[soareschen]

Overview

[deepseek-v4.1-flash] The cgp crate now builds for a target without std, and its default features need neither std nor alloc. A no_std test crate builds the library for x86_64-unknown-none with and without alloc, so a leak fails the build.

Motivation

The library could not be used in a no_std environment. cgp-base-types, cgp-runtime, and cgp-base lacked #![no_std], so cargo check -p cgp --target x86_64-unknown-none failed on cgp-base-types with "can't find crate for std". Two defaults also turned alloc on: cgp-extra's default = ["full"], where full enabled cgp-error-extra/alloc, and cgp-error-extra's own default = ["alloc"], which turned the feature on regardless of who asked.

Impact

The three crates carry #![no_std]. cgp-error-extra's default is empty and its alloc feature gates DebugError and DisplayError; cgp-extra's default is empty and forwards alloc; and cgp gained an alloc feature that forwards to it. A no_std user who needs an allocator writes default-features = false, features = ["alloc"].

The error backends keep their requirements: cgp-error-anyhow and cgp-error-std need alloc, and cgp-error-eyre needs std.

cgp-no-std-tests is #![no_std], uses a component, a provider, #[cgp_fn], Symbol!, and a wiring table, and gates an alloc-using provider behind its alloc feature. Building it for x86_64-unknown-none fails if any crate in the tree needs std, and planting a std use in it fails with "cannot find module or crate std".

One finding is left for a follow-up: a #[cgp_fn] with an #[implicit] name: &str argument generates a String field bound, so it needs alloc. The test crate uses a u32 implicit instead.