This commit adds a new attribute to the Rust compiler specific to the wasm
target (and no other targets). The `#[wasm_import_module]` attribute is used to
specify the module that a name is imported from, and is used like so:
#[wasm_import_module = "./foo.js"]
extern {
fn some_js_function();
}
Here the import of the symbol `some_js_function` is tagged with the `./foo.js`
module in the wasm output file. Wasm-the-format includes two fields on all
imports, a module and a field. The field is the symbol name (`some_js_function`
above) and the module has historically unconditionally been `"env"`. I'm not
sure if this `"env"` convention has asm.js or LLVM roots, but regardless we'd
like the ability to configure it!
The proposed ES module integration with wasm (aka a wasm module is "just another
ES module") requires that the import module of wasm imports is interpreted as an
ES module import, meaning that you'll need to encode paths, NPM packages, etc.
As a result, we'll need this to be something other than `"env"`!
Unfortunately neither our version of LLVM nor LLD supports custom import modules
(aka anything not `"env"`). My hope is that by the time LLVM 7 is released both
will have support, but in the meantime this commit adds some primitive
encoding/decoding of wasm files to the compiler. This way rustc postprocesses
the wasm module that LLVM emits to ensure it's got all the imports we'd like to
have in it.
Eventually I'd ideally like to unconditionally require this attribute to be
placed on all `extern { ... }` blocks. For now though it seemed prudent to add
it as an unstable attribute, so for now it's not required (as that'd force usage
of a feature gate). Hopefully it doesn't take too long to "stabilize" this!
cc rust-lang-nursery/rust-wasm#29
This commit is an implementation of adding custom sections to wasm artifacts in
rustc. The intention here is to expose the ability of the wasm binary format to
contain custom sections with arbitrary user-defined data. Currently neither our
version of LLVM nor LLD supports this so the implementation is currently custom
to rustc itself.
The implementation here is to attach a `#[wasm_custom_section = "foo"]`
attribute to any `const` which has a type like `[u8; N]`. Other types of
constants aren't supported yet but may be added one day! This should hopefully
be enough to get off the ground with *some* custom section support.
The current semantics are that any constant tagged with `#[wasm_custom_section]`
section will be *appended* to the corresponding section in the final output wasm
artifact (and this affects dependencies linked in as well, not just the final
crate). This means that whatever is interpreting the contents must be able to
interpret binary-concatenated sections (or each constant needs to be in its own
custom section).
To test this change the existing `run-make` test suite was moved to a
`run-make-fulldeps` folder and a new `run-make` test suite was added which
applies to all targets by default. This test suite currently only has one test
which only runs for the wasm target (using a node.js script to use `WebAssembly`
in JS to parse the wasm output).
Add crate name to "main function not found" error message.
Fixes#44798 and rust-lang/cargo#4948.
I was wondering if it might be cleaner to update the ui tests to add a simple `fn main() {}` for the unrelated tests. Let me know if you would prefer that.
NLL: Limit two-phase borrows to autoref-introduced borrows
This imposes a restriction on two-phase borrows so that it only applies to autoref-introduced borrows.
The goal is to ensure that our initial deployment of two-phase borrows is very conservative. We want it to still cover the `v.push(v.len());` example, but we do not want it to cover cases like `let imm = &v; let mu = &mut v; mu.push(imm.len());`
(Why do we want it to be conservative? Because when you are not conservative, then the results you get, at least with the current analysis, are tightly coupled to details of the MIR construction that we would rather remain invisible to the end user.)
Fix#46747
I decided, for this PR, to add a debug-flag `-Z two-phase-beyond-autoref`, to re-enable the more general approach. But my intention here is *not* that we would eventually turn on that debugflag by default; the main reason I added it was that I thought it was useful for writing tests to be able to write source that looks like desugared MIR.
Namely, the mutable borrows also carries a flag indicating whether
they should support two-phase borrows.
This allows us to thread down, from the point of the borrow's
introduction, whether the particular adjustment that created it is one
that yields two-phase mutable borrows.
