- Introduced minimum publish age configurations, also known as dependency cooldowns. When the relevant config is set, the resolver ignores versions published more recently than that, unless they are already in Cargo.lock. (RFC 3923) docs #17335
- cargo-install: now uses the existing lockfile in the .crate tarball by default. --locked in cargo install becomes a no-op. #17388
I updated to 1.100 during a Claude session and it complained about new warnings, so I told it to fix them. It removed a large number of unused dependencies without issue.
I believe so. The maintaner of cargo-udeps did most of the work as an effort to upstream it.
The main limitation is in dev-dep detection since there isn't a way to exhaustively run everything that uses dev-deps yet. You can look at logging statements to get an approximation though.
Faster compile and smaller build-dir can be at odds with each other.
That said, this release includes some incremental improvements as well as the unused-dependency lint to help reduce wasted work within the ecosystem.
Some changes that have been or are about to be merged for upcoming releases
- We will be reducing the debug info generated for the `dev` profile which reduces build-dir size and speeds up builds. We've split off a `debug` profile for when that is needed.
- Cargo will be deleting the directory rustc writes before each invocation, avoiding the leaking of debug files when split-debug is enabled (default on Mac)
- rlibs for workspace members will no longer be copied from build-dir to target-dir which takes up extra space on systems without hardlinking or where we skip it (like Mac)
- redundant information in rlibs and rmeta's is going to be de-duplicated
Examples of further out changes
- This release includes the foundational work to add a build-dir GC
Any faster vs what baseline? They’ve constantly made improvements and Rust today is pretty darn quick, especially for incremental. There’s work to parallelize the front end which will help a little bit and you can always use the cranelift backend for debugging which is substantially faster than LLVM.
They’re also doing work to reduce the amount of disk space usage (by clearing out unused articacts) and make it easier to maintain.
Best to do some benchmarks for cranelift on your codebases and system. It used to be quite a lot faster, but for me the advantage has disappeared over the last year of Rust improvements.
There's no paradox here. You can use any benchmark you like to prove that Rust is a fast language. The work that the compiler does is irrespective of the language that rustc is written in.
On macOS there is a known bug where some temp files are always created anew, not reused, which slows down compilation and wastes more space than other platforms.
Yes this is why I switched to Go for backend, much faster compiling and performance isn't an issue for the application yes using 100GB+ is just bad tooling.
I don't understand why people complain about this non-stop. If compilation time is such an issue use a different language. I can't say I've been bottlenecked by compilation in a very long time.
The primary challenge in having a stable ABI is that we have generics. So, even if we never changed the calling conventions, an ABI is not as simple as exporting a symbol with the right name. We implement generics by providing MIR (our main intermediate representation) that gets compiled by the linking program for each instantiation of a generic.
Swift handles this through the equivalent of Rust's `dyn`. We could have a stable ABI that's based entirely on `dyn`. Such an ABI would have some limitations, since there are traits `dyn` can't represent (anything that's generic over something other than the type that implements the trait, which is quite common), though we're working on some of those.
Essentially, you wouldn't be able to have a `Vec<T>` in your ABI without either pinning down T or using something like `Vec<Box<dyn Trait>>`. Which is possible, but kind of awful.
We're still planning to ship a stable ABI at some point, but that gives a flavor for some of the kinds of problems we'd need to solve in order for that stable ABI to be useful.
(C++ typically handles generics by having types defined in header files, and those get compiled with the program consuming the library, which is effectively the same situation Rust is in. You could export symbols from a shared library for specific instantiation of a template, but people rarely do that.)
A generic could be seen as a pure (in the functional sense) program that is run at link time that takes various type information as input and outputs an implementation.
I wonder why not make the ABI contract explicit, instead of do what C do that froze the lang.
Similar to :
#[rust_abi]
struct MustConform
fn must_conform
So the user must write the shims instead of rust magically build it. This also mean that ABI changes become visible, and changes to rust not mean worries about ABI.
I don't think a stable ABI has enough advantages to be worth it. C++, IMHO, is a great examples of the downsides of a stable-enough ABI, where stability was never guaranteed, but is now so entrenched that it'll likely never be broken again (limiting the language & the usability in a bunch of ways).
It might make sense to have a subset Swift-style stable ABI, but that's a huge engineering effort, has lots of overhead and is also likely not worth it IMHO.
Yes, in that it's primarily a linux thing as MS has gone the route of saving off basically all dlls for all their OSes for backwards compatibility (though they still backpatch).
No, in that other than Rust and Go (and maybe a few others that emit single binaries, zig?) this is how it works with OS distributed programming language packages. Python, ruby, java, perl, C#, the OS will for all of them control distribute and update the libs independent of the apps that use them.
Also, C/C++ still make up a huge percentage of all apps in pretty much any OS.
Well yes, but then your interface is a C ABI. That's fantastic if the side using my library is any language where C is the only common ground. When the application side is Rust though, it leaves a lot to be desired. It would be delicious to actually interface in a way that respects Rust!
Hell, even if all exposed functions and types would need to be fully monomorphized at the interface, it would be a lot nicer to pass a `&'a [i64]` rather than a `const * int64_t` together with a `size_t n` and have to marshall the slice on both sides.
Another year or three of insane memory and disk prices and people will come around.
A stable Rust ABI would be nice for not just Rust, especially if they refine or extend (formally or de facto) the SysV ABI to optimize passing and returning of discriminants. That could then smooth the way for developing these features in C and C++, such as a primitive error-result type that saw some brief attention in both C and C++ WGs a couple of years ago. Doing it properly--absolute minimum cost, ABI stable, and cross-language--seemed to require too much orchestration across the ecosystem so enthusiasm and ambition seemed to peter out. The work required for a stable Rust ABI could provide the inertia to get that done.
Rust will almost certainly never have a stable ABI by default, and libraries will continue to be compiled from source by default. It might one day have an opt-in stable ABI.
Mathematically, types are sets of possible values.
Any type (like in TypeScript; Rust doesn't have one) is a set of every possible value; a supertype of all types. Every expression regardless of type can be assigned to a variable of type any.
The opposite is the never type, which is an empty set; no value is of type never. Per set theory, an empty set is a subset of every set, which makes the never type a subtype of all types. An expression of type never can be assigned to every variable regardless of type.
If never type has no values, then how can an expression have never type? Easy: it must never evaluate. Infinite loops, unconditional panics/exceptions, process exit/abort, etc. Also, generics - you can have Vec<!> that's always empty, Result<T,!> that can never be an error, etc.
A few other langs have it too. It's just something to return when no return is actually possible. And then it can propagate, so it makes some nice things possible that weren't before.
Without looking up the Rust implementation I would hazard a guess that it is loose language to say "something to return when no return is actually possible" because if it is anything like the Bottom Type then there is no something that is being returned which is what this function signature indicates. Generally used for exception handling or intentional infinite loops (in both cases the function does not return from whence it came) … please correct me if I'm wrong here …
Basic use cases like that have always been possible in Rust, either via defining your own enum with zero variants (`enum Foo {}`), or by using a function return type of `!` which was hardcoded to work for certain things, e.g. infinite loops. What this release does is generalizes it so that `!` can participate in types in general, and the coolest part is that pattern matching is aware of this, so for example if you have a `Result<u8, !>` where the error variant is impossible, a `match` over this would allow you to omit the impossible error arm, and furthermore because this enum now effectively only has a single variant, it would allow you to use the pleasant irrefutable destructuring assignment syntax `let Ok(foo) = blah();`.
It has existed as a real type for a very long time (I believe in the beginning it really wasn't a real type but that's a long time ago), you just weren't allowed to name it. There was also an (unsupported) hack that allowed you to use it on stable.
It's the type called "!", or the return value of diverging control flow, such as infinite loops, returns or function calls that panic or abort. It's an uninhabited type, meaning no values of it can actually exist, and that any code that would encounter such a value is unreachable.
I just spent last few days fixing arena leaks (Bumpalo doesn't call drop) and had to use allocator-api2 for Vec::new_in which is now available in stable Rust.
when can we expect `Result::into_ok` and `Result::into_err` to land? the blog post includes the `infallible_unwrap` demo which is the exact functionality these two functions implement. i wonder why they didn't release these at the same time as never?
(As for why they weren't stabilized at the same time: because it's not worth adding more baggage to a major, difficult stabilization process; as that would just be more surface area that has to be reviewed and another source of potential issues or delays. Instead, the stabilization process for infallible_unwrap was started immediately after `!` was stabilized. That process includes a 2-week final comment period for community feedback which is why they landed in different releases.)
I haven’t seen any blog on the topic but I fully believe in the age of coding agents and LLM backward compatibility is a bit less important than it has been in the past and should be relaxed in some cases to allow language to move faster.
I get your point but disagree strongly. One topic that's been on my mind a lot is durability. The culture of LLMs is that everything is transitory. Why bother keeping a vibe coded codebase around for more than a few weeks, when the next big model iteration will be able to vibe code it better?
By contrast, free software in general, and Rust very much in particular, has cultural norms that things should last a while, rather than immediately being thrown away. I think that's worth preserving.
You can marshal values, but you can't marshal lifetimes, ownership, (lack of) thread-safety, (lack of) side-effects, etc. The ABI carries far less information than the Rust compiler relies on. Thus, any FFI call is inherently unsafe. It takes you, the programmer, with knowledge the compiler doesn't have and the architecture doesn't provide, to determine whether the code as you use it actually is safe or not.
It is explained elsewhere, but a summary is that any language with generics is going to have any stable abi as a subset of the language. There is already a subset of the language that is a stable abi, it is the c abi. Expanding that subset has to be worth it in terms of what people actually want to export from a library. As I use generics fairly heavily I don't think I would use that expanded abi for anything.
- Stabilize never type
- Stabilize custom allocators
- Introduced minimum publish age configurations, also known as dependency cooldowns. When the relevant config is set, the resolver ignores versions published more recently than that, unless they are already in Cargo.lock. (RFC 3923) docs #17335
- cargo-install: now uses the existing lockfile in the .crate tarball by default. --locked in cargo install becomes a no-op. #17388
Long time follower of this. Very grateful it's been implemented.
> warning: unused dependency `tracing-subscriber` --> Cargo.toml:23:1 | 23 | tracing-subscriber.workspace = true | ^^^^^^^^^^^^^^^^^^ | = note: `cargo::unused_dependencies` is set to `warn` by default help: consider removing the dependency on `tracing-subscriber`
Heck yes
The main limitation is in dev-dep detection since there isn't a way to exhaustively run everything that uses dev-deps yet. You can look at logging statements to get an approximation though.
- bool::toggle() https://doc.rust-lang.org/stable/std/primitive.bool.html#met...
- Box::map() https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#m...
- str::trim_prefix(), str::trim_suffix, Path::trim_prefix()
That said, this release includes some incremental improvements as well as the unused-dependency lint to help reduce wasted work within the ecosystem.
Some changes that have been or are about to be merged for upcoming releases
- We will be reducing the debug info generated for the `dev` profile which reduces build-dir size and speeds up builds. We've split off a `debug` profile for when that is needed.
- Cargo will be deleting the directory rustc writes before each invocation, avoiding the leaking of debug files when split-debug is enabled (default on Mac)
- rlibs for workspace members will no longer be copied from build-dir to target-dir which takes up extra space on systems without hardlinking or where we skip it (like Mac)
- redundant information in rlibs and rmeta's is going to be de-duplicated
Examples of further out changes
- This release includes the foundational work to add a build-dir GC
- Cross-workspace de-duplicating of build-dirs
- Cross-workspace build-dir cache
- Early cut off
“Relink, don't rebuild” #790
https://github.com/rust-lang/compiler-team/issues/790
And the large target directories is also being worked on as well.
They’re also doing work to reduce the amount of disk space usage (by clearing out unused articacts) and make it easier to maintain.
Swift handles this through the equivalent of Rust's `dyn`. We could have a stable ABI that's based entirely on `dyn`. Such an ABI would have some limitations, since there are traits `dyn` can't represent (anything that's generic over something other than the type that implements the trait, which is quite common), though we're working on some of those.
Essentially, you wouldn't be able to have a `Vec<T>` in your ABI without either pinning down T or using something like `Vec<Box<dyn Trait>>`. Which is possible, but kind of awful.
We're still planning to ship a stable ABI at some point, but that gives a flavor for some of the kinds of problems we'd need to solve in order for that stable ABI to be useful.
(C++ typically handles generics by having types defined in header files, and those get compiled with the program consuming the library, which is effectively the same situation Rust is in. You could export symbols from a shared library for specific instantiation of a template, but people rarely do that.)
Similar to :
So the user must write the shims instead of rust magically build it. This also mean that ABI changes become visible, and changes to rust not mean worries about ABI.https://github.com/joshtriplett/rfcs/blob/crabi-v1/text/3470...
It might make sense to have a subset Swift-style stable ABI, but that's a huge engineering effort, has lots of overhead and is also likely not worth it IMHO.
An actual stable native Rust ABI sounds like a forward compatibility nightmare.
If there's a CVE in tokio, the OS could theoretically publish a patched version of tokio and all apps that depend on that end up using the fixed code.
As it stands now, the OS needs to publish updated versions of all rust apps that depend on tokio.
Yes, in that it's primarily a linux thing as MS has gone the route of saving off basically all dlls for all their OSes for backwards compatibility (though they still backpatch).
No, in that other than Rust and Go (and maybe a few others that emit single binaries, zig?) this is how it works with OS distributed programming language packages. Python, ruby, java, perl, C#, the OS will for all of them control distribute and update the libs independent of the apps that use them.
Also, C/C++ still make up a huge percentage of all apps in pretty much any OS.
Hell, even if all exposed functions and types would need to be fully monomorphized at the interface, it would be a lot nicer to pass a `&'a [i64]` rather than a `const * int64_t` together with a `size_t n` and have to marshall the slice on both sides.
A stable Rust ABI would be nice for not just Rust, especially if they refine or extend (formally or de facto) the SysV ABI to optimize passing and returning of discriminants. That could then smooth the way for developing these features in C and C++, such as a primitive error-result type that saw some brief attention in both C and C++ WGs a couple of years ago. Doing it properly--absolute minimum cost, ABI stable, and cross-language--seemed to require too much orchestration across the ecosystem so enthusiasm and ambition seemed to peter out. The work required for a stable Rust ABI could provide the inertia to get that done.
As this release seems to include breaking changes, shouldn't the major version number have been bumped, as per semver?
Has the Rust book(s) been updated to include the new APIs?
Any type (like in TypeScript; Rust doesn't have one) is a set of every possible value; a supertype of all types. Every expression regardless of type can be assigned to a variable of type any.
The opposite is the never type, which is an empty set; no value is of type never. Per set theory, an empty set is a subset of every set, which makes the never type a subtype of all types. An expression of type never can be assigned to every variable regardless of type.
If never type has no values, then how can an expression have never type? Easy: it must never evaluate. Infinite loops, unconditional panics/exceptions, process exit/abort, etc. Also, generics - you can have Vec<!> that's always empty, Result<T,!> that can never be an error, etc.
https://blog.rust-lang.org/2026/11/12/Rust-1.100.0/#never-ty...
Two jokes that are expiring this month
[1]: https://www.youtube.com/watch?v=RFm9ClqlGuo
I just spent last few days fixing arena leaks (Bumpalo doesn't call drop) and had to use allocator-api2 for Vec::new_in which is now available in stable Rust.
https://github.com/bancek/rust-sass/pull/1
Wait for the timing of the next release. It will be a Christmas present.
when can we expect `Result::into_ok` and `Result::into_err` to land? the blog post includes the `infallible_unwrap` demo which is the exact functionality these two functions implement. i wonder why they didn't release these at the same time as never?
(As for why they weren't stabilized at the same time: because it's not worth adding more baggage to a major, difficult stabilization process; as that would just be more surface area that has to be reviewed and another source of potential issues or delays. Instead, the stabilization process for infallible_unwrap was started immediately after `!` was stabilized. That process includes a 2-week final comment period for community feedback which is why they landed in different releases.)
By contrast, free software in general, and Rust very much in particular, has cultural norms that things should last a while, rather than immediately being thrown away. I think that's worth preserving.