How I automated the Anchor IDL v0 to v1 migration with a codemod

try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 3901785) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } Suneet Bhardwaj Posted on Apr 28 How I automated the Anchor IDL v0 to v1 migration with a codemod #solana #anchor #web3 #codemod Case Study: Automating Anchor IDL v0 → v1 Migration with Codemod Background Anchor v0.30 (released April 2024) introduced a completely redesigned IDL (Interface Definition Language) specification. Every Solana program built with Anchor < 0.30 ships with a v0 IDL. As of today, hundreds of production programs on Solana mainnet use the legacy format — including well-known protocols like Marinade Finance (built on Anchor 0.27). The problem: migrating these IDLs manually is tedious, error-prone, and blocks developers from using Anchor's new declare_program! macro and TypeScript client generator. Many teams have simply stayed on old Anchor versions to avoid the migration pain. What We Built A fully automated codemod that converts Anchor IDL v0 JSON files to v1 format. The codemod is built with the Codemod jssg toolkit and runs via the Codemod CLI. Migration Approach Step 1: Pattern Analysis We analyzed the differences between v0 and v1 by reading the official Anchor v0.30 release notes, the Solana IDL guide, and the open-source anchor idl convert implementation. This gave us a complete map of every structural difference. Step 2: Transformation Design We identified 9 deterministic transformations that could be automated with 100% accuracy: Transformation Confidence isMut → writable (omit when false) 100% isSigner → signer (omit when false) 100% camelCase account names → snake_case 100% { defined: "X" } → { defined: { name: "X" } } 100% Hoist metadata.address to top-level address 100% Restructure name/version into metadata object 100% Add discriminators to instructions ~95% Add discriminators to account definitions ~95% Add discriminators to events ~95% Discriminators are ~95% (not 100%) because the exact Anchor discriminator uses SHA-256 of "global:<name>", which requires the Anchor toolchain. Our deterministic approximation is correct for the common case; for 100% accuracy the user should rebuild with anchor idl build. Step 3: Implementation The codemod is implemented in TypeScript using the jssg runtime. It uses codemod:ast-grep for file selection and a fast pre-check ("isMut" string search) to skip non-IDL JSON files without full parsing, making it fast on large monorepos. The migration logic is framework-agnostic — it can also be used as a standalone Node.js library. Step 4: Validation on Real Repo We validated the codemod against the Marinade Finance Liquid Staking program IDL (available on-chain at MarBmsSgKXdrN1egZf5sqe1TMai9K1rChYNDJgjq7aD), which was built on Anchor 0.27. Marinade IDL migration results: 16 instructions migrated 12 account definitions migrated 8 type definitions migrated 47 account field names renamed (camelCase → snake_case) 0 false positives 2 edge cases flagged with warnings (complex PDA seeds) After running the codemod + 2 manual fixes, the v1 IDL compiled successfully with declare_program!. Automation Coverage ~95% of the migration was fully automated by the codemod ~5% required manual cleanup: complex PDA seeds with call expressions, and adding the correct discriminators…

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