Panic with unowned subjects

Author: lpil

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## v1.0.0-rc2 - Unreleased
+
+- `process.receive` will now panic if given a non-named subject that is not
+  owned by the current process.
+
 ## v1.0.0-rc1 - 2025-04-24
 
 - In the `gleam/erlang/process` module:

src/gleam/erlang/process.gleam

@@ -219,10 +219,30 @@ pub fn send(subject: Subject(message), message: message) -> Nil {
 ///
 /// The `within` parameter specifies the timeout duration in milliseconds.
 ///
-@external(erlang, "gleam_erlang_ffi", "receive")
+/// ## Panics
+///
+/// This function will panic if a process tries to receive with a non-named
+/// subject that it does not own.
+///
 pub fn receive(
   from subject: Subject(message),
   within timeout: Int,
+) -> Result(message, Nil) {
+  case subject {
+    NamedSubject(..) -> perform_receive(subject, timeout)
+    Subject(owner:, ..) ->
+      case owner == self() {
+        True -> perform_receive(subject, timeout)
+        False ->
+          panic as "Cannot receive with a subject owned by another process"
+      }
+  }
+}
+
+@external(erlang, "gleam_erlang_ffi", "receive")
+fn perform_receive(
+  subject: Subject(message),
+  timeout: Int,
 ) -> Result(message, Nil)
 
 /// Receive a message that has been sent to current process using the `Subject`.

test/gleam/erlang/process_test.gleam

@@ -76,6 +76,18 @@ pub fn receive_test() {
   let assert Error(Nil) = process.receive(subject, 0)
 }
 
+@external(erlang, "gleam_erlang_test_ffi", "assert_gleam_panic")
+fn assert_panic(f: fn() -> t) -> String
+
+pub fn receive_other_test() {
+  let subject = process.new_subject()
+  process.spawn(fn() { process.send(subject, process.new_subject()) })
+  let assert Ok(subject) = process.receive(subject, 20)
+
+  assert_panic(fn() { process.receive(subject, 0) })
+  |> should.equal("Cannot receive with a subject owned by another process")
+}
+
 pub fn receive_forever_test() {
   let subject = process.new_subject()
 

test/gleam_erlang_test_ffi.erl

@@ -0,0 +1,10 @@
+-module(gleam_erlang_test_ffi).
+-export([assert_gleam_panic/1]).
+
+assert_gleam_panic(F) ->
+    try
+        F(),
+        erlang:error(expected_panic)
+    catch
+        error:#{gleam_error := _, message := M} -> M
+    end.