refactor expr & stmt parsing + improve recovery
Summary of important changes (best read commit-by-commit, ignoring whitespace changes):
- `AttrVec` is introduces as an alias for `ThinVec<Attribute>`
- `parse_expr_bottom` and `parse_stmt` are thoroughly refactored.
- Extract diagnostics logic for `vec![...]` in a pattern context.
- Recovery is added for `do catch { ... }`
- Recovery is added for `'label: non_block_expr`
- Recovery is added for `var $local`, `auto $local`, and `mut $local`. Fixes#65257.
- Recovery is added for `e1 and e2` and `e1 or e2`.
- ~~`macro_legacy_warnings` is turned into an error (has been a warning for 3 years!)~~
- Fixes#63396 by forward-porting #64105 which now works thanks to added recovery.
- `ui-fulldeps/ast_stmt_expr_attr.rs` is turned into UI and pretty tests.
- Recovery is fixed for `#[attr] if expr {}`
r? @estebank
Rollup of 6 pull requests
Successful merges:
- #67130 (Const prop should finish propagation into user defined variables)
- #67163 (Split up ptr/mod.rs in libcore...)
- #67314 (Don't suppress move errors for union fields)
- #67392 (Fix unresolved type span inside async object)
- #67404 (Separate region inference logic from error handling better)
- #67428 (`is_binding_pat`: use explicit match & include or-pats in grammar)
Failed merges:
r? @ghost
Split up ptr/mod.rs in libcore...
...one with implementation detail for const ptr and the other with mut ptr
I am not sure if the "stable since 1.0.0" flags are the correct choice for the two additional mods.
Also, is it necessary for them to be "pub"? If so, there should be a good description for them.
Closes#66891
save LTO import info and check it when trying to reuse build products
Fix#59535
Previous runs of LTO optimization on the previous incremental build can import larger portions of the dependence graph into a codegen unit than the current compilation run is choosing to import. We need to take that into account when we choose to reuse PostLTO-optimization object files from previous compiler invocations.
This PR accomplishes that by serializing the LTO import information on each incremental build. We load up the previous LTO import data as well as the current LTO import data. Then as we decide whether to reuse previous PostLTO objects or redo LTO optimization, we check whether the LTO import data matches. After we finish with this decision process for every object, we write the LTO import data back to disk.
----
What is the scenario where comparing against past LTO import information is necessary?
I've tried to capture it in the comments in the regression test, but here's yet another attempt from me to summarize the situation:
1. Consider a call-graph like `[A] -> [B -> D] <- [C]` (where the letters are functions and the modules are enclosed in `[]`)
2. In our specific instance, the earlier compilations were inlining the call to`B` into `A`; thus `A` ended up with a external reference to the symbol `D` in its object code, to be resolved at subsequent link time. The LTO import information provided by LLVM for those runs reflected that information: it explicitly says during those runs, `B` definition and `D` declaration were imported into `[A]`.
3. The change between incremental builds was that the call `D <- C` was removed.
4. That change, coupled with other decisions within `rustc`, made the compiler decide to make `D` an internal symbol (since it was no longer accessed from other codegen units, this makes sense locally). And then the definition of `D` was inlined into `B` and `D` itself was eliminated entirely.
5. The current LTO import information reported that `B` alone is imported into `[A]` for the *current compilation*. So when the Rust compiler surveyed the dependence graph, it determined that nothing `[A]` imports changed since the last build (and `[A]` itself has not changed either), so it chooses to reuse the object code generated during the previous compilation.
6. But that previous object code has an unresolved reference to `D`, and that causes a link time failure!
----
The interesting thing is that its quite hard to actually observe the above scenario arising, which is probably why no one has noticed this bug in the year or so since incremental LTO support landed (PR #53673).
I've literally spent days trying to observe the bug on my local machine, but haven't managed to find the magic combination of factors to get LLVM and `rustc` to do just the right set of the inlining and `internal`-reclassification choices that cause this particular problem to arise.
----
Also, I have tried to be careful about injecting new bugs with this PR. Specifically, I was/am worried that we could get into a scenario where overwriting the current LTO import data with past LTO import data would cause us to "forget" a current import. ~~To guard against this, the PR as currently written always asserts, at overwrite time, that the past LTO import-set is a *superset* of the current LTO import-set. This way, the overwriting process should always be safe to run.~~
* The previous note was written based on the first version of this PR. It has since been revised to use a simpler strategy, where we never attempt to merge the past LTO import information into the current one. We just *compare* them, and act accordingly.
* Also, as you can see from the comments on the PR itself, I was quite right to be worried about forgetting past imports; that scenario was observable via a trivial transformation of the regression test I had devised.
Rollup of 5 pull requests
Successful merges:
- #64588 (Add a raw "address of" operator)
- #67031 (Update tokio crates to latest versions)
- #67131 (Merge `TraitItem` & `ImplItem into `AssocItem`)
- #67354 (Fix pointing at arg when cause is outside of call)
- #67363 (Fix handling of wasm import modules and names)
Failed merges:
r? @ghost
Fix handling of wasm import modules and names
The WebAssembly targets of rustc have weird issues around name mangling
and import the same name from different modules. This all largely stems
from the fact that we're using literal symbol names in LLVM IR to
represent what a function is called when it's imported, and we're not
using the wasm-specific `wasm-import-name` attribute. This in turn leads
to two issues:
* If, in the same codegen unit, the same FFI symbol is referenced twice
then rustc, when translating to LLVM IR, will only reference one
symbol from the first wasm module referenced.
* There's also a bug in LLD [1] where even if two codegen units
reference different modules, having the same symbol names means that
LLD coalesces the symbols and only refers to one wasm module.
Put another way, all our imported wasm symbols from the environment are
keyed off their LLVM IR symbol name, which has lots of collisions today.
This commit fixes the issue by implementing two changes:
1. All wasm symbols with `#[link(wasm_import_module = "...")]` are
mangled by default in LLVM IR. This means they're all given unique names.
2. Symbols then use the `wasm-import-name` attribute to ensure that the
WebAssembly file uses the correct import name.
When put together this should ensure we don't trip over the LLD bug [1]
and we also codegen IR correctly always referencing the right symbols
with the right import module/name pairs.
Closes#50021Closes#56309Closes#63562
[1]: https://bugs.llvm.org/show_bug.cgi?id=44316
Merge `TraitItem` & `ImplItem into `AssocItem`
In this PR we:
- Merge `{Trait,Impl}Item{Kind?}` into `AssocItem{Kind?}` as discussed in https://github.com/rust-lang/rust/issues/65041#issuecomment-538105286.
- This is done by using the cover grammar of both forms.
- In particular, it requires that we syntactically allow (under `#[cfg(FALSE)]`):
- `default`ness on `trait` items,
- `impl` items without a body / definition (`const`, `type`, and `fn`),
- and associated `type`s in `impl`s with bounds, e.g., `type Foo: Ord;`.
- The syntactic restrictions are replaced by semantic ones in `ast_validation`.
- Move syntactic restrictions around C-variadic parameters from the parser into `ast_validation`:
- `fn`s in all contexts now syntactically allow `...`,
- `...` can occur anywhere in the list syntactically (`fn foo(..., x: usize) {}`),
- and `...` can be the sole parameter (`fn foo(...) {}`.
r? @petrochenkov
