Merge pull request #787 from hmakholm/pr/fix-useless-parameter

Fix false positives in java/unused parameter

Author: aschackmull

java/ql/src/semmle/code/java/deadcode/DeadCode.qll

@@ -292,6 +292,10 @@ class RootdefCallable extends Callable {
     // a body that also doesn't.
     not hasUsefulBody(this) and
     not exists(Method m | hasUsefulBody(m) | m.overridesOrInstantiates+(this))
+    or
+    // Methods that are the target of a member reference need to implement
+    // the exact signature of the resulting functional interface.
+    exists(MemberRefExpr mre | mre.getReferencedCallable() = this)
   }
 }
 

java/ql/test/query-tests/dead-code/UselessParameter/Test.java

@@ -40,6 +40,10 @@ abstract class C implements I {
 	}
 }
 
+interface F {
+	void doSomething(int arg2);
+}
+
 public class Test {
 	// OK: external interface
 	public static void main(String[] args) {}
@@ -54,6 +58,13 @@ public static void premain(String arg, java.lang.instrument.Instrumentation i) {
 	public static void foo(Object bar) {
 		throw new UnsupportedOperationException();
 	}
+
+	public static F getF() {
+		return Test::myFImplementation;
+	}
+
+	// OK: mentioned in member reference
+	private static void myFImplementation(int foo) {}
 
 	// OK: native method
 	native int baz(int x);