Java: Add CompilationUnit.getATypeAvailableBySimpleName()

This predicate is mainly helpful for Javadoc queries and for queries which
check whether the name of an element shadows another type.

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

@@ -31,5 +31,50 @@ class CompilationUnit extends Element, File {
    */
   Module getModule() { cumodule(this, result) }
 
+  /**
+   * Gets a type which is available by its simple name in this compilation unit.
+   * Reasons for this can be:
+   * - The type is declared in this compilation unit as top-level type
+   * - The type is imported
+   * - The type is declared in the same package as this compilation unit
+   * - The type is declared in the package `java.lang`
+   */
+  ClassOrInterface getATypeAvailableBySimpleName() {
+    // See "Shadowing", https://docs.oracle.com/javase/specs/jls/se17/html/jls-6.html#jls-6.4.1
+    // Note: Currently the logic below does not consider shadowing and might have multiple results
+    // with the same type name
+    result.(TopLevelType).getCompilationUnit() = this
+    or
+    exists(ImportStaticTypeMember importDecl |
+      importDecl.getCompilationUnit() = this and
+      result = importDecl.getATypeImport()
+    )
+    or
+    exists(ImportType importDecl |
+      importDecl.getCompilationUnit() = this and
+      result = importDecl.getImportedType()
+    )
+    or
+    exists(ImportStaticOnDemand importDecl |
+      importDecl.getCompilationUnit() = this and
+      result = importDecl.getATypeImport()
+    )
+    or
+    exists(ImportOnDemandFromType importDecl |
+      importDecl.getCompilationUnit() = this and
+      result = importDecl.getAnImport()
+    )
+    or
+    exists(ImportOnDemandFromPackage importDecl |
+      importDecl.getCompilationUnit() = this and
+      result = importDecl.getAnImport()
+    )
+    or
+    // From same package or java.lang, see https://docs.oracle.com/javase/specs/jls/se17/html/jls-7.html
+    result.(TopLevelType).getPackage() = this.getPackage()
+    or
+    result.(TopLevelType).getPackage().hasName("java.lang")
+  }
+
   override string getAPrimaryQlClass() { result = "CompilationUnit" }
 }