1//===---- MatchSwitch.h -----------------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9//  This file defines the `ASTMatchSwitch` abstraction for building a "switch"
10//  statement, where each case of the switch is defined by an AST matcher. The
11//  cases are considered in order, like pattern matching in functional
12//  languages.
13//
14//  Currently, the design is catered towards simplifying the implementation of
15//  `DataflowAnalysis` transfer functions. Based on experience here, this
16//  library may be generalized and moved to ASTMatchers.
17//
18//===----------------------------------------------------------------------===//
19//
20// FIXME: Rename to ASTMatchSwitch.h
21
22#ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_MATCHSWITCH_H_
23#define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_MATCHSWITCH_H_
24
25#include "clang/AST/ASTContext.h"
26#include "clang/AST/Stmt.h"
27#include "clang/ASTMatchers/ASTMatchFinder.h"
28#include "clang/ASTMatchers/ASTMatchers.h"
29#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
30#include "llvm/ADT/StringRef.h"
31#include <functional>
32#include <string>
33#include <type_traits>
34#include <utility>
35#include <vector>
36
37namespace clang {
38namespace dataflow {
39
40/// A common form of state shared between the cases of a transfer function.
41template <typename LatticeT> struct TransferState {
42  TransferState(LatticeT &Lattice, Environment &Env)
43      : Lattice(Lattice), Env(Env) {}
44
45  /// Current lattice element.
46  LatticeT &Lattice;
47  Environment &Env;
48};
49
50/// A read-only version of TransferState.
51///
52/// FIXME: this type is being used as a general (typed) view type for untyped
53/// dataflow analysis state, rather than strictly for transfer-function
54/// purposes. Move it (and rename it) to DataflowAnalysis.h.
55template <typename LatticeT> struct TransferStateForDiagnostics {
56  TransferStateForDiagnostics(const LatticeT &Lattice, const Environment &Env)
57      : Lattice(Lattice), Env(Env) {}
58
59  /// Current lattice element.
60  const LatticeT &Lattice;
61  const Environment &Env;
62};
63
64template <typename T>
65using MatchSwitchMatcher = ast_matchers::internal::Matcher<T>;
66
67template <typename T, typename State, typename Result = void>
68using MatchSwitchAction = std::function<Result(
69    const T *, const ast_matchers::MatchFinder::MatchResult &, State &)>;
70
71template <typename BaseT, typename State, typename Result = void>
72using ASTMatchSwitch =
73    std::function<Result(const BaseT &, ASTContext &, State &)>;
74
75/// Collects cases of a "match switch": a collection of matchers paired with
76/// callbacks, which together define a switch that can be applied to a node
77/// whose type derives from `BaseT`. This structure can simplify the definition
78/// of `transfer` functions that rely on pattern-matching.
79///
80/// For example, consider an analysis that handles particular function calls. It
81/// can define the `ASTMatchSwitch` once, in the constructor of the analysis,
82/// and then reuse it each time that `transfer` is called, with a fresh state
83/// value.
84///
85/// \code
86/// ASTMatchSwitch<Stmt, TransferState<MyLattice> BuildSwitch() {
87///   return ASTMatchSwitchBuilder<TransferState<MyLattice>>()
88///     .CaseOf(callExpr(callee(functionDecl(hasName("foo")))), TransferFooCall)
89///     .CaseOf(callExpr(argumentCountIs(2),
90///                      callee(functionDecl(hasName("bar")))),
91///             TransferBarCall)
92///     .Build();
93/// }
94/// \endcode
95template <typename BaseT, typename State, typename Result = void>
96class ASTMatchSwitchBuilder {
97public:
98  /// Registers an action that will be triggered by the match of a pattern
99  /// against the input statement.
100  ///
101  /// Requirements:
102  ///
103  ///  `NodeT` should be derived from `BaseT`.
104  template <typename NodeT>
105  ASTMatchSwitchBuilder &&CaseOf(MatchSwitchMatcher<BaseT> M,
106                                 MatchSwitchAction<NodeT, State, Result> A) && {
107    static_assert(std::is_base_of<BaseT, NodeT>::value,
108                  "NodeT must be derived from BaseT.");
109    Matchers.push_back(std::move(M));
110    Actions.push_back(
111        [A = std::move(A)](const BaseT *Node,
112                           const ast_matchers::MatchFinder::MatchResult &R,
113                           State &S) { return A(cast<NodeT>(Node), R, S); });
114    return std::move(*this);
115  }
116
117  ASTMatchSwitch<BaseT, State, Result> Build() && {
118    return [Matcher = BuildMatcher(), Actions = std::move(Actions)](
119               const BaseT &Node, ASTContext &Context, State &S) -> Result {
120      auto Results = ast_matchers::matchDynamic(Matcher, Node, Context);
121      if (Results.empty()) {
122        return Result();
123      }
124      // Look through the map for the first binding of the form "TagN..." use
125      // that to select the action.
126      for (const auto &Element : Results[0].getMap()) {
127        llvm::StringRef ID(Element.first);
128        size_t Index = 0;
129        if (ID.consume_front("Tag") && !ID.getAsInteger(10, Index) &&
130            Index < Actions.size()) {
131          return Actions[Index](
132              &Node,
133              ast_matchers::MatchFinder::MatchResult(Results[0], &Context), S);
134        }
135      }
136      return Result();
137    };
138  }
139
140private:
141  ast_matchers::internal::DynTypedMatcher BuildMatcher() {
142    using ast_matchers::anything;
143    using ast_matchers::stmt;
144    using ast_matchers::unless;
145    using ast_matchers::internal::DynTypedMatcher;
146    if (Matchers.empty())
147      return stmt(unless(anything()));
148    for (int I = 0, N = Matchers.size(); I < N; ++I) {
149      std::string Tag = ("Tag" + llvm::Twine(I)).str();
150      // Many matchers are not bindable, so ensure that tryBind will work.
151      Matchers[I].setAllowBind(true);
152      auto M = *Matchers[I].tryBind(Tag);
153      // Each anyOf explicitly controls the traversal kind. The anyOf itself is
154      // set to `TK_AsIs` to ensure no nodes are skipped, thereby deferring to
155      // the kind of the branches. Then, each branch is either left as is, if
156      // the kind is already set, or explicitly set to `TK_AsIs`. We choose this
157      // setting because it is the default interpretation of matchers.
158      Matchers[I] =
159          !M.getTraversalKind() ? M.withTraversalKind(TK_AsIs) : std::move(M);
160    }
161    // The matcher type on the cases ensures that `Expr` kind is compatible with
162    // all of the matchers.
163    return DynTypedMatcher::constructVariadic(
164        DynTypedMatcher::VO_AnyOf, ASTNodeKind::getFromNodeKind<BaseT>(),
165        std::move(Matchers));
166  }
167
168  std::vector<ast_matchers::internal::DynTypedMatcher> Matchers;
169  std::vector<MatchSwitchAction<BaseT, State, Result>> Actions;
170};
171
172} // namespace dataflow
173} // namespace clang
174#endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_MATCHSWITCH_H_
175