Kotlin: Improve file class support

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

@@ -643,6 +643,10 @@ open class KotlinFileExtractor(
                         logger.warnElement("Unrecognised class kind $kind", c)
                     }
 
+                    if (c.origin == IrDeclarationOrigin.FILE_CLASS) {
+                        tw.writeFile_class(id)
+                    }
+
                     if (c.isData) {
                         tw.writeKtDataClasses(id)
                     }

java/ql/integration-tests/all-platforms/kotlin/file_classes/A.kt

@@ -0,0 +1,2 @@
+fun a() {
+}

java/ql/integration-tests/all-platforms/kotlin/file_classes/B.kt

@@ -0,0 +1,3 @@
+fun b() {
+    a()
+}

java/ql/integration-tests/all-platforms/kotlin/file_classes/C.kt

@@ -0,0 +1,3 @@
+class C {
+    fun c() {}
+}

java/ql/integration-tests/all-platforms/kotlin/file_classes/classes.expected

@@ -0,0 +1,3 @@
+| AKt.class:0:0:0:0 | AKt | true |
+| B.kt:0:0:0:0 | BKt | true |
+| C.kt:1:1:3:1 | C | false |

java/ql/integration-tests/all-platforms/kotlin/file_classes/classes.ql

@@ -0,0 +1,5 @@
+import java
+
+from Class c
+where exists(c.getLocation().getFile().getRelativePath())
+select c, any(boolean b | if c.isFileClass() then b = true else b = false)

java/ql/integration-tests/all-platforms/kotlin/file_classes/test.py

@@ -0,0 +1,4 @@
+from create_database_utils import *
+
+runSuccessfully([get_cmd("kotlinc"), 'A.kt'])
+run_codeql_database_create(['kotlinc -cp . B.kt C.kt'], lang="java")

java/ql/lib/change-notes/2023-07-11-file-classes.md

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* A `Class.isFileClass()` predicate, to identify Kotlin file classes, has been added.

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

@@ -709,6 +709,12 @@ class Class extends ClassOrInterface {
     )
   }
 
+  /**
+   * Holds if this class is a Kotlin "file class", e.g. the class FooKt
+   * for top-level entities in Foo.kt.
+   */
+  predicate isFileClass() { file_class(this) }
+
   override string getAPrimaryQlClass() { result = "Class" }
 }
 

java/ql/test/library-tests/file_classes/A.kt

@@ -0,0 +1,2 @@
+fun a() {
+}

java/ql/test/library-tests/file_classes/B.kt

@@ -0,0 +1,3 @@
+fun b() {
+    a()
+}

java/ql/test/library-tests/file_classes/C.kt

@@ -0,0 +1,3 @@
+class C {
+    fun c() {}
+}

java/ql/test/library-tests/file_classes/classes.expected

@@ -0,0 +1,3 @@
+| A.kt:0:0:0:0 | AKt | true |
+| B.kt:0:0:0:0 | BKt | true |
+| C.kt:1:1:3:1 | C | false |

java/ql/test/library-tests/file_classes/classes.ql

@@ -0,0 +1,5 @@
+import java
+
+from Class c
+where c.fromSource()
+select c, any(boolean b | if c.isFileClass() then b = true else b = false)