fix(lang/syn): allow destructure/wildcard patterns on Context arg

[cryptomotifs]

Summary

Closes #3838.

parse_args previously rejected any argument whose pattern was not Pat::Ident. Combined with .ok()? in the instruction-collection loop, this caused instructions whose Context argument used a destructure or wildcard pattern to be silently filtered out of the program's IDL — no warning, no error.

Examples that previously produced an empty IDL:

#[program]
pub mod foobar {
    use super::*;

    pub fn initialize(Context { .. }: Context<Initialize>) -> Result<()> { Ok(()) }
    // and
    pub fn ping(_: Context<Ping>) -> Result<()> { Ok(()) }
}

Fix

Only the type of the Context argument matters for the derive macro — ctx_accounts_ident (in parser/program/mod.rs) reads path_ty.ty, never the pattern name. So we now:

• Accept any pattern for the first argument (Context), and substitute a synthetic ctx identifier when it is not a Pat::Ident.
• Continue to require a named Pat::Ident for subsequent (instruction) arguments, since those names appear in the generated IDL and codegen.

Diff

lang/syn/src/parser/program/instructions.rs::parse_args — 11 additions, 3 deletions.

Test plan

• CI: existing test suite should pass unchanged (no semantics changed for the Pat::Ident path).
• Local: I'd like a maintainer's preference on where to add the regression — I can extend tests/anchor-cli-idl with a program that uses Context { .. } and assert the IDL contains the instruction. Happy to follow up with a test commit if that placement works.

🤖 Generated with Claude Code

[vercel]

@cryptomotifs is attempting to deploy a commit to the Solana Foundation Team on Vercel.

A member of the Team first needs to authorize it.

[jamie-osec]

Please add the test to https://github.com/solana-foundation/anchor/blob/master/tests/idl/programs/idl/src/lib.rs