Add create account helper

Author: febo

programs/system/src/lib.rs

@@ -1,5 +1,78 @@
 #![no_std]
 
+use pinocchio::{
+    account_info::AccountInfo,
+    instruction::Signer,
+    pubkey::Pubkey,
+    sysvars::{rent::Rent, Sysvar},
+    ProgramResult,
+};
+
+use crate::instructions::{Allocate, CreateAccount, Transfer};
+
 pub mod instructions;
 
 pinocchio_pubkey::declare_id!("11111111111111111111111111111111");
+
+/// Create an account with a minimal balance to be rent-exempt.
+///
+/// The account with be funded by the `payer` if the current lamports
+/// are insufficient for rent-exemption.
+///
+/// # Safety
+///
+/// This function assigns the `account` to the specified `owner` program.
+/// The caller must ensure that no references to the current account
+/// owner exist.
+#[inline(always)]
+pub unsafe fn create_account_with_minimal_balance(
+    account: &AccountInfo,
+    space: usize,
+    owner: &Pubkey,
+    payer: &AccountInfo,
+    signers: &[Signer],
+    rent_sysvar: Option<&AccountInfo>,
+) -> ProgramResult {
+    let lamports = if let Some(rent_sysvar) = rent_sysvar {
+        let rent = Rent::from_account_info(rent_sysvar)?;
+        rent.minimum_balance(space)
+    } else {
+        Rent::get()?.minimum_balance(space)
+    };
+
+    if account.lamports() == 0 {
+        CreateAccount {
+            from: payer,
+            to: account,
+            lamports,
+            space: space as u64,
+            owner,
+        }
+        .invoke_signed(signers)
+    } else {
+        let required_lamports = lamports.saturating_sub(account.lamports());
+
+        // Transfer lamports from `payer` to `account` if needed.
+        if required_lamports > 0 {
+            Transfer {
+                from: payer,
+                to: account,
+                lamports: required_lamports,
+            }
+            .invoke()?;
+        }
+
+        Allocate {
+            account,
+            space: space as u64,
+        }
+        .invoke_signed(signers)?;
+
+        // Assign `account` to the owner program.
+        unsafe {
+            account.assign(owner);
+        }
+
+        Ok(())
+    }
+}