Check called functions with noexcept(unknown)

change_notes/2024-12-17-fix-fp-824-a15-4-4

@@ -1,2 +1,2 @@
  - `A15-4-4` - `MissingNoExcept.ql`:
-   - Reduce false positives by not reporting on functions that have a noexcept specification with a complex expression.
+   - Reduce false positives by not reporting on functions that have a noexcept specification with a complex expression or call other such functions.

cpp/autosar/src/rules/A15-4-4/MissingNoExcept.ql

@@ -19,6 +19,36 @@ import codingstandards.cpp.autosar
 import codingstandards.cpp.exceptions.ExceptionSpecifications
 import codingstandards.cpp.exceptions.ExceptionFlow
 
+// These functions have a noexcept specification that could not be resolved
+// to noexcept(true). So either, they are noexcept(false) functions which
+// means, they can throw an exception OR they have an expression which
+// could not be resolved to "true" or "false". Even in this case, lets
+// be more conservative and assume they may thrown an exception.
+class FunctionWithUnknownNoExcept extends Function {
+  FunctionWithUnknownNoExcept() {
+    // Exists a noexcept specification but not noexcept(true)
+    exists(this.getADeclarationEntry().getNoExceptExpr()) and
+    not isNoExceptTrue(this)
+  }
+}
+
+// This predicate checks if a function can call to other functions
+// that may have a noexcept specification which cannot be resolved to
+// noexcept(true).
+predicate mayCallThrowingFunctions(Function f) {
+  // Exists a call in this function
+  exists(Call fc |
+    fc.getEnclosingFunction() = f and
+    (
+      // Either this call is to a function with an unknown noexcept OR
+      fc.getTarget() instanceof FunctionWithUnknownNoExcept
+      or
+      // That function can further have calls to unknown noexcept functions.
+      mayCallThrowingFunctions(fc.getTarget())
+    )
+  )
+}
+
 from Function f
 where
   not isExcluded(f, Exceptions1Package::missingNoExceptQuery()) and
@@ -31,6 +61,9 @@ where
   // Not having a noexcept specification that
   // could not be computed as true or false above.
   not exists(f.getADeclarationEntry().getNoExceptExpr()) and
+  // Not calling function(s) which have a noexcept specification that
+  // could not be computed as true.
+  not mayCallThrowingFunctions(f) and
   // Not compiler generated
   not f.isCompilerGenerated() and
   // The function is defined in this database