lang: Fix instruction return type generation with `declare_program!` (#2977)

CHANGELOG.md

@@ -32,6 +32,7 @@ The minor version will be incremented upon a breaking change and the patch versi
 - lang: Fix using `Vec<u8>` type with `declare_program!` ([#2966](https://github.com/coral-xyz/anchor/pull/2966)).
 - lang: Fix `ProgramError::ArithmeticOverflow` not found error ([#2975](https://github.com/coral-xyz/anchor/pull/2975)).
 - lang: Fix using optional accounts with `declare_program!` ([#2967](https://github.com/coral-xyz/anchor/pull/2967)).
+- lang: Fix instruction return type generation with `declare_program!` ([#2977](https://github.com/coral-xyz/anchor/pull/2977)).
 
 ### Breaking
 

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

@@ -50,7 +50,7 @@ fn gen_cpi_instructions(idl: &Idl) -> proc_macro2::TokenStream {
                 let ty = convert_idl_type_to_syn_type(ty);
                 (
                     quote! { anchor_lang::Result<Return::<#ty>> },
-                    quote! { Ok(Return::<#ty> { phantom:: std::marker::PhantomData }) },
+                    quote! { Ok(Return::<#ty> { phantom: std::marker::PhantomData }) },
                 )
             },
             None => (

tests/declare-program/idls/external.json

@@ -45,53 +45,66 @@
       "args": []
     },
     {
-      "name": "update",
+      "name": "test_compilation_defined_type_param",
       "discriminator": [
-        219,
-        200,
-        88,
-        176,
-        158,
-        63,
-        253,
-        127
+        61,
+        118,
+        87,
+        242,
+        137,
+        97,
+        90,
+        223
       ],
       "accounts": [
         {
-          "name": "authority",
+          "name": "signer",
           "signer": true
-        },
-        {
-          "name": "my_account",
-          "writable": true,
-          "pda": {
-            "seeds": [
-              {
-                "kind": "account",
-                "path": "authority"
-              }
-            ]
-          }
         }
       ],
       "args": [
         {
-          "name": "value",
-          "type": "u32"
+          "name": "_my_account",
+          "type": {
+            "defined": {
+              "name": "MyAccount"
+            }
+          }
         }
       ]
     },
     {
-      "name": "update_all",
+      "name": "test_compilation_return_type",
       "discriminator": [
-        205,
-        139,
-        239,
-        66,
-        134,
-        131,
-        110,
-        182
+        174,
+        51,
+        51,
+        121,
+        52,
+        61,
+        38,
+        28
+      ],
+      "accounts": [
+        {
+          "name": "signer",
+          "signer": true
+        }
+      ],
+      "args": [],
+      "returns": "bool"
+    },
+    {
+      "name": "update",
+      "discriminator": [
+        219,
+        200,
+        88,
+        176,
+        158,
+        63,
+        253,
+        127
       ],
       "accounts": [
         {
@@ -113,12 +126,8 @@
       ],
       "args": [
         {
-          "name": "my_account",
-          "type": {
-            "defined": {
-              "name": "MyAccount"
-            }
-          }
+          "name": "value",
+          "type": "u32"
         }
       ]
     },

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

@@ -21,10 +21,22 @@ pub mod external {
     }
 
     // Compilation test for whether a defined type (an account in this case) can be used in `cpi` client.
-    pub fn update_all(ctx: Context<Update>, my_account: MyAccount) -> Result<()> {
-        *ctx.accounts.my_account = my_account;
+    pub fn test_compilation_defined_type_param(
+        _ctx: Context<TestCompilation>,
+        _my_account: MyAccount,
+    ) -> Result<()> {
         Ok(())
     }
+
+    // Compilation test for whether a custom return type can be specified in `cpi` client
+    pub fn test_compilation_return_type(_ctx: Context<TestCompilation>) -> Result<bool> {
+        Ok(true)
+    }
+}
+
+#[derive(Accounts)]
+pub struct TestCompilation<'info> {
+    pub signer: Signer<'info>,
 }
 
 #[derive(Accounts)]