fix: declare_program with optional accounts

lang/attribute/program/src/declare_program/mods/parsers.rs

@@ -133,17 +133,40 @@ fn gen_instruction(idl: &Idl) -> proc_macro2::TokenStream {
                     let name = format_ident!("{}", acc.name);
                     let signer = acc.signer;
                     let writable = acc.writable;
-                    quote! {
-                        #name: {
-                            let acc = accs.next().ok_or_else(|| ProgramError::NotEnoughAccountKeys)?;
-                            if acc.is_signer != #signer {
-                                return Err(ProgramError::InvalidAccountData.into());
+                    let optional = acc.optional;
+                    if optional {
+                        // For optional accounts, the program ID is used as a placeholder when missing
+                        let program_id = get_canonical_program_id();
+                        quote! {
+                            #name: {
+                                let acc = accs.next().ok_or_else(|| ProgramError::NotEnoughAccountKeys)?;
+                                // Check if this is a placeholder (program_id used for missing optional accounts)
+                                if acc.pubkey == #program_id {
+                                    None
+                                } else {
+                                    if acc.is_signer != #signer {
+                                        return Err(ProgramError::InvalidAccountData.into());
+                                    }
+                                    if acc.is_writable != #writable {
+                                        return Err(ProgramError::InvalidAccountData.into());
+                                    }
+                                    Some(acc.pubkey)
+                                }
                             }
-                            if acc.is_writable != #writable {
-                                return Err(ProgramError::InvalidAccountData.into());
+                        }
+                    } else {
+                        quote! {
+                            #name: {
+                                let acc = accs.next().ok_or_else(|| ProgramError::NotEnoughAccountKeys)?;
+                                if acc.is_signer != #signer {
+                                    return Err(ProgramError::InvalidAccountData.into());
+                                }
+                                if acc.is_writable != #writable {
+                                    return Err(ProgramError::InvalidAccountData.into());
+                                }
+
+                                acc.pubkey
                             }
-
-                            acc.pubkey
                         }
                     }
                 }

tests/declare-program/idls/optional.json

@@ -0,0 +1,45 @@
+{
+  "address": "GjYjDUDpPNhE72Gw7ktmP81QqzZhx4LYPfFawrk3ucDA",
+  "metadata": {
+    "name": "anchor_1_0_0_rc_2_optional_bug",
+    "version": "0.1.0",
+    "spec": "0.1.0",
+    "description": "Created with Anchor"
+  },
+  "instructions": [
+    {
+      "name": "initialize",
+      "discriminator": [
+        175,
+        175,
+        109,
+        31,
+        13,
+        152,
+        155,
+        237
+      ],
+      "accounts": [
+        {
+          "name": "optional_account",
+          "optional": true
+        }
+      ],
+      "args": []
+    }
+  ],
+  "errors": [
+    {
+      "code": 6000,
+      "name": "CustomError",
+      "msg": "Custom error message"
+    }
+  ],
+  "constants": [
+    {
+      "name": "SEED",
+      "type": "string",
+      "value": "\"anchor\""
+    }
+  ]
+}

tests/declare-program/programs/declare-program/src/lib.rs

@@ -12,6 +12,10 @@ declare_program!(external_legacy);
 // https://github.com/raydium-io/raydium-idl/blob/6123104304ebcb42be175cc297a2c221ac96bb96/raydium_clmm/amm_v3.json
 declare_program!(amm_v3);
 
+// Compilation check for optional accounts
+// https://github.com/solana-foundation/anchor/issues/4179
+declare_program!(optional);
+
 #[program]
 pub mod declare_program {
     use super::*;