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+//===- CallDescription.h - function/method call matching       --*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file This file defines a generic mechanism for matching for function and
+/// method calls of C, C++, and Objective-C languages. Instances of these
+/// classes are frequently used together with the CallEvent classes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_STATICANALYZER_CORE_PATHSENSITIVE_CALLDESCRIPTION_H
+#define LLVM_CLANG_STATICANALYZER_CORE_PATHSENSITIVE_CALLDESCRIPTION_H
+
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Compiler.h"
+#include <optional>
+#include <vector>
+
+namespace clang {
+class IdentifierInfo;
+} // namespace clang
+
+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.
+class CallDescription {
+  friend class CallEvent;
+  using MaybeCount = std::optional<unsigned>;
+
+  mutable std::optional<const IdentifierInfo *> II;
+  // The list of the qualified names used to identify the specified CallEvent,
+  // e.g. "{a, b}" represent the qualified names, like "a::b".
+  std::vector<std::string> QualifiedName;
+  MaybeCount RequiredArgs;
+  MaybeCount RequiredParams;
+  int Flags;
+
+public:
+  /// Constructs a CallDescription object.
+  ///
+  /// @param QualifiedName The list of the name qualifiers of the function that
+  /// will be matched. The user is allowed to skip any of the qualifiers.
+  /// For example, {"std", "basic_string", "c_str"} would match both
+  /// std::basic_string<...>::c_str() and std::__1::basic_string<...>::c_str().
+  ///
+  /// @param RequiredArgs The number of arguments that is expected to match a
+  /// call. Omit this parameter to match every occurrence of call with a given
+  /// name regardless the number of arguments.
+  CallDescription(CallDescriptionFlags Flags, ArrayRef<StringRef> QualifiedName,
+                  MaybeCount RequiredArgs = std::nullopt,
+                  MaybeCount RequiredParams = std::nullopt);
+
+  /// Construct a CallDescription with default flags.
+  CallDescription(ArrayRef<StringRef> QualifiedName,
+                  MaybeCount RequiredArgs = std::nullopt,
+                  MaybeCount RequiredParams = std::nullopt);
+
+  CallDescription(std::nullptr_t) = delete;
+
+  /// Get the name of the function that this object matches.
+  StringRef getFunctionName() const { return QualifiedName.back(); }
+
+  /// Get the qualified name parts in reversed order.
+  /// E.g. { "std", "vector", "data" } -> "vector", "std"
+  auto begin_qualified_name_parts() const {
+    return std::next(QualifiedName.rbegin());
+  }
+  auto end_qualified_name_parts() const { return QualifiedName.rend(); }
+
+  /// It's false, if and only if we expect a single identifier, such as
+  /// `getenv`. It's true for `std::swap`, or `my::detail::container::data`.
+  bool hasQualifiedNameParts() const { return QualifiedName.size() > 1; }
+
+  /// @name Matching CallDescriptions against a CallEvent
+  /// @{
+
+  /// Returns true if the CallEvent is a call to a function that matches
+  /// the CallDescription.
+  ///
+  /// \note This function is not intended to be used to match Obj-C method
+  /// calls.
+  bool matches(const CallEvent &Call) const;
+
+  /// Returns true whether the CallEvent matches on any of the CallDescriptions
+  /// supplied.
+  ///
+  /// \note This function is not intended to be used to match Obj-C method
+  /// calls.
+  friend bool matchesAny(const CallEvent &Call, const CallDescription &CD1) {
+    return CD1.matches(Call);
+  }
+
+  /// \copydoc clang::ento::CallDescription::matchesAny(const CallEvent &, const CallDescription &)
+  template <typename... Ts>
+  friend bool matchesAny(const CallEvent &Call, const CallDescription &CD1,
+                         const Ts &...CDs) {
+    return CD1.matches(Call) || matchesAny(Call, CDs...);
+  }
+  /// @}
+
+  /// @name Matching CallDescriptions against a CallExpr
+  /// @{
+
+  /// Returns true if the CallExpr is a call to a function that matches the
+  /// CallDescription.
+  ///
+  /// When available, always prefer matching with a CallEvent! This function
+  /// exists only when that is not available, for example, when _only_
+  /// syntactic check is done on a piece of code.
+  ///
+  /// Also, StdLibraryFunctionsChecker::Signature is likely a better candicade
+  /// for syntactic only matching if you are writing a new checker. This is
+  /// handy if a CallDescriptionMap is already there.
+  ///
+  /// The function is imprecise because CallEvent may know path sensitive
+  /// information, such as the precise argument count (see comments for
+  /// CallEvent::getNumArgs), the called function if it was called through a
+  /// function pointer, and other information not available syntactically.
+  bool matchesAsWritten(const CallExpr &CE) const;
+
+  /// Returns true whether the CallExpr matches on any of the CallDescriptions
+  /// supplied.
+  ///
+  /// \note This function is not intended to be used to match Obj-C method
+  /// calls.
+  friend bool matchesAnyAsWritten(const CallExpr &CE,
+                                  const CallDescription &CD1) {
+    return CD1.matchesAsWritten(CE);
+  }
+
+  /// \copydoc clang::ento::CallDescription::matchesAnyAsWritten(const CallExpr &, const CallDescription &)
+  template <typename... Ts>
+  friend bool matchesAnyAsWritten(const CallExpr &CE,
+                                  const CallDescription &CD1,
+                                  const Ts &...CDs) {
+    return CD1.matchesAsWritten(CE) || matchesAnyAsWritten(CE, CDs...);
+  }
+  /// @}
+
+private:
+  bool matchesImpl(const FunctionDecl *Callee, size_t ArgCount,
+                   size_t ParamCount) const;
+};
+
+/// An immutable map from CallDescriptions to arbitrary data. Provides a unified
+/// way for checkers to react on function calls.
+template <typename T> class CallDescriptionMap {
+  friend class CallDescriptionSet;
+
+  // Some call descriptions aren't easily hashable (eg., the ones with qualified
+  // names in which some sections are omitted), so let's put them
+  // in a simple vector and use linear lookup.
+  // TODO: Implement an actual map for fast lookup for "hashable" call
+  // descriptions (eg., the ones for C functions that just match the name).
+  std::vector<std::pair<CallDescription, T>> LinearMap;
+
+public:
+  CallDescriptionMap(
+      std::initializer_list<std::pair<CallDescription, T>> &&List)
+      : LinearMap(List) {}
+
+  template <typename InputIt>
+  CallDescriptionMap(InputIt First, InputIt Last) : LinearMap(First, Last) {}
+
+  ~CallDescriptionMap() = default;
+
+  // These maps are usually stored once per checker, so let's make sure
+  // we don't do redundant copies.
+  CallDescriptionMap(const CallDescriptionMap &) = delete;
+  CallDescriptionMap &operator=(const CallDescription &) = delete;
+
+  CallDescriptionMap(CallDescriptionMap &&) = default;
+  CallDescriptionMap &operator=(CallDescriptionMap &&) = default;
+
+  [[nodiscard]] const T *lookup(const CallEvent &Call) const {
+    // Slow path: linear lookup.
+    // TODO: Implement some sort of fast path.
+    for (const std::pair<CallDescription, T> &I : LinearMap)
+      if (I.first.matches(Call))
+        return &I.second;
+
+    return nullptr;
+  }
+
+  /// When available, always prefer lookup with a CallEvent! This function
+  /// exists only when that is not available, for example, when _only_
+  /// syntactic check is done on a piece of code.
+  ///
+  /// Also, StdLibraryFunctionsChecker::Signature is likely a better candicade
+  /// for syntactic only matching if you are writing a new checker. This is
+  /// handy if a CallDescriptionMap is already there.
+  ///
+  /// The function is imprecise because CallEvent may know path sensitive
+  /// information, such as the precise argument count (see comments for
+  /// CallEvent::getNumArgs), the called function if it was called through a
+  /// function pointer, and other information not available syntactically.
+  [[nodiscard]] const T *lookupAsWritten(const CallExpr &Call) const {
+    // Slow path: linear lookup.
+    // TODO: Implement some sort of fast path.
+    for (const std::pair<CallDescription, T> &I : LinearMap)
+      if (I.first.matchesAsWritten(Call))
+        return &I.second;
+
+    return nullptr;
+  }
+};
+
+/// An immutable set of CallDescriptions.
+/// Checkers can efficiently decide if a given CallEvent matches any
+/// CallDescription in the set.
+class CallDescriptionSet {
+  CallDescriptionMap<bool /*unused*/> Impl = {};
+
+public:
+  CallDescriptionSet(std::initializer_list<CallDescription> &&List);
+
+  CallDescriptionSet(const CallDescriptionSet &) = delete;
+  CallDescriptionSet &operator=(const CallDescription &) = delete;
+
+  [[nodiscard]] bool contains(const CallEvent &Call) const;
+
+  /// When available, always prefer lookup with a CallEvent! This function
+  /// exists only when that is not available, for example, when _only_
+  /// syntactic check is done on a piece of code.
+  ///
+  /// Also, StdLibraryFunctionsChecker::Signature is likely a better candicade
+  /// for syntactic only matching if you are writing a new checker. This is
+  /// handy if a CallDescriptionMap is already there.
+  ///
+  /// The function is imprecise because CallEvent may know path sensitive
+  /// information, such as the precise argument count (see comments for
+  /// CallEvent::getNumArgs), the called function if it was called through a
+  /// function pointer, and other information not available syntactically.
+  [[nodiscard]] bool containsAsWritten(const CallExpr &CE) const;
+};
+
+} // namespace ento
+} // namespace clang
+
+#endif // LLVM_CLANG_STATICANALYZER_CORE_PATHSENSITIVE_CALLDESCRIPTION_H