8019340: varargs-related warnings are meaningless on signature-polymorphic...

8019340: varargs-related warnings are meaningless on signature-polymorphic methods such as MethodHandle.invokeExact
Summary: Disable certain varargs warnings when compiling polymorphic signature calls
Reviewed-by: jjg

src/share/classes/com/sun/tools/javac/comp/Check.java

@@ -897,7 +897,8 @@ public class Check {
                     assertConvertible(arg, arg.type, varArg, warn);
                     args = args.tail;
                 }
-            } else if ((sym.flags() & VARARGS) != 0 && allowVarargs) {
+            } else if ((sym.flags() & (VARARGS | SIGNATURE_POLYMORPHIC)) == VARARGS &&
+                    allowVarargs) {
                 // non-varargs call to varargs method
                 Type varParam = owntype.getParameterTypes().last();
                 Type lastArg = argtypes.last();

test/tools/javac/meth/VarargsWarn.java

+/*
+ * @test /nodynamiccopyright/
+ * @bug 8019340
+ * @summary varargs-related warnings are meaningless on signature-polymorphic methods such as MethodHandle.invokeExact
+ *
+ * @compile/fail/ref=VarargsWarn.out -XDrawDiagnostics -Werror VarargsWarn.java
+ */
+
+import java.lang.invoke.*;
+
+class VarargsWarn {
+    void test(MethodHandle mh) throws Throwable {
+        mh.invokeExact((Integer[])null);
+        mh.invoke((Integer[])null);
+        mh.invokeWithArguments((Integer[])null); //not a sig poly method - warning here!
+    }
+}

test/tools/javac/meth/VarargsWarn.out

+VarargsWarn.java:15:32: compiler.warn.inexact.non-varargs.call: java.lang.Object, java.lang.Object[]
+- compiler.err.warnings.and.werror
+1 error
+1 warning