Anchor 0.30.1 IDL generation ignores #[cfg(feature = ...)] gates — only default features reach the IDL

Problem: a program keeps two variants behind Cargo features (#[cfg(feature = "v2_0_0")] pub version: u8, etc.). cargo build respects the flags, but anchor idl build always emits the IDL for whatever is in default = [...] in Cargo.toml. Passing the feature explicitly does not help and can fail outright:

anchor idl build -p platform_control -- --features v2_0_0,idl-build
error: stack offset of 6344 exceeded maximum offset of 4096 by 2248 bytes

Answer, for Anchor 0.30.1: there is no supported way to generate a feature-specific IDL. IDL build works from the default feature set, so the only reliable lever is which features are default at build time. Don't spend hours looking for a flag.

Workarounds, in order of robustness: - Split each variant into its own crate (or its own workspace), each with the appropriate default features, and generate the IDL per crate. Clean and CI-friendly. - Script the toggle: have a build wrapper rewrite default = [...] in Cargo.toml, run anchor idl build, and restore the file. Works but is fragile and easy to leave in a bad state; make it idempotent and never run two builds concurrently.

The secondary "stack offset exceeded" error is a separate consequence of the IDL-build pass compiling with a larger account struct; reducing stack usage (boxing large accounts, Box<Account<'info, T>>) is what addresses that, not the feature flags.

Worth re-testing on current Anchor: this was raised as a bug against 0.30.1 with an expectation that 0.31.0 improves it, so verify against the version you are on before adopting the multi-crate workaround.

Source: adapted from a Stack Exchange answer by Aseneca (question by ivanhoe1982), https://solana.stackexchange.com/questions/19053/anchor-idl-generation-ignores-rust-feature-flags-in-solana-program — CC BY-SA 4.0