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Version: 0.42

Cadence 1.0 Migration Guide

This upgrade roadmap offers developers guidance, actionable steps, and expectations around updating your project to be compatible with Cadence 1.0.

The Cadence 1.0 release, introduced in the Crescendo network upgrade, is a breaking change.Developers need to update all Cadence code used by their app (including all existing smart contracts deployed on Flow, their transactions and scripts) to Cadence 1.0, to ensure it continues to work after the network upgrade.

Many of the improvements of Cadence 1.0 fundamentally change how Cadence works and is used. This means it is necessary to break existing code to release this version, which will guarantee stability going forward.

The dates for the Crescendo upgrade are as follows:

  • Testnet: June 20
  • Mainnet: July 31

Any contracts not upgraded on their respective networks by these dates will break.

Benefits of Cadence 1.0​

Cadence 1.0 is the latest version of the Cadence smart contract programming language. The stable release of Cadence 1.0 represents a significant milestone in the language’s maturity, delivering a comprehensive suite of improvements that increase speed, security and efficiency. With Cadence 1.0, developers gain access to over 20 new features and enhancements. Each change is thoughtfully designed to streamline workflows, reduce duplication and improve code readability, making writing and understanding smart contracts much easier.

Staging and State Migration Process​

The migration to Crescendo requires developers to adapt their code for compatibility with the latest Cadence 1.0 updates, a process that involves rewriting contracts and ‘staging’ them against the currently deployed versions. The new staging mechanism is run via a Flow CLI command. Staged code swaps and replaces deployed code at the time of the upgrade, contracts not updated by this time will cease to function.

To make the migration process smooth, new tools, testing environments, and networks have been introduced. Previewnet, is a temporary network featuring the upgraded core contracts and Cadence 1.0 language features, it’s designed for experimentation and not involved in the staging process. Additionally, for both Testnet and Mainnet, "Migration Environment" networks will be created which fork all staged contracts, and their dependencies along with their data and state. These migration environments are reset weekly, pulling in any newly staged contracts, static analysis typechecker reports will also be published on all staged contracts that were not updated correctly.

The Testnet Migration environment is currently being run weekly and the Mainnet Migration environment is scheduled for mid year.

Help is available during the Cadence 1.0 Office Hours each week at 10:00am PST on the Flow Developer Discord.

Expectations​

  • Any contracts that are not upgraded will fail after the Testnet and Mainnet upgrade. They cannot be upgraded again, so it is imperative that developers stage their upgrades before the Cadence 1.0 migration.
  • After the Testnet upgrade, Cadence versions will differ on Testnet (v1.0) and Mainnet (v0.42).
  • Developers must take extra considerations if they wish to continue deploying on the Mainnet during this period. Otherwise, incompatibilities between different Cadence versions will lead to failed deployments.

Developer Steps to Upgrade​

What you need to do you and when you need to do it

  1. Understand the Changes: Start by familiarizing yourself with the changes to identify how they might affect your code.
  2. Modify Your Code: Update your contracts, transactions, and scripts in accordance with the new changes.
  3. Test Your Code: The latest emulator release includes all updated standards and core contracts. You should test your code changes locally and additionally on the Crescendo Previewnet and/or Testnet. You can also prepare for the Mainnet Migration, by simulating staging and state migration on the Flow Emulator.
  4. Stage your Contracts for Migration: The last step is to get your updated code ready to replace your live pre-cadence 1.0 code when the upgrade occurs, to do this you need to stage your contracts. Stage them on testnet and ensure that they are working as expected along with their staged dependencies. Staging for mainnet contracts is coming soon.

Developer Milestones​

Under each Milestone breakdown we include the steps you need to take, the tools and reference materials available (or planned) and an estimate of time/resources commitment for each step.

MilestoneOverviewDescriptionDatesExample NFT Time EstRequirements
1Update and Test Your CodeUpdate your code (contracts, scripts, transactions, and event listeners) and test on Emulator/PreviewnetOngoing~ 1-2 weeksCadence 1.0 documentation, CLI/Emulator support for Cadence 1.0, Previewnet
2Perform Local Staging/Migration TestingTest contract staging and state migration on EmulatorOngoing~ 1 dayCLI Emulator support for staging, state migration
3Stage and Confirm on Testnet Migration EnvTest contract staging and state migrations on Testnet Migration EnvironmentApril 1 - June 20~ 1 Week (Stage/QA)Flow CLI, Testnet Migration Environment
4Stage and Confirm on Mainnet Migration EnvTest contract staging and state migrations on Mainnet Migration EnvironmentApril 15 - June 20~ 1 Week (Stage/QA)Flow CLI, Mainnet Migration Environment
5Mainnet MigrationMainnet MigrationJune 20 - July 31n/aAll contracts staged to Mainnet

Update and Test Your Code​

Estimated Time Required: ~1-2 Weeks

Review The Cadence 1.0 Breaking Improvements and Upgrade Plan​

In order to determine the changes needed for your application, you’ll first need to familiarize yourself with Cadence 1.0 breaking improvements, code updates, and the planned upgrade process.

  • Learn how Cadence will be changing for 1.0
  • Understand the upgrade, the timeline, and how it affects you
  • Check out the Cadence Language 1.0 docs

Once you understand what changes are required for your app, you can use the Cadence 1.0 CLI to update, test, and run your upgraded code. Ensure to update and test all your contracts, transactions, scripts and event listeners to valid Cadence 1.0 code.

warning

IMPORTANT NOTE ABOUT AVOIDING CHANGES IN BUSINESS LOGIC

  • The on-chain data migration logic relies on assumption that the updated contracts uploaded by dapp developers limits updates to the minimum changes required by the Cadence 1.0 version - in other words, the updated contract should be behaviour-preserving.
  • If the contract upgrade to Cadence 1.0 also includes changes to business logic, the on-chain data migration won’t work as expected and might result in security vulnerabilities in the migrated on-chain data.

Install Cadence 1.0 CLI​

This video guide demonstrates how to install the pre-release version of Flow CLI and start working towards a feature branch that is Cadence 1.0 compatible.

Run the following command to install the CLI version with support for Cadence 1.0.

  • Linux/MacOS: sudo sh -ci "$(curl -fsSL https://raw.githubusercontent.com/onflow/flow-cli/feature/stable-cadence/install.sh)"
  • Windows: iex "& { $(irm 'https://raw.githubusercontent.com/onflow/flow-cli/feature/stable-cadence/install.ps1') }"

The Cadence 1.0 CLI will now be installed on your machine and can be accessed via the flow-c1 command. To verify the installation, run: flow-c1 version

Additionally you can use the Cadence VSCode Extension, Cadence Linter, and Chat GPT Flow Migration Assistant to help identify sections of code which must be migrated to Cadence 1.0, view details about what must change as well as suggested fixes for straightforward migrations.

Using Cadence 1.0 in VSCode​

The Cadence VSCode Extension now supports Cadence 1.0. Instantly identify and learn about all the changes you need to make to become Crescendo ready.

Cadence 1.0 in VSCode

Test Code Changes on Crescendo Previewnet​

Crescendo Previewnet is Flow's official testing and development network. It is intended to provide a testing environment for app developers. It aims to balance similarity with Mainnet with being a productive development environment with two key differences:

  1. Faster block rate
  2. Shorter epochs (~12 hours)

Crescendo Previewnet is available for access at the following URLs:

  • GRPC: access.previewnet.nodes.onflow.org:9000
  • REST: https://rest-previewnet.onflow.org
  1. Generate a new key pair with the Flow CLI
  2. Fund your account with Previewnet Faucet - If you generated the keypair through the CLI, you can click on the URL provided to create an account and request crescendo FLOW tokens.
  3. Use Flow Reference Wallet (Chrome Extension) which provides support for Crescendo Previewnet
    1. Install Flow Wallet Chrome Extension from Chrome Web Store
    2. Navigate to settings
    3. Enable "Developer Mode"
    4. Select Previewnet
  4. Use FlowDiver, the Flow Blockchain Explorer to review analytics, transactions, block, account and contract information for Previewnet.

Upgrading NFT and FT Contracts​

In addition to changes to the Cadence programming language, the Cadence token standards are also being streamlined and improved. All NFTs and FTs will also need to prepare and migrate their existing Cadence smart contracts, scripts, and transactions for the update. If you do not update your code, your applications will become non-functional after the network upgrade.

NFT Standard v2​

This document describes the changes to the Cadence Non-Fungible Token (NFT) standard and gives a step-by-step guide for how to upgrade your NFT contract from Cadence 0.42 to Cadence 1.0.

FT Standard v2​

This document describes the changes to the Cadence Non-Fungible Token (NFT) standard and gives a step-by-step guide for how to upgrade your NFT contract from Cadence 0.42 to Cadence 1.0.

Perform Local Staging/Migration Testing​

Estimated Time Required: ~1 Day

Review the documentation and use Flow CLI to test staging and state migration locally.

Make sure your flow.json has the correct accounts and deployments specified for the contracts that you are staging.


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// Stage a Cadence 1.0 supported contract project using the Flow CLI.
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$ flow-c1 migrate stage <contract_name>
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Unstage a Cadence 1.0 supported contract project using the Flow CLI.
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$ flow-c1 migrate unstage-contract <contract_name>
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Check to see if a contract has been staged from the Flow CLI
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$ flow-c1 migrate is-staged <contract_name>
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Get the staged contract code from a contract that's been correctly staged.
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$ flow-c1 migrate staged-code <contract_name>
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.

Test Local State Migration​

Flow CLI provides the flow migrate state command to migrate your local emulator state to Cadence 1.0, and to deploy upgraded contracts to the emulator. This is useful for locally testing the staged contract upgrades, and to see how the new network and the upgraded contracts would behave with the migrated data.

To test the migration, first you would need an emulator state, created with an emulator/CLI release that uses a pre-1.0 Cadence version. It is recommended to use the latest pre-1.0 CLI version (e.g: v1.17.0) for creating the old state.

  1. Get Emulator State
    1. To get an emulator state with Flow CLI 1.17.0, start the emulator with the --persist flag (e.g. flow emulator --persist)
    2. Deploy the pre-1.0 project/contracts to the emulator
    3. Run transactions if there are any.
    4. Stop the emulator (Ctrl-C on *nix platforms, and Ctrl-Break or Ctrl-Pause on Windows). It is important to make sure the emulator is stopped before taking the snapshot, so that any pending in-memory data would be written to the persisted state properly.
    5. Locate the persisted state ./flowdb/emulator.sqlite file, from the project root.
  2. Migrate
    1. Download and install the latest CLI, that runs Cadence 1.0.
    2. Run flow-c1 migrate against the previously created state. The state file (emulator.sqlite) can be provided using the --db-path flag.
    3. If there are any contracts that also need to be upgraded, those can be specified using the --contracts flag. Note that, the paths to these updated contracts and their deployed addresses must be specified in the flow.json file. (see (Flow CLI documentation about contract deployments)[https://developers.flow.com/tools/flow-cli/deployment/project-contracts#define-contract-deployment-targets] for more info)
    4. A sample migrate command would look like: flow-c1 migrate state --db-path=/path/to/emulator.sqlite --save-report=./reports --contracts="Test"
  3. Testing the Migrated State Once the migration is completed successfully, the emulator can be started with the migrated state. For that, ensure the emulator is started again using the new CLI version (that runs Cadence 1.0), with the --persist flag. Now the emulator should be up and running using the migrated state and the updated contracts.

Run any transactions to verify the correctness of the existing data.

Stage and Confirm on Testnet Migration Env​

Estimated Time Required: ~1 Week

Beginning April 3rd, 2024, the Flow team triggered migration of contracts that were staged for upgrade, ran all Cadence 1.0 migrations and simulated a snapshot of Testnet state in is called the Testnet Migration Enviroment. This completes the first full upgrade process to Cadence 1.0 and the environment is run weekly. Following the upgrade on Testnet, the migrations will begin on Mainnet. This step creates a fully working “real” environment, where developers can see if their staged code is valid, has any failing dependenceis, or test their app's interactions with other contracts and projects available on Crescendo network. The Flow team may repeat this step multiple times (resetting the Crescendo network to pre-upgrade state and performing the upgrade again) to fix issues found during the upgrade process.

In order to migrate your updated smart contract to Cadence 1.0, it's crucial to stage it on the network. This preliminary step not only verifies the contract's compatibility and syntactical correctness but also ensures a seamless transition to the new environment.

Use the CLI to stage your contracts to the Migration Environment for state migration testing. Automatic state migrations will happen several times over the Testnet Migration Environment testing period on a weekly cadence.


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// Stage a Cadence 1.0 supported contract project using the Flow CLI.
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$ flow-c1 migrate stage <contract_name> --network=testnet
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Check to see if a contract has been successfully staged on Testnet.
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$ flow-c1 migrate is-staged <contract_name> --network=testnet
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Lists all Cadence 1.0 supported contracts that are staged on Testnet.
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$ flow-c1 migrate list-staged --network=testnet
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Arguments: network_name

You can view all currently staged contracts for Testnet by inspecting the account of the staging contract, 0x2ceae959ed1a7e7a, for example through https://f.dnz.dev/0x2ceae959ed1a7e7a.

You can see reports on migration status in the Cadence Repository.

Staging not only allows a developer to test their migration. At the time of the official network upgrades, all staged contracts will replace currently deployed code.

Stage and Confirm on Mainnet Migration Env​

Estimated Time Required: ~1 Week

warning

IMPORTANT NOTE ABOUT STAGING YOUR CONTRACTS FOR UPGRADE

Developers must stage their contracts to be upgraded in this step. The Entitlements migration requires the Cadence 1.0 version of a contract to be staged for upgrade in order to successfully complete the migration of the related on-chain data as described in the Entitlements Migration Proposal. If a contract is not staged for the upgrade before Mainnnet Upgrade, the Entitlements migration for the related on-chain data will not be run, and it won’t be possible to test the contract on Crescendo network.

Use the CLI to stage your contracts to Mainnet Migration Environment for state migration testing. State migrations will happen several times over the Testnet Migration Environment testing period.


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// Stage a Cadence 1.0 supported contract project using the Flow CLI.
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$ flow-c1 migrate stage <contract_name> --network=mainnet
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Check to see if a contract has been successfully staged on Mainnet.
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$ flow-c1 migrate is-staged <contract_name> --network=mainnet
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Arguments: contract_name
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Valid Input: Existing contract name in flow.json.
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// Lists all Cadence 1.0 supported contracts that are staged on Mainnet.
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$ flow-c1 migrate list-staged --network --network=mainnet
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Arguments: network_name

Validate your contract​

To validate your contract, execute the following command:


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// Lists all Cadence 1.0 supported contracts that are staged on Mainnet.
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$ flow-c1 migrate is-validated --network --network=mainnet
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Arguments: network_name

A response of true indicates that your contract has been successfully staged and validated. Validation passes if the contract was successfully migrated over in the last emulated migration.

Additional Resources​