lang: Add custom error for raw constraint (#905)

CHANGELOG.md

@@ -18,6 +18,7 @@ incremented for features.
 * ts: `Program<T>` can now be typed with an IDL type ([#795](https://github.com/project-serum/anchor/pull/795)).
 * lang: Add `mint::freeze_authority` keyword for mint initialization within `#[derive(Accounts)]` ([#835](https://github.com/project-serum/anchor/pull/835)).
 * lang: Add `AccountLoader` type for `zero_copy` accounts with support for CPI ([#792](https://github.com/project-serum/anchor/pull/792)).
+* lang: Add custom errors support for raw constraints ([#905](https://github.com/project-serum/anchor/pull/905)).
 
 ### Breaking
 

lang/derive/accounts/src/lib.rs

@@ -44,7 +44,7 @@ use syn::parse_macro_input;
 /// | `#[account(close = <target>)]` | On `ProgramAccount` and `Loader` structs. | Marks the account as being closed at the end of the instruction's execution, sending the rent exemption lamports to the specified <target>. |
 /// | `#[account(has_one = <target>)]` | On `ProgramAccount` or `CpiAccount` structs | Checks the `target` field on the account matches the `target` field in the struct deriving `Accounts`. |
 /// | `#[account(seeds = [<seeds>], bump? = <target>, payer? = <target>, space? = <target>, owner? = <target>)]` | On `AccountInfo` structs | Seeds for the program derived address an `AccountInfo` struct represents. If bump is provided, then appends it to the seeds. On initialization, validates the given bump is the bump provided by `Pubkey::find_program_address`.|
-/// | `#[account(constraint = <expression>)]` | On any type deriving `Accounts` | Executes the given code as a constraint. The expression should evaluate to a boolean. |
+/// | `#[account(constraint = <expression>)]`<br><br>`#[account(constraint = <expression> @ <custom_error>)]` | On any type deriving `Accounts` | Executes the given code as a constraint. The expression should evaluate to a boolean. Custom errors are supported via `@`. |
 /// | `#[account("<literal>")]` | Deprecated | Executes the given code literal as a constraint. The literal should evaluate to a boolean. |
 /// | `#[account(rent_exempt = <skip>)]` | On `AccountInfo` or `ProgramAccount` structs | Optional attribute to skip the rent exemption check. By default, all accounts marked with `#[account(init)]` will be rent exempt, and so this should rarely (if ever) be used. Similarly, omitting `= skip` will mark the account rent exempt. |
 /// | `#[account(executable)]` | On `AccountInfo` structs | Checks the given account is an executable program. |

lang/syn/src/codegen/accounts/constraints.rs

@@ -235,9 +235,10 @@ pub fn generate_constraint_literal(c: &ConstraintLiteral) -> proc_macro2::TokenS
 
 pub fn generate_constraint_raw(c: &ConstraintRaw) -> proc_macro2::TokenStream {
     let raw = &c.raw;
+    let error = generate_custom_error(&c.error, quote! { ConstraintRaw });
     quote! {
         if !(#raw) {
-            return Err(anchor_lang::__private::ErrorCode::ConstraintRaw.into());
+            return Err(#error);
         }
     }
 }
@@ -658,3 +659,13 @@ pub fn generate_constraint_state(f: &Field, c: &ConstraintState) -> proc_macro2:
         }
     }
 }
+
+fn generate_custom_error(
+    custom_error: &Option<Expr>,
+    error: proc_macro2::TokenStream,
+) -> proc_macro2::TokenStream {
+    match custom_error {
+        Some(error) => quote! { #error.into() },
+        None => quote! { anchor_lang::__private::ErrorCode::#error.into() },
+    }
+}

lang/syn/src/lib.rs

@@ -618,6 +618,7 @@ pub struct ConstraintLiteral {
 #[derive(Debug, Clone)]
 pub struct ConstraintRaw {
     pub raw: Expr,
+    pub error: Option<Expr>,
 }
 
 #[derive(Debug, Clone)]

lang/syn/src/parser/accounts/constraints.rs

@@ -229,6 +229,7 @@ pub fn parse_token(stream: ParseStream) -> ParseResult<ConstraintToken> {
                     span,
                     ConstraintRaw {
                         raw: stream.parse()?,
+                        error: parse_optional_custom_error(&stream)?,
                     },
                 )),
                 "close" => ConstraintToken::Close(Context::new(
@@ -251,6 +252,15 @@ pub fn parse_token(stream: ParseStream) -> ParseResult<ConstraintToken> {
     Ok(c)
 }
 
+fn parse_optional_custom_error(stream: &ParseStream) -> ParseResult<Option<Expr>> {
+    if stream.peek(Token![@]) {
+        stream.parse::<Token![@]>()?;
+        stream.parse().map(Some)
+    } else {
+        Ok(None)
+    }
+}
+
 #[derive(Default)]
 pub struct ConstraintGroupBuilder<'ty> {
     pub f_ty: Option<&'ty Ty>,

tests/errors/programs/errors/src/lib.rs

@@ -32,6 +32,10 @@ mod errors {
     pub fn signer_error(_ctx: Context<SignerError>) -> Result<()> {
         Ok(())
     }
+
+    pub fn raw_custom_error(_ctx: Context<RawCustomError>) -> Result<()> {
+        Ok(())
+    }
 }
 
 #[derive(Accounts)]
@@ -61,10 +65,17 @@ pub struct HasOneAccount {
     owner: Pubkey,
 }
 
+#[derive(Accounts)]
+pub struct RawCustomError<'info> {
+    #[account(constraint = *my_account.key == ID @ MyError::HelloCustom)]
+    my_account: AccountInfo<'info>
+}
+
 #[error]
 pub enum MyError {
     #[msg("This is an error message clients will automatically display")]
     Hello,
     HelloNoMsg = 123,
     HelloNext,
+    HelloCustom,
 }

tests/errors/tests/errors.js

@@ -112,4 +112,20 @@ describe("errors", () => {
       assert.equal(err.toString(), errMsg);
     }
   });
+
+  it("Emits a raw custom error", async () => {
+    try {
+      const tx = await program.rpc.rawCustomError({
+        accounts: {
+          myAccount: anchor.web3.SYSVAR_RENT_PUBKEY,
+        },
+      });
+      assert.ok(false);
+    } catch (err) {
+      const errMsg = "HelloCustom";
+      assert.equal(err.toString(), errMsg);
+      assert.equal(err.msg, errMsg);
+      assert.equal(err.code, 300 + 125);
+    }
+  });
 });