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 
37 namespace clang {
38 namespace dataflow {
39 
40 /// A common form of state shared between the cases of a transfer function.
41 template <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 template <typename LatticeT> struct TransferStateForDiagnostics {
52   TransferStateForDiagnostics(const LatticeT &Lattice, const Environment &Env)
53       : Lattice(Lattice), Env(Env) {}
54 
55   /// Current lattice element.
56   const LatticeT &Lattice;
57   const Environment &Env;
58 };
59 
60 template <typename T>
61 using MatchSwitchMatcher = ast_matchers::internal::Matcher<T>;
62 
63 template <typename T, typename State, typename Result = void>
64 using MatchSwitchAction = std::function<Result(
65     const T *, const ast_matchers::MatchFinder::MatchResult &, State &)>;
66 
67 template <typename BaseT, typename State, typename Result = void>
68 using ASTMatchSwitch =
69     std::function<Result(const BaseT &, ASTContext &, State &)>;
70 
71 /// Collects cases of a "match switch": a collection of matchers paired with
72 /// callbacks, which together define a switch that can be applied to a node
73 /// whose type derives from `BaseT`. This structure can simplify the definition
74 /// of `transfer` functions that rely on pattern-matching.
75 ///
76 /// For example, consider an analysis that handles particular function calls. It
77 /// can define the `ASTMatchSwitch` once, in the constructor of the analysis,
78 /// and then reuse it each time that `transfer` is called, with a fresh state
79 /// value.
80 ///
81 /// \code
82 /// ASTMatchSwitch<Stmt, TransferState<MyLattice> BuildSwitch() {
83 ///   return ASTMatchSwitchBuilder<TransferState<MyLattice>>()
84 ///     .CaseOf(callExpr(callee(functionDecl(hasName("foo")))), TransferFooCall)
85 ///     .CaseOf(callExpr(argumentCountIs(2),
86 ///                      callee(functionDecl(hasName("bar")))),
87 ///             TransferBarCall)
88 ///     .Build();
89 /// }
90 /// \endcode
91 template <typename BaseT, typename State, typename Result = void>
92 class ASTMatchSwitchBuilder {
93 public:
94   /// Registers an action that will be triggered by the match of a pattern
95   /// against the input statement.
96   ///
97   /// Requirements:
98   ///
99   ///  `NodeT` should be derived from `BaseT`.
100   template <typename NodeT>
101   ASTMatchSwitchBuilder &&CaseOf(MatchSwitchMatcher<BaseT> M,
102                                  MatchSwitchAction<NodeT, State, Result> A) && {
103     static_assert(std::is_base_of<BaseT, NodeT>::value,
104                   "NodeT must be derived from BaseT.");
105     Matchers.push_back(std::move(M));
106     Actions.push_back(
107         [A = std::move(A)](const BaseT *Node,
108                            const ast_matchers::MatchFinder::MatchResult &R,
109                            State &S) { return A(cast<NodeT>(Node), R, S); });
110     return std::move(*this);
111   }
112 
113   ASTMatchSwitch<BaseT, State, Result> Build() && {
114     return [Matcher = BuildMatcher(), Actions = std::move(Actions)](
115                const BaseT &Node, ASTContext &Context, State &S) -> Result {
116       auto Results = ast_matchers::matchDynamic(Matcher, Node, Context);
117       if (Results.empty()) {
118         return Result();
119       }
120       // Look through the map for the first binding of the form "TagN..." use
121       // that to select the action.
122       for (const auto &Element : Results[0].getMap()) {
123         llvm::StringRef ID(Element.first);
124         size_t Index = 0;
125         if (ID.consume_front("Tag") && !ID.getAsInteger(10, Index) &&
126             Index < Actions.size()) {
127           return Actions[Index](
128               &Node,
129               ast_matchers::MatchFinder::MatchResult(Results[0], &Context), S);
130         }
131       }
132       return Result();
133     };
134   }
135 
136 private:
137   ast_matchers::internal::DynTypedMatcher BuildMatcher() {
138     using ast_matchers::anything;
139     using ast_matchers::stmt;
140     using ast_matchers::unless;
141     using ast_matchers::internal::DynTypedMatcher;
142     if (Matchers.empty())
143       return stmt(unless(anything()));
144     for (int I = 0, N = Matchers.size(); I < N; ++I) {
145       std::string Tag = ("Tag" + llvm::Twine(I)).str();
146       // Many matchers are not bindable, so ensure that tryBind will work.
147       Matchers[I].setAllowBind(true);
148       auto M = *Matchers[I].tryBind(Tag);
149       // Each anyOf explicitly controls the traversal kind. The anyOf itself is
150       // set to `TK_AsIs` to ensure no nodes are skipped, thereby deferring to
151       // the kind of the branches. Then, each branch is either left as is, if
152       // the kind is already set, or explicitly set to `TK_AsIs`. We choose this
153       // setting because it is the default interpretation of matchers.
154       Matchers[I] =
155           !M.getTraversalKind() ? M.withTraversalKind(TK_AsIs) : std::move(M);
156     }
157     // The matcher type on the cases ensures that `Expr` kind is compatible with
158     // all of the matchers.
159     return DynTypedMatcher::constructVariadic(
160         DynTypedMatcher::VO_AnyOf, ASTNodeKind::getFromNodeKind<BaseT>(),
161         std::move(Matchers));
162   }
163 
164   std::vector<ast_matchers::internal::DynTypedMatcher> Matchers;
165   std::vector<MatchSwitchAction<BaseT, State, Result>> Actions;
166 };
167 
168 } // namespace dataflow
169 } // namespace clang
170 #endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_MATCHSWITCH_H_
171