Method name parsing in ExternalStubxLibraryModels class is missing a corner case (uber#1344)

When loading external library models through the
`ExternalStubxLibraryModels` class, it previously didn't parse the
method name for methods with wildcard types properly. This PR fixes the
method parsing so that it will work for those cases.

The unit test for this is located in
`java/com/uber/nullaway/jdkannotations/JDKIntegrationTest.java` and is
`libraryLoadMethodParser()`.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a new public API method returning a parameterized List
(annotated and unannotated variants).

* **Tests**
* Added an integration test covering library parser behavior for
return-value handling.

* **Bug Fixes**
* Improved library-model method-signature parsing and normalization to
handle irregular spacing/formatting.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Manu Sridharan <msridhar@gmail.com>

Author: haewiful

jdk-annotations/jdk-integration-test/src/test/java/com/uber/nullaway/jdkannotations/JDKIntegrationTest.java

@@ -329,4 +329,28 @@ public void genericParameterTest() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void libraryLoadMethodParserReturn() {
+    compilationHelper
+        .setArgs(
+            Arrays.asList(
+                "-d",
+                temporaryFolder.getRoot().getAbsolutePath(),
+                "-XepOpt:NullAway:AnnotatedPackages=com.uber",
+                "-XepOpt:NullAway:JarInferEnabled=true"))
+        .addSourceLines(
+            "Test.java",
+            "package com.uber;",
+            "import org.jspecify.annotations.Nullable;",
+            "import com.uber.nullaway.jdkannotations.ReturnAnnotation;",
+            "import java.util.List;",
+            "class Test<T> {",
+            "  void testCall() {",
+            "    // BUG: Diagnostic contains: dereferenced expression ReturnAnnotation.getList(6, null) is @Nullable",
+            "    ReturnAnnotation.getList(6, null).isEmpty();",
+            "  }",
+            "}")
+        .doTest();
+  }
 }

jdk-annotations/test-annotated/src/main/java/com/uber/nullaway/jdkannotations/ReturnAnnotation.java

@@ -1,5 +1,6 @@
 package com.uber.nullaway.jdkannotations;
 
+import java.util.List;
 import java.util.Locale;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
@@ -76,4 +77,8 @@ public static Object getNewObjectIfNull(@Nullable Object object) {
       returnNullableGenericContainingNullable() {
     return null;
   }
+
+  public static @Nullable List<? super String> getList(Integer i, @Nullable Character c) {
+    return null;
+  }
 }

jdk-annotations/test-unannotated/src/main/java/com/uber/nullaway/jdkannotations/ReturnAnnotation.java

@@ -1,5 +1,6 @@
 package com.uber.nullaway.jdkannotations;
 
+import java.util.List;
 import java.util.Locale;
 
 public class ReturnAnnotation {
@@ -66,4 +67,8 @@ public static UpperBoundExample<String> returnNonNullGenericContainingNullable()
   public static UpperBoundExample<String> returnNullableGenericContainingNullable() {
     return null;
   }
+
+  public static List<? super String> getList(Integer i, Character c) {
+    return null;
+  }
 }

nullaway/src/main/java/com/uber/nullaway/handlers/LibraryModelsHandler.java

@@ -28,6 +28,7 @@
 import static com.uber.nullaway.Nullness.NULLABLE;
 
 import com.google.common.base.Preconditions;
+import com.google.common.base.Verify;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
@@ -1441,8 +1442,7 @@ public ImmutableSetMultimap<MethodRef, Integer> explicitlyNullableParameters() {
         String className = outerEntry.getKey();
         for (Map.Entry<String, Map<Integer, Set<String>>> innerEntry :
             outerEntry.getValue().entrySet()) {
-          String methodNameAndSignature =
-              innerEntry.getKey().substring(innerEntry.getKey().indexOf(" ") + 1);
+          String methodNameAndSignature = getMethodNameAndSignature(innerEntry.getKey());
           for (Map.Entry<Integer, Set<String>> entry : innerEntry.getValue().entrySet()) {
             Integer index = entry.getKey();
             if (index >= 0 && entry.getValue().stream().anyMatch(a -> a.contains("Nullable"))) {
@@ -1463,9 +1463,7 @@ public ImmutableSetMultimap<MethodRef, Integer> nonNullParameters() {
       for (String className : argAnnotCache.keySet()) {
         for (Map.Entry<String, Map<Integer, Set<String>>> methodEntry :
             argAnnotCache.get(className).entrySet()) {
-          String methodNameAndSignature =
-              methodEntry.getKey().substring(methodEntry.getKey().indexOf(" ") + 1);
-
+          String methodNameAndSignature = getMethodNameAndSignature(methodEntry.getKey());
           for (Map.Entry<Integer, Set<String>> argEntry : methodEntry.getValue().entrySet()) {
             Integer index = argEntry.getKey();
             if (index >= 0) {
@@ -1491,6 +1489,13 @@ public ImmutableSetMultimap<MethodRef, Integer> nonNullParameters() {
       return mapBuilder.build();
     }
 
+    private static String getMethodNameAndSignature(String methodInfo) {
+      int openParenIndex = methodInfo.indexOf('(');
+      Verify.verify(openParenIndex != -1, "Malformed method info: %s", methodInfo);
+      int methodNameIndex = methodInfo.lastIndexOf(' ', openParenIndex) + 1;
+      return methodInfo.substring(methodNameIndex);
+    }
+
     @Override
     public ImmutableSetMultimap<MethodRef, Integer> nullImpliesTrueParameters() {
       return ImmutableSetMultimap.of();
@@ -1512,9 +1517,7 @@ public ImmutableSet<MethodRef> nullableReturns() {
       for (String className : argAnnotCache.keySet()) {
         for (Map.Entry<String, Map<Integer, Set<String>>> methodEntry :
             argAnnotCache.get(className).entrySet()) {
-          String methodNameAndSignature =
-              methodEntry.getKey().substring(methodEntry.getKey().indexOf(" ") + 1);
-
+          String methodNameAndSignature = getMethodNameAndSignature(methodEntry.getKey());
           for (Map.Entry<Integer, Set<String>> argEntry : methodEntry.getValue().entrySet()) {
             Integer index = argEntry.getKey();
             if (index == -1) {