Generate stubs for generic arguments

README.md

@@ -38,7 +38,7 @@ The interfaces can have generic parameter declarations. Assuming the target clas
 we could implement `Supplier<T>` using `java/util/function/Supplier<T>`.
 
 > [!NOTE]  
-> Generics are *copied verbatim*. If you need the generics to reference a class, please use its fully qualified name (e.g. `java/util/function/Supplier<java.util.concurrent.atomic.AtomicInteger>`).
+> Generics are *copied verbatim*. If you need the generics to reference a class, please use its fully qualified name (e.g. `java/util/function/Supplier<java.util.concurrent.atomic.AtomicInteger>`). As an exception to this rule, inner classes should be separated by `$` (e.g. `java/util/function/Supplier<java.util.Map$Entry>`).
 
 ### Custom transformers
 Third parties can use JST to implement their source file own transformations.  

interfaceinjection/src/main/java/net/neoforged/jst/interfaceinjection/StubStore.java

@@ -12,9 +12,11 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.zip.ZipEntry;
@@ -50,8 +52,18 @@ public InterfaceInformation createStub(String jvm) {
                 if (generics.isBlank()) {
                     logger.error("Interface injection %s has blank type parameters", jvm);
                 } else {
-                    // Ignore any nested generics when counting the amount of parameters the interface has
-                    typeParameterCount = generics.replaceAll("<[^>]*>", "").split(",").length;
+                    var reader = new StringReader(generics);
+                    List<String> typeArgs = new ArrayList<>();
+                    while (reader.hasNext()) {
+                        typeArgs.add(stubGenericArguments(reader));
+                        reader.skipWhitespace();
+                        if (reader.hasNext() && reader.next() != ',') {
+                            logger.error("Interface injection generics declaration %s is invalid", generics);
+                        }
+                    }
+
+                    generics = String.join(", ", typeArgs);
+                    typeParameterCount = typeArgs.size();
                 }
             }
             jvm = jvm.substring(0, genericsStart);
@@ -60,6 +72,53 @@ public InterfaceInformation createStub(String jvm) {
         return new InterfaceInformation(createStub(jvm, typeParameterCount), generics);
     }
 
+    private static final Pattern BOUNDED_WILDCARD_PATTERN = Pattern.compile("\\?\\s+(extends|super)\\s+(.+)");
+
+    private String stubGenericArguments(StringReader generics) {
+        StringBuilder typeName = new StringBuilder();
+        List<String> genericArgs = new ArrayList<>();
+        while (generics.hasNext() && generics.peek() != ',' && generics.peek() != '>') {
+            var ch = generics.next();
+            if (ch == '<') {
+                do {
+                    genericArgs.add(stubGenericArguments(generics));
+                    generics.skipWhitespace();
+                } while (generics.next() != '>'); // The next character can either be a comma or a >. If it's a > we exit the generic declaration, otherwise we consume the comma and stub the next argument
+                break; // No point in continuing to parse if we found and parsed the nested generic arguments
+            } else {
+                typeName.append(ch);
+            }
+        }
+
+        String base;
+
+        var type = typeName.toString().trim();
+        // Within bounded wildcards (? extends X) or (? super X) we need to make sure we stub the type
+        var boundedMatcher = BOUNDED_WILDCARD_PATTERN.matcher(type);
+        if (boundedMatcher.matches()) {
+            var name = boundedMatcher.group(2);
+            base = "? " + boundedMatcher.group(1) + " " + possiblyStubTypeName(name, genericArgs.size());
+        } else {
+            base = possiblyStubTypeName(type, genericArgs.size());
+        }
+
+        if (genericArgs.isEmpty()) {
+            return base;
+        } else {
+            return base + "<" + String.join(", ", genericArgs) + ">";
+        }
+    }
+
+    private String possiblyStubTypeName(String name, int genericCount) {
+        // If the type argument contains a dot we assume it is a class, so we have to stub it
+        if (name.contains(".")) {
+            return createStub(name.replace('.', '/'), genericCount);
+        } else {
+            // Otherwise, it could be a wildcard or it could be another type parameter
+            return name;
+        }
+    }
+
     private synchronized String createStub(String jvm, int typeParameterCount) {
         var fqn = jvmToFqn.get(jvm);
         if (fqn != null) return fqn;
@@ -142,4 +201,34 @@ public String toString() {
             return generics.isBlank() ? interfaceDeclaration : interfaceDeclaration + "<" + generics + ">";
         }
     }
+
+    private static class StringReader {
+        private final String string;
+        private int i = -1;
+
+        private StringReader(String string) {
+            this.string = string;
+        }
+
+        public boolean hasNext() {
+            return i < string.length() - 1;
+        }
+
+        public char peek() {
+            return string.charAt(i + 1);
+        }
+
+        public char next() {
+            return string.charAt(++i);
+        }
+
+        public void skipWhitespace() {
+            while (hasNext() && peek() == ' ') next();
+        }
+
+        @Override
+        public String toString() {
+            return string;
+        }
+    }
 }

tests/data/interfaceinjection/nested_generic_stubs/expected/com/MyTarget.java

@@ -0,0 +1,7 @@
+package com;
+
+import com.CustomInterface;
+import com.InjectedInterface;
+
+public class MyTarget<T> implements CustomInterface<com.example.TypeParameter.InnerClass>, InjectedInterface<java.util.Map.Entry<? extends com.example.WeirdSupplier<T>, com.example.Classes.Generics<T, java.lang.Integer, com.example.WeirdSupplier<?>>>> {
+}

tests/data/interfaceinjection/nested_generic_stubs/expected_stub/com/CustomInterface.java

@@ -0,0 +1,4 @@
+package com;
+
+public interface CustomInterface<A> {
+}

tests/data/interfaceinjection/nested_generic_stubs/expected_stub/com/InjectedInterface.java

@@ -0,0 +1,4 @@
+package com;
+
+public interface InjectedInterface<A> {
+}

tests/data/interfaceinjection/nested_generic_stubs/expected_stub/com/example/Classes.java

@@ -0,0 +1,6 @@
+package com.example;
+
+public interface Classes {
+    public interface Generics<A, B, C> {
+    }
+}

tests/data/interfaceinjection/nested_generic_stubs/expected_stub/com/example/TypeParameter.java

@@ -0,0 +1,6 @@
+package com.example;
+
+public interface TypeParameter {
+    public interface InnerClass {
+    }
+}

tests/data/interfaceinjection/nested_generic_stubs/expected_stub/com/example/WeirdSupplier.java

@@ -0,0 +1,4 @@
+package com.example;
+
+public interface WeirdSupplier<A> {
+}

tests/data/interfaceinjection/nested_generic_stubs/injectedinterfaces.json

@@ -0,0 +1,6 @@
+{
+  "com/MyTarget": [
+    "com/InjectedInterface<java.util.Map$Entry<? extends com.example.WeirdSupplier<T>, com.example.Classes$Generics<T, java.lang.Integer, com.example.WeirdSupplier<?>>>>",
+    "com/CustomInterface<com.example.TypeParameter$InnerClass>"
+  ]
+}

tests/data/interfaceinjection/nested_generic_stubs/source/com/MyTarget.java

@@ -0,0 +1,4 @@
+package com;
+
+public class MyTarget<T> {
+}

tests/src/test/java/net/neoforged/jst/tests/EmbeddedTest.java

@@ -350,6 +350,11 @@ void testInjectedMarker() throws Exception {
         void testGenerics() throws Exception {
             runInterfaceInjectionTest("generics", tempDir);
         }
+
+        @Test
+        void testNestedGenericStubs() throws Exception {
+            runInterfaceInjectionTest("nested_generic_stubs", tempDir);
+        }
     }
 
     protected final void runInterfaceInjectionTest(String testDirName, Path tempDir, String... additionalArgs) throws Exception {