7071: Pass --all-targets to "cargo check" when discovering external resources r=matklad a=WasabiFan
There is a repro case and background in the linked issue.
In short, the goal of this MR is to allow rust-analyzer to discover proc-macros which come from your tests (including, most importantly, dev-dependencies).
By default, `cargo check` implies the equivalent of `--lib --bins`, meaning it'll check your libraries and binaries -- but not tests! This means proc-macros (or, I guess, build scripts as well) weren't discovered by rust-analyzer if they came from tests.
One solution would be to manually add `--lib --bins --tests` (i.e., just augment the effective options to include tests). However, in this MR, I threw in `--all-targets`, which [according to the docs](https://doc.rust-lang.org/cargo/commands/cargo-check.html#target-selection) implies `--benches --examples` too. I have absolutely no idea what repercussions that will have on rust-analyzer for other projects, nor do I know if it's a problem that build scripts will now be discovered for tests/examples/benches. But I am not aware of a reason you _wouldn't_ want to discover these things in your examples too.
I think the main drawback of this change is that it will likely slow down the `cargo check`. At a minimum, it'll now be checking your tests _and_ their dependencies. The `cargo check` docs also say that including `--tests` as I have here may cause your lib crate to be built _twice_, once for the normal target and again for unit tests. My reading of that caveat suggests that "building twice" means it's built once for the tests _inside_ your lib, with a test profile, and again for any consumers of your lib, now using a normal release profile or similar. This doesn't seem surprising.
Very minor caveat: `--tests` will not include tests within a binary if it has `test = false` set in `Cargo.toml`. (I discovered this manually by trial-and-error, but hey, it actually says that in the docs!) This is likely not an issue, but _does_ mean that if you are -- for whatever reason -- disabling tests like that and then manually specifying `cargo test --package <...> --bin <...>` to run them, rust-analyzer will remain unaware of proc-macros in your tests.
I have confirmed this fixes the original issue in my sandbox example linked in #7034 and in my own project in which I originally discovered this. I've left it configured as my default RA language server and will report back if I notice any unexpected side-effects.
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