, you don't need to know anything about the LLVM target configuration. This is just a json file required to build your code for a specific target (it sets up data alignment requirements, among other things), including panic handling, linker used etc.

As long as you pass it down to the rustc all should be good.

[RalfJung]

Is there a good default/standard target file to use as a test?

[berkus]

What would be useful for testing is to have a reasonably standard JSON file target. Is there something that can be relied upon to keep working, or all these all prone to breakage from rustc/LLVM changes?

You can dump a default one using the commands I linked above. If you don't modify it then it will be the same as used by rustc for compiling for that target by default (one is used regardless of if you specify it or not).