classfile: writer honors itf flag for invokestatic on interfaces

crates/noxis-classfile/tests/roundtrip/code.rs

@@ -0,0 +1,108 @@
+//! Code-level round trips that the IR must survive.
+
+use noxis_classfile::Insn;
+use noxis_classfile::format;
+use ristretto_classfile::attributes::{Attribute as RtAttr, Instruction as Rt};
+use ristretto_classfile::{
+    ClassAccessFlags, ClassFile as RtClass, ConstantPool, JAVA_21, Method as RtMethod,
+    MethodAccessFlags,
+};
+
+/// `invokestatic` on an *interface* method (`List.of`) needs a
+/// `CONSTANT_InterfaceMethodref`: writing a plain `Methodref` passes the
+/// verifier's structural check but HotSpot rejects the linkage with
+/// `IncompatibleClassChangeError` at first call.
+#[test]
+fn invokestatic_interface_method_ref_round_trip() {
+    let mut pool = ConstantPool::default();
+    let this = pool.add_class("demo/IfStatic").expect("this");
+    let object = pool.add_class("java/lang/Object").expect("object");
+    let name = pool.add_utf8("main").expect("name");
+    let desc = pool.add_utf8("([Ljava/lang/String;)V").expect("desc");
+    let code_name = pool.add_utf8("Code").expect("code name");
+    let list_class = pool.add_class("java/util/List").expect("list");
+    let of = pool
+        .add_interface_method_ref(
+            list_class,
+            "of",
+            "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/util/List;",
+        )
+        .expect("interface ref");
+
+    let code = vec![
+        Rt::Aload_0,
+        Rt::Aload_0,
+        Rt::Invokestatic(of),
+        Rt::Pop,
+        Rt::Return,
+    ];
+    let rt = RtClass {
+        version: JAVA_21,
+        constant_pool: pool,
+        access_flags: ClassAccessFlags::PUBLIC | ClassAccessFlags::SUPER,
+        this_class: this,
+        super_class: object,
+        interfaces: vec![],
+        fields: vec![],
+        methods: vec![RtMethod {
+            access_flags: MethodAccessFlags::PUBLIC | MethodAccessFlags::STATIC,
+            name_index: name,
+            descriptor_index: desc,
+            attributes: vec![RtAttr::Code {
+                name_index: code_name,
+                max_stack: 2,
+                max_locals: 1,
+                code,
+                exception_table: vec![],
+                attributes: vec![],
+            }],
+        }],
+        attributes: vec![],
+        ..RtClass::default()
+    };
+
+    let mut original = Vec::new();
+    rt.to_bytes(&mut original).expect("to_bytes");
+    let parsed = format::parse(&original).expect("parse");
+    let method = &parsed.methods[0];
+    let invoke = method
+        .code
+        .as_ref()
+        .expect("code")
+        .insns
+        .iter()
+        .find_map(|i| match i {
+            Insn::Invoke {
+                kind, owner, itf, ..
+            } => Some((*kind, owner.clone(), *itf)),
+            _ => None,
+        })
+        .expect("invokestatic");
+    assert!(invoke.2, "parse must keep the interface flag");
+
+    let written = format::write(&parsed).expect("write");
+    let reparsed = format::parse(&written).expect("re-parse");
+    let method = &reparsed.methods[0];
+    let invoke = method
+        .code
+        .as_ref()
+        .expect("code")
+        .insns
+        .iter()
+        .find_map(|i| match i {
+            Insn::Invoke {
+                kind, owner, itf, ..
+            } => Some((*kind, owner.clone(), *itf)),
+            _ => None,
+        })
+        .expect("invokestatic");
+    assert_eq!(
+        invoke,
+        (
+            noxis_classfile::InvokeKind::Static,
+            "java/util/List".to_string(),
+            true
+        ),
+        "InterfaceMethodref must survive write"
+    );
+}