Add build support for Cargo's build-std feature.
This makes some changes to the standard library to make it easier to use with Cargo's build-std feature. The primary goal is to make it so that Cargo and its users do not need to know which crates to build and which features to use for every platform.
Conditional cfgs are adjusted so that there is usually a fall-through for unsupported platforms. Additionally, there is a "restricted-std" feature to mark `std` as unstable when used with build-std on no_std platforms. There is no intent to stabilize this feature for the foreseeable future.
This borrows some of the implementation for wasm which already does what this needs. More code sharing can be done with some other platforms (there is a lot of duplication with cloudabi, hermit, and sgx), but I figure that can be done in a future PR.
There are some small changes to stable behavior in this PR:
- `std::env::consts::ARCH` on asmjs now reports "wasm32", to match its actual architecture.
- Some of the wasm error messages for unsupported features report a slightly different error message so that the code can be reused.
There should otherwise not be any changes to how std is built for distribution via bootstrap.
This does not yet support all platforms when used with build-std.
- It doesn't work with 16-bit targets (hashbrown does not support that).
- It does not work with JSON spec targets.
- In particular, all target triple snooping will need to be replaced with appropriate target option checking.
- Switching to gimli (#73441) will make cross-building *much* easier.
- There are still a ton of issues on the Cargo side to resolve. A big one is panic strategy support.
Future PRs are intended to address some of these issues.
This commit makes it so `std` no longer has a `default` feature, but
instead the `test` crate has a `default` feature doing the same thing.
The purpose of this commit is to allow Cargo's `-Zbuild-std` command,
which could customize the features of the standard library, to handle
the `default` feature for libstd. Currently Cargo's `-Zbuild-std`
support starts at libtests's manifest as the entry point to the std set
of crates.
Explicitly requests the "-Z unstable-options" flag if someone attempts to use
a cargo option gated by it. This enhances discoverability, particularly in the
instance where the user is on the nightly compiler but isn't using the flag.
Don't propagate __RUST_TEST_INVOKE to subprocess
When -Z panic_abort_tests is enabled, we use an environment variable to
tell the subprocess which test to invoke. If that subprocess then
invokes another Rust test binary, chaos ensues.
r? @alexcrichton
When -Z panic_abort_tests is enabled, we use an environment variable to
tell the subprocess which test to invoke. If that subprocess then
invokes another Rust test binary, chaos ensues.
Passes LLVM codegen and Emscripten link-time flags for exception
handling if and only if the panic strategy is `unwind`. Sets the
default panic strategy for Emscripten targets to `unwind`. Re-enables
tests that depend on unwinding support for Emscripten, including
`should_panic` tests.
