It has clang tidy, -std=lang-version, and preprocessor that is version aware.

Rust editions don't cover all use cases that one can think of regarding language evolution, and requires full access to source code.

> requires full access to source code

What do you mean? Editions don't require full access to source code. Rust in general relies heavily on having access to source code, but that has nothing to do with how editions work

You can write a binary library that exposes a C ABI using Rust (which is indistinguishable from an ordinary C/C++ library) and then provide source for a Rust wrapper crate that provides a "safe" interface to it, much like a C header file.

Yes they do, when mixing crates from various editions and how changes interact together.

> when mixing crates from various editions and how changes interact together.

Could you elaborate more on this? It's not obvious to me right now why (for example) Crate A using the 2024 edition and Crate B using the 2015 edition would require both full access to both crates' source beyond the standard lack of a stable ABI.

Because in order to have standard library breaking changes across editions, if those types are exposed in the crate public types, or change their semantics across editions, the compiler has to be able to translate between them when generating code.

See the Rust documentation on what editions are allowed to change, and the advanced migration guide on examples regarding manual code migration.

Not so much what has happened thus far, rather the limitations imposed in what is possible to actually break across editions.

Or put another way, a hypothetical feature that you made up in your head is the thing that requires source access. Editions do not let you change the semantics of types.

To be fair, Rust tooling does tend toward build-from-source. But this is for completely different reasons than the edition system: if you had a way to build a crate and then feed the binary into builds by future compilers, it would require zero additional work to link it into a crate using a different edition.

Exactly, hence why people should stop talking about editions as if they sort out all Rust evolution problems, in your own words it doesn't allow changing type semantics

I think you're too stuck on the current implementation. Work is going into investigating how to evolve the standard library over editions. The "easiest" win would be to have a way to do edition-dependent re-exports of types.

What I am stuck is Rust folks advocating editions as the solution for everything in language evolution, when it clearly isn't.

What you're describing sounds more like a potential issue with editions if/when they allow breaking stdlib changes more than a problem with editions as they exist today, which is more what I took the original comment to be talking about.

Exactly because they don't allow it, they don't cover all scenarios regarding language evolution

OK, sure, but again what breaking changes editions do/don't currently allow is independent from what SkiFire13/I was responding to, which was the "requires full access to source code" bit.

How do you expect a compiler to be able to mix and match changes across editions between crates, if those happen to be changes in semantic behaviour?

Depends on the change. Obviously the compiler doesn't need to care about cross-edition compatibility between crates if the changes in question don't impact the public API. Otherwise, I'd expect the compiler to canonicalize the changes, and from what I understand that is precisely how edition changes are chosen/designed/implemented.

Can you explain how this is relevant here?

Adding a new feature to unify existing features is perfectly isomorphic to defining a new standard to unify existing standards.

It's not though, unless the new feature and existing features continue to exist as disjoint things. If the new feature subsumes the old ones, then you've reduced the number of features in the language.

The same is true of standards.

This comparison is useless until rust commits to a stable ABI.

Unifying surface features increases the combinatorics of interactions between traits, lifetimes, generics, specialization, and macros and leads to surprising edge cases.

Editions buy migration safety and let the standard evolve, but they do not shrink the mental model newcomers must carry and they force tooling and libraries to support multiple modes at once, which is a different kind of maintenance tax than evolving C++ compilers and feature test macros impose.

Require RFCs to include an interaction test matrix, compile time and code size measurements, and a pass from rust-analyzer and clippy so ergonomics regressions are visible before users hit them.

> and they force [] libraries to support multiple modes at once,

I'm not entirely sure I agree? I don't think any library except for the standard library needs to "support multiple modes at once"; everything else just sets its own edition and can remain blissfully unaware of whatever edition its downstream consumer(s) are using.

> which is a different kind of maintenance tax than evolving C++ compilers and feature test macros impose.

I'm not sure I agree here either? Both Rust and C/C++ tooling and their standard libraries needs to support multiple "modes" due to codebases not all using the same "mode", so to me the maintenance burden should be (abstractly) the same for the two.

> Require RFCs to include an interaction test matrix, compile time and code size measurements, and a pass from rust-analyzer and clippy

IIRC rustc already tracks various compilation-related benchmarks at perf.rust-lang.org. rustc also has edition-related warnings [0] (see the rust-YYYY-compatibility groups), so you don't even need clippy/rust-analyzer.

[0]: https://doc.rust-lang.org/rustc/lints/groups.html

In practice library authors must consider the editions used by downstream crates because public APIs cross crate boundaries. Even if a crate compiles under a single edition, exported APIs often avoid edition specific idioms that could cause friction for consumers compiled under older editions. This leads to a conservative design style where libraries effectively target the lowest common denominator of the ecosystem. The result is that authors informally maintain compatibility across editions even if the compiler technically allows them to ignore downstream edition choices.

Large Rust organizations often run mixed-edition workspaces because upgrading hundreds of crates simultaneously is impractical. Libraries in the workspace therefore interact across editions during migration periods. So while technically each crate chooses its edition, ecosystem reality introduces cross-edition friction.

Feature test macros in C and C++ primarily gate access to optional APIs or compiler capabilities. Rust editions can change language semantics rather than merely enabling features. Examples include changes to module path resolution, trait object syntax requirements such as dyn, or additions to the prelude. Semantic differences influence parsing, name resolution, and type checking in ways that exceed the scope of a conditional feature macro.

Tooling complexity is structurally different. Rust tools such as rustc, rust analyzer, rustfmt, and clippy must understand edition dependent grammar and semantics simultaneously. The tooling stack therefore contains logic branches for multiple language modes. In contrast, feature test macros generally affect conditional compilation paths inside user code but do not require parsers or analysis tools to support different core language semantics.

Rust promises permanent support for previous editions, which implies that compiler infrastructure must preserve older semantics indefinitely. Over time this creates a cumulative maintenance burden similar to maintaining compatibility with many historical language versions.

> Even if a crate compiles under a single edition, exported APIs often avoid edition specific idioms that could cause friction for consumers compiled under older editions.

Do you have some concrete examples of this outside the expected bump to the minimum required Rust version? I'm coming up blank, and this sounds like it goes against one of the primary goals of editions (i.e., seamless interop) as well.

> So while technically each crate chooses its edition, ecosystem reality introduces cross-edition friction.

And this is related to the above; I can't think of any actual sources of friction in a mixed-edition project beyond needing to support new-enough rustc versions.

> Rust tools such as rustc, rust analyzer, rustfmt, and clippy must understand edition dependent grammar and semantics simultaneously.

I'm not entirely convinced here? Editions are a crate-wide property and crates are Rust's translation units, so I don't think there should be anything more "simultaneous" going on compared to -std=c++xx/etc. flags.

> Over time this creates a cumulative maintenance burden similar to maintaining compatibility with many historical language versions.

Sure, but that's more or less what I was saying in the first place!