Fix issue 1008 (#1009)

Author: msridhar

nullaway/src/main/java/com/uber/nullaway/generics/GenericsChecks.java

@@ -557,11 +557,14 @@ public static void compareGenericTypeParameterNullabilityForCall(
           (Type.ArrayType) formalParams.get(formalParams.size() - 1).type;
       Type varargsElementType = varargsArrayType.elemtype;
       for (int i = formalParams.size() - 1; i < actualParams.size(); i++) {
-        Type actualParameter = getTreeType(actualParams.get(i), state);
-        if (actualParameter != null) {
-          if (!subtypeParameterNullability(varargsElementType, actualParameter, state)) {
+        Type actualParameterType = getTreeType(actualParams.get(i), state);
+        // If the actual parameter type is assignable to the varargs array type, then the call site
+        // is passing the varargs directly in an array, and we should skip our check.
+        if (actualParameterType != null
+            && !state.getTypes().isAssignable(actualParameterType, varargsArrayType)) {
+          if (!subtypeParameterNullability(varargsElementType, actualParameterType, state)) {
             reportInvalidParametersNullabilityError(
-                varargsElementType, actualParameter, actualParams.get(i), state, analysis);
+                varargsElementType, actualParameterType, actualParams.get(i), state, analysis);
           }
         }
       }

nullaway/src/test/java/com/uber/nullaway/jspecify/GenericsTests.java

@@ -1839,6 +1839,23 @@ public void boxInteger() {
         .doTest();
   }
 
+  @Test
+  public void issue1008() {
+    // testing for no crash
+    makeHelper()
+        .addSourceLines(
+            "EnumCombinations.java",
+            "package com.uber;",
+            "public class EnumCombinations {",
+            "    public static void combinations(Class<? extends Enum<?>> first, Class<? extends Enum<?>>... others) {",
+            "    }",
+            "    public static void args(Class<? extends Enum<?>> first, Class<? extends Enum<?>>... others) {",
+            "        combinations(first, others);",
+            "    }",
+            "}")
+        .doTest();
+  }
+
   private CompilationTestHelper makeHelper() {
     return makeTestHelperWithArgs(
         Arrays.asList(