C++: Add a test of unknown format specifiers (with specsAreKnown check disabled).

Author: geoffw0

cpp/ql/src/semmle/code/cpp/commons/Printf.qll

@@ -921,7 +921,7 @@ class FormatLiteral extends Literal {
    * format specifiers are present in the format string).
    */
   predicate specsAreKnown() {
-    this.getNumConvSpec() = count(int n | exists(this.getNumArgNeeded(n)))
+    any()
   }
 
   /**

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/TooManyFormatArguments.expected

@@ -12,3 +12,6 @@
 | test.c:39:3:39:8 | call to printf | Format expects 2 arguments but given 5 |
 | test.c:40:3:40:8 | call to printf | Format expects 2 arguments but given 4 |
 | test.c:41:3:41:8 | call to printf | Format expects 2 arguments but given 3 |
+| test.c:46:2:46:7 | call to printf | Format expects 1 arguments but given 2 |
+| test.c:47:2:47:7 | call to printf | Format expects 1 arguments but given 2 |
+| test.c:48:2:48:7 | call to printf | Format expects 1 arguments but given 2 |

cpp/ql/test/query-tests/Likely Bugs/Format/WrongNumberOfFormatArguments/test.c

@@ -42,4 +42,8 @@ void test(int i, const char *str)
 	}
 
 	printf("%@ %i %i", 1, 2); // GOOD
+
+	printf("%Y", 1, 2); // GOOD (unknown format character, this might be correct) [FALSE POSITIVE]
+	printf("%1.1Y", 1, 2); // GOOD (unknown format character, this might be correct) [FALSE POSITIVE]
+	printf("%*.*Y", 1, 2); // GOOD (unknown format character, this might be correct) [FALSE POSITIVE]
 }