Add ProgramError::CustomError and truncate value to 32 bytes

runtime/src/runtime.rs

@@ -107,7 +107,14 @@ fn execute_instruction(
         executable_accounts,
         program_accounts,
         tick_height,
-    )?;
+    )
+    .map_err(|err| match err {
+        ProgramError::CustomError(mut error) => {
+            error.truncate(32);
+            ProgramError::CustomError(error)
+        }
+        e => e,
+    })?;
 
     // Verify the instruction
     for ((pre_program_id, pre_lamports, pre_userdata), post_account) in

sdk/src/native_program.rs

@@ -36,6 +36,12 @@ pub enum ProgramError {
 
     /// SystemInstruction::Assign was attempted on an account unowned by the system program
     AssignOfUnownedAccount,
+
+    /// CustomError allows on-chain programs to implement program-specific error types and see
+    /// them returned by the Solana runtime. A CustomError may be any type that is serialized
+    /// to a Vec of bytes, max length 32 bytes. Any CustomError Vec greater than this length will
+    /// be truncated by the runtime.
+    CustomError(Vec<u8>),
 }
 
 impl std::fmt::Display for ProgramError {