frontend: Support index-traits in bytecode generator

dora-frontend/src/generator.rs

@@ -1778,7 +1778,7 @@ impl<'a> AstBytecodeGen<'a> {
             CallType::Method(..)
             | CallType::GenericMethod(..)
             | CallType::TraitObjectMethod(..) => {
-                let obj_expr = expr.object().expect("method target required");
+                let obj_expr = expr.object().unwrap_or(expr.callee());
                 let reg = gen_expr(self, obj_expr, DataDest::Alloc);
 
                 Some(reg)

tests/ops/ops-index-get1.dora

@@ -0,0 +1,29 @@
+struct Foo { a: Float64, b: Float64 }
+
+impl std::traits::IndexGet for Foo {
+    type Index = Int;
+    type Item = Float64;
+
+    fn get(index: Self::Index): Self::Item {
+        if index == 0 {
+            self.a
+        } else {
+            assert(index == 1);
+            self.b
+        }
+    }
+}
+
+fn get0(x: Foo): Float64 {
+    x(0)
+}
+
+fn get1(x: Foo): Float64 {
+    x(1)
+}
+
+fn main() {
+    let x = Foo(a=12.0, b=17.0);
+    assert(get0(x) == 12.0);
+    assert(get1(x) == 17.0);
+}

tests/ops/ops-index-set1.dora

@@ -0,0 +1,34 @@
+class Foo { a: Float64, b: Float64 }
+
+impl std::traits::IndexSet for Foo {
+    type Index = Int;
+    type Item = Float64;
+
+    fn set(index: Self::Index, value: Self::Item) {
+        if index == 0 {
+            self.a = value;
+        } else {
+            assert(index == 1);
+            self.b = value;
+        }
+    }
+}
+
+fn set0(x: Foo, value: Float64) {
+    x(0) = value;
+}
+
+fn set1(x: Foo, value: Float64) {
+    x(1) = value;
+}
+
+fn main() {
+    let x = Foo(a=12.0, b=18.0);
+    set0(x, 16.0);
+    assert(x.a == 16.0);
+    assert(x.b == 18.0);
+
+    set1(x, 32.0);
+    assert(x.a == 16.0);
+    assert(x.b == 32.0);
+}