improve panic message for slice windows and chunks

[lukas-code]

before:

thread 'main' panicked at 'size is zero', /rustc/1e225413a21fa69570bd3fefea9eb05e33f8b917/library/core/src/slice/mod.rs:809:44

thread 'main' panicked at 'assertion failed: `(left != right)`
  left: `0`,
 right: `0`: chunks cannot have a size of zero', /rustc/1e225413a21fa69570bd3fefea9eb05e33f8b917/library/core/src/slice/mod.rs:843:9

after:

thread 'main' panicked at 'chunk size must be non-zero', src/main.rs:4:22

fixes #107437

[rustbot]

r? @cuviper

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[albertlarsan68]

Bringing my 2 cents:
I think it should be a diagnostic rather than a panic, but I don't know whether this is feasible.

[eggyal]

@albertlarsan68: there are unstable/nightly-only APIs like array_windows that can be enforced at compile-time, but for windows etc the window-size is not known until runtime.

[lukas-code]

like array_windows that can be enforced at compile-time

That's #99471.

diagnostic

It's probably possible to create a lint similar to unconditional_panic, but that's out of scope for this PR.

[eggyal]

It's probably possible to create a lint similar to unconditional_panic

Sure, but only for situations where the runtime size can be const-folded and evaluated to be 0 at compile-time.

[cuviper]

I think ArrayChunks::new's direct style is better, and a strong "must" is appropriate:

rust/library/core/src/iter/adapters/array_chunks.rs

Line 28 in a322848

assert!(N != 0, "chunk size must be non-zero");

It's also clear to say just "chunk size" or "window size", rather than mixing up windows/chunks/rchunks variants.

[lukas-code]

I've updated the wording to "chunk size must be non-zero" everywhere and use assert! instead of assert_ne! to remove the redundant 0 != 0.

[cuviper]

Windows are different than chunks. :)

[lukas-code]

Sorry, I thought that was what you meant by #107442 (comment). I changed window back now.

[cuviper]

Ah, I only meant that "window/chunk size" should be the subject, rather than "windows/chunks" (the methods) as the subject having a size. Anyway, looks good now!

@bors r+

[bors]

📌 Commit 2fbe927 has been approved by cuviper

It is now in the queue for this repository.