Forbid usage of `hir` `Infer` const/ty variants in ambiguous contexts
The feature `generic_arg_infer` allows providing `_` as an argument to const generics in order to infer them. This introduces a syntactic ambiguity as to whether generic arguments are type or const arguments. In order to get around this we introduced a fourth `GenericArg` variant, `Infer` used to represent `_` as an argument to generic parameters when we don't know if its a type or a const argument.
This made hir visitors that care about `TyKind::Infer` or `ConstArgKind::Infer` very error prone as checking for `TyKind::Infer`s in `visit_ty` would find *some* type infer arguments but not *all* of them as they would sometimes be lowered to `GenericArg::Infer` instead.
Additionally the `visit_infer` method would previously only visit `GenericArg::Infer` not *all* infers (e.g. `TyKind::Infer`), this made it very easy to override `visit_infer` and expect it to visit all infers when in reality it would only visit *some* infers.
---
This PR aims to fix those issues by making the `TyKind` and `ConstArgKind` types generic over whether the infer types/consts are represented by `Ty/ConstArgKind::Infer` or out of line (e.g. by a `GenericArg::Infer` or accessible by overiding `visit_infer`). We then make HIR Visitors convert all const args and types to the versions where infer vars are stored out of line and call `visit_infer` in cases where a `Ty`/`Const` would previously have had a `Ty/ConstArgKind::Infer` variant:
API Summary
```rust
enum AmbigArg {}
enum Ty/ConstArgKind<Unambig = ()> {
...
Infer(Unambig),
}
impl Ty/ConstArg {
fn try_as_ambig_ty/ct(self) -> Option<Ty/ConstArg<AmbigArg>>;
}
impl Ty/ConstArg<AmbigArg> {
fn as_unambig_ty/ct(self) -> Ty/ConstArg;
}
enum InferKind {
Ty(Ty),
Const(ConstArg),
Ambig(InferArg),
}
trait Visitor {
...
fn visit_ty/const_arg(&mut self, Ty/ConstArg<AmbigArg>) -> Self::Result;
fn visit_infer(&mut self, id: HirId, sp: Span, kind: InferKind) -> Self::Result;
}
// blanket impl'd, not meant to be overriden
trait VisitorExt {
fn visit_ty/const_arg_unambig(&mut self, Ty/ConstArg) -> Self::Result;
}
fn walk_unambig_ty/const_arg(&mut V, Ty/ConstArg) -> Self::Result;
fn walk_ty/const_arg(&mut V, Ty/ConstArg<AmbigArg>) -> Self::Result;
```
The end result is that `visit_infer` visits *all* infer args and is also the *only* way to visit an infer arg, `visit_ty` and `visit_const_arg` can now no longer encounter a `Ty/ConstArgKind::Infer`. Representing this in the type system means that it is now very difficult to mess things up, either accessing `TyKind::Infer` "just works" and you won't miss *some* type infers- or it doesn't work and you have to look at `visit_infer` or some `GenericArg::Infer` which forces you to think about the full complexity involved.
Unfortunately there is no lint right now about explicitly matching on uninhabited variants, I can't find the context for why this is the case 🤷♀️
I'm not convinced the framing of un/ambig ty/consts is necessarily the right one but I'm not sure what would be better. I somewhat like calling them full/partial types based on the fact that `Ty<Partial>`/`Ty<Full>` directly specifies how many of the type kinds are actually represented compared to `Ty<Ambig>` which which leaves that to the reader to figure out based on the logical consequences of it the type being in an ambiguous position.
---
tool changes have been modified in their own commits for easier reviewing by anyone getting cc'd from subtree changes. I also attempted to split out "bug fixes arising from the refactoring" into their own commit so they arent lumped in with a big general refactor commit
Fixes#112110
I ran across this message while writing code and thought it was quite
odd. I've simplified it and hopefully made it clearer for non-native
English speakers.
changelog: clarify message for non-obvious precedence
`manual_ok_or` covers the same case that were covered by
`option_map_or_err_ok` which is not deprecated. The latter was in the
"style" category. Also, the lint is machine applicable, and leads to
shorter and more readable code, so "style" is appropriate.
The only difference is that the η-expanded form of `Result::Ok()` was
not covered by `option_map_or_err_ok` while it is by `manual_ok_or`, so
the category change may expose some new occurrences.
Without this check, the lint would suggest that
```rust
match test {
true if option == 5 => 10,
_ => 1,
};
```
is replaced by `if test { 10 } else { 1 }`.
changelog: [`match_bool`]: omit suggestion when guards are present in
`match` expression
Before edition 2024, some temporaries used in scrutinees of a `match`
used as the last expression of a block may outlive some referenced local
variables. Prevent those cases from happening by checking that alive
temporaries with significant drop do have a static lifetime.
The check is performed only for edition 2021 and earlier, and for the
last statement if it would become the last expression of the block.
changelog: [`unnecessary_semicolon`]: prevent borrow errors in editions
lower than 2024
r? @y21
Using `Vec::extend(std::iter::repeat_n(item, N))` allows to use the more
natural number of elements to add `N`, as is probably done in the
original loop, instead of computing the difference between the existing
number of elements and the wanted one.
Before MSRV 1.82, the older suggestion to use `Vec::resize()` is still
issued.
Inspired by #6156 (which predates `repeat_n()`).
changelog: [`same_item_push`]: recommend using `Vec::extend()` to extend
a vector
Before edition 2024, some temporaries used in scrutinees in a `match`
used as the last expression of a block may outlive some referenced
local variables. Prevent those cases from happening by checking that
alive temporaries with significant drop do have a static lifetime.
The check is performed only for edition 2021 and earlier, and for the
last statement if it would become the last expression of the block.
- The lint no longer triggers if one of the operands in the boolean
expression comes from a macro expansion.
- Parenthesis are now removed inside the generated block if they are no
longer necessary.
- Error markers have been added.
changelog: [`short_circuit_statement`]: better handling of macros and
better looking suggestions
changelog: none
`x & 15 == 0` is not equivalent to `x.trailing_zeros() > 4`, as `x = 0b10000` is true for
the former and false for the latter.
In fact, clippy itself suggests the following:
```rust
pub fn src(x: i32) -> bool {
x & 15 == 0 // ~error: bit mask could be simplified with a call to `trailing_zeros`
^^^^^^^^^^^ help: try: `x.trailing_zeros() >= 4`
}
```
remove support for the (unstable) #[start] attribute
As explained by `@Noratrieb:`
`#[start]` should be deleted. It's nothing but an accidentally leaked implementation detail that's a not very useful mix between "portable" entrypoint logic and bad abstraction.
I think the way the stable user-facing entrypoint should work (and works today on stable) is pretty simple:
- `std`-using cross-platform programs should use `fn main()`. the compiler, together with `std`, will then ensure that code ends up at `main` (by having a platform-specific entrypoint that gets directed through `lang_start` in `std` to `main` - but that's just an implementation detail)
- `no_std` platform-specific programs should use `#![no_main]` and define their own platform-specific entrypoint symbol with `#[no_mangle]`, like `main`, `_start`, `WinMain` or `my_embedded_platform_wants_to_start_here`. most of them only support a single platform anyways, and need cfg for the different platform's ways of passing arguments or other things *anyways*
`#[start]` is in a super weird position of being neither of those two. It tries to pretend that it's cross-platform, but its signature is a total lie. Those arguments are just stubbed out to zero on ~~Windows~~ wasm, for example. It also only handles the platform-specific entrypoints for a few platforms that are supported by `std`, like Windows or Unix-likes. `my_embedded_platform_wants_to_start_here` can't use it, and neither could a libc-less Linux program.
So we have an attribute that only works in some cases anyways, that has a signature that's a total lie (and a signature that, as I might want to add, has changed recently, and that I definitely would not be comfortable giving *any* stability guarantees on), and where there's a pretty easy way to get things working without it in the first place.
Note that this feature has **not** been RFCed in the first place.
*This comment was posted [in May](https://github.com/rust-lang/rust/issues/29633#issuecomment-2088596042) and so far nobody spoke up in that issue with a usecase that would require keeping the attribute.*
Closes https://github.com/rust-lang/rust/issues/29633
try-job: x86_64-gnu-nopt
try-job: x86_64-msvc-1
try-job: x86_64-msvc-2
try-job: test-various
- The lint no longer triggers if the expression comes from macro
expansion
- Parenthesis are now removed inside the generated block if they are no
longer necessary.
This PR fixes an issue with the `significant_drop_in_scrutinee`, where
the lint generates invalid Rust syntax when suggesting fixes for match
expressions that are part of larger expressions, such as in assignment
contexts. For example:
```rust
let mutex = Mutex::new(State {});
let _ = match mutex.lock().unwrap().foo() {
true => 0,
false => 1,
};
```
would suggest:
```rust
let _ = let value = mutex.lock().unwrap().foo();
match value {
```
With this PR, it now suggests:
```rust
let value = mutex.lock().unwrap().foo();
let _ = match value {
```
closes: #13986
changelog: [`significant_drop_in_scrutinee`] Fix incorrect suggestion
for `significant_drop_in_scrutinee` lint in expression context
Without this check, the lint would suggest that
```rust
match test {
true if option == 5 => 10,
_ => 1,
};
```
is replaced by `if test { 10 } else { 1 }`.
This lint detects and removes the unnecessary semicolon after a `match`
or `if` statement returning `()`. It seems to be quite a common
"mistake", given the number of hits (88) we had in the Clippy sources
themselves.
The lint doesn't bother about loops, as `rustfmt` already removes the
extra semicolon. It doesn't handle blocks either, as an extra block
level, followed or not by a semicolon, is likely intentional.
I propose to put the lint in `pedantic`, as putting it in `style` seems
quite hazardous given the number of hits.
Note: there exists a `redundant-semicolon` lint in the compiler, but it
is an early lint and cannot check that the expression evaluates to `()`,
so it ignores the cases we're handling here.
----
changelog: [`unnecessary_semicolon`]: new lint
A multipart suggestion will be used whenever the method call can be
replaced by another one with the first argument removed. It helps place
the new method call in context, especially when it is part of a larger
expression.
This fixes#13995 by applying a suggestion made by @y21.
r? @y21
changelog: [`unnecessary_map_or`]: better representation of suggestions
by placing them in context
This PR changes literal_string_with_formatting_args category from
`suspicious` to `nursery` since there are thousands of false positive on
GitHub.
Closes#13989 since it's no longer problematic with such false positive
with ~~`pedantic`~~ `nursery` category.
changelog: [`literal_string_with_formatting_args` ] change category to
`nursery` from `suspicious`
A multipart suggestion will be used whenever the method call can be
replaced by another one with the first argument removed. It helps place
the new method call in context, especially when it is part of a larger
expression.
