8026374: javac accepts void as a method parameter

Changing Check.validate to reject void types.

Reviewed-by: jjg, vromero

langtools/src/share/classes/com/sun/tools/javac/comp/Attr.java

@@ -933,7 +933,8 @@ public class Attr extends JCTree.Visitor {
             chk.validate(tree.typarams, localEnv);
 
             // Check that result type is well-formed.
-            chk.validate(tree.restype, localEnv);
+            if (tree.restype != null && !tree.restype.type.hasTag(VOID))
+                chk.validate(tree.restype, localEnv);
 
             // Check that receiver type is well-formed.
             if (tree.recvparam != null) {

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

@@ -1326,6 +1326,14 @@ public class Check {
             tree.underlyingType.accept(this);
         }
 
+        @Override
+        public void visitTypeIdent(JCPrimitiveTypeTree that) {
+            if (that.type.hasTag(TypeTag.VOID)) {
+                log.error(that.pos(), "void.not.allowed.here");
+            }
+            super.visitTypeIdent(that);
+        }
+
         /** Default visitor method: do nothing.
          */
         @Override

langtools/test/tools/javac/declaration/method/MethodVoidParameter.java

@@ -0,0 +1,9 @@
+/* @test /nodynamiccopyright/
+ * @bug 8026374
+ * @summary Cannot use void as a variable type
+ * @compile/fail/ref=MethodVoidParameter.out -XDrawDiagnostics MethodVoidParameter.java
+ */
+public class MethodVoidParameter {
+    void method(void v) { }
+    void method(void... v) { }
+}

langtools/test/tools/javac/declaration/method/MethodVoidParameter.out

@@ -0,0 +1,3 @@
+MethodVoidParameter.java:7:17: compiler.err.void.not.allowed.here
+MethodVoidParameter.java:8:17: compiler.err.void.not.allowed.here
+2 errors