[clang] [analyzer] Refactor CallDescription match mode (NFC) (PR #83432)

[Balázs Kéri via cfe-commits]

================
@@ -27,20 +27,48 @@ class IdentifierInfo;
 
 namespace clang {
 namespace ento {
-
-enum CallDescriptionFlags : unsigned {
-  CDF_None = 0,
-
-  /// Describes a C standard function that is sometimes implemented as a macro
-  /// that expands to a compiler builtin with some __builtin prefix.
-  /// The builtin may as well have a few extra arguments on top of the requested
-  /// number of arguments.
-  CDF_MaybeBuiltin = 1 << 0,
-};
-
-/// This class represents a description of a function call using the number of
-/// arguments and the name of the function.
+/// A `CallDescription` is a pattern that can be used to _match_ calls
+/// based on the qualified name and the argument/parameter counts.
 class CallDescription {
+public:
+  enum class Mode {
+    /// Match calls to functions from the C standard library. On some platforms
+    /// some functions may be implemented as macros that expand to calls to
+    /// built-in variants of the given functions, so in this mode we use some
+    /// heuristics to recognize these implementation-defined variants:
+    ///  - We also accept calls where the name is derived from the specified
+    ///    name by adding "__builtin" or similar prefixes/suffixes.
+    ///  - We also accept calls where the number of arguments or parameters is
+    ///    greater than the specified value.
+    /// For the exact heuristics, see CheckerContext::isCLibraryFunction().
+    /// Note that functions whose declaration context is not a TU (e.g.
+    /// methods, functions in namespaces) are not accepted as C library
+    /// functions.
+    /// FIXME: If I understand it correctly, this discards calls where C++ code
+    /// refers a C library function through the namespace `std::` via headers
+    /// like <cstdlib>.
+    CLibrary,
+
+    /// Matches "simple" functions that are not methods. (Static methods are
+    /// methods.)
+    SimpleFunc,
+
+    /// Matches a C+ method (may be static, may be virtual, may be an
+    /// overloaded operator, a constructor or a destructor).
+    CXXMethod,
+
+    /// Match any CallEvent that is not an ObjCMethodCall.
+    /// FIXME: Previously this was the default behavior of CallDescription, but
+    /// its use should be replaced by a more specific mode almost everywhere.
+    Unspecified,
----------------
balazske wrote:

My concern was really that we can think that "Unspecified" means one from the other modes is used. But this is likely not a big problem.

https://github.com/llvm/llvm-project/pull/83432