Rust + Solana (Anchor) Best Practices

---
description: Rust best practices for Solana smart contract development using Anchor framework and Solana SDK
globs: programs/**/*.rs, src/**/*.rs, tests/**/*.ts
---

# Rust + Solana (Anchor) Best Practices

## Program Structure
- Structure Solana programs using `Anchor` framework standards
- Place program entrypoint logic in `lib.rs`, not `main.rs`
- Organize handlers into modules (e.g., `initialize`, `update`, `close`)
- Separate state definitions, errors, instructions, and utils
- Group reusable logic under a `utils` module (e.g., account validation)
- Use `declare_id!()` to define program ID

## Anchor Framework
- Use `#[derive(Accounts)]` for all instruction contexts
- Validate accounts strictly using constraint macros (e.g., `#[account(mut)]`, `seeds`, `bump]`)
- Define all state structs with `#[account]` and `#[derive(AnchorSerialize, AnchorDeserialize)]`
- Prefer `Init`, `Close`, `Realloc`, `Mut`, and constraint macros to avoid manual deserialization
- Use `ctx.accounts` to access validated context accounts
- Handle CPI (Cross-Program Invocation) calls via Anchor’s CPI helpers

## Serialization
- Use **Borsh** or Anchor's custom serializer (not Serde) for on-chain data
- Always include `#[account(zero_copy)]` or `#[repr(C)]` for packed structures
- Avoid floating point types — use `u64`, `u128`, or fixed-point math
- Zero out or close unused accounts to reduce rent costs

## Testing
- Write tests in TypeScript using Anchor’s Mocha + Chai setup (`tests/*.ts`)
- Use `anchor.workspace.MyProgram` to load deployed contracts
- Use `provider.simulate()` to inspect failed txs
- Spin up a local validator (`anchor test`) and reset between tests
- Airdrop SOL to wallets with `provider.connection.requestAirdrop(...)`
- Validate program logs using `tx.confirmation.logMessages`

## Solana SDK (Manual)
- Use `solana_program` crate when not using Anchor (bare-metal programs)
- Carefully deserialize accounts using `AccountInfo`, `try_from_slice_unchecked`
- Use `solana_program::msg!` for lightweight debugging logs
- Verify accounts via `is_signer`, `is_writable`, `key == expected`
- Never panic! Use `ProgramError::Custom(u32)` or `ErrorCode` enums

## Security Patterns
- Always validate `msg.sender`/signer with `account_info.is_signer`
- Prevent replay attacks via `seeds`, `bump`, and unique PDAs
- Use strict size checks before reallocating or deserializing
- Avoid unsafe unchecked casting; prefer Anchor deserialization
- For CPIs, validate `target_program` against expected program ID
- When using randomness, never rely on timestamps — use oracles or off-chain VRFs

## Performance
- Prefer zero-copy deserialization when accounts are large
- Minimize compute usage; avoid loops and recursion
- Avoid memory reallocations mid-instruction
- Use `#[account(zero_copy)]` and `#[repr(packed)]` for tight layout
- Profile compute units with `solana logs` and `anchor run`

## Dev Workflow
- Use `anchor init` to scaffold projects
- Add Anchor IDL support for front-end usage (JSON ABI)
- Use `anchor build`, `anchor deploy`, `anchor test` consistently
- Use separate `Anchor.toml` environments for devnet/mainnet/localnet
- Format all Rust code with `cargo fmt`, lint with `cargo clippy`
- Keep `Cargo.lock` checked into `programs/` but not root

## Documentation
- Use `///` Rust doc comments for all instructions and accounts
- Include doc examples for each instruction
- Document PDA derivation logic and bump seed expectations
- Maintain up-to-date `README.md` with test commands and deployment steps

## Wallet & Network Handling
- Use `anchorProvider.wallet.publicKey` for signer verification in tests
- Do not hardcode keypairs — use env-based loading (`process.env.ANCHOR_WALLET`)
- Deploy with clear `cluster` targets (`localnet`, `devnet`, `mainnet`)
- Use `anchor keys sync` to propagate program ID changes
- Commit `target/idl/` and `target/types/` to share with front end

## CI/CD & Deploy
- Use GitHub Actions with `solana-cli`, `anchor-cli`, and `node` installed
- Run `anchor test` in CI for every PR
- Use `solana program deploy` with explicit `--program-id` on production deploys
- Upload IDLs to a central registry (e.g., GitHub, IPFS, or `anchor.cloud`)