RULE-8-2-10: Avoid callers of recursive functions being flagged

The rule forbids only recursive functions. It can be fair to have a
recursive function and justify this within one. With the behavior before
this change, also every caller would need to be argued.

This is additonal burden that is not required and intended by the MISRA
standard.

Fixes #935

Author: castler

c/misra/test/rules/RULE-17-2/test.c

@@ -8,7 +8,7 @@ void f3() {
   f3(); // NON_COMPLIANT
 }
 void f6() {
-  f3(); // NON_COMPLIANT
+  f3(); // COMPLIANT - merely calls a recursive function
 }
 
 void f5() {

change_notes/2026-06-18-fix-fp-recursive-functions.md

@@ -0,0 +1,2 @@
+`A7-5-2`, `RULE-8-2-10`: `FunctionsCallThemselvesEitherDirectlyOrIndirectly.ql`:
+    - Fix false positives where callers of recursive functions were incorrectly reported as recursive. Only calls that participate in a recursive cycle are now reported.

cpp/common/src/codingstandards/cpp/rules/functionscallthemselveseitherdirectlyorindirectly/FunctionsCallThemselvesEitherDirectlyOrIndirectly.qll

@@ -23,13 +23,14 @@ class RecursiveFunction extends Function {
   RecursiveFunction() { exists(RecursiveCall fc | fc.getEnclosingFunction() = this) }
 }
 
-query predicate problems(FunctionCall fc, string message, RecursiveFunction f, string functionName) {
+query predicate problems(RecursiveCall fc, string message, Function f, string functionName) {
   not isExcluded(fc, getQuery()) and
   f = fc.getTarget() and
   functionName = f.getName() and
   if f = fc.getEnclosingFunction()
   then message = "This call directly invokes its containing function $@."
   else
     message =
-      "The function " + fc.getEnclosingFunction() + " is indirectly recursive via this call to $@."
+      "The function " + fc.getEnclosingFunction() +
+        " is indirectly recursive via this call to $@."
 }

cpp/common/test/rules/functionscallthemselveseitherdirectlyorindirectly/FunctionsCallThemselvesEitherDirectlyOrIndirectly.expected

@@ -1,5 +1,4 @@
 | test.cpp:7:13:7:35 | call to test_recursive_function | This call directly invokes its containing function $@. | test.cpp:5:5:5:27 | test_recursive_function | test_recursive_function |
-| test.cpp:21:9:21:31 | call to test_recursive_function | The function test_indirect_recursive_function is indirectly recursive via this call to $@. | test.cpp:5:5:5:27 | test_recursive_function | test_recursive_function |
-| test.cpp:27:5:27:30 | call to test_indirect_recursive_f2 | The function test_indirect_recursive_f1 is indirectly recursive via this call to $@. | test.cpp:36:5:36:30 | test_indirect_recursive_f2 | test_indirect_recursive_f2 |
-| test.cpp:38:9:38:34 | call to test_indirect_recursive_f1 | The function test_indirect_recursive_f2 is indirectly recursive via this call to $@. | test.cpp:25:5:25:30 | test_indirect_recursive_f1 | test_indirect_recursive_f1 |
-| test.cpp:75:10:75:19 | call to operator== | This call directly invokes its containing function $@. | test.cpp:74:6:74:15 | operator== | operator== |
+| test.cpp:31:5:31:30 | call to test_indirect_recursive_f2 | The function test_indirect_recursive_f1 is indirectly recursive via this call to $@. | test.cpp:40:5:40:30 | test_indirect_recursive_f2 | test_indirect_recursive_f2 |
+| test.cpp:42:9:42:34 | call to test_indirect_recursive_f1 | The function test_indirect_recursive_f2 is indirectly recursive via this call to $@. | test.cpp:29:5:29:30 | test_indirect_recursive_f1 | test_indirect_recursive_f1 |
+| test.cpp:79:10:79:19 | call to operator== | This call directly invokes its containing function $@. | test.cpp:78:6:78:15 | operator== | operator== |

cpp/common/test/rules/functionscallthemselveseitherdirectlyorindirectly/test.cpp

@@ -18,10 +18,14 @@ int test_nonrecursive_function(int i) { // COMPLIANT
 
 int test_indirect_recursive_function(int i) {
   if (i > 10) {
-    i = test_recursive_function(i * i); // NON_COMPLIANT
+    i = test_recursive_function(i * i); // COMPLIANT - merely calls a recursive function
   }
 }
 
+int test_calls_recursive_function(int i) {
+  return test_recursive_function(i); // COMPLIANT - not part of a recursive cycle
+}
+
 int test_indirect_recursive_f1(int i) {
   if (i > 10) {
     test_indirect_recursive_f2(i + i); // NON_COMPLIANT