Kotlin: Add support for objects

java/kotlin-extractor/src/main/kotlin/KotlinExtractorExtension.kt

@@ -873,18 +873,43 @@ open class KotlinFileExtractor(
             }
         }
 
+        val locId = tw.getLocation(c)
+        tw.writeHasLocation(id, locId)
+
         c.typeParameters.map { extractTypeParameter(it) }
         c.declarations.map { extractDeclaration(it, id) }
         extractObjectInitializerFunction(c, id)
-
-        val locId = tw.getLocation(c)
-        tw.writeHasLocation(id, locId)
+        if(c.isObject) {
+            // For `object MyObject { ... }`, the .class has an
+            // automatically-generated `public static final MyObject INSTANCE`
+            // field that may be referenced from Java code, and is used in our
+            // IrGetObjectValue support. We therefore need to fabricate it
+            // here.
+            val instance = useObjectClassInstance(c)
+            val type = useSimpleTypeClass(c, emptyList(), false)
+            tw.writeFields(instance.id, instance.name, type.javaResult.id, type.kotlinResult.id, id, instance.id)
+            tw.writeHasLocation(instance.id, locId)
+            @Suppress("UNCHECKED_CAST")
+            tw.writeClass_object(id as Label<DbClass>, instance.id)
+        }
 
         extractClassCommon(c, id)
 
         return id
     }
 
+    data class ObjectClassInstance(val id: Label<DbField>, val name: String)
+    fun useObjectClassInstance(c: IrClass): ObjectClassInstance {
+        if(!c.isObject) {
+            logger.warn(Severity.ErrorSevere, "Using instance for non-object class")
+        }
+        val classId = useClassSource(c)
+        val instanceName = "INSTANCE"
+        val instanceLabel = "@\"field;{$classId};$instanceName\""
+        val instanceId: Label<DbField> = tw.getLabelFor(instanceLabel)
+        return ObjectClassInstance(instanceId, instanceName)
+    }
+
     private fun isQualifiedThis(vp: IrValueParameter): Boolean {
         return isQualifiedThisFunction(vp) ||
                isQualifiedThisClass(vp)
@@ -1623,6 +1648,22 @@ open class KotlinFileExtractor(
                 val exprParent = parent.expr(e, callable)
                 extractTypeOperatorCall(e, callable, exprParent.parent, exprParent.idx)
             }
+            is IrGetObjectValue -> {
+                // For `object MyObject { ... }`, the .class has an
+                // automatically-generated `public static final MyObject INSTANCE`
+                // field that we are accessing here.
+                val exprParent = parent.expr(e, callable)
+                val c: IrClass = e.symbol.owner
+                val instance = useObjectClassInstance(c)
+
+                val id = tw.getFreshIdLabel<DbVaraccess>()
+                val type = useType(e.type)
+                val locId = tw.getLocation(e)
+                tw.writeExprs_varaccess(id, type.javaResult.id, type.kotlinResult.id, exprParent.parent, exprParent.idx)
+                tw.writeHasLocation(id, locId)
+
+                tw.writeVariableBinding(id, instance.id)
+            }
             else -> {
                 logger.warnElement(Severity.ErrorSevere, "Unrecognised IrExpression: " + e.javaClass, e)
             }

java/ql/lib/config/semmlecode.dbscheme

@@ -314,6 +314,11 @@ classes(
   int sourceid: @class ref
 );
 
+class_object(
+  unique int id: @class ref,
+  unique int instance: @field ref
+);
+
 kt_nullable_types(
   unique int id: @kt_nullable_type,
   int classid: @classorinterface ref

java/ql/lib/semmle/code/java/Type.qll

@@ -712,6 +712,18 @@ class Class extends ClassOrInterface, @class {
   override string getAPrimaryQlClass() { result = "Class" }
 }
 
+/** A Kotlin `object`. */
+class ClassObject extends Class {
+  ClassObject() {
+    class_object(this, _)
+  }
+
+  /** Gets the instance variable that implements this `object`. */
+  Field getInstance() {
+    class_object(this, result)
+  }
+}
+
 /**
  * A record declaration.
  */

java/ql/test/kotlin/library-tests/object/accesses.expected

@@ -0,0 +1 @@
+| objects.kt:2:1:4:1 | MyObject | objects.kt:7:17:7:24 | INSTANCE |

java/ql/test/kotlin/library-tests/object/accesses.ql

@@ -0,0 +1,8 @@
+import java
+
+from VarAccess va, ClassObject co
+where va.getVariable() = co.getInstance()
+select co, va
+
+// select count(VarAccess va)
+

java/ql/test/kotlin/library-tests/object/objects.expected

@@ -0,0 +1 @@
+| objects.kt:2:1:4:1 | MyObject | objects.kt:2:1:4:1 | INSTANCE |

java/ql/test/kotlin/library-tests/object/objects.kt

@@ -0,0 +1,9 @@
+
+object MyObject {
+    fun MyObjectFunction() {}
+}
+
+fun useMyObject() {
+    val myObj = MyObject
+}
+

java/ql/test/kotlin/library-tests/object/objects.ql

@@ -0,0 +1,5 @@
+import java
+
+from ClassObject co
+where co.fromSource()
+select co, co.getInstance()