CPP: Restrict to #elif, #else, #endif.

Author: geoffw0

cpp/ql/src/Documentation/CommentedOutCode.qll

@@ -49,10 +49,21 @@ private predicate looksLikeCode(string line) {
 
 /**
  * Holds if there is a preprocessor directive on the line indicated by
- * `f` and `line`.
+ * `f` and `line` that we permit code comments besides.  For example this
+ * is considered acceptable:
+ * ```
+ * #ifdef MYMACRO
+ * ...
+ * #endif // #ifdef MYMACRO
+ * ```
  */
 private predicate preprocLine(File f, int line) {
   exists(PreprocessorDirective pd, Location l |
+    (
+      pd instanceof PreprocessorElse or
+      pd instanceof PreprocessorElif or
+      pd instanceof PreprocessorEndif
+    ) and
     pd.getLocation() = l and
     l.getFile() = f and
     l.getStartLine() = line

cpp/ql/test/query-tests/Documentation/CommentedOutCode/CommentedOutCode.expected

@@ -9,6 +9,8 @@
 | test2.cpp:65:1:65:17 | //  # pragma once | This comment appears to contain commented-out code |
 | test2.cpp:67:1:67:19 | /*#error"myerror"*/ | This comment appears to contain commented-out code |
 | test2.cpp:91:1:95:2 | /*\n#ifdef MYMACRO\n\t// ...\n#endif // #ifdef MYMACRO\n*/ | This comment appears to contain commented-out code |
+| test2.cpp:107:21:107:43 | // #include "config2.h" | This comment appears to contain commented-out code |
+| test2.cpp:115:16:115:35 | /* #ifdef MYMACRO */ | This comment appears to contain commented-out code |
 | test.c:2:1:2:22 | // commented out code; | This comment appears to contain commented-out code |
 | test.c:4:1:7:8 | // some; | This comment appears to contain commented-out code |
 | test.c:9:1:13:8 | // also; | This comment appears to contain commented-out code |