Add support for idiomatic error handling to BPF instruction processors (#7968)

programs/bpf/rust/external_spend/src/lib.rs

@@ -1,18 +1,20 @@
 //! @brief Example Rust-based BPF program that moves a lamport from one account to another
 
 extern crate solana_sdk;
-use solana_sdk::{account_info::AccountInfo, entrypoint, entrypoint::SUCCESS, pubkey::Pubkey};
+use solana_sdk::{
+    account_info::AccountInfo, entrypoint, program_error::ProgramError, pubkey::Pubkey,
+};
 
 entrypoint!(process_instruction);
 fn process_instruction(
     _program_id: &Pubkey,
     accounts: &[AccountInfo],
     _instruction_data: &[u8],
-) -> u32 {
+) -> Result<(), ProgramError> {
     // account 0 is the mint and not owned by this program, any debit of its lamports
     // should result in a failed program execution.  Test to ensure that this debit
     // is seen by the runtime and fails as expected
     **accounts[0].lamports.borrow_mut() -= 1;
 
-    SUCCESS
+    Ok(())
 }