From ec3990c6197bf28762bae73709823a35f5cc2168 Mon Sep 17 00:00:00 2001
From: Anders Schack-Mulligen <aschackmull@github.com>
Date: Thu, 9 Sep 2021 15:04:22 +0200
Subject: [PATCH 1/2] Java: Fix FunctionalInterface.

---
 java/ql/lib/semmle/code/java/Type.qll         | 38 +++++++++++++++++++
 .../code/java/dispatch/WrappedInvocation.qll  | 31 ---------------
 2 files changed, 38 insertions(+), 31 deletions(-)

diff --git a/java/ql/lib/semmle/code/java/Type.qll b/java/ql/lib/semmle/code/java/Type.qll
index 3b05665d0557..5395e855701d 100755
--- a/java/ql/lib/semmle/code/java/Type.qll
+++ b/java/ql/lib/semmle/code/java/Type.qll
@@ -874,6 +874,44 @@ class ClassOrInterface extends RefType, @classorinterface {
   }
 }
 
+private string getAPublicObjectMethodSignature() {
+  exists(Method m |
+    m.getDeclaringType() instanceof TypeObject and
+    m.isPublic() and
+    result = m.getSignature()
+  )
+}
+
+private Method getAnAbstractMethod(Interface interface) {
+  interface.inherits(result) and
+  result.isAbstract() and
+  // JLS 9.8, ignore Object methods
+  not result.getSignature() = getAPublicObjectMethodSignature() and
+  // Make sure that there is no other non-abstract method
+  // (e.g. `default`) which overrides the abstract one
+  not exists(Method m |
+    interface.inherits(m) and
+    not m.isAbstract() and
+    m.overrides(result)
+  )
+}
+
+/**
+ * A functional interface is an interface that has just one abstract method
+ * (aside from the methods of Object), and thus represents a single function
+ * contract.
+ *
+ * See JLS 9.8, Functional Interfaces.
+ */
+class FunctionalInterface extends Interface {
+  Method run;
+
+  FunctionalInterface() { run = unique(Method r | r = getAnAbstractMethod(this)) }
+
+  /** Gets the single abstract method of this interface. */
+  Method getRunMethod() { result = run }
+}
+
 /**
  * A primitive type.
  *
diff --git a/java/ql/lib/semmle/code/java/dispatch/WrappedInvocation.qll b/java/ql/lib/semmle/code/java/dispatch/WrappedInvocation.qll
index cbff880ca961..26fcd109df2c 100644
--- a/java/ql/lib/semmle/code/java/dispatch/WrappedInvocation.qll
+++ b/java/ql/lib/semmle/code/java/dispatch/WrappedInvocation.qll
@@ -6,37 +6,6 @@
 import java
 import VirtualDispatch
 
-private string getAPublicObjectMethodSignature() {
-  exists(Method m |
-    m.getDeclaringType() instanceof TypeObject and
-    m.isPublic() and
-    result = m.getSignature()
-  )
-}
-
-private Method getAPotentialRunMethod(Interface i) {
-  i.inherits(result) and
-  result.isPublic() and
-  not result.getSignature() = getAPublicObjectMethodSignature()
-}
-
-/**
- * A functional interface is an interface that has just one abstract method
- * (aside from the methods of Object), and thus represents a single function
- * contract.
- *
- * See JLS 9.8, Functional Interfaces.
- */
-class FunctionalInterface extends Interface {
-  FunctionalInterface() {
-    1 = strictcount(getAPotentialRunMethod(this)) and
-    not exists(Method m | this.inherits(m) and m.isDefault())
-  }
-
-  /** Gets the single method of this interface. */
-  Method getRunMethod() { getAPotentialRunMethod(this).getSourceDeclaration() = result }
-}
-
 /**
  * Holds if `m` might invoke `runmethod` through a functional interface on the
  * `n`th parameter.

From a0bf170d0206d380b9ac55e9f6b6179aaaa47052 Mon Sep 17 00:00:00 2001
From: Chris Smowton <smowton@github.com>
Date: Thu, 9 Sep 2021 15:00:42 +0100
Subject: [PATCH 2/2] Add test for functional interfaces

---
 .../functional-interfaces/Test.java           | 29 +++++++++++++++++++
 .../functional-interfaces/test.expected       |  3 ++
 .../functional-interfaces/test.ql             |  3 ++
 3 files changed, 35 insertions(+)
 create mode 100644 java/ql/test/library-tests/functional-interfaces/Test.java
 create mode 100644 java/ql/test/library-tests/functional-interfaces/test.expected
 create mode 100644 java/ql/test/library-tests/functional-interfaces/test.ql

diff --git a/java/ql/test/library-tests/functional-interfaces/Test.java b/java/ql/test/library-tests/functional-interfaces/Test.java
new file mode 100644
index 000000000000..ad0d4c079b42
--- /dev/null
+++ b/java/ql/test/library-tests/functional-interfaces/Test.java
@@ -0,0 +1,29 @@
+public class Test {
+
+  interface Functional {
+    int f();
+  }
+
+  class Concrete implements Functional {
+    public int f() { return 0; }
+  }
+
+  interface FunctionalWithDefaults {
+    int f();
+
+    default int g() { return 1; }
+  }
+
+  interface NotFunctional {
+    default int g() { return 1; }
+  }
+
+  interface FunctionalWithObjectMethods {
+    int f();
+
+    String toString();
+
+    int hashCode();
+  }
+
+}
diff --git a/java/ql/test/library-tests/functional-interfaces/test.expected b/java/ql/test/library-tests/functional-interfaces/test.expected
new file mode 100644
index 000000000000..4d6b4a1a4c05
--- /dev/null
+++ b/java/ql/test/library-tests/functional-interfaces/test.expected
@@ -0,0 +1,3 @@
+| Test.java:3:13:3:22 | Functional |
+| Test.java:11:13:11:34 | FunctionalWithDefaults |
+| Test.java:21:13:21:39 | FunctionalWithObjectMethods |
diff --git a/java/ql/test/library-tests/functional-interfaces/test.ql b/java/ql/test/library-tests/functional-interfaces/test.ql
new file mode 100644
index 000000000000..514df6a634ca
--- /dev/null
+++ b/java/ql/test/library-tests/functional-interfaces/test.ql
@@ -0,0 +1,3 @@
+import java
+
+select any(FunctionalInterface fi | fi.fromSource())