RFC: add discriminator to idl

lang/Cargo.toml

@@ -16,6 +16,7 @@ anchor-debug = [
     "anchor-attribute-access-control/anchor-debug",
     "anchor-attribute-account/anchor-debug",
     "anchor-attribute-constant/anchor-debug",
+    "anchor-attribute-discriminator/anchor-debug",
     "anchor-attribute-error/anchor-debug",
     "anchor-attribute-event/anchor-debug",
     "anchor-attribute-interface/anchor-debug",
@@ -29,6 +30,7 @@ anchor-debug = [
 anchor-attribute-access-control = { path = "./attribute/access-control", version = "0.25.0" }
 anchor-attribute-account = { path = "./attribute/account", version = "0.25.0" }
 anchor-attribute-constant = { path = "./attribute/constant", version = "0.25.0" }
+anchor-attribute-discriminator = { path = "./attribute/discriminator", version = "0.25.0" }
 anchor-attribute-error = { path = "./attribute/error", version = "0.25.0" }
 anchor-attribute-program = { path = "./attribute/program", version = "0.25.0" }
 anchor-attribute-state = { path = "./attribute/state", version = "0.25.0" }

lang/attribute/discriminator/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "anchor-attribute-discriminator"
+version = "0.25.0"
+authors = ["Serum Foundation <[email protected]>"]
+repository = "https://github.com/coral-xyz/anchor"
+license = "Apache-2.0"
+description = "Anchor attribute macro for creating discriminator types"
+rust-version = "1.56"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[features]
+anchor-debug = ["anchor-syn/anchor-debug"]
+
+[dependencies]
+proc-macro2 = "1.0"
+syn = { version = "1.0.60", features = ["full"] }
+anchor-syn = { path = "../../syn", version = "0.25.0" }

lang/attribute/discriminator/src/lib.rs

@@ -0,0 +1,10 @@
+extern crate proc_macro;
+
+/// A marker attribute used to override the discriminator value that should be used.
+#[proc_macro_attribute]
+pub fn discriminator(
+    _attr: proc_macro::TokenStream,
+    input: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    input
+}

lang/src/lib.rs

@@ -47,6 +47,7 @@ pub use crate::bpf_upgradeable_state::*;
 pub use anchor_attribute_access_control::access_control;
 pub use anchor_attribute_account::{account, declare_id, zero_copy};
 pub use anchor_attribute_constant::constant;
+pub use anchor_attribute_discriminator::discriminator;
 pub use anchor_attribute_error::*;
 pub use anchor_attribute_event::{emit, event};
 pub use anchor_attribute_interface::interface;
@@ -238,9 +239,10 @@ pub mod prelude {
         accounts::account_loader::AccountLoader, accounts::program::Program,
         accounts::signer::Signer, accounts::system_account::SystemAccount,
         accounts::sysvar::Sysvar, accounts::unchecked_account::UncheckedAccount, constant,
-        context::Context, context::CpiContext, declare_id, emit, err, error, event, interface,
-        program, require, require_eq, require_gt, require_gte, require_keys_eq, require_keys_neq,
-        require_neq, solana_program::bpf_loader_upgradeable::UpgradeableLoaderState, source, state,
+        context::Context, context::CpiContext, declare_id, discriminator, emit, err, error, event,
+        interface, program, require, require_eq, require_gt, require_gte, require_keys_eq,
+        require_keys_neq, require_neq,
+        solana_program::bpf_loader_upgradeable::UpgradeableLoaderState, source, state,
         system_program::System, zero_copy, AccountDeserialize, AccountSerialize, Accounts,
         AccountsExit, AnchorDeserialize, AnchorSerialize, Id, Key, Owner, ProgramData, Result,
         ToAccountInfo, ToAccountInfos, ToAccountMetas,

lang/syn/src/idl/file.rs

@@ -83,6 +83,7 @@ pub fn parse(
                                 );
                                 IdlInstruction {
                                     name,
+                                    discriminator: None,
                                     docs: None,
                                     accounts,
                                     args,
@@ -131,6 +132,7 @@ pub fn parse(
                         idl_accounts(&ctx, accounts_strct, &accs, seeds_feature, no_docs);
                     IdlInstruction {
                         name,
+                        discriminator: None,
                         docs: None,
                         accounts,
                         args,
@@ -216,6 +218,7 @@ pub fn parse(
             };
             IdlInstruction {
                 name: ix.ident.to_string().to_mixed_case(),
+                discriminator: ix.discriminator.clone(),
                 docs: ix.docs.clone(),
                 accounts,
                 args,

lang/syn/src/idl/mod.rs

@@ -46,6 +46,8 @@ pub struct IdlState {
 pub struct IdlInstruction {
     pub name: String,
     #[serde(skip_serializing_if = "Option::is_none")]
+    pub discriminator: Option<Vec<u8>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub docs: Option<Vec<String>>,
     pub accounts: Vec<IdlAccountItem>,
     pub args: Vec<IdlField>,

lang/syn/src/lib.rs

@@ -85,6 +85,7 @@ pub struct StateInterface {
 pub struct Ix {
     pub raw_method: ItemFn,
     pub ident: Ident,
+    pub discriminator: Option<Vec<u8>>,
     pub docs: Option<Vec<String>>,
     pub args: Vec<IxArg>,
     pub returns: IxReturn,

lang/syn/src/parser/program/instructions.rs

@@ -3,6 +3,7 @@ use crate::parser::program::ctx_accounts_ident;
 use crate::{FallbackFn, Ix, IxArg, IxReturn};
 use syn::parse::{Error as ParseError, Result as ParseResult};
 use syn::spanned::Spanned;
+use syn::Lit;
 
 // Parse all non-state ix handlers from the program mod definition.
 pub fn parse(program_mod: &syn::ItemMod) -> ParseResult<(Vec<Ix>, Option<FallbackFn>)> {
@@ -25,11 +26,13 @@ pub fn parse(program_mod: &syn::ItemMod) -> ParseResult<(Vec<Ix>, Option<Fallbac
         .map(|method: &syn::ItemFn| {
             let (ctx, args) = parse_args(method)?;
             let docs = docs::parse(&method.attrs);
+            let discriminator = parse_discriminator(&method.attrs)?;
             let returns = parse_return(method)?;
             let anchor_ident = ctx_accounts_ident(&ctx.raw_arg)?;
             Ok(Ix {
                 raw_method: method.clone(),
                 ident: method.sig.ident.clone(),
+                discriminator,
                 docs,
                 args,
                 anchor_ident,
@@ -129,3 +132,32 @@ pub fn parse_return(method: &syn::ItemFn) -> ParseResult<IxReturn> {
         )),
     }
 }
+
+pub fn parse_discriminator(attrs: &[syn::Attribute]) -> ParseResult<Option<Vec<u8>>> {
+    let mut discriminators = Vec::new();
+
+    for attr in attrs {
+        if attr.path.segments.last().unwrap().ident == "discriminator" {
+            if let Ok(Lit::Int(dis)) = attr.parse_args::<Lit>() {
+                if let Ok(value) = dis.base10_parse::<u64>() {
+                    discriminators.push((attr.span(), value));
+                    continue;
+                }
+            }
+
+            return Err(ParseError::new(
+                attr.span(),
+                "Discriminator value like `#[discriminator(0xdeadbeeffeedcafe)]` expected",
+            ));
+        }
+    }
+
+    match discriminators.len() {
+        0 => Ok(None),
+        1 => Ok(Some(discriminators[0].1.to_be_bytes().to_vec())),
+        _ => Err(ParseError::new(
+            discriminators[1].0,
+            "More than one discriminator function found",
+        )),
+    }
+}