codeql/change-notes/1.23/analysis-cpp.md

Improvements to C/C++ analysis

The following changes in version 1.23 affect C/C++ analysis in all applications.

General improvements

New queries

Query	Tags	Purpose
Hard-coded Japanese era start date (cpp/japanese-era/exact-era-date)	reliability, japanese-era	This query is a combination of two old queries that were identical in purpose but separate as an implementation detail. This new query replaces Hard-coded Japanese era start date in call (cpp/japanese-era/constructor-or-method-with-exact-era-date) and Hard-coded Japanese era start date in struct (cpp/japanese-era/struct-with-exact-era-date).
Signed overflow check (cpp/signed-overflow-check)	correctness, security	Finds overflow checks that rely on signed integer addition to overflow, which has undefined behavior. Example: a + b < a.
Pointer overflow check (cpp/pointer-overflow-check)	correctness, security	Finds overflow checks that rely on pointer addition to overflow, which has undefined behavior. Example: ptr + a < ptr.

Changes to existing queries

Query	Expected impact	Change
Query name (query id)	Expected impact	Message.
Hard-coded Japanese era start date in call (cpp/japanese-era/constructor-or-method-with-exact-era-date)	Deprecated	This query has been deprecated. Use the new combined query Hard-coded Japanese era start date (cpp/japanese-era/exact-era-date) instead.
Hard-coded Japanese era start date in struct (cpp/japanese-era/struct-with-exact-era-date)	Deprecated	This query has been deprecated. Use the new combined query Hard-coded Japanese era start date (cpp/japanese-era/exact-era-date) instead.
Hard-coded Japanese era start date (cpp/japanese-era/exact-era-date)	More correct results	This query now checks for the beginning date of the Reiwa era (1st May 2019).
Sign check of bitwise operation (cpp/bitwise-sign-check)	Fewer false positive results	Results involving >= or <= are no longer reported.
Too few arguments to formatting function (cpp/wrong-number-format-arguments)	Fewer false positive results	Fixed false positives resulting from mistmatching declarations of a formatting function.
Too many arguments to formatting function (cpp/too-many-format-arguments)	Fewer false positive results	Fixed false positives resulting from mistmatching declarations of a formatting function.
Unclear comparison precedence (cpp/comparison-precedence)	Fewer false positive results	False positives involving template classes and functions have been fixed.
Comparison of narrow type with wide type in loop condition (cpp/comparison-with-wider-type)	Higher precision	The precision of this query has been increased to "high" as the alerts from this query have proved to be valuable on real-world projects. With this precision, results are now displayed by default in LGTM.
Non-constant format string (cpp/non-constant-format)	Fewer false positive results	Fixed false positives resulting from mistmatching declarations of a formatting function.
Wrong type of arguments to formatting function (cpp/wrong-type-format-argument)	More correct results and fewer false positive results	This query now understands explicitly specified argument numbers in format strings, such as the 1$ in %1$s.

Changes to libraries

• The data-flow library has been extended with a new feature to aid debugging. Instead of specifying isSink(Node n) { any() } on a configuration to explore the possible flow from a source, it is recommended to use the new Configuration::hasPartialFlow predicate, as this gives a more complete picture of the partial flow paths from a given source. The feature is disabled by default and can be enabled for individual configurations by overriding int explorationLimit().
• The data-flow library now supports flow out of C++ reference parameters.
• The data-flow library now allows flow through the address-of operator (&).
• The DataFlow::DefinitionByReferenceNode class now considers f(x) to be a definition of x when x is a variable of pointer type. It no longer considers deep paths such as f(&x.myField) to be definitions of x. These changes are in line with the user expectations we've observed.
• The data-flow library now makes it easier to specify barriers/sanitizers arising from guards by overriding the predicate isBarrierGuard/isSanitizerGuard on data-flow and taint-tracking configurations respectively.
• There is now a DataFlow::localExprFlow predicate and a TaintTracking::localExprTaint predicate to make it easy to use the most common case of local data flow and taint: from one Expr to another.
• The member predicates of the FunctionInput and FunctionOutput classes have been renamed for clarity (e.g. isOutReturnPointer() to isReturnValueDeref()). The existing member predicates have been deprecated, and will be removed in a future release. Code that uses the old member predicates should be updated to use the corresponding new member predicate.
• The control-flow graph is now computed in QL, not in the extractor. This can lead to regressions (or improvements) in how queries are optimized because optimization in QL relies on static size estimates, and the control-flow edge relations will now have different size estimates than before.
• Support has been added for non-type template arguments. This means that the return type of Declaration::getTemplateArgument() and Declaration::getATemplateArgument have changed to Locatable. See the documentation for Declaration::getTemplateArgument() and Declaration::getTemplateArgumentKind() for details.