CPP: Create HeaderFile.noTopLevelCode from existing logic.

cpp/ql/src/jsf/4.07 Header Files/AV Rule 35.ql

@@ -133,11 +133,7 @@ where not hf instanceof IncludeGuardedHeader
   // Exclude files which contain no declaration entries or top level
   // declarations (e.g. just preprocessor directives; or non-top level
   // code).
-  and (
-    exists(DeclarationEntry de | de.getFile() = hf) or
-    exists(Declaration d | d.getFile() = hf and d.isTopLevel()) or
-    exists(UsingEntry ue | ue.getFile() = hf)
-  )
+  and not hf.noTopLevelCode()
   // Exclude files which look like they contain 'x-macros'
   and not hasXMacro(hf)
   // Exclude files which are always #imported.

cpp/ql/src/semmle/code/cpp/File.qll

@@ -453,6 +453,20 @@ class HeaderFile extends File {
     exists(Include i | i.getIncludedFile() = this)
   }
 
+  /**
+   * Holds if this header file does not contain any declaration entries or top level
+   * declarations.  For example it might be:
+   *  - a file containing only preprocessor directives and/or comments
+   *  - an empty file
+   *  - a file that contains non-top level code or data that's included in an
+   *    unusual way
+   */
+  predicate noTopLevelCode()
+  {
+    not exists(DeclarationEntry de | de.getFile() = this) and
+    not exists(Declaration d | d.getFile() = this and d.isTopLevel()) and
+    not exists(UsingEntry ue | ue.getFile() = this)
+  }
 }
 
 /**