Implement get_id native function

fastx_programmability/framework/sources/ID.move

@@ -65,11 +65,7 @@ module FastX::ID {
     /// Get the ID for `obj`. Safe because fastX has an extra
     /// bytecode verifier pass that forces every struct with
     /// the `key` ability to have a distinguished `ID` field.
-    //public native fun get_id<T: key>(obj: &T): &ID;
-    public fun get_id<T: key>(_obj: &T): &ID {
-        // TODO: implement native function for this.
-        abort(0)
-    }
+    public native fun get_id<T: key>(obj: &T): &ID;
 
     public native fun bytes_to_address(bytes: vector<u8>): address;
 }

fastx_programmability/framework/src/natives/id.rs

@@ -9,7 +9,7 @@ use move_vm_types::{
     loaded_data::runtime_types::Type,
     natives::function::{native_gas, NativeResult},
     pop_arg,
-    values::Value,
+    values::{StructRef, Value},
 };
 use smallvec::smallvec;
 use std::collections::VecDeque;
@@ -34,3 +34,20 @@ pub fn bytes_to_address(
 
     Ok(NativeResult::ok(cost, smallvec![Value::address(addr)]))
 }
+
+pub fn get_id(
+    context: &mut NativeContext,
+    ty_args: Vec<Type>,
+    mut args: VecDeque<Value>,
+) -> PartialVMResult<NativeResult> {
+    debug_assert!(ty_args.len() == 1);
+    debug_assert!(args.len() == 1);
+
+    let obj = pop_arg!(args, StructRef);
+    let id_field = obj.borrow_field(0)?;
+
+    // TODO: what should the cost of this be?
+    let cost = native_gas(context.cost_table(), NativeCostIndex::SIGNER_BORROW, 0);
+
+    Ok(NativeResult::ok(cost, smallvec![id_field]))
+}

fastx_programmability/framework/src/natives/mod.rs

@@ -16,6 +16,7 @@ pub fn all_natives(
     const FASTX_NATIVES: &[(&str, &str, NativeFunction)] = &[
         ("Event", "emit", event::emit),
         ("ID", "bytes_to_address", id::bytes_to_address),
+        ("ID", "get_id", id::get_id),
         ("Transfer", "transfer_internal", transfer::transfer_internal),
         (
             "Transfer",

fastx_programmability/framework/tests/IDTests.move

@@ -0,0 +1,21 @@
+#[test_only]
+module FastX::IDTests {
+    use FastX::ID;
+    use FastX::TxContext;
+
+    const ID_BYTES_MISMATCH: u64 = 0;
+
+    struct Object has key, drop {
+        id: ID::ID,
+    }
+
+    #[test]
+    fun test_get_id() {
+        let ctx = TxContext::dummy();
+        let id = TxContext::new_id(&mut ctx);
+        let id_bytes = *ID::get_inner(&id);
+        let obj = Object { id };
+
+        assert!(ID::get_id_bytes(&obj) == &id_bytes, ID_BYTES_MISMATCH);
+    }
+}