Michelson parser/AST in go

[jevonearth]

Summary

Implement a Michelson parser/AST in Go to enable rich policy rules for smart contract calls. This would allow Signatory to inspect transaction parameters and enforce granular policies beyond simple operation type filtering.

Use Cases

1. Entrypoint Allowlist

Only allow calls to specific contract entrypoints:

allow:
  generic:
    - transaction:
        entrypoints: [stake, unstake, claim]

2. Entrypoint Blocklist

Block dangerous entrypoints while allowing others:

deny:
  generic:
    - transaction:
        entrypoints: [withdraw_all, emergency_exit]

3. Parameter Constraints

Limit values in transaction parameters:

allow:
  generic:
    - transaction:
        entrypoint: transfer
        constraints:
          - path: $.amount
            max: 10000000000  # max 10k tez

4. Destination + Entrypoint Combinations

allow:
  generic:
    - transaction:
        destination: KT1StakingContract...
        entrypoints: [stake, unstake]
    - transaction:
        destination: KT1GovernanceContract...
        entrypoints: [vote, propose]

Technical Approach

1. Parse Michelson parameters from transaction operations
2. Build AST representation of the parameter data
3. Implement JSONPath-like query language for policy rules
4. Integrate with existing policy engine

Related Issues

• (Rich policy rules) Transfer limits: maximum amount/TX #60 - Transfer limits: maximum amount/TX
• (Rich policy rules) Transfer limits: maximum TX/time period #61 - Transfer limits: maximum TX/time period
• (Rich policy rules) Approved destination list #62 - Approved destination list
• (Rich policy rules) Transfer limits: time of day rules #63 - Transfer limits: time of day rules
• Approval groups: allowing human approval for key operations #64 - Approval groups

Notes

This is a significant undertaking but would enable enterprise-grade policy control for institutional users managing treasury keys, staking operations, or DeFi interactions.