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

[Endre Fülöp via cfe-commits]

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@@ -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,
----------------
gamesh411 wrote:

I suggest that we go with the enumerator name 'Default', as the name of the enum is Mode, so it would be easily understood that this is something that comes out of the box.
(Those interested in how or what it matches will look at the docs of this enum anyway. I find this to be a conventional and non-surprising nomenclature).

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