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# ABI Utilities
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Translate and update ABI definitions across different Solidity compiler versions to ensure compatibility with modern tooling and standards.
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## Capabilities
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### ABI Update
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Update ABI definitions from older compiler versions to include modern fields and comply with current standards.
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```typescript { .api }
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/**
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 * Update ABI to latest standard format with modern fields
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 * @param compilerVersion - Semantic version string of the compiler that generated the ABI
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 * @param abi - Original ABI array from compiler output
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 * @returns Updated ABI array with modern fields added
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 */
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function update(compilerVersion: string, abi: any[]): any[];
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```
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**Usage Examples:**
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```typescript
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import abi from "solc/abi";
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// Update ABI from old compiler version
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const oldABI = [
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  {
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    constant: false,
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    inputs: [],
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    name: 'hello',
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    outputs: [{ name: '', type: 'string' }],
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    payable: false,
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    type: 'function'
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  }
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];
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const updatedABI = abi.update('0.3.6', oldABI);
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console.log(updatedABI);
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/* Output includes modern fields:
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[
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  {
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    constant: false,
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    inputs: [],
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    name: 'hello',
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    outputs: [{ name: '', type: 'string' }],
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    payable: true,
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    stateMutability: 'payable',
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    type: 'function'
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  },
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  {
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    type: 'fallback',
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    payable: true,
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    stateMutability: 'payable'
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  }
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]
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*/
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```
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### Version-Specific Updates
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The ABI updater applies different transformations based on the compiler version:
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**Pre-0.4.0 Changes:**
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- Adds `payable: true` to all non-constant functions
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- Adds default constructor if missing
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- Adds default fallback function
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**Pre-0.4.5 Changes:**
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- Assumes all constructors are payable
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**Pre-0.4.16 Changes:**
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- Adds `stateMutability` field based on `payable` and `constant` flags:
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  - `payable: true` → `stateMutability: 'payable'`
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  - `constant: true` → `stateMutability: 'view'`
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  - Otherwise → `stateMutability: 'nonpayable'`
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**Pre-0.1.2 Changes:**
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- Adds default constructor with payable state
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```typescript
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import abi from "solc/abi";
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// Different behavior based on version
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const modernVersion = abi.update('0.8.0', originalABI); // Minimal changes
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const oldVersion = abi.update('0.3.0', originalABI);    // Many compatibility additions
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```
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### ABI Field Evolution
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Understanding how ABI fields have evolved across compiler versions:
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```typescript { .api }
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interface ABIFunction {
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  type: 'function' | 'constructor' | 'fallback' | 'receive' | 'event';
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  name?: string;
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  inputs: ABIParameter[];
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  outputs?: ABIParameter[];
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  // Legacy field (pre-0.4.16)
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  constant?: boolean;
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  // Legacy field (pre-0.4.16) 
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  payable?: boolean;
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  // Modern field (0.4.16+)
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  stateMutability?: 'pure' | 'view' | 'nonpayable' | 'payable';
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}
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interface ABIParameter {
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  name: string;
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  type: string;
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  components?: ABIParameter[]; // For structs and tuples
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  indexed?: boolean; // For events
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}
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```
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### Practical Usage Scenarios
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**Legacy Contract Integration:**
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```typescript
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import solc from "solc";
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import abi from "solc/abi";
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// When working with contracts compiled by old versions
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const legacyOutput = JSON.parse(fs.readFileSync('legacy-contract-output.json'));
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const contractABI = legacyOutput.contracts['Contract.sol']['MyContract'].interface;
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// Parse and update the ABI
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const parsedABI = JSON.parse(contractABI);
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const modernABI = abi.update('0.3.6', parsedABI);
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// Now compatible with modern web3 libraries
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const contract = new web3.eth.Contract(modernABI, contractAddress);
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```
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**ABI Compatibility Checking:**
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```typescript
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import abi from "solc/abi";
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function ensureModernABI(contractABI: any[], compilerVersion: string) {
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  // Check if ABI needs updating
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  const hasStateMutability = contractABI.some(item => 
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    item.type === 'function' && 'stateMutability' in item
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  );
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  if (!hasStateMutability) {
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    console.log('Updating legacy ABI to modern format');
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    return abi.update(compilerVersion, contractABI);
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  }
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  return contractABI;
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}
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```
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### State Mutability Migration
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The most significant change handled by the ABI updater is the migration from `constant`/`payable` flags to `stateMutability`:
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```typescript
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// Before (legacy format)
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const legacyFunction = {
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  type: 'function',
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  name: 'getValue',
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  constant: true,
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  payable: false,
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  inputs: [],
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  outputs: [{ name: '', type: 'uint256' }]
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};
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// After ABI update
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const modernFunction = {
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  type: 'function',
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  name: 'getValue',
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  constant: true,        // Preserved for compatibility
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  payable: false,        // Preserved for compatibility
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  stateMutability: 'view', // Added based on constant: true
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  inputs: [],
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  outputs: [{ name: '', type: 'uint256' }]
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};
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```
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### Default Function Addition
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For very old compiler versions, the updater adds missing default functions:
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```typescript
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// Original ABI from pre-0.1.2 compiler
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const originalABI = [
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  {
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    type: 'function',
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    name: 'myFunction',
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    inputs: [],
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    outputs: []
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  }
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];
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// Updated ABI includes default constructor and fallback
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const updatedABI = abi.update('0.1.1', originalABI);
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/* Result:
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[
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  {
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    type: 'function',
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    name: 'myFunction',
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    inputs: [],
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    outputs: [],
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    payable: true,
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    stateMutability: 'payable'
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  },
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  {
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    type: 'constructor',
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    payable: true,
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    stateMutability: 'payable',
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    inputs: []
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  },
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  {
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    type: 'fallback',
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    payable: true,
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    stateMutability: 'payable'
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  }
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]
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*/
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```