Collections.empty*, Collections.singleton*

Author: Gaming32

src/main/java/net/raphimc/javadowngrader/transformer/j8/methodcallreplacer/ListOfMCR.java

@@ -31,9 +31,27 @@ public InsnList getReplacement(ClassNode classNode, MethodNode methodNode, Strin
 
         final Type[] args = Type.getArgumentTypes(originalDesc);
         if (args.length != 1 || args[0].getSort() != Type.ARRAY) {
+            final int argCount = args.length;
+            if (argCount == 0) {
+                replacement.add(new MethodInsnNode(
+                    Opcodes.INVOKESTATIC,
+                    "java/util/Collections",
+                    "emptyList",
+                    "()Ljava/util/List;"
+                ));
+                return replacement;
+            } else if (argCount == 1) {
+                replacement.add(new MethodInsnNode(
+                    Opcodes.INVOKESTATIC,
+                    "java/util/Collections",
+                    "singletonList",
+                    "(Ljava/lang/Object;)Ljava/util/Set;"
+                ));
+                return replacement;
+            }
+
             final int freeVarIndex = ASMUtil.getFreeVarIndex(methodNode);
 
-            final int argCount = args.length;
             replacement.add(new TypeInsnNode(Opcodes.NEW, "java/util/ArrayList"));
             replacement.add(new InsnNode(Opcodes.DUP));
             replacement.add(new MethodInsnNode(Opcodes.INVOKESPECIAL, "java/util/ArrayList", "<init>", "()V"));

src/main/java/net/raphimc/javadowngrader/transformer/j8/methodcallreplacer/MapOfMCR.java

@@ -30,13 +30,31 @@ public InsnList getReplacement(ClassNode classNode, MethodNode methodNode, Strin
         final InsnList replacement = new InsnList();
 
         final Type[] args = Type.getArgumentTypes(originalDesc);
-        final int freeVarIndex = ASMUtil.getFreeVarIndex(methodNode);
 
         final int argCount = args.length;
         if (argCount % 2 != 0) {
             throw new RuntimeException("Map.of() requires an even number of arguments");
         }
 
+        if (argCount == 0) {
+            replacement.add(new MethodInsnNode(
+                Opcodes.INVOKESTATIC,
+                "java/util/Collections",
+                "emptyMap",
+                "()Ljava/util/Map;"
+            ));
+            return replacement;
+        } else if (argCount == 2) {
+            replacement.add(new MethodInsnNode(
+                Opcodes.INVOKESTATIC,
+                "java/util/Collections",
+                "singletonMap",
+                "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/util/Map;"
+            ));
+            return replacement;
+        }
+        final int freeVarIndex = ASMUtil.getFreeVarIndex(methodNode);
+
         replacement.add(new TypeInsnNode(Opcodes.NEW, "java/util/HashMap"));
         replacement.add(new InsnNode(Opcodes.DUP));
         replacement.add(new MethodInsnNode(Opcodes.INVOKESPECIAL, "java/util/HashMap", "<init>", "()V"));

src/main/java/net/raphimc/javadowngrader/transformer/j8/methodcallreplacer/SetOfMCR.java

@@ -31,9 +31,27 @@ public InsnList getReplacement(ClassNode classNode, MethodNode methodNode, Strin
 
         final Type[] args = Type.getArgumentTypes(originalDesc);
         if (args.length != 1 || args[0].getSort() != Type.ARRAY) {
+            final int argCount = args.length;
+            if (argCount == 0) {
+                replacement.add(new MethodInsnNode(
+                    Opcodes.INVOKESTATIC,
+                    "java/util/Collections",
+                    "emptySet",
+                    "()Ljava/util/Set;"
+                ));
+                return replacement;
+            } else if (argCount == 1) {
+                replacement.add(new MethodInsnNode(
+                    Opcodes.INVOKESTATIC,
+                    "java/util/Collections",
+                    "singleton",
+                    "(Ljava/lang/Object;)Ljava/util/Set;"
+                ));
+                return replacement;
+            }
+
             final int freeVarIndex = ASMUtil.getFreeVarIndex(methodNode);
 
-            final int argCount = args.length;
             replacement.add(new TypeInsnNode(Opcodes.NEW, "java/util/HashSet"));
             replacement.add(new InsnNode(Opcodes.DUP));
             replacement.add(new MethodInsnNode(Opcodes.INVOKESPECIAL, "java/util/HashSet", "<init>", "()V"));