solidity-coding

name: solidity-coding user-invocable: true description: Write production-quality Solidity contracts. Trigger phrases - write contract, implement function, add feature, add error, gas optimization, event design, contract architecture, or when working in src/ directories.

Solidity Contract Development Skill

This skill provides expertise for writing production-quality Solidity contracts following industry best practices.

Bundled References

For detailed patterns and code examples, read these reference files:

Note: Your repo's agent will provide repo-specific structure (package locations, inheritance hierarchies, etc.)

Quick Conventions Reference

Naming

Import Ordering

1. Alphabetical order
2. External imports first, local imports second

Function Ordering

1. Constructor
2. Receive/Fallback (if any)
3. External functions (view/pure first, then state-changing)
4. Public functions (view/pure first, then state-changing)
5. Internal functions
6. Private functions

Key Principles

1. NatSpec: Use @inheritdoc in implementations; full docs live in interfaces
2. Errors: One specific error per failure mode; never use generic catch-all errors
3. CEI Pattern: Always checks → effects → interactions
4. SafeERC20: Always use safeTransfer and safeTransferFrom
5. Timestamps: Use uint40 for all timestamps
6. Amounts: Use uint128 for token amounts

Contract Structure Pattern

Standard Directory Layout

src/
├── MainContract.sol     # Entry point
├── abstracts/           # Inheritance chain (state, features, base contracts)
├── interfaces/          # Public APIs - NatSpec lives here (use @inheritdoc in impl)
├── libraries/           # Errors.sol, Helpers.sol, Math libraries
└── types/               # Structs, enums, namespace libraries

Inheritance Pattern

Inherit in alphabetical order:

contract TokenVault is Batch, ERC721, ITokenVault, VaultDynamic, VaultLinear { ... }

Writing New Contract Code

Contract Checklist

When writing a new contract or function:

• Correct license and pragma
• Imports ordered: external → internal → local
• Named imports only (use curly braces)
• Section comments for code organization
• @inheritdoc for interface implementations
• Specific errors for each failure mode
• Checks-effects-interactions ordering
• SafeERC20 for token transfers
• uint40 for timestamps, uint128 for amounts
• Storage packing considered for new structs
• Contract size under 24kb limit

Contract Size Limit

Contracts must stay under the 24kb bytecode limit. Verify with the optimized profile:

forge build --sizes

If a contract exceeds the limit:

1. Extract logic into external libraries - Use public/external library functions instead of internal
2. Split into multiple contracts via inheritance
3. Remove unused functions
4. Use shorter error messages or custom errors

External Libraries Pattern

Use public library functions to reduce contract size (called via DELEGATECALL rather than inlined):

// Library with PUBLIC functions (not inlined, reduces contract size)
library VaultMath {
    function calculateAmount(...) public pure returns (uint128) { ... }
}

library Helpers {
    function validateParams(...) public view { ... }
}

// Main contract calls library functions (DELEGATECALL, not inlined)
contract TokenVault {
    function _computeAmount(uint256 id) private view returns (uint128) {
        return VaultMath.calculateAmount(...);
    }
}

Key insight: internal library functions are inlined into the contract bytecode. public/external library functions are called via DELEGATECALL, keeping bytecode smaller but costing slightly more gas per call.

Stack Too Deep

When you encounter "Stack Too Deep" errors, use an in-memory struct to bundle local variables:

/// @dev Needed to avoid Stack Too Deep.
struct ComputeVars {
    address token;
    string tokenSymbol;
    uint128 depositedAmount;
    string json;
    ITokenVault vault;
    string status;
}

function compute(uint256 id) external view returns (string memory result) {
    ComputeVars memory vars;

    vars.vault = ITokenVault(address(this));
    vars.depositedAmount = vars.vault.getDepositedAmount(id);
    vars.token = address(vars.vault.getToken(id));
    // ... use vars.field instead of separate local variables
}

Place *Vars structs in types/DataTypes.sol if reused, or inline in the contract if function-specific.

Adding Errors

1. Add error to package's libraries/Errors.sol
2. Use naming: {ContractName}_{ErrorDescription}
3. Add NatSpec: /// @notice Thrown when...
4. Include relevant parameters for debugging

/// @notice Thrown when trying to withdraw more than available.
error TokenVault_Overdraw(uint256 id, uint128 amount, uint128 withdrawableAmount);

Adding Functions

1. Add signature and full NatSpec to interface
2. Implement in contract with @inheritdoc
3. Place in correct section (external/public/internal/private)
4. Order modifiers: visibility → mutability → override → custom

Common Patterns

Safe Token Transfers

using SafeERC20 for IERC20;

// Safe transfers handle non-standard ERC20s
token.safeTransfer(to, amount);
token.safeTransferFrom(from, to, amount);

Common Tasks

Add a view function

1. Add to interface with full NatSpec (notice, dev, param, return)
2. Implement with @inheritdoc InterfaceName
3. Add appropriate modifiers (e.g., notNull(id) if accessing resource state)

Add a state-changing function

1. Add to interface with NatSpec (include Notes and Requirements sections)
2. Implement with @inheritdoc
3. Add modifiers: noDelegateCall, notNull(id), etc.
4. Follow CEI pattern
5. Emit events after state changes

Add a new error

1. Define in libraries/Errors.sol with section comment
2. Add NatSpec: /// @notice Thrown when...
3. Include debugging parameters
4. Use in contract: revert Errors.ContractName_ErrorDesc(...)

Add a new struct

1. Define in types/ directory
2. Pack fields for gas efficiency (see .claude/skills/solidity-coding/references/coding-patterns.md)
3. Add NatSpec for struct and each field
4. Use @param for each field in struct NatSpec

Example Invocations

Test this skill with these prompts:

1. New function: "Add a getStreamBalance view function to the ISablierFlow interface"
2. Error handling: "Add a Flow_InsufficientBalance error with debugging parameters"
3. Gas optimization: "Optimize the _withdraw function using storage caching"
4. Contract structure: "Create the interface for a new TokenVesting contract with deposit, withdraw, and claim functions"