java: test type tracking through flow summaries

java/ql/test/library-tests/dispatch/CallableViaSummary.java

@@ -0,0 +1,31 @@
+import java.util.*;
+
+public class CallableViaSummary {
+    public interface Element {
+        public void handle(String message);
+    }
+
+    public void main(String[] args) {
+        List<Element> elements = new ArrayList<>();
+
+        List<Element> elements2 = new ArrayList<>();
+
+        elements.add(new Element() {
+            @Override
+            public void handle(String message) {
+                System.out.println(message);
+            }
+        });
+
+        elements.add(message -> System.out.println(message));
+
+        // This dispatches to the two added elements because
+        // the summary of ArrayList causes flow via type tracking.
+        elements.get(0).handle("Hello, world!");
+
+        // This does not dispatch to anything, showing that the
+        // open-world assumption does not apply
+        // (and hence that type tracking is necessary above).
+        elements2.get(0).handle("Hello, world!");
+    }
+}

java/ql/test/library-tests/dispatch/viaSummary.expected

@@ -0,0 +1,2 @@
+| CallableViaSummary.java:24:9:24:47 | handle(...) | CallableViaSummary.java:15:25:15:30 | handle |
+| CallableViaSummary.java:24:9:24:47 | handle(...) | CallableViaSummary.java:20:22:20:59 | handle |

java/ql/test/library-tests/dispatch/viaSummary.ql

@@ -0,0 +1,9 @@
+import java
+import semmle.code.java.dispatch.VirtualDispatch
+
+from MethodAccess ma, Method m
+where
+  m = viableImpl(ma) and
+  m.fromSource() and
+  ma.getFile().toString().matches("CallableViaSummary")
+select ma, m