Merge pull request #21421 from geoffw0/wrongtypeformat

C++: Add some test cases for cpp/wrong-type-format-argument

Author: geoffw0

cpp/ql/src/Likely Bugs/Format/WrongTypeFormatArguments.ql

@@ -168,9 +168,11 @@ where
     formatOtherArgType(ffc, n, expected, arg, actual) and
     not actual.getUnspecifiedType().(IntegralType).getSize() = sizeof_IntType()
   ) and
+  // Exclude some cases where we're less confident the result is correct / clear / valuable
   not arg.isAffectedByMacro() and
   not arg.isFromUninstantiatedTemplate(_) and
   not actual.stripType() instanceof ErroneousType and
+  not arg.getType().stripType().(RoutineType).getReturnType() instanceof ErroneousType and
   not arg.(Call).mayBeFromImplicitlyDeclaredFunction() and
   // Make sure that the format function definition is consistent
   count(ffc.getTarget().getFormatParameterIndex()) = 1

cpp/ql/src/change-notes/2026-03-16-wrong-type-format-argument.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Fixed an issue with the "Wrong type of arguments to formatting function" (`cpp/wrong-type-format-argument`) query causing false positive results in `build-mode: none` databases.

cpp/ql/test/query-tests/Likely Bugs/Format/WrongTypeFormatArguments/Buildless/WrongTypeFormatArguments.expected

@@ -1 +1,3 @@
+| second.cpp:26:18:26:39 | ... - ... | This format specifier for type 'int' does not match the argument type 'long'. |
+| second.cpp:29:18:29:39 | ... - ... | This format specifier for type 'unsigned int' does not match the argument type 'long'. |
 | tests.c:7:18:7:18 | 1 | This format specifier for type 'char *' does not match the argument type 'int'. |

cpp/ql/test/query-tests/Likely Bugs/Format/WrongTypeFormatArguments/Buildless/first.cpp

@@ -0,0 +1,3 @@
+
+// defines type size_t plausibly
+typedef unsigned long size_t;

cpp/ql/test/query-tests/Likely Bugs/Format/WrongTypeFormatArguments/Buildless/second.cpp

@@ -0,0 +1,32 @@
+// semmle-extractor-options: --expect_errors
+
+int printf(const char * format, ...);
+
+// defines type `myFunctionPointerType`, referencing `size_t`
+typedef size_t (*myFunctionPointerType) ();
+
+void test_size_t() {
+    size_t s = 0;
+
+    printf("%zd", s); // GOOD
+    printf("%zi", s); // GOOD
+    printf("%zu", s); // GOOD (we generally permit signedness changes)
+    printf("%zx", s); // GOOD (we generally permit signedness changes)
+    printf("%d", s); // BAD [NOT DETECTED]
+    printf("%ld", s); // DUBIOUS [NOT DETECTED]
+    printf("%lld", s); // DUBIOUS [NOT DETECTED]
+    printf("%u", s); // BAD [NOT DETECTED]
+
+    char buffer[1024];
+
+    printf("%zd", &buffer[1023] - buffer); // GOOD
+    printf("%zi", &buffer[1023] - buffer); // GOOD
+    printf("%zu", &buffer[1023] - buffer); // GOOD
+    printf("%zx", &buffer[1023] - buffer); // GOOD
+    printf("%d", &buffer[1023] - buffer); // BAD
+    printf("%ld", &buffer[1023] - buffer); // DUBIOUS [NOT DETECTED]
+    printf("%lld", &buffer[1023] - buffer); // DUBIOUS [NOT DETECTED]
+    printf("%u", &buffer[1023] - buffer); // BAD
+    // (for the `%ld` and `%lld` cases, the signedness and type sizes match, `%zd` would be most correct
+    //  and robust but the developer may know enough to make this safe)
+}