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Lint against expressions that unnecessarily create references #127724
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A-lints
Area: Lints (warnings about flaws in source code) such as unused_mut.
T-compiler
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Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang#127679 (comment) for rationale - Implementation: rust-lang#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang#64490 cc `@rust-lang/lang` `@rust-lang/opsem` try-job: x86_64-msvc try-job: i686-mingw try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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Aug 18, 2024
Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang#127679 (comment) for rationale - Implementation: rust-lang#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang#64490 cc `@rust-lang/lang` `@rust-lang/opsem` // try-job: i686-mingw // `dump-ice-to-disk` is flaky try-job: x86_64-msvc try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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…,jieyouxu Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang#127679 (comment) for rationale - Implementation: rust-lang#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang#64490 cc `@rust-lang/lang` `@rust-lang/opsem` try-job: x86_64-msvc try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang#127679 (comment) for rationale - Implementation: rust-lang#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang#64490 cc `@rust-lang/lang` `@rust-lang/opsem` try-job: x86_64-msvc try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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Rollup merge of rust-lang#127679 - RalfJung:raw_ref_op, r=jieyouxu Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang#127679 (comment) for rationale - Implementation: rust-lang#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang#64490 cc `@rust-lang/lang` `@rust-lang/opsem` try-job: x86_64-msvc try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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Stabilize `raw_ref_op` (RFC 2582) This stabilizes the syntax `&raw const $expr` and `&raw mut $expr`. It has existed unstably for ~4 years now, and has been exposed on stable via the `addr_of` and `addr_of_mut` macros since Rust 1.51 (released more than 3 years ago). I think it has become clear that these operations are here to stay. So it is about time we give them proper primitive syntax. This has two advantages over the macro: - Being macros, `addr_of`/`addr_of_mut` could in theory do arbitrary magic with the expression on which they work. The only "magic" they actually do is using the argument as a place expression rather than as a value expression. Place expressions are already a subtle topic and poorly understood by many programmers; having this hidden behind a macro using unstable language features makes this even worse. Conversely, people do have an idea of what happens below `&`/`&mut`, so we can make the subtle topic a lot more approachable by connecting to existing intuition. - The name `addr_of` is quite unfortunate from today's perspective, given that we have accepted provenance as a reality, which means that a pointer is *not* just an address. Strict provenance has a method, `addr`, which extracts the address of a pointer; using the term `addr` in two different ways is quite unfortunate. That's why this PR soft-deprecates `addr_of` -- we will wait a long time before actually showing any warning here, but we should start telling people that the "addr" part of this name is somewhat misleading, and `&raw` avoids that potential confusion. In summary, this syntax improves developers' ability to conceptualize the operational semantics of Rust, while making a fundamental operation frequently used in unsafe code feel properly built in. Possible questions to consider, based on the RFC and [this](rust-lang/rust#64490 (comment)) great summary by `@CAD97:` - Some questions are entirely about the semantics. The semantics are the same as with the macros so I don't think this should have any impact on this syntax PR. Still, for completeness' sake: - Should `&raw const *mut_ref` give a read-only pointer? - Tracked at: rust-lang/unsafe-code-guidelines#257 - I think ideally the answer is "no". Stacked Borrows says that pointer is read-only, but Tree Borrows says it is mutable. - What exactly does `&raw const (*ptr).field` require? Answered in [the reference](https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html): the arithmetic to compute the field offset follows the rules of `ptr::offset`, making it UB if it goes out-of-bounds. Making this a safe operation (using `wrapping_offset` rules) is considered too much of a loss for alias analysis. - Choose a different syntax? I don't want to re-litigate the RFC. The only credible alternative that has been proposed is `&raw $place` instead of `&raw const $place`, which (IIUC) could be achieved by making `raw` a contextual keyword in a new edition. The type is named `*const T`, so the explicit `const` is consistent in that regard. `&raw expr` lacks the explicit indication of immutability. However, `&raw const expr` is quite a but longer than `addr_of!(expr)`. - Shouldn't we have a completely new, better raw pointer type instead? Yes we all want to see that happen -- but I don't think we should block stabilization on that, given that such a nicer type is not on the horizon currently and given the issues with `addr_of!` mentioned above. (If we keep the `&raw $place` syntax free for this, we could use it in the future for that new type.) - What about the lint the RFC talked about? It hasn't been implemented yet. Given that the problematic code is UB with or without this stabilization, I don't think the lack of the lint should block stabilization. - I created an issue to track adding it: rust-lang/rust#127724 - Other points from the "future possibilites of the RFC - "Syntactic sugar" extension: this has not been implemented. I'd argue this is too confusing, we should stick to what the RFC suggested and if we want to do anything about such expressions, add the lint. - Encouraging / requiring `&raw` in situations where references are often/definitely incorrect: this has been / is being implemented. On packed fields this already is a hard error, and for `static mut` a lint suggesting raw pointers is being rolled out. - Lowering of casts: this has been implemented. (It's also an invisible implementation detail.) - `offsetof` woes: we now have native `offset_of` so this is not relevant any more. To be done before landing: - [x] Suppress `unused_parens` lint around `&raw {const|mut}` expressions - See bottom of rust-lang/rust#127679 (comment) for rationale - Implementation: rust-lang/rust#128782 - [ ] Update the Reference. - rust-lang/reference#1567 Fixes rust-lang/rust#64490 cc `@rust-lang/lang` `@rust-lang/opsem` try-job: x86_64-msvc try-job: test-various try-job: dist-various-1 try-job: armhf-gnu try-job: aarch64-apple
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A-lints
Area: Lints (warnings about flaws in source code) such as unused_mut.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
rust-lang/rfcs#2582 suggested the addition of a lint that warns against unnecessary intermediate references: expressions like
&x as *const _
, that could be written as&raw const x
and thus avoid creating a reference. The rest of this RFC has been implemented (Cc #64490), but the lint has not -- that's what this issue tracks.The essence of the problem is that
direct_raw
andvia_ref
below are not equivalent:When people write the latter, we should nudge them towards the former, as that avoids UB. That said, the cases where that really makes a difference are probably rather rare: they occur when
x
is unaligned for some reason, or when the beginning of the projected field is still in-bounds but the end of the field is not.This is related to #99437 in that both are about "lint against cases where references are created but a raw pointer would have sufficed".
Unresolved questions:
&[mut] <place> as *[mut|const] ?T
in the surface syntax but had a method call inserted, thus manifesting a reference (with the associated guarantees). The lint as described would not fire because the reference actually gets used as such (being passed toderef
). However, what would the lint suggest to do instead? There just is no way to write this code without creating a reference.The text was updated successfully, but these errors were encountered: