Re: [gentoo-dev] [PATCH] cargo.eclass: use CARGO_CRATE_URIS if already available

["Michał Górny" <mgorny@gentoo.org>]

On Mon, 2023-07-31 at 12:41 +0200, Florian Schmaus wrote:
> With 59dbfb80f748 ("cargo.eclass: Add variable alternative to
> $(cargo_crate_uris)") the _cargo_set_crate_uris function was
> introduced. This function runs when the elcass is inherited and sets
> CARGO_CRATE_URIS.
> 
> Ebuilds that use $(cargo_crate_uris) in SRC_URI will again invoke this
> function, even though CARGO_CRATE_URIS is already set. Avoiding this
> unnecessary computation reduces the ebuild source time of
> app-shells/nushell-0.83.0 from 21 ms to 14 ms.
> 
> This is a significant reduction when compared to the variable-setting
> alternative that the commit 59dbfb80f748 ("cargo.eclass: Add variable
> alternative to $(cargo_crate_uris)") introduced. Using the
> variable-setting approach would reduce the ebuild source time only by a
> little bit more than one millisecond.
> 
> Using
> 
> pk pkg source --bench 10s '=app-shells/nushell-0.83.0'
> 
> as benchmark, yields
> 
> >                           | Cached CARGO_CRATE_URIS | Non-Cached CARGO_CRATE_URIS |
> > ---------------------------+-------------------------+-----------------------------|
> > $(cargo_crate_uris)       | mean: 14.189ms          | mean: 21.445ms              |
> > variable-setting approach | mean: 12.822ms          | mean: 12.852ms              |
> 
> full benchmark output
> 
> >                           | Cached CARGO_CRATE_URIS (this commit)                            | Non-Cached CARGO_CRATE_URIS                                      |
> > ---------------------------+------------------------------------------------------------------+------------------------------------------------------------------|
> > $(cargo_crate_uris)       | mean: 14.189ms, min: 13.646ms, max: 15.103ms, σ = 149µs, N = 705 | mean: 21.445ms, min: 20.79ms,  max: 22.832ms, σ = 228µs, N = 467 |
> > variable-setting approach | mean: 12.822ms, min: 12.41ms,  max: 13.909ms, σ = 165µs, N = 780 | mean: 12.852ms, min: 12.367ms, max: 15.437ms, σ = 227µs, N = 779 |
> 
> Signed-off-by: Florian Schmaus <flow@gentoo.org>
> ---
>  eclass/cargo.eclass | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/eclass/cargo.eclass b/eclass/cargo.eclass
> index 70b6008d9cd8..5d6911801097 100644
> --- a/eclass/cargo.eclass
> +++ b/eclass/cargo.eclass
> @@ -240,6 +240,14 @@ _cargo_set_crate_uris "${CRATES}"
>  # Constructs a list of crates from its arguments.
>  # If no arguments are provided, it uses the CRATES variable.
>  cargo_crate_uris() {
> +	# Use already existing value for CARGO_CRATE_URIS, computed by
> +	# _cargo_set_crate_uris, when this function is invoked without
> +	# arguments.
> +	if [[ $# -eq 0 && -n "${CARGO_CRATE_URIS}" ]]; then
> +		echo "${CARGO_CRATE_URIS}"
> +		return
> +	fi
> +
>  	local crates=${*-${CRATES}}
>  	if [[ -z ${crates} ]]; then
>  		eerror "CRATES variable is not defined and nothing passed as argument"

This incorrectly assumes that the value of CRATES did not change which
isn't guaranteed anywhere.

-- 
Best regards,
Michał Górny