From f507084eafc41875003f0ca9351fc0ee93f50f64 Mon Sep 17 00:00:00 2001
From: ngundotra <noah@gundotra.org>
Date: Wed, 3 May 2023 12:17:53 -0400
Subject: [PATCH] explicitly only parse two args

---
 lang/attribute/event/src/lib.rs         | 42 ++++++++++++++++++-------
 tests/events/programs/events/src/lib.rs |  6 ++--
 2 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/lang/attribute/event/src/lib.rs b/lang/attribute/event/src/lib.rs
index 68f7e8c46c..573576d97f 100644
--- a/lang/attribute/event/src/lib.rs
+++ b/lang/attribute/event/src/lib.rs
@@ -1,7 +1,10 @@
 extern crate proc_macro;
 
 use quote::quote;
-use syn::parse_macro_input;
+use syn::{
+    parse::{Parse, ParseStream},
+    parse_macro_input, Expr, Token,
+};
 
 /// The event attribute allows a struct to be used with
 /// [emit!](./macro.emit.html) so that programs can log significant events in
@@ -81,23 +84,40 @@ pub fn emit(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     })
 }
 
-#[proc_macro]
-pub fn emit_cpi(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
-    let tuple = parse_macro_input!(input as syn::ExprTuple);
+// Custom wrapper struct (thanks ChatGPT!)
+struct TwoArgs {
+    arg1: Expr,
+    arg2: Expr,
+}
+
+// Implement the `Parse` trait for the `TwoArgs` struct
+impl Parse for TwoArgs {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let arg1: Expr = input.parse()?;
+        input.parse::<Token![,]>()?;
+        let arg2: Expr = input.parse()?;
+
+        if !input.is_empty() {
+            return Err(input.error("Expected exactly 2 arguments"));
+        }
 
-    let elems = tuple.elems;
-    if elems.len() != 2 {
-        panic!("Expected a tuple with exactly two elements.");
+        Ok(TwoArgs { arg1, arg2 })
     }
+}
+
+#[proc_macro]
+pub fn emit_cpi(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    // let tuple = parse_macro_input!(input as syn::ExprTuple);
+    let two_args = parse_macro_input!(input as TwoArgs);
 
-    let first = &elems[0];
-    let second = &elems[1];
+    let self_program_info = &two_args.arg1;
+    let event_struct = &two_args.arg2;
 
     proc_macro::TokenStream::from(quote! {
-        let program_info: anchor_lang::solana_program::account_info::AccountInfo = #first;
+        let program_info: anchor_lang::solana_program::account_info::AccountInfo = #self_program_info;
 
         let __disc = crate::event::EVENT_IX_TAG_LE;
-        let __inner_data: Vec<u8> = anchor_lang::Event::data(&#second);
+        let __inner_data: Vec<u8> = anchor_lang::Event::data(&#event_struct);
         let __ix_data: Vec<u8> = __disc.into_iter().chain(__inner_data.into_iter()).collect();
 
         let __ix = anchor_lang::solana_program::instruction::Instruction::new_with_bytes(
diff --git a/tests/events/programs/events/src/lib.rs b/tests/events/programs/events/src/lib.rs
index 1dac02b881..7d0fffc777 100644
--- a/tests/events/programs/events/src/lib.rs
+++ b/tests/events/programs/events/src/lib.rs
@@ -25,13 +25,13 @@ pub mod events {
     }
 
     pub fn test_event_cpi(ctx: Context<TestEventCpi>) -> Result<()> {
-        emit_cpi!((
+        emit_cpi!(
             ctx.accounts.program.to_account_info(),
             MyOtherEvent {
                 data: 7,
                 label: "cpi".to_string(),
-            },
-        ));
+            }
+        );
         Ok(())
     }
 }