1 //===--- MatchConsumer.h - MatchConsumer abstraction ------------*- 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 /// \file This file defines the *MatchConsumer* abstraction: a computation over
10 /// match results, specifically the `ast_matchers::MatchFinder::MatchResult`
11 /// class.
12 ///
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H
16 #define LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H
17 
18 #include "clang/AST/ASTTypeTraits.h"
19 #include "clang/ASTMatchers/ASTMatchFinder.h"
20 #include "llvm/ADT/StringRef.h"
21 #include "llvm/Support/Errc.h"
22 #include "llvm/Support/Error.h"
23 
24 namespace clang {
25 namespace transformer {
26 /// A failable computation over nodes bound by AST matchers.
27 ///
28 /// The computation should report any errors though its return value (rather
29 /// than terminating the program) to enable usage in interactive scenarios like
30 /// clang-query.
31 ///
32 /// This is a central abstraction of the Transformer framework.
33 template <typename T>
34 using MatchConsumer =
35     std::function<Expected<T>(const ast_matchers::MatchFinder::MatchResult &)>;
36 
37 /// Creates an error that signals that a `MatchConsumer` expected a certain node
38 /// to be bound by AST matchers, but it was not actually bound.
39 inline llvm::Error notBoundError(llvm::StringRef Id) {
40   return llvm::make_error<llvm::StringError>(llvm::errc::invalid_argument,
41                                              "Id not bound: " + Id);
42 }
43 
44 /// Chooses between the two consumers, based on whether \p ID is bound in the
45 /// match.
46 template <typename T>
47 MatchConsumer<T> ifBound(std::string ID, MatchConsumer<T> TrueC,
48                          MatchConsumer<T> FalseC) {
49   return [=](const ast_matchers::MatchFinder::MatchResult &Result) {
50     auto &Map = Result.Nodes.getMap();
51     return (Map.find(ID) != Map.end() ? TrueC : FalseC)(Result);
52   };
53 }
54 
55 /// A failable computation over nodes bound by AST matchers, with (limited)
56 /// reflection via the `toString` method.
57 ///
58 /// The computation should report any errors though its return value (rather
59 /// than terminating the program) to enable usage in interactive scenarios like
60 /// clang-query.
61 ///
62 /// This is a central abstraction of the Transformer framework. It is a
63 /// generalization of `MatchConsumer` and intended to replace it.
64 template <typename T> class MatchComputation {
65 public:
66   virtual ~MatchComputation() = default;
67 
68   /// Evaluates the computation and (potentially) updates the accumulator \c
69   /// Result.  \c Result is undefined in the case of an error. `Result` is an
70   /// out parameter to optimize case where the computation involves composing
71   /// the result of sub-computation evaluations.
72   virtual llvm::Error eval(const ast_matchers::MatchFinder::MatchResult &Match,
73                            T *Result) const = 0;
74 
75   /// Convenience version of `eval`, for the case where the computation is being
76   /// evaluated on its own.
77   llvm::Expected<T> eval(const ast_matchers::MatchFinder::MatchResult &R) const;
78 
79   /// Constructs a string representation of the computation, for informational
80   /// purposes. The representation must be deterministic, but is not required to
81   /// be unique.
82   virtual std::string toString() const = 0;
83 
84 protected:
85   MatchComputation() = default;
86 
87   // Since this is an abstract class, copying/assigning only make sense for
88   // derived classes implementing `clone()`.
89   MatchComputation(const MatchComputation &) = default;
90   MatchComputation &operator=(const MatchComputation &) = default;
91 };
92 
93 template <typename T>
94 llvm::Expected<T> MatchComputation<T>::eval(
95     const ast_matchers::MatchFinder::MatchResult &R) const {
96   T Output;
97   if (auto Err = eval(R, &Output))
98     return std::move(Err);
99   return Output;
100 }
101 } // namespace transformer
102 } // namespace clang
103 #endif // LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H
104