revert approve removal

contracts/src/token/psp22/psp22.rs

@@ -77,6 +77,12 @@ pub trait PSP22Impl: Storage<Data> + Internal {
         Ok(())
     }
 
+    fn approve(&mut self, spender: AccountId, value: Balance) -> Result<(), PSP22Error> {
+        let owner = Self::env().caller();
+        self._approve_from_to(owner, spender, value)?;
+        Ok(())
+    }
+
     fn increase_allowance(&mut self, spender: AccountId, delta_value: Balance) -> Result<(), PSP22Error> {
         let owner = Self::env().caller();
         self._approve_from_to(owner, spender, self._allowance(&owner, &spender) + delta_value)

contracts/src/traits/psp22/psp22.rs

@@ -78,6 +78,21 @@ pub trait PSP22 {
         data: Vec<u8>,
     ) -> Result<(), PSP22Error>;
 
+    /// Allows `spender` to withdraw from the caller's account multiple times, up to
+    /// the `value` amount.
+    ///
+    /// If this function is called again it overwrites the current allowance with `value`.
+    ///
+    /// An `Approval` event is emitted.
+    ///
+    /// # Important
+    ///
+    /// This function is vulnerable to the double spending attack. 
+    /// Based on the OpenZeppelin security review of OpenBrush, we recommend using the
+    /// `increase_allowance` and `decrease_allowance` functions.
+    #[ink(message)]
+    fn approve(&mut self, spender: AccountId, value: Balance) -> Result<(), PSP22Error>;
+
     /// Atomically increases the allowance granted to `spender` by the caller.
     ///
     /// An `Approval` event is emitted.

lang/codegen/src/implementations.rs

@@ -170,6 +170,11 @@ pub(crate) fn impl_psp22(impl_args: &mut ImplArgs, capped: bool) {
                 PSP22Impl::transfer_from(self, from, to, value, data)
             }
 
+            #[ink(message)]
+            fn approve(&mut self, spender: AccountId, value: Balance) -> Result<(), PSP22Error> {
+                PSP22Impl::approve(self, spender, value)
+            }
+
             #[ink(message)]
             fn increase_allowance(&mut self, spender: AccountId, delta_value: Balance) -> Result<(), PSP22Error> {
                 PSP22Impl::increase_allowance(self, spender, delta_value)
@@ -891,6 +896,11 @@ pub(crate) fn impl_psp22_pallet(impl_args: &mut ImplArgs) {
                 PSP22PalletImpl::transfer_from(self, from, to, value, data)
             }
 
+            #[ink(message)]
+            fn approve(&mut self, spender: AccountId, value: Balance) -> Result<(), PSP22Error> {
+                PSP22PalletImpl::approve(self, spender, value)
+            }
+
             #[ink(message)]
             fn increase_allowance(&mut self, spender: AccountId, delta_value: Balance) -> Result<(), PSP22Error> {
                 PSP22PalletImpl::increase_allowance(self, spender, delta_value)