Rule 14.3: Permit infinite loops using literals

Author: lcartey

c/misra/src/rules/RULE-14-3/ControllingExprInvariant.ql

@@ -39,7 +39,9 @@ where
       (
         conditionAlwaysFalse(expr)
         or
-        conditionAlwaysTrue(expr)
+        conditionAlwaysTrue(expr) and
+        // Exception allows for infinite loops, but we only permit that for literals like `true`
+        not expr instanceof Literal
       )
     ) and
     message = "Controlling expression in loop statement has invariant value."
@@ -53,6 +55,7 @@ where
     ) and
     message = "Controlling expression in switch statement has invariant value."
   ) and
-  // Exclude macros, which may generate seemingly invariant expressions
+  // Exclude cases where the controlling expressions is affected by a macro, because they can appear
+  // invariant in a particular invocation, but be variant between invocations.
   not expr.isAffectedByMacro()
 select expr, message

c/misra/test/rules/RULE-14-3/ControllingExprInvariant.expected

@@ -1,4 +1,5 @@
-| test.c:2:7:2:11 | ... > ... | Controlling expression in if statement has invariant value. |
-| test.c:13:10:13:16 | ... > ... | Controlling expression in loop statement has invariant value. |
-| test.c:14:9:14:13 | ... > ... | Controlling expression in if statement has invariant value. |
-| test.c:18:20:18:24 | ... < ... | Controlling expression in loop statement has invariant value. |
+| test.c:4:7:4:11 | ... > ... | Controlling expression in if statement has invariant value. |
+| test.c:15:10:15:16 | ... > ... | Controlling expression in loop statement has invariant value. |
+| test.c:16:9:16:13 | ... > ... | Controlling expression in if statement has invariant value. |
+| test.c:20:20:20:24 | ... < ... | Controlling expression in loop statement has invariant value. |
+| test.c:27:10:27:14 | ... < ... | Controlling expression in loop statement has invariant value. |

c/misra/test/rules/RULE-14-3/test.c

@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 void f1(int p1) {
   if (2 > 3) { // NON_COMPLIANT
   }
@@ -18,3 +20,10 @@ void f2() {
   for (int i = 10; i < 5; i++) { // NON_COMPLIANT
   }
 }
+
+void f3() {
+  while (true) { // Permitted by exception
+  }
+  while (1 < 2) { // NON_COMPLIANT - likely an indication of a bug
+  }
+}