compiletest directives docs for "ignore-" are incorrect or confusing

[RalfJung]

https://rustc-dev-guide.rust-lang.org/tests/directives.html states that I can write ignore-x wherex is "A full target triple: aarch64-apple-ios". However, that's not correct -- some target triples work, but not all of them. I realized this when my PR failed because ignore-i686-pc-windows-gnullvm dies not work, and neither does //@ ignore-i686-unknown-uefi.

CC @jieyouxu

[jieyouxu]

It's technically correct in that I believe those would work if they're included in the directives allow list (lol).

[RalfJung]

If every new target has to be added to some allow list, that will never be up-to-date. compiletest should accept all targets supported by rustc then.

[jieyouxu]

The intention in the long term is to not have to rely on any allow list, it obviously doesn't scale

[RalfJung]

Also, I assume then this is similar for architectures etc? Would be good to document that so that one knows what to do when an architecture is not recognized.

[RalfJung]

The intention in the long term is to not have to rely on any allow list, it obviously doesn't scale

compiletest already queries rustc for various things, right? Can't it query the target list?

[jieyouxu]

There's two parts to this:

1. compiletest already does the target list query. Those targets are already valid ignore-$targets cf

   rust/src/tools/compiletest/src/header/cfg.rs

   Lines 103 to 107 in c6c1796

   	condition! {
   	name: &config.target,
   	allowed_names: &target_cfgs.all_targets,
   	message: "when the target is {name}"
   	}

   .
2. But they just get denied by the allow-list (which is a short-term bandaid to detect unknown directives) that I want to get rid of soon

[jieyouxu]

Also, I assume then this is similar for architectures etc? Would be good to document that so that one knows what to do when an architecture is not recognized.

Yes, it's the same for archs. The valid archs are already computed based on all the builtion-targets combined + some extra archs

rust/src/tools/compiletest/src/header/cfg.rs

Lines 133 to 137 in c6c1796

	condition! {
	name: &target_cfg.arch,
	allowed_names: ContainsEither { a: &target_cfgs.all_archs, b: &EXTRA_ARCHS },
	message: "when the architecture is {name}"
	}

[jieyouxu]

I'll send a PR to document the current impl limitation in rustc-dev-guide.

If you still need those //@ ignore-$target_tuple for your PR, then you should only need to add them to

rust/src/tools/compiletest/src/directive-list.rs

Line 4 in c6c1796

const KNOWN_DIRECTIVE_NAMES: &[&str] = &[

.

[jieyouxu]

rust-lang/rustc-dev-guide#2319