Add runnable assert equal hook

Author: olwang

README.md

@@ -418,7 +418,7 @@ If a lowered package contains `fn main() -> Unit` or `fn main() -> Result<Unit,
 
 `rss verify-rust <file.rss> --out-dir <directory>` keeps the generated package used for backend checking, including `rsscript-source-map.json`, so unmappable rustc diagnostics can be inspected against the generated Rust.
 
-The first observable runtime boundary is `Log.write(message: read String)`, which lowers to an explicit runtime output hook.
+The first observable runtime boundaries are `Log.write(message: read String)` and `Assert.equal(left: read String, right: read String)`, which lower to explicit runtime hooks.
 
 Smallest runnable example:
 

examples/assert_equal.rss

@@ -0,0 +1,5 @@
+fn main() -> Unit {
+    Assert.equal(left: read "rss", right: read "rss")
+    Log.write(message: read "assert equal passed")
+    return Unit
+}

runtime/src/lib.rs

@@ -93,6 +93,10 @@ pub fn log_write(message: &str) {
     println!("{message}");
 }
 
+pub fn assert_equal(left: &str, right: &str) {
+    assert_eq!(left, right);
+}
+
 pub struct GcRead<'a, T>(Ref<'a, T>);
 
 impl<T> Deref for GcRead<'_, T> {

src/rust_lower.rs

@@ -1016,6 +1016,7 @@ fn is_native_boundary(effect: &EffectDecl) -> bool {
 fn lower_callee(callee: &Callee) -> String {
     match callee {
         callee if is_log_write_callee(callee) => "rsscript_runtime::log_write".to_string(),
+        callee if is_assert_equal_callee(callee) => "rsscript_runtime::assert_equal".to_string(),
         Callee::Name(name) => rust_ident(name),
         Callee::Qualified { namespace, name } if type_root_name(namespace) == "ResourcePool" => {
             format!("rsscript_runtime::ResourcePool::{}", rust_ident(name))
@@ -1030,6 +1031,10 @@ fn is_log_write_callee(callee: &Callee) -> bool {
     matches!(callee, Callee::Qualified { namespace, name } if type_root_name(namespace) == "Log" && name == "write")
 }
 
+fn is_assert_equal_callee(callee: &Callee) -> bool {
+    matches!(callee, Callee::Qualified { namespace, name } if type_root_name(namespace) == "Assert" && name == "equal")
+}
+
 fn is_resource_pool_borrow_callee(callee: &Callee) -> bool {
     matches!(callee, Callee::Qualified { namespace, name } if type_root_name(namespace) == "ResourcePool" && name == "borrow")
 }

tests/checker.rs

@@ -278,6 +278,23 @@ fn main() -> Unit {
     assert!(rust.contains("rsscript_runtime::log_write(&\"hello RSScript\".to_string());"));
 }
 
+#[test]
+fn rust_lowering_maps_assert_equal_to_runtime_hook() {
+    let source = r#"
+fn main() -> Unit {
+    Assert.equal(left: read "rss", right: read "rss")
+    return Unit
+}
+"#;
+    let rust = lower_source_to_rust("assert.rss", source).expect("source should lower");
+
+    assert!(
+        rust.contains(
+            "rsscript_runtime::assert_equal(&\"rss\".to_string(), &\"rss\".to_string());"
+        )
+    );
+}
+
 #[test]
 fn rust_lowering_maps_try_operator_to_rust_result_propagation() {
     let source = r#"