fix: fallback to eth_sign for permit approval (#5847)

* fix: fallback to eth_sign for permit approval

* chore: clean up comments/logs

* refactor: mirror ethers impl

* chore: add comment re: impl

src/hooks/usePermitAllowance.ts

+import 'utils/signTypedData'
+
 import { AllowanceTransfer, MaxAllowanceTransferAmount, PERMIT2_ADDRESS, PermitSingle } from '@uniswap/permit2-sdk'
 import { CurrencyAmount, Token } from '@uniswap/sdk-core'
 import { useWeb3React } from '@web3-react/core'

src/utils/signTypedData.ts

+import { _TypedDataEncoder } from '@ethersproject/hash'
+import { JsonRpcSigner } from '@ethersproject/providers'
+
+/**
+ * Overrides the _signTypedData method to add support for wallets without EIP-712 support (eg Zerion) by adding a fallback to eth_sign.
+ * The implementation is copied from ethers (and linted), except for the catch statement, which removes the logger and adds the fallback.
+ * @see https://github.com/ethers-io/ethers.js/blob/c80fcddf50a9023486e9f9acb1848aba4c19f7b6/packages/providers/src.ts/json-rpc-provider.ts#L334
+ */
+JsonRpcSigner.prototype._signTypedData = async function signTypedDataWithFallbacks(this, domain, types, value) {
+  // Populate any ENS names (in-place)
+  const populated = await _TypedDataEncoder.resolveNames(domain, types, value, (name: string) => {
+    return this.provider.resolveName(name) as Promise<string>
+  })
+
+  const address = await this.getAddress()
+
+  try {
+    return await this.provider.send('eth_signTypedData_v4', [
+      address.toLowerCase(),
+      JSON.stringify(_TypedDataEncoder.getPayload(populated.domain, types, populated.value)),
+    ])
+  } catch (error) {
+    if (typeof error.message === 'string' && error.message.match(/not found/i)) {
+      console.warn('eth_signTypedData_v4 failed, falling back to eth_sign:', error)
+      const hash = _TypedDataEncoder.hash(populated.domain, types, populated.value)
+      return await this.provider.send('eth_sign', [address, hash])
+    }
+    throw error
+  }
+}