match lowering: Clarify the main loop of the algorithm
Now that we expand or-patterns in a single place in the algorithm, we can move it (back) to the main part of the loop. This makes the call-graph of the main loop rather simple: `match_candidates` has three branches that each call back to `match_candidates`. The remaining tricky part is `finalize_or_candidate`.
I also factored out the whole "process a prefix of the candidates then process the rest" thing which I think helps legibility.
The first two commits are a fix for an indexing mistake I introduced in https://github.com/rust-lang/rust/pull/126553, already sumitted in https://github.com/rust-lang/rust/pull/127028 but feel free to merge this first.
r? `@matthewjasper`
Rollup of 8 pull requests
Successful merges:
- #124599 (Suggest borrowing on fn argument that is `impl AsRef`)
- #127572 (Don't mark `DEBUG_EVENT` struct as `repr(packed)`)
- #127588 (core: Limit remaining f16 doctests to x86_64 linux)
- #127591 (Make sure that labels are defined after the primary span in diagnostics)
- #127598 (Allows `#[diagnostic::do_not_recommend]` to supress trait impls in suggestions as well)
- #127599 (Rename `lazy_cell_consume` to `lazy_cell_into_inner`)
- #127601 (check is_ident before parse_ident)
- #127605 (Remove extern "wasm" ABI)
r? `@ghost`
`@rustbot` modify labels: rollup
Remove extern "wasm" ABI
Remove the unstable `extern "wasm"` ABI (`wasm_abi` feature tracked in #83788).
As discussed in https://github.com/rust-lang/rust/pull/127513#issuecomment-2220410679 and following, this ABI is a failed experiment that did not end up being used for anything. Keeping support for this ABI in LLVM 19 would require us to switch wasm targets to the `experimental-mv` ABI, which we do not want to do.
It should be noted that `Abi::Wasm` was internally used for two things: The `-Z wasm-c-abi=legacy` ABI that is still used by default on some wasm targets, and the `extern "wasm"` ABI. Despite both being `Abi::Wasm` internally, they were not the same. An explicit `extern "wasm"` additionally enabled the `+multivalue` feature.
I've opted to remove `Abi::Wasm` in this patch entirely, instead of keeping it as an ABI with only internal usage. Both `-Z wasm-c-abi` variants are now treated as part of the normal C ABI, just with different different treatment in
adjust_for_foreign_abi.
Allows `#[diagnostic::do_not_recommend]` to supress trait impls in suggestions as well
This commit changes the error reporting mechanism for not implemented traits to skip impl marked as `#[diagnostic::do_not_recommend]` in the help part of the error message ("the following other types implement trait `Foo`:"). The main use case here is to allow crate authors to skip non-meaningful confusing suggestions. A common example for this are fully generic impls on tuples.
Related to https://github.com/rust-lang/rust/issues/51992
r? `@compiler-errors`
Make sure that labels are defined after the primary span in diagnostics
Putting a `#[label]` before a `#[primary_span]` results in that label being overwritten, due to the semantics of `Diagnostic::span` and the fact that labels are stored in the `MultiSpan` of the diagnostic.
This isn't possible to fix in general, since a lot of code actually *relies* in this overwriting behavior (e.g. `rustc_on_unimplemented`). However, it's useful to enforce this for derive-diagnostics, since this is certainly never what you intend to do in a derived diagnostic, where all the fields are meaningful parts of the diagnostic being rendered.
This only matters for `#[label]`, since those are the ones stored in the `MultiSpan` of the error.
We could also make this "just work" by sorting the attrs or processing the primary span attr first, however I think it's kinda pointless to do.
There was 1 case where this mattered, but we literally didn't have a test exercising that diagnostic 🙃
Suggest borrowing on fn argument that is `impl AsRef`
When encountering a move conflict, on an expression that is `!Copy` passed as an argument to an `fn` that is `impl AsRef`, suggest borrowing the expression.
```
error[E0382]: use of moved value: `bar`
--> f204.rs:14:15
|
12 | let bar = Bar;
| --- move occurs because `bar` has type `Bar`, which does not implement the `Copy` trait
13 | foo(bar);
| --- value moved here
14 | let baa = bar;
| ^^^ value used here after move
|
help: borrow the value to avoid moving it
|
13 | foo(&bar);
| +
```
Fix#41708
Add `f16` and `f128` as simd types in LLVM
`@sayantn` is working on adding SIMD for `f16` and hitting the `FloatingPointVector` error. This should fix it and unblock adding support for `simd_fma` and `simd_fabs` in stdarch.
Avoid follow-up errors and ICEs after missing lifetime errors on data structures
Tuple struct constructors are functions, so when we call them typeck will use the signature tuple struct constructor function to provide type hints. Since typeck mostly ignores and erases lifetimes, we end up never seeing the error lifetime in writeback, thus not tainting the typeck result.
Now, we eagerly taint typeck results by tainting from `resolve_vars_if_possible`, which is called all over the place.
I did not carry over all the `crashes` test suite tests, as they are really all the same cause (missing or unknown lifetime names in tuple struct definitions or generic arg lists).
fixes#124262fixes#124083fixes#125155fixes#125888fixes#125992fixes#126666fixes#126648fixes#127268fixes#127266fixes#127304
Remove the unstable `extern "wasm"` ABI (`wasm_abi` feature tracked
in #83788).
As discussed in https://github.com/rust-lang/rust/pull/127513#issuecomment-2220410679
and following, this ABI is a failed experiment that did not end
up being used for anything. Keeping support for this ABI in LLVM 19
would require us to switch wasm targets to the `experimental-mv`
ABI, which we do not want to do.
It should be noted that `Abi::Wasm` was internally used for two
things: The `-Z wasm-c-abi=legacy` ABI that is still used by
default on some wasm targets, and the `extern "wasm"` ABI. Despite
both being `Abi::Wasm` internally, they were not the same. An
explicit `extern "wasm"` additionally enabled the `+multivalue`
feature.
I've opted to remove `Abi::Wasm` in this patch entirely, instead
of keeping it as an ABI with only internal usage. Both
`-Z wasm-c-abi` variants are now treated as part of the normal
C ABI, just with different different treatment in
adjust_for_foreign_abi.
Implement simple, unstable lint to suggest turning closure-of-async-block into async-closure
We want to eventually suggest people to turn `|| async {}` to `async || {}`. This begins doing that. It's a pretty rudimentary lint, but I wanted to get something down so I wouldn't lose the code.
Tracking:
* #62290
This commit changes the error reporting mechanism for not implemented
traits to skip impl marked as `#[diagnostic::do_not_recommend]` in the
help part of the error message ("the following other types implement
trait `Foo`:"). The main use case here is to allow crate authors to skip
non-meaningful confusing suggestions. A common example for this are
fully generic impls on tuples.
Make `visit_clobber`'s impl safe
This was originally introduced in #58061 but I didn't see any perf discussion about it, so let's see what perf says.
r? `@nnethercote`
instantiate higher ranked goals in candidate selection again
This reverts #119820 as that PR has a significant impact and breaks code which *feels like it should work*. The impact ended up being larger than we expected during the FCP and we've ended up with some ideas for how we can work around this issue in the next solver. This has been discussed in the previous high bandwidth t-types meeting: https://rust-lang.zulipchat.com/#narrow/stream/326132-t-types.2Fmeetings/topic/2024-07-09.20high.20bandwidth.20meeting.
We'll therefore keep this inconsistency between the two solvers for now and will have to deal with it before stabilizating the use of the new solver outside of coherence: https://github.com/rust-lang/trait-system-refactor-initiative/issues/120.
fixes#125194 after a beta-backport.
The pattern which is more widely used than expected and feels like it should work, especially without deep knowledge of the type system is
```rust
trait Trait<'a> {}
impl<'a, T> Trait<'a> for T {}
fn trait_bound<T: for<'a> Trait<'a>>() {}
// A function with a where-bound which is more restrictive than the impl.
fn function1<T: Trait<'static>>() {
// stable: ok
// with #119820: error as we prefer the where-bound over the impl
// with this PR: back to ok
trait_bound::<T>();
}
```
r? `@rust-lang/types`
This commit does the following.
- Pulls the code out of `AttrTokenStream::to_token_trees` into a new
function `attrs_and_tokens_to_token_trees`.
- Simplifies `TokenStream::from_ast` by calling the new function. This
is nicer than the old way, which created a temporary
`AttrTokenStream` containing a single `AttrsTarget` (which required
some cloning) just to call `to_token_trees` on it. (It is good to
remove this use of `AttrsTarget` which isn't related to `cfg_attr`
expansion.)
The new condition is equivalent in practice, but it's much more obvious
that it would result in an empty range, because the condition lines up
with the contents of the iterator.
Update `f16`/`f128` FIXMEs that needed `(NEG_)INFINITY`
Just a small fix to the pattern matching tests now that we can. Also contains a small unrelated comment tweak.
More trait error reworking
More work on #127492, specifically those sub-bullets under "Move trait error reporting to `error_reporting::traits`". Stacked on top of #127493.
This does introduce new `TypeErrCtxt.*Ext` traits, but those will be deleted soon. Splitting this work into bite-sized pieces is the only way that it's gonna be feasible to both author and review ❤️
r? lcnr
Automatically taint when reporting errors from ItemCtxt
This isn't very robust yet, as you need to use `itemctxt.dcx()` instead of `tcx.dcx()` for it to take effect, but it's at least more convenient than sprinkling `set_tainted_by_errors` calls in individual places.
based on https://github.com/rust-lang/rust/pull/127357
r? `@fmease`
[Coverage][MCDC] Group mcdc tests and fix panic when generating mcdc code for inlined expressions.
### Changes
1. Group all mcdc tests to one directory.
2. Since mcdc instruments different mappings for boolean expressions with normal branch coverage as #125766 introduces, it would be better also trace branch coverage results in mcdc tests.
3. So far rustc does not call `CoverageInfoBuilderMethods::init_coverage` for inlined functions. As a result, it could panic if it tries to instrument mcdc statements for inlined functions due to uninitialized cond bitmaps. We can reproduce this issue by current nightly rustc and [the test](https://github.com/rust-lang/rust/pull/127234/files#diff-c81af6bf4869aa42f5c7334e3e86344475de362f673f54ce439ec75fcb5ac3e5) with flag `--release`. This patch fixes it.
This is adding a migration lint for the current (in the 2021 edition and previous)
to move expr to expr_2021 from expr
Co-Developed-by: Eric Holk
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Fix regression in the MIR lowering of or-patterns
In https://github.com/rust-lang/rust/pull/126553 I made a silly indexing mistake and regressed the MIR lowering of or-patterns. This fixes it.
r? `@compiler-errors` because I'd like this to be merged quickly 🙏
Consolidate region error reporting in `rustc_infer`
More work on https://github.com/rust-lang/rust/issues/127492. Separate but important step, since I'm gonna likely pull everything else here into another module.
I don't think I'm confident whether `nice_region_error` should be a submodule of the new `rustc_infer::infer::error_reporting::region` module, so I left it alone for now.
r? lcnr
Move trait selection error reporting to its own top-level module
This effectively moves `rustc_trait_selection::traits::error_reporting` to `rustc_trait_selection::error_reporting::traits`. There are only a couple of actual changes to the code, like moving the `pretty_impl_header` fn out of the specialization module for privacy reasons.
This is quite pointless on its own, but having `error_reporting` as a top-level module in `rustc_trait_selection` is very important to make sure we have a meaningful file structure for when we move **type** error reporting (and region error reporting, with which it's incredibly entangled currently) into `rustc_trait_selection`. I've opened a tracking issue here: #127492
r? lcnr
Add Natvis visualiser and debuginfo tests for `f16`
To render `f16`s in debuggers on MSVC targets, this PR changes the compiler to output `f16`s as `struct f16 { bits: u16 }`, and includes a Natvis visualiser that manually converts the `f16`'s bits to a `float` which is can then be displayed by debuggers. `gdb`, `lldb` and `cdb` tests are also included for `f16` .
`f16`/`f128` MSVC debug info issue: #121837
Tracking issue: #116909
Infer async closure signature from (old-style) two-part `Fn` + `Future` bounds
When an async closure is passed to a function that has a "two-part" `Fn` and `Future` trait bound, like:
```rust
use std::future::Future;
fn not_exactly_an_async_closure(_f: F)
where
F: FnOnce(String) -> Fut,
Fut: Future<Output = ()>,
{}
```
The we want to be able to extract the signature to guide inference in the async closure, like:
```rust
not_exactly_an_async_closure(async |string| {
for x in string.split('\n') { ... }
//~^ We need to know that the type of `string` is `String` to call methods on it.
})
```
Closure signature inference will see two bounds: `<?F as FnOnce<Args>>::Output = ?Fut`, `<?Fut as Future>::Output = String`. We need to extract the signature by looking through both projections.
### Why?
I expect the ecosystem's move onto `async Fn` trait bounds (which are not affected by this PR, and already do signature inference fine) to be slow. In the mean time, I don't see major overhead to supporting this "old–style" of trait bounds that were used to model async closures.
r? oli-obk
Fixes#127468Fixes#127425
Make casts of pointers to trait objects stricter
This is an attempt to `fix` https://github.com/rust-lang/rust/issues/120222 and https://github.com/rust-lang/rust/issues/120217.
This is done by adding restrictions on casting pointers to trait objects.
Before this PR the rules were as follows:
> When casting `*const X<dyn A>` -> `*const Y<dyn B>`, principal traits in `A` and `B` must refer to the same trait definition (or no trait).
With this PR the rules are changed to
> When casting `*const X<dyn Src>` -> `*const Y<dyn Dst>`
> - if `Dst` has a principal trait `DstP`,
> - `Src` must have a principal trait `SrcP`
> - `dyn SrcP` and `dyn DstP` must be the same type (modulo the trait object lifetime, `dyn T+'a` -> `dyn T+'b` is allowed)
> - Auto traits in `Dst` must be a subset of auto traits in `Src`
> - Not adhering to this is currently a FCW (warn-by-default + `FutureReleaseErrorReportInDeps`), instead of an error
> - if `Src` has a principal trait `Dst` must as well
> - this restriction will be removed in a follow up PR
This ensures that
1. Principal trait's generic arguments match (no `*const dyn Tr<A>` -> `*const dyn Tr<B>` casts, which are a problem for [#120222](https://github.com/rust-lang/rust/issues/120222))
2. Principal trait's lifetime arguments match (no `*const dyn Tr<'a>` -> `*const dyn Tr<'b>` casts, which are a problem for [#120217](https://github.com/rust-lang/rust/issues/120217))
3. No auto traits can be _added_ (this is a problem for arbitrary self types, see [this comment](https://github.com/rust-lang/rust/pull/120248#discussion_r1463835350))
Some notes:
- We only care about the metadata/last field, so you can still cast `*const dyn T` to `*const WithHeader<dyn T>`, etc
- The lifetime of the trait object itself (`dyn A + 'lt`) is not checked, so you can still cast `*mut FnOnce() + '_` to `*mut FnOnce() + 'static`, etc
- This feels fishy, but I couldn't come up with a reason it must be checked
The diagnostics are currently not great, to say the least, but as far as I can tell this correctly fixes the issues.
cc `@oli-obk` `@compiler-errors` `@lcnr`
coverage: Extract hole spans from HIR instead of MIR
This makes it possible to treat more kinds of nested item/code as holes, instead of being restricted to closures.
(It also potentially opens up the possibility of using HIR holes to modify branch or MC/DC spans, though we currently don't actually do this.)
Thus, this new implementation treats the following as holes:
- Closures (as before, including `async` and coroutines)
- All nested items
- Inline `const` (because why not)
This gives more accurate coverage reports, because lines occupied by holes don't show the execution count from the enclosing function.
Fixes#126626.
Make `push_outlives_components` into a `TypeVisitor`
This involves removing the `visited: &mut SsoHashSet<GenericArg<'tcx>>` that is being passed around the `VerifyBoundCx`. The fact that we were using it when decomposing different type tests seems sketchy, so I don't think, though it may technically result in us registering more redundant outlives components 🤷
I did end up deleting some of the comments that referred back to RFC 1214 during this refactor. I can add them back if you think they were useful.
r? lcnr
There's a comment saying we don't do it for performance reasons, but it
doesn't actually affect performance.
The commit also tweaks the control flow, to make clearer that two code
paths are mutually exclusive.
Rollup of 10 pull requests
Successful merges:
- #126841 ([`macro_metavar_expr_concat`] Add support for literals)
- #126881 (Make `NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE` a deny-by-default lint in edition 2024)
- #126921 (Give VaList its own home)
- #127367 (Run alloc sync tests)
- #127431 (Use field ident spans directly instead of the full field span in diagnostics on local fields)
- #127437 (Uplift trait ref is knowable into `rustc_next_trait_solver`)
- #127439 (Uplift elaboration into `rustc_type_ir`)
- #127451 (Improve `run-make/output-type-permutations` code and improve `filename_not_in_denylist` API)
- #127452 (Fix intrinsic const parameter counting with `effects`)
- #127459 (rustdoc-json: add type/trait alias tests)
r? `@ghost`
`@rustbot` modify labels: rollup
Uplift elaboration into `rustc_type_ir`
Allows us to deduplicate and consolidate elaboration (including these stupid elaboration duplicate fns i added for pretty printing like 3 years ago) so I'm pretty hyped about this change :3
r? lcnr
Use field ident spans directly instead of the full field span in diagnostics on local fields
This improves diagnostics and avoids having to store the `DefId`s of fields
Make `NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE` a deny-by-default lint in edition 2024
I don't actually really care about this, but ``@traviscross`` asked me to do this, because lang team briefly discussed this before.
(TC here:)
Specifically, our original FCPed plan included this step:
- Add a lint against fallback affecting a generic that is passed to an `unsafe` function.
- Perhaps make this lint `deny-by-default` or a hard error in Rust 2024.
That is, we had left as an open question strengthening this in Rust 2024, and had marked it as an open question on the tracking issue. We're nominating here to address the open question. (Closing the remaining open question helps us to fully mark this off for Rust 2024.)
r? ``@compiler-errors``
Tracking:
- https://github.com/rust-lang/rust/issues/123748
[`macro_metavar_expr_concat`] Add support for literals
Adds support for things like `${concat($variable, 123)}` or `${concat("hello", "_world")}` .
cc #124225
Support tail calls in mir via `TerminatorKind::TailCall`
This is one of the interesting bits in tail call implementation — MIR support.
This adds a new `TerminatorKind` which represents a tail call:
```rust
TailCall {
func: Operand<'tcx>,
args: Vec<Operand<'tcx>>,
fn_span: Span,
},
```
*Structurally* this is very similar to a normal `Call` but is missing a few fields:
- `destination` — tail calls don't write to destination, instead they pass caller's destination to the callee (such that eventual `return` will write to the caller of the function that used tail call)
- `target` — similarly to `destination` tail calls pass the caller's return address to the callee, so there is nothing to do
- `unwind` — I _think_ this is applicable too, although it's a bit confusing
- `call_source` — `become` forbids operators and is not created as a lowering of something else; tail calls always come from HIR (at least for now)
It might be helpful to read the interpreter implementation to understand what `TailCall` means exactly, although I've tried documenting it too.
-----
There are a few `FIXME`-questions still left, ideally we'd be able to answer them during review ':)
-----
r? `@oli-obk`
cc `@scottmcm` `@DrMeepster` `@JakobDegen`
Cache hir_owner_nodes in ParentHirIterator.
Lint level computation may traverse deep HIR trees using that iterator. This calls `hir_owner_nodes` many times for the same HIR owner, which is wasterful.
This PR caches the value to allow a more efficient iteration scheme.
r? ghost for perf
Make `can_eq` process obligations (almost) everywhere
Move `can_eq` to an extension trait on `InferCtxt` in `rustc_trait_selection`, and change it so that it processes obligations. This should strengthen it to be more accurate in some cases, but is most important for the new trait solver which delays relating aliases to `AliasRelate` goals. Without this, we always basically just return true when passing aliases to `can_eq`, which can lead to weird errors, for example #127149.
I'm not actually certain if we should *have* `can_eq` be called on the good path. In cases where we need `can_eq`, we probably should just be using a regular probe.
Fixes#127149
r? lcnr
Emit a wrap expr span_bug only if context is not tainted
Fixes#127332
The ICE occurs because of this `span_bug`: 51917e2e69/compiler/rustc_hir_typeck/src/expr_use_visitor.rs (L732-L738)
which is triggered by the fact that we're trying to use an `enum` in a `with` expression instead of a `struct`.
The issue originates in commit 814bfe9335 from PR #127202. As per the title of that commit the ICEing code should not be reachable any more, but looks like it still is.
This PR changes the code so that the `span_bug` will be emitted only if the context is not tainted by a previous error.
Currently the second element is a `Vec<(FlatToken, Spacing)>`. But the
vector always has zero or one elements, and the `FlatToken` is always
`FlatToken::AttrTarget` (which contains an `AttributesData`), and the
spacing is always `Alone`. So we can simplify it to
`Option<AttributesData>`.
An assertion in `to_attr_token_stream` can can also be removed, because
`new_tokens.len()` was always 0 or 1, which means than `range.len()`
is always greater than or equal to it, because `range.is_empty()` is
always false (as per the earlier assertion).
The only place it is meaningfully used is in a panic message in
`TokenStream::from_ast`. But `node.span()` doesn't need to be printed
because `node` is also printed and it must contain the span.
Don't try to label `ObligationCauseCode::CompareImplItem` for an RPITIT, since it has no name
The old (current) trait solver has a limitation that when a where clause in param-env must be normalized using the same where clause, then we get spurious errors in `normalize_param_env_or_error`. I don't think there's an issue tracking it, but it's the root cause for many of the "fixed-by-next-solver" labeled issues.
Specifically, these errors may occur when checking predicate entailment of the GAT that comes out of desugaring RPITITs. Since we use `ObligationCauseCode::CompareImplItem` for these predicates, we try calling `item_name` on an RPITIT which fails, since the RPITIT has no name.
We simply suppress this logic when we're reporting a predicate entailment error for an RPITIT. RPITITs should never have predicate entailment errors, *by construction*, but they may due to this bug in the old solver.
Addresses the ICE in #127331, though doesn't fix the underlying issue (which is fundamental to the old solver).
r? types
Uplift outlives components to `rustc_type_ir`
We need this to uplift `push_outlives_components`, since the elaborator uses `push_outlives_components` to elaborate type outlives obligations and I want to uplift elaboration.
This ends up reworking and inlining a fair portion of the `GenericArg::walk_shallow` function, whose only callsite was this one. I believe I got the logic correct, but may be worthwhile to look at it closely just in case. Unfortunately github was too dumb to understand that this is a rename + change -- I could also rework the git history to split the "copy the file over" part from the actual logical changes if that makes this easier to review.
r? lcnr
Elaboration tweaks
Removes `Filter::OnlySelfThatDefines` and reimplements `transitive_bounds_that_define_assoc_item` as a separate function, since I don't want to have to uplift that mode since it's both an implementation detail (only exists to avoid cycles in astconv) and requires exposing `Ident` as an associated type on `Interner`.
r? lcnr
offset_from, offset: clearly separate safety requirements the user needs to prove from corollaries that automatically follow
By landing https://github.com/rust-lang/rust/pull/116675 we decided that objects larger than `isize::MAX` cannot exist in the address space of a Rust program, which lets us simplify these rules.
For `offset_from`, we can even state that the *absolute* distance fits into an `isize`, and therefore exclude `isize::MIN`. This PR also changes Miri to treat an `isize::MIN` difference like the other isize-overflowing cases.
Match ergonomics 2024: align with RFC again
- `&` matches `&mut` on old editions
- Add some more tests
r? ``@Nadrieril``
cc https://github.com/rust-lang/rust/issues/123076
``@rustbot`` label A-edition-2024 A-patterns
Added dots at the sentence ends of rustc AST doc
Just a tiny improvement for the AST documentation by bringing consistency to sentence ends. I intentionally didn't terminate every sentence, there are still some members not having them, but at least there's no mixing style on the type level.
Use `ControlFlow` results for visitors that are only looking for a single value
These visitors all had a `Option<Value>` or `bool` field, that, once set, was never unset or modified again. They have been refactored by removing the field and returning `ControlFlow` directly from the visitor
Split `SolverDelegate` back out from `InferCtxtLike`
This is because in order to uplift things like the `Generalizer` and other `TypeRelation`s, we want to be able to interface with `InferCtxtLike` (and `InferCtxt` as its implementation), rather that `SolverDelegate`, which only really exists as a hack to be able to define some downstream methods in `rustc_type_ir`.
r? lcnr
Improve well known value check-cfg diagnostic for the standard library
This PR adjust the current logic for hidding the rustc/Cargo suggestion to add a value to a well-known name to exclude the standard library and rustc crates.
This is done in order to improve the contributor experience, in particular when adding a new target, which often requires adding some cfgs like `target_os` which may not be available yet in stage0.
<details>
The diagnostic code would look like this.
```text
error: unexpected `cfg` condition value: `blable`
--> library/core/src/lib.rs:369:7
|
369 | #[cfg(target_os = "blable")]
| ^^^^^^^^^^^^^^^^^^^^
|
= note: expected values for `target_os` are: `aix`, `android`, `cuda`, `dragonfly`, `emscripten`, `espidf`, `freebsd`, `fuchsia`, `haiku`, `hermit`, `horizon`, `hurd`, `illumos`, `ios`, `l4re`, `linux`, `macos`, `netbsd`, `none`, `nto`, `openbsd`, `psp`, `redox`, `solaris`, `solid_asp3`, `teeos`, `tvos`, `uefi`, `unknown`, `visionos`, `vita`, `vxworks`, `wasi`, `watchos`, and `windows` and 2 more
= help: consider using a Cargo feature instead
= help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(target_os, values("blable"))'] }
= help: or consider adding `println!("cargo::rustc-check-cfg=cfg(target_os, values(\"blable\"))");` to the top of the `build.rs`
= note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
= note: `-D unexpected-cfgs` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(unexpected_cfgs)]`
```
</details>
Improve dead code analysis
Fixes#120770
1. check impl items later if self ty is private although the trait method is public, cause we must use the ty firstly if it's private
2. mark the adt live if it appears in pattern, like generic argument, this implies the use of the adt
3. based on the above, we can handle the case that private adts impl Default, so that we don't need adding rustc_trivial_field_reads on Default, and the logic in should_ignore_item
r? ``@pnkfelix``
