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The backwards compatibility guarantee for C is "C99 compilers can compile C99 code". If they can't, that's a compiler bug. Same for other C standards. Since Ru

by gkbrk 2y ago

The backwards compatibility guarantee for C is "C99 compilers can compile C99 code". If they can't, that's a compiler bug. Same for other C standards. Since Rust doesn't have a standard, the guarantee is "whatever the current version of the compiler can compile". To check if they broke anything they compile everything on crates.io (called a crater run). But if you check results of crater runs, almost every release some crates that compiled in the previous version stop compiling in the new version. But as long as the number of such breakages it not too large, they say "nothing is broken" and push the release.

purplesyringa 2y ago
Can you provide an example for the broken-crater claim? As far as I'm aware, Rust folks don't break compatibility that easily, and the one time that happened recently (an old version of the `time` crate getting broken by a compiler update), there were a lot of foul words thrown around and the maintainers learned their lesson. Are you sure you aren't talking about crates triggering UB or crates with unreliable tests that were broken anyway?
- uecker 2y ago
  I am not following this too closely (the time issue seemed pretty severe though), but there are compatibility changes listed in the release notes very frequently: https://github.com/rust-lang/rust/blob/master/RELEASES.md https://github.com/rust-lang/rust/blob/master/RELEASES.md
knowitnone 2y ago
What do you mean? Rust 1.0 can compile Rust 1.0. Rust 1.1 can compile Rust 1.1.
- School-Cotton 2y ago
  Right, which is basically the opposite of what backwards incompatibility means. Imagine if GCC 14.2.0 was only guaranteed to be able to compile "C 14.2.0".
- gkbrk 2y ago
  C99 isn't a compiler version. It's a standard. Many versions of GCC, Clang and other compilers can compile C99 code. If you update your compiler from gcc 14.1 to gcc 14.2, both versions can still compile standard code.
  - uecker 2y ago
    There is also a very high level of backwards compatibility between versions of ISO C because there is a gigantic amount of code is updated if there is change. So such changes are done only for important reasons or after a very long deprecation period.
- johnisgood 2y ago
  But Rust 1.0 can't compile Rust 1.1. And as others have noted, C99 is a standard and Rust lacks one.
  - tremon 2y ago
    But Rust 1.0 can't compile Rust 1.1 That's an impossible standard to hold Rust to, did you mean it the other way around? A C89 compiler can't compile all of C99 either.
    - gkbrk 2y ago
      But v1 of a C99 compiler can compile all of C99, and v2 of a C99 compiler can still compile all of C99.
- chongli 2y ago
  C makes a distinction between the language version and the compiler version. Rust does not. That's the problem people are discussing here.

by gkbrk 2y ago

purplesyringa 2y ago

Can you provide an example for the broken-crater claim? As far as I'm aware, Rust folks don't break compatibility that easily, and the one time that happened recently (an old version of the `time` crate getting broken by a compiler update), there were a lot of foul words thrown around and the maintainers learned their lesson. Are you sure you aren't talking about crates triggering UB or crates with unreliable tests that were broken anyway?

uecker 2y ago
I am not following this too closely (the time issue seemed pretty severe though), but there are compatibility changes listed in the release notes very frequently: https://github.com/rust-lang/rust/blob/master/RELEASES.md https://github.com/rust-lang/rust/blob/master/RELEASES.md

knowitnone 2y ago

What do you mean? Rust 1.0 can compile Rust 1.0. Rust 1.1 can compile Rust 1.1.

School-Cotton 2y ago
Right, which is basically the opposite of what backwards incompatibility means. Imagine if GCC 14.2.0 was only guaranteed to be able to compile "C 14.2.0".
gkbrk 2y ago
C99 isn't a compiler version. It's a standard. Many versions of GCC, Clang and other compilers can compile C99 code. If you update your compiler from gcc 14.1 to gcc 14.2, both versions can still compile standard code.
- uecker 2y ago
  There is also a very high level of backwards compatibility between versions of ISO C because there is a gigantic amount of code is updated if there is change. So such changes are done only for important reasons or after a very long deprecation period.
johnisgood 2y ago
But Rust 1.0 can't compile Rust 1.1. And as others have noted, C99 is a standard and Rust lacks one.
- tremon 2y ago
  But Rust 1.0 can't compile Rust 1.1 That's an impossible standard to hold Rust to, did you mean it the other way around? A C89 compiler can't compile all of C99 either.
  - gkbrk 2y ago
    But v1 of a C99 compiler can compile all of C99, and v2 of a C99 compiler can still compile all of C99.
chongli 2y ago
C makes a distinction between the language version and the compiler version. Rust does not. That's the problem people are discussing here.