move #[pyclass] docstring generation to compile time
#5286
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| const L: &'static str = $l; | ||
| const R: &'static str = $crate::impl_::concat::const_concat!($($r),*); | ||
| const LEN: usize = L.len() + R.len(); | ||
| const fn combine(l: &'static [u8], r: &'static [u8]) -> [u8; LEN] { | ||
| let mut out = [0u8; LEN]; | ||
| let mut i = 0; | ||
| while i < l.len() { | ||
| out[i] = l[i]; | ||
| i += 1; | ||
| const PIECES: &[&str] = &[$l, $($r),+]; | ||
| const RAW_BYTES: &[u8] = &$crate::impl_::concat::combine_to_array::<{ | ||
| $crate::impl_::concat::combined_len(PIECES) | ||
| }>(PIECES); | ||
| // Safety: `RAW_BYTES` is combined from valid &str pieces | ||
| unsafe { ::std::str::from_utf8_unchecked(RAW_BYTES) } |
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I rewrote this a bit so that instead of needing to apply the machinery recursively to concatenate pairs, it concatenates a whole slice of pieces.
I also moved as much machinery as possible out into the const fn helpers below. There are some for str inputs and some for bytes inputs (maybe one day with const AsRef<[u8]> implementations we could avoid the duplication).
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Thank you! I think we can migrate the introspection code to use directly these const functions and drop the macro entirely. It might allow us to only use the byte variant of the functions and drop the string variants entirely. Happy to do it in a follow-up.
Icxolu
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Icxolu
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Quite some const layers to peel off 😅, but pretty clever solution. LGTM
CodSpeed Performance ReportMerging #5286 will degrade performances by 13.78%Comparing Summary
Benchmarks breakdown
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* Drop const_concat! macro and str-focused const combine functions Follow up to #5286 * Makes combine not `pub`
* move `#[pyclass]` docstring generation to compile time * improve error message * clean up to use cstr all the way through * fixup msrv * fixup final tests, newsfragment * runtime test coverage * use "copy_from_slice" (with a note for the future) * fix clippy beta
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Inspired by #5223 (comment), this cleans up the Python docstring generation by moving the work to compile time. Avoids a runtime allocation in startup as well as removes a use of a
GILOnceCellstatic cache, for each#[pyclass].The interesting new machinery is in
src/impl_/pyclass/doc.rs. It is responsible for assembling the pieces of the docstring together according to what's available, and then the proc macros invoke the const concat machinery (thanks @Tpt) to build the docstring into the binary.