Add test to ensure instructions sysvar behaves as expected from withi…

…n a CPI

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

@@ -3,13 +3,14 @@
 extern crate solana_program;
 use solana_program::{
     account_info::next_account_info, account_info::AccountInfo, entrypoint,
-    entrypoint::ProgramResult, msg, program_error::ProgramError, pubkey::Pubkey,
+    entrypoint::ProgramResult, msg, program::invoke, program_error::ProgramError, pubkey::Pubkey,
     sysvar::instructions,
+    instruction::{Instruction,AccountMeta},
 };
 
 entrypoint!(process_instruction);
 fn process_instruction(
-    _program_id: &Pubkey,
+    program_id: &Pubkey,
     accounts: &[AccountInfo],
     instruction_data: &[u8],
 ) -> ProgramResult {
@@ -41,5 +42,19 @@ fn process_instruction(
 
     msg!(&format!("data[0]: {}", instruction.data[0]));
     msg!(&format!("index: {}", current_instruction));
+
+    if instruction_data.len() == 2 {
+        // CPI ourself with the same arguments to confirm the instructions sysvar reports the same
+        // results from within a CPI
+        invoke(
+            &Instruction::new_with_bytes(
+                *program_id,
+                &[instruction_data[0], instruction_data[1], 1],
+                vec![AccountMeta::new_readonly(instructions::id(), false)],
+            ),
+            &[instruction_accounts.clone()],
+        )?;
+    }
+
     Ok(())
 }