bors [Thu, 11 Feb 2021 13:44:00 +0000 (13:44 +0000)]
Auto merge of #81350 - tmiasko:instrument-debug, r=lcnr
Reduce log level used by tracing instrumentation from info to debug
Restore log level to debug to avoid make info log level overly verbose (the uses of instrument attribute modified there, were for the most part a replacement for `debug!`; one use was novel).
bors [Thu, 11 Feb 2021 04:40:57 +0000 (04:40 +0000)]
Auto merge of #81126 - oxalica:retain-early-drop, r=m-ou-se
Optimize Vec::retain
Use `copy_non_overlapping` instead of `swap` to reduce memory writes, like what we've done in #44355 and `String::retain`.
#48065 already tried to do this optimization but it is reverted in #67300 due to bad codegen of `DrainFilter::drop`.
This PR re-implement the drop-then-move approach. I did a [benchmark](https://gist.github.com/oxalica/3360eec9376f22533fcecff02798b698) on small-no-drop, small-need-drop, large-no-drop elements with different predicate functions. It turns out that the new implementation is >20% faster in average for almost all cases. Only 2/24 cases are slower by 3% and 5%. See the link above for more detail.
I think regression in may-panic cases is due to drop-guard preventing some optimization. If it's permitted to leak elements when predicate function of element's `drop` panic, the new implementation should be almost always faster than current one.
I'm not sure if we should leak on panic, since there is indeed an issue (#52267) complains about it before.
resolve: Remove visibility hacks for enum variants and trait items
Special treatment like this was necessary before `pub(restricted)` had been implemented and only two visibilities existed - `pub` and non-`pub`.
Now it's no longer necessary and the desired behavior follows from `pub(restricted)`-style visibilities naturally assigned to enum variants and trait items.
bors [Wed, 10 Feb 2021 07:10:43 +0000 (07:10 +0000)]
Auto merge of #81929 - pietroalbini:pgo-bootstrap, r=Mark-Simulacrum
Allow unstable features in some PGO benchmarks
Some of the benchmarks we're using for PGO require unstable features (such as compiling the standard library and some rustc-perf benchmarks), breaking CI on the beta and stable branches. For the past two releases we cherry-picked a commit directly onto the beta branch that unconditionally sets `RUSTC_BOOTSTRAP=1`, and this PR backports a similar change to the master branch.
The difference between this commit and the one we backported previously (483c1a83ca7cf53fd8f3432edb32cbe70ba39d45) is that this is more scoped in which benchmarks we allow unstable features, to prevent unintentionally enabling unstable features.
bors [Wed, 10 Feb 2021 03:30:17 +0000 (03:30 +0000)]
Auto merge of #81952 - JohnTitor:rollup-i28kgfb, r=JohnTitor
Rollup of 11 pull requests
Successful merges:
- #79849 (Clarify docs regarding sleep of zero duration)
- #80438 (Add `Box::into_inner`.)
- #81466 (Add suggest mut method for loop)
- #81687 (Make Vec::split_at_spare_mut public)
- #81904 (Bump stabilization version for const int methods)
- #81909 ([compiler/rustc_typeck/src/check/expr.rs] Remove unnecessary refs in pattern matching)
- #81910 (Use format string in bootstrap panic instead of a string directly)
- #81913 (Rename HIR UnOp variants)
- #81925 (Add long explanation for E0547)
- #81926 (add suggestion to use the `async_recursion` crate)
- #81951 (Update cargo)
Yuki Okushi [Wed, 10 Feb 2021 03:24:32 +0000 (12:24 +0900)]
Rollup merge of #81951 - ehuss:update-cargo, r=ehuss
Update cargo
5 commits in 34170fcd6e0947808a1ac63ac85ffc0da7dace2f..ab64d1393b5b77c66b6534ef5023a1b89ee7bf64
2021-02-04 15:52:52 +0000 to 2021-02-10 00:19:10 +0000
- Allow `true` and `false` as options for `strip` option (rust-lang/cargo#9153)
- Change git dependencies to use `HEAD` by default (rust-lang/cargo#9133)
- appendix auth gcm link to new repo (which is xplat) (rust-lang/cargo#9152)
- Fix warnings of the new non_fmt_panic lint (rust-lang/cargo#9148)
- Fix panic with doc collision orphan. (rust-lang/cargo#9142)
Yuki Okushi [Wed, 10 Feb 2021 03:24:28 +0000 (12:24 +0900)]
Rollup merge of #81913 - osa1:rename_unop_variants, r=matthewjasper
Rename HIR UnOp variants
This renames the variants in HIR UnOp from
enum UnOp {
UnDeref,
UnNot,
UnNeg,
}
to
enum UnOp {
Deref,
Not,
Neg,
}
Motivations:
- This is more consistent with the rest of the code base where most enum
variants don't have a prefix.
- These variants are never used without the `UnOp` prefix so the extra
`Un` prefix doesn't help with readability. E.g. we don't have any
`UnDeref`s in the code, we only have `UnOp::UnDeref`.
- MIR `UnOp` type variants don't have a prefix so this is more
consistent with MIR types.
- "un" prefix reads like "inverse" or "reverse", so as a beginner in
rustc code base when I see "UnDeref" what comes to my mind is
something like `&*` instead of just `*`.
Yuki Okushi [Wed, 10 Feb 2021 03:24:26 +0000 (12:24 +0900)]
Rollup merge of #81910 - jyn514:bootstrap-1.52, r=jackh726
Use format string in bootstrap panic instead of a string directly
This fixes the following warning when compiling with nightly:
```
warning: panic message is not a string literal
--> src/bootstrap/builder.rs:1515:24
|
1515 | panic!(out);
| ^^^
|
= note: `#[warn(non_fmt_panic)]` on by default
= note: this is no longer accepted in Rust 2021
help: add a "{}" format string to Display the message
|
1515 | panic!("{}", out);
| ^^^^^
help: or use std::panic::panic_any instead
|
1515 | std::panic::panic_any(out);
| ^^^^^^^^^^^^^^^^^^^^^^
```
Found while working on https://github.com/rust-lang/rust/pull/79540. cc https://github.com/rust-lang/rust/pull/81645, which landed in 1.51.
The method returns 2 slices, one slice references the content of the vector,
and the other references the remaining spare capacity.
The method was previously implemented while adding `Vec::extend_from_within` in #79015,
and used to implement `Vec::spare_capacity_mut` (as the later is just a
subset of former one).
See also previous [discussion in `Vec::spare_capacity_mut` tracking issue](https://github.com/rust-lang/rust/issues/75017#issuecomment-770381335).
## Unresolved questions
- [ ] Should we consider changing the name? `split_at_spare_mut` doesn't seem like an intuitive name
- [ ] Should we deprecate `Vec::spare_capacity_mut`? Any usecase of `Vec::spare_capacity_mut` can be replaced with `Vec::split_at_spare_mut` (but not vise-versa)
Yuki Okushi [Wed, 10 Feb 2021 03:24:19 +0000 (12:24 +0900)]
Rollup merge of #80438 - crlf0710:box_into_inner, r=m-ou-se
Add `Box::into_inner`.
This adds a `Box::into_inner` method to the `Box` type. <del>I actually suggest deprecating the compiler magic of `*b` if this gets stablized in the future.</del>
bors [Tue, 9 Feb 2021 21:28:58 +0000 (21:28 +0000)]
Auto merge of #81132 - bugadani:map-prealloc, r=matthewjasper
Borrowck: refactor visited map to a bitset
This PR refactors `Borrows` and the `precompute_borrows_out_of_scope` function so that this initial phase has a much reduced memory pressure. This is achieved by reducing what is stored on the heap, and also reusing heap memory as much as possible.
bors [Tue, 9 Feb 2021 18:37:33 +0000 (18:37 +0000)]
Auto merge of #81892 - jyn514:no-inline, r=cjgillot
[experiment] remove `#[inline]` from rustc_query_system::plumbing
These functions have a ton of generic parameters and are instantiated
over and over again. Hopefully this will reduce binary bloat and speed
up bootstrapping times.
bors [Tue, 9 Feb 2021 15:28:28 +0000 (15:28 +0000)]
Auto merge of #79540 - jyn514:no-xpy, r=Mark-Simulacrum
Allow building rustdoc without first building rustc (MVP)
## Motivation
The compile times for rustc are extremely long and a major issue for
recruiting new contributors to rustdoc. People interested in joining
often give up after running into issues with submodules or python
versions. stage1 rustdoc fundamentally doesn't care about bootstrapping
or stages, it just needs `rustc_private` available.
## Summary of Changes
- Add an opt-in `[rust] download_rustc` option
- Determine the version of the compiler to download using `log --author=bors`
- Do no work for any component other than `Rustdoc` for any stage. Instead, copy the CI artifacts from the downloaded sysroot stage0/ to stage0-sysroot/ or stage1/ in `Sysroot`. This is done with an `ENABLE_DOWNLOAD_STAGE1` constant which is off by default.
- Don't download different versions of rustfmt or cargo - those should still use the beta version (rustfmt especially).
The vast majority of work is done in bootstrap.py, which downloads the artifacts and extracts them to stage0/ in place of the beta compiler. Rustbuild just takes care of copying the artifacts to stage1 if necessary.
## Future work
- I turned off verification for the commit tarballs because the .sha256 URLs gave a 404. This seems not ideal, it would be nice to start signing them.
- This will break if you rebase an old enough branch (I think commits are kept at most 160 days?). This doesn't need to be supported, but it would be nice to give a reasonable error. https://github.com/rust-lang/rust/pull/79540#issuecomment-751481291
- Right now, every time you rebase, stage0 tools (bootstrap, tidy, ...) will have to be recompiled. Additionally running `x.py setup tools` will compile rustbuild twice. Instead, this should download a separate beta compiler for stage0 and only use CI artifacts for stage1 onward. https://github.com/rust-lang/rust/pull/79540#issuecomment-757047321
- Add `x.py setup tools` to enable this conveniently (it doesn't make sense to use this for compiler developers). https://github.com/jyn514/rust/commit/cb5d8c85226c501bf9deb39082a08af0ebfae850
- Compile a new version of tracing so that rustdoc still gets debug logging (since CI artifacts always disable `debug` and `trace` logging). https://github.com/rust-lang/rust/pull/79540#issuecomment-742756411, https://github.com/jyn514/rust/commit/6a5d5124209bec7652e745725a995bd77bb3f881
- Right now only rustdoc is ever rebuilt. This is not ideal and should probably at least compile compiler tools (rustfmt, clippy, miri). https://github.com/rust-lang/rust/pull/79540#issuecomment-775634693
- Using `git log --author=bors` sometimes breaks. This should use `git merge-base` instead. https://github.com/rust-lang/rust/pull/79540#discussion_r572572280
- It would be nice to support cross-compiling the standard library. Right now this gives an assertion failure I think.
bors [Tue, 9 Feb 2021 08:47:38 +0000 (08:47 +0000)]
Auto merge of #81384 - tmiasko:partial-ord, r=petrochenkov
Fix derived PartialOrd operators
The derived implementation of `partial_cmp` compares matching fields one
by one, stopping the computation when the result of a comparison is not
equal to `Some(Equal)`.
On the other hand the derived implementation for `lt`, `le`, `gt` and
`ge` continues the computation when the result of a field comparison is
`None`, consequently those operators are not transitive and inconsistent
with `partial_cmp`.
Fix the inconsistency by using the default implementation that fall-backs
to the `partial_cmp`. This also avoids creating very deeply nested
closures that were quite costly to compile.
- This is more consistent with the rest of the code base where most enum
variants don't have a prefix.
- These variants are never used without the `UnOp` prefix so the extra
`Un` prefix doesn't help with readability. E.g. we don't have any
`UnDeref`s in the code, we only have `UnOp::UnDeref`.
- MIR `UnOp` type variants don't have a prefix so this is more
consistent with MIR types.
- "un" prefix reads like "inverse" or "reverse", so as a beginner in
rustc code base when I see "UnDeref" what comes to my mind is
something like "&*" instead of just "*".
bors [Tue, 9 Feb 2021 05:57:18 +0000 (05:57 +0000)]
Auto merge of #81905 - Dylan-DPC:rollup-mxpz1j7, r=Dylan-DPC
Rollup of 11 pull requests
Successful merges:
- #72209 (Add checking for no_mangle to unsafe_code lint)
- #80732 (Allow Trait inheritance with cycles on associated types take 2)
- #81697 (Add "every" as a doc alias for "all".)
- #81826 (Prefer match over combinators to make some Box methods inlineable)
- #81834 (Resolve typedef in HashMap lldb pretty-printer only if possible)
- #81841 ([rustbuild] Output rustdoc-json-types docs )
- #81849 (Expand the docs for ops::ControlFlow a bit)
- #81876 (parser: Fix panic in 'const impl' recovery)
- #81882 (:arrow_up: rust-analyzer)
- #81888 (Fix pretty printer macro_rules with semicolon.)
- #81896 (Remove outdated comment in windows' mutex.rs)
Joshua Nelson [Fri, 22 Jan 2021 05:31:17 +0000 (00:31 -0500)]
Absolute bare minimum for downloading rustc from CI
- Use the same compiler for stage0 and stage1. This should be fixed at
some point (so bootstrap isn't constantly rebuilt).
- Make sure `x.py build` and `x.py check` work.
- Use `git merge-base` to determine the most recent commit to download.
- Copy stage0 to the various sysroots in `Sysroot`, and delegate to
Sysroot in Assemble. Leave all other code unchanged.
- Rename date -> key
This can also be a commit hash, so 'date' is no longer a good name.
- Add the commented-out option to config.toml.example
- Disable all steps by default when `download-rustc` is enabled
Most steps don't make sense when downloading a compiler, because they'll
be pre-built in the sysroot. Only enable the ones that might be useful,
in particular Rustdoc and all `check` steps.
At some point, this should probably enable other tools, but rustdoc is
enough to test out `download-rustc`.
- Don't print 'Skipping' twice in a row
Bootstrap forcibly enables a dry run if it isn't already set, so
previously it would print the message twice:
```
Skipping bootstrap::compile::Std because it is not enabled for `download-rustc`
Skipping bootstrap::compile::Std because it is not enabled for `download-rustc`
```
Now it correctly only prints once.
## Future work
- Add FIXME about supporting beta commits
- Debug logging will never work. This should be fixed.
Joshua Nelson [Tue, 9 Feb 2021 03:51:21 +0000 (22:51 -0500)]
Use format string in bootstrap panic instead of a string directly
This fixes the following warning when compiling with nightly:
```
warning: panic message is not a string literal
--> src/bootstrap/builder.rs:1515:24
|
1515 | panic!(out);
| ^^^
|
= note: `#[warn(non_fmt_panic)]` on by default
= note: this is no longer accepted in Rust 2021
help: add a "{}" format string to Display the message
|
1515 | panic!("{}", out);
| ^^^^^
help: or use std::panic::panic_any instead
|
1515 | std::panic::panic_any(out);
| ^^^^^^^^^^^^^^^^^^^^^^
```
Dylan DPC [Tue, 9 Feb 2021 01:40:06 +0000 (02:40 +0100)]
Rollup merge of #81896 - m-ou-se:oudated-comment, r=Mark-Simulacrum
Remove outdated comment in windows' mutex.rs
After https://github.com/rust-lang/rust/pull/81250, this `Mutex` no longer falls back to the `ReentrantMutex` implementation, so this comment is no longer relevant.
Dylan DPC [Tue, 9 Feb 2021 01:40:05 +0000 (02:40 +0100)]
Rollup merge of #81888 - ehuss:macro_rules-pp, r=petrochenkov
Fix pretty printer macro_rules with semicolon.
The pretty printer was not including the trailing semicolon for a macro_rules definition that used parenthesis or brackets, which results in invalid code. This adds the semicolon in those two cases.
Dylan DPC [Tue, 9 Feb 2021 01:40:01 +0000 (02:40 +0100)]
Rollup merge of #81876 - osa1:issue81806, r=matthewjasper
parser: Fix panic in 'const impl' recovery
The panic happens when in recovery parsing a full `impl`
(`parse_item_impl`) fails and we drop the `DiagnosticBuilder` for the
recovery suggestion and return the `parse_item_impl` error.
We now raise the original error "expected identifier found `impl`" when
parsing the `impl` fails.
Note that the regression test is slightly simplified version of the
original repro in #81806, to make the error output smaller and more
resilient to unrelated changes in parser error messages.
Previously, `GetTypedefedType` was invoked unconditionally.
But this did not work in case of `rust-lldb` without Rust patches since there was no typedef.
Dylan DPC [Tue, 9 Feb 2021 01:39:50 +0000 (02:39 +0100)]
Rollup merge of #80732 - spastorino:trait-inheritance-self2, r=nikomatsakis
Allow Trait inheritance with cycles on associated types take 2
This reverts the revert of #79209 and fixes the ICEs that's occasioned by that PR exposing some problems that are addressed in #80648 and #79811.
For easier review I'd say, check only the last commit, the first one is just a revert of the revert of #79209 which was already approved.
This also could be considered part or the actual fix of #79560 but I guess for that to be closed and fixed completely we would need to land #80648 and #79811 too.
Tomasz Miąsko [Mon, 25 Jan 2021 00:00:00 +0000 (00:00 +0000)]
Fix derived PartialOrd operators
The derived implementation of `partial_cmp` compares matching fields one
by one, stopping the computation when the result of a comparison is not
equal to `Some(Equal)`.
On the other hand the derived implementation for `lt`, `le`, `gt` and
`ge` continues the computation when the result of a field comparison is
`None`, consequently those operators are not transitive and inconsistent
with `partial_cmp`.
Fix the inconsistency by using the default implementation that fall-backs
to the `partial_cmp`. This also avoids creating very deeply nested
closures that were quite costly to compile.
Joshua Nelson [Mon, 8 Feb 2021 19:57:15 +0000 (14:57 -0500)]
[experiment] remove `#[inline]` from rustc_query_system::plumbing
These functions have a ton of generic parameters and are instantiated
over and over again. Hopefully this will reduce binary bloat and speed
up bootstrapping times.
Mara Bos [Mon, 8 Feb 2021 18:28:15 +0000 (19:28 +0100)]
Rollup merge of #81735 - klensy:span-fix, r=varkor
faster few span methods
Touched few methods, so it should be (hopefully) faster.
First two changes: instead splitting string from start and taking only last piece, split it from the end.
Last: swapped conditions, to first check boolean parameter.
bors [Mon, 8 Feb 2021 10:46:10 +0000 (10:46 +0000)]
Auto merge of #81313 - LeSeulArtichaut:revert-32558, r=jyn514
Restore linking to itself in implementors section of trait page
Reverts #32558 as proposed in [this Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/Trait.20implementation.20self-links/near/223773273)
r? `@jyn514` cc `@camelid`
bors [Mon, 8 Feb 2021 07:56:04 +0000 (07:56 +0000)]
Auto merge of #79245 - ssomers:btree_curb_ord_bound, r=dtolnay
BTree: remove Ord bound where it is absent elsewhere
Some btree methods don't really need an Ord bound and don't have one, while some methods that more obviously don't need it, do have one.
An example of the former is `iter`, even though it explicitly exposes the work of the Ord implementation (["sorted by key"](https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.iter) - but I'm not suggesting it should have the Ord bound). An example of the latter is `new`, which doesn't involve any keys whatsoever.
The panic happens when in recovery parsing a full `impl`
(`parse_item_impl`) fails and we drop the `DiagnosticBuilder` for the
recovery suggestion and return the `parse_item_impl` error.
We now raise the original error "expected identifier found `impl`" when
parsing the `impl` fails.
Note that the regression test is slightly simplified version of the
original repro in #81806, to make the error output smaller and more
resilient to unrelated changes in parser error messages.
These can all be implemented on the current stable (1.49). There are two unstable details: const likely/unlikely and unchecked division/remainder. Both of these are for optimizations, and are in no way required to make the methods function; there is no exposure of these details publicly. Per comments below, it seems best practice is to stabilize the intrinsics. As such, `intrinsics::unchecked_div` and `intrinsics::unchecked_rem` have been stabilized as `const` as part of this pull request as well. The methods themselves remain unstable.
I believe part of the reason these were not stabilized previously was the behavior around division by 0 and modulo 0. After testing on nightly, the diagnostic for something like `const _: i8 = 5i8 % 0i8;` is similar to that of `const _: i8 = 5i8.rem_euclid(0i8);` (assuming the appropriate feature flag is enabled). As such, I believe these methods are ready to be stabilized as `const fn`.
This pull request represents the final methods mentioned in #53718. As such, this PR closes #53718.
bors [Mon, 8 Feb 2021 02:23:17 +0000 (02:23 +0000)]
Auto merge of #72603 - jsgf:extern-loc, r=nikomatsakis
Implement `--extern-location`
This PR implements `--extern-location` as a followup to #72342 as part of the implementation of #57274. The goal of this PR is to allow rustc, in coordination with the build system, to present a useful diagnostic about how to remove an unnecessary dependency from a dependency specification file (eg Cargo.toml).
EDIT: Updated to current PR state.
The location is specified for each named crate - that is, for a given `--extern foo[=path]` there can also be `--extern-location foo=<location>`. It supports ~~three~~ two styles of location:
~~1. `--extern-location foo=file:<path>:<line>` - a file path and line specification
1. `--extern-location foo=span:<path>:<start>:<end>` - a span specified as a file and start and end byte offsets~~
1. `--extern-location foo=raw:<anything>` - a raw string which is included in the output
1. `--extern-location foo=json:<anything>` - an arbitrary Json structure which is emitted via Json diagnostics in a `tool_metadata` field.
~~1 & 2 are turned into an internal `Span`, so long as the path exists and is readable, and the location is meaningful (within the file, etc). This is used as the `Span` for a fix suggestion which is reported like other fix suggestions.~~
`raw` and `json` are for the case where the location isn't best expressed as a file and location within that file. For example, it could be a rule name and the name of a dependency within that rule. `rustc` makes no attempt to parse the raw string, and simply includes it in the output diagnostic text. `json` is only included in json diagnostics. `raw` is emitted as text and also as a json string in `tool_metadata`.
If no `--extern-location` option is specified then it will emit a default json structure consisting of `{"name": name, "path": path}` corresponding to the name and path in `--extern name=path`.
This is a prototype/RFC to make some of the earlier conversations more concrete. It doesn't stand on its own - it's only useful if implemented by Cargo and other build systems. There's also a ton of implementation details which I'd appreciate a second eye on as well.
~~**NOTE** The first commit in this PR is #72342 and should be ignored for the purposes of review. The first commit is a very simplistic implementation which is basically raw-only, presented as a MVP. The second implements the full thing, and subsequent commits are incremental fixes.~~
...so we can skip serializing `tool_metadata` if it hasn't been set.
This makes the output a bit cleaner, and avoiding having to update a
bunch of unrelated tests.
Add `--extern-loc` to augment unused crate dependency diagnostics
This allows a build system to indicate a location in its own dependency
specification files (eg Cargo's `Cargo.toml`) which can be reported
along side any unused crate dependency.
This supports several types of location:
- 'json' - provide some json-structured data, which is included in the json diagnostics
in a `tool_metadata` field
- 'raw' - emit the provided string into the output. This also appears as a json string in
`tool_metadata`.
If no `--extern-location` is explicitly provided then a default json entry of the form
`"tool_metadata":{"name":<cratename>,"path":<cratepath>}` is emitted.
bors [Sun, 7 Feb 2021 22:25:14 +0000 (22:25 +0000)]
Auto merge of #80652 - calebzulawski:simd-lanes, r=nagisa
Improve SIMD type element count validation
Resolves rust-lang/stdsimd#53.
These changes are motivated by `stdsimd` moving in the direction of const generic vectors, e.g.:
```rust
#[repr(simd)]
struct SimdF32<const N: usize>([f32; N]);
```
This makes a few changes:
* Establishes a maximum SIMD lane count of 2^16 (65536). This value is arbitrary, but attempts to validate lane count before hitting potential errors in the backend. It's not clear what LLVM's maximum lane count is, but cranelift's appears to be much less than `usize::MAX`, at least.
* Expands some SIMD intrinsics to support arbitrary lane counts. This resolves the ICE in the linked issue.
* Attempts to catch invalid-sized vectors during typeck when possible.
Unresolved questions:
* Generic-length vectors can't be validated in typeck and are only validated after monomorphization while computing layout. This "works", but the errors simply bail out with no context beyond the name of the type. Should these errors instead return `LayoutError` or otherwise provide context in some way? As it stands, users of `stdsimd` could trivially produce monomorphization errors by making zero-length vectors.
Dániel Buga [Sun, 17 Jan 2021 20:20:21 +0000 (21:20 +0100)]
Optimize Borrows
Reuse as much memory as possible, reduce number of allocations.
Use BitSet instead of a HashMap, since only a single bit of
information was used as the map's value.
bors [Sun, 7 Feb 2021 19:36:10 +0000 (19:36 +0000)]
Auto merge of #79078 - petrochenkov:derattr, r=Aaron1011
expand/resolve: Turn `#[derive]` into a regular macro attribute
This PR turns `#[derive]` into a regular attribute macro declared in libcore and defined in `rustc_builtin_macros`, like it was previously done with other "active" attributes in https://github.com/rust-lang/rust/pull/62086, https://github.com/rust-lang/rust/pull/62735 and other PRs.
This PR is also a continuation of #65252, #69870 and other PRs linked from them, which layed the ground for converting `#[derive]` specifically.
`#[derive]` still asks `rustc_resolve` to resolve paths inside `derive(...)`, and `rustc_expand` gets those resolution results through some backdoor (which I'll try to address later), but otherwise `#[derive]` is treated as any other macro attributes, which simplifies the resolution-expansion infra pretty significantly.
The change has several observable effects on language and library.
Some of the language changes are **feature-gated** by [`feature(macro_attributes_in_derive_output)`](https://github.com/rust-lang/rust/issues/81119).
#### Library
- `derive` is now available through standard library as `{core,std}::prelude::v1::derive`.
#### Language
- `derive` now goes through name resolution, so it can now be renamed - `use derive as my_derive; #[my_derive(Debug)] struct S;`.
- `derive` now goes through name resolution, so this resolution can fail in corner cases. Crater found one such regression, where import `use foo as derive` goes into a cycle with `#[derive(Something)]`.
- **[feature-gated]** `#[derive]` is now expanded as any other attributes in left-to-right order. This allows to remove the restriction on other macro attributes following `#[derive]` (https://github.com/rust-lang/reference/issues/566). The following macro attributes become a part of the derive's input (this is not a change, non-macro attributes following `#[derive]` were treated in the same way previously).
- `#[derive]` is now expanded as any other attributes in left-to-right order. This means two derive attributes `#[derive(Foo)] #[derive(Bar)]` are now expanded separately rather than together. It doesn't generally make difference, except for esoteric cases. For example `#[derive(Foo)]` can now produce an import bringing `Bar` into scope, but previously both `Foo` and `Bar` were required to be resolved before expanding any of them.
- **[feature-gated]** `#[derive()]` (with empty list in parentheses) actually becomes useful. For historical reasons `#[derive]` *fully configures* its input, eagerly evaluating `cfg` everywhere in its target, for example on fields.
Expansion infra doesn't do that for other attributes, but now when macro attributes attributes are allowed to be written after `#[derive]`, it means that derive can *fully configure* items for them.
```rust
#[derive()]
#[my_attr]
struct S {
#[cfg(FALSE)] // this field in removed by `#[derive()]` and not observed by `#[my_attr]`
field: u8
}
```
- `#[derive]` on some non-item targets is now prohibited. This was accidentally allowed as noop in the past, but was warned about since early 2018 (#50092), despite that crater found a few such cases in unmaintained crates.
- Derive helper attributes used before their introduction are now reported with a deprecation lint. This change is long overdue (since macro modularization, https://github.com/rust-lang/rust/issues/52226#issuecomment-422605033), but it was hard to do without fixing expansion order for derives. The deprecation is tracked by #79202.
```rust
#[trait_helper] // warning: derive helper attribute is used before it is introduced
#[derive(Trait)]
struct S {}
```
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