Java/Kotlin: Add File.is{,Java,Kotlin}SourceFile()

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

@@ -181,6 +181,15 @@ class File extends Container, @file {
   override string getURL() { result = "file://" + this.getAbsolutePath() + ":0:0:0:0" }
 
   override string getAPrimaryQlClass() { result = "File" }
+
+  /** Holds if this is a (Java or Kotlin) source file. */
+  predicate isSourceFile() { this.isJavaSourceFile() or this.isKotlinSourceFile() }
+
+  /** Holds if this is a Java source file. */
+  predicate isJavaSourceFile() { this.getExtension() = "java" }
+
+  /** Holds if this is a Kotlin source file. */
+  predicate isKotlinSourceFile() { this.getExtension() = "kt" }
 }
 
 /**

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

@@ -196,7 +196,7 @@ class Location extends @location {
 }
 
 private predicate hasSourceLocation(Top l, Location loc, File f) {
-  hasLocation(l, loc) and f = loc.getFile() and f.getExtension() = ["java", "kt"]
+  hasLocation(l, loc) and f = loc.getFile() and f.isSourceFile()
 }
 
 cached

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

@@ -34,7 +34,7 @@ class Element extends @element, Top {
    * Elements pertaining to source files may include generated elements
    * not visible in source code, such as implicit default constructors.
    */
-  predicate fromSource() { this.getCompilationUnit().getExtension() = ["java", "kt"] }
+  predicate fromSource() { this.getCompilationUnit().isSourceFile() }
 
   /** Gets the compilation unit that this element belongs to. */
   CompilationUnit getCompilationUnit() { result = this.getFile() }