Cairo snforge Troubleshooting

Overview

Guide debugging snforge test failures, particularly Sierra compilation errors that occur after successful Cairo compilation.

Quick Use

• Read references/common-errors.md before diagnosing.
• Check Scarb.toml settings first - enable-gas = false causes many issues.
• Verify toolchain version compatibility (snforge, universal-sierra-compiler, Cairo).
• Generic implementations need proper trait bounds.

Response Checklist

• If error mentions "cycle during cost computation": check enable-gas setting.
• If error mentions "universal-sierra-compiler": check version compatibility.
• If generic code fails: ensure +Drop<T>, +Copy<T> bounds and struct derives.
• If scarb build passes but scarb test fails: issue is test-specific compilation.

Common Error Patterns

"unexpected cycle during cost computation"

Cause: enable-gas = false in [cairo] section of Scarb.toml Fix: Remove enable-gas = false or set to true

"Error while compiling Sierra"

Cause: Version mismatch between Cairo and universal-sierra-compiler Fix: Run snfoundryup to update toolchain

Generic impl compilation issues

Cause: Missing trait bounds on generic implementations Fix: Add +Drop<T>, +Copy<T> to impl and #[derive(Drop, Copy)] to structs

Example Requests

• "My tests fail with 'unexpected cycle during cost computation'"
• "snforge test fails but scarb build works"
• "universal-sierra-compiler error after Cairo upgrade"