rustc: prefer ParamEnvAnd and LayoutCx over tuples for LayoutOf.
This PR provides `tcx.layout_of(param_env.and(ty))` as the idiomatic replacement for the existing `(tcx, param_env).layout_of(ty)` and removes fragile (coherence-wise) layout-related tuple impls.
r? @nikomatsakis
Dist builds should always be as fast as we can make them, and since
those run on CI we don't care quite as much for the build being somewhat
slower. As such, we don't automatically enable ThinLTO on builds for the
dist builders.
copy_nonoverlapping example: Fixed typo
The comment referred to a variable using an incorrect name. (it has probably been renamed since the comment was written, or the comment was copied elsewhere - I noted the example in libcore has the `tmp` name for the temporary variable.)
Tweak presentation on lifetime trait mismatch
- On trait/impl method discrepancy, add label pointing at trait signature.
- Point only at method definition when referring to named lifetimes on lifetime mismatch.
- When the sub and sup expectations are the same, tweak the output to avoid repeated spans.
Fix#30790, CC #18759.
The comment referred to a variable using an incorrect name. (it has probably been renamed since the comment was written, or the comment was copied elsewhere - I noted the example in libcore has the `tmp` name for the temporary variable.)
Implement extensible syscall interface for wasm
Currently it's possible to run tests with the native wasm target, but it's not possible to tell whether they pass or to capture the output, because libstd throws away stdout, stderr and the exit code. While advanced libstd features should probably require more specific targets (eg. wasm-unknown-web) I think even the unknown target should at least support basic I/O.
Any solution is constrained by these factors:
- It must not be javascript specific
- There must not be too strong coupling between libstd and the host environment (because it's an "unknown" target)
- WebAssembly does not allow "optional" imports - all imports *must* be resolved.
- WebAssembly does not support calling the host environment through any channel *other* than imports.
The best solution I could find to these constraints was to give libstd a single required import, and implement a syscall-style interface through that import. Each syscall is designed such that a no-op implementation gives the most reasonable fallback behaviour. This means that the following import table would be perfectly valid:
```javascript
imports.env = { rust_wasm_syscall: function(index, data) {} }
```
Currently I have implemented these system calls:
- Read from stdin
- Write to stdout/stderr
- Set the exit code
- Get command line arguments
- Get environment variable
- Set environment variable
- Get time
It need not be extended beyond this set if being able to run tests for this target is the only goal.
edit:
As part of this PR I had to make a further change. Previously, the rust entry point would be automatically called when the webassembly module was instantiated. This was problematic because from the javascript side it was impossible to call exported functions, access program memory or get a reference to the instance.
To solve this, ~I changed the default behaviour to not automatically call the entry point, and added a crate-level attribute to regain the old behaviour. (`#![wasm_auto_run]`)~ I disabled this behaviour when building tests.
