1 //===- CalledOnceCheck.h - Check 'called once' parameters -------*- 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 a check for function-like parameters that should be
10 //  called exactly one time.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_CLANG_ANALYSIS_ANALYSES_CALLEDONCECHECK_H
15 #define LLVM_CLANG_ANALYSIS_ANALYSES_CALLEDONCECHECK_H
16 
17 namespace clang {
18 
19 class AnalysisDeclContext;
20 class BlockDecl;
21 class CFG;
22 class Decl;
23 class DeclContext;
24 class Expr;
25 class ParmVarDecl;
26 class Stmt;
27 
28 /// Classification of situations when parameter is not called on every path.
29 /// \enum IfThen -- then branch of the if statement has no call.
30 /// \enum IfElse -- else branch of the if statement has no call.
31 /// \enum Switch -- one of the switch cases doesn't have a call.
32 /// \enum SwitchSkipped -- there is no call if none of the cases appies.
33 /// \enum LoopEntered -- no call when the loop is entered.
34 /// \enum LoopSkipped -- no call when the loop is not entered.
35 /// \enum FallbackReason -- fallback case when we were not able to figure out
36 /// the reason.
37 enum class NeverCalledReason {
38   IfThen,
39   IfElse,
40   Switch,
41   SwitchSkipped,
42   LoopEntered,
43   LoopSkipped,
44   FallbackReason,
45   LARGEST_VALUE = FallbackReason
46 };
47 
48 class CalledOnceCheckHandler {
49 public:
50   CalledOnceCheckHandler() = default;
51   virtual ~CalledOnceCheckHandler() = default;
52 
53   /// Called when parameter is called twice.
54   /// \param Parameter -- parameter that should be called once.
55   /// \param Call -- call to report the warning.
56   /// \param PrevCall -- previous call.
57   /// \param IsCompletionHandler -- true, if parameter is a completion handler.
58   /// \param Poised -- true, if the second call is guaranteed to happen after
59   /// the first call.
60   virtual void handleDoubleCall(const ParmVarDecl *Parameter, const Expr *Call,
61                                 const Expr *PrevCall, bool IsCompletionHandler,
62                                 bool Poised) {}
63 
64   /// Called when parameter is not called at all.
65   /// \param Parameter -- parameter that should be called once.
66   /// \param IsCompletionHandler -- true, if parameter is a completion handler.
67   virtual void handleNeverCalled(const ParmVarDecl *Parameter,
68                                  bool IsCompletionHandler) {}
69 
70   /// Called when captured parameter is not called at all.
71   /// \param Parameter -- parameter that should be called once.
72   /// \param Where -- declaration that captures \p Parameter
73   /// \param IsCompletionHandler -- true, if parameter is a completion handler.
74   virtual void handleCapturedNeverCalled(const ParmVarDecl *Parameter,
75                                          const Decl *Where,
76                                          bool IsCompletionHandler) {}
77 
78   /// Called when parameter is not called on one of the paths.
79   /// Usually we try to find a statement that is the least common ancestor of
80   /// the path containing the call and not containing the call.  This helps us
81   /// to pinpoint a bad path for the user.
82   /// \param Parameter -- parameter that should be called once.
83   /// \param Function -- function declaration where the problem occured.
84   /// \param Where -- the least common ancestor statement.
85   /// \param Reason -- a reason describing the path without a call.
86   /// \param IsCalledDirectly -- true, if parameter actually gets called on
87   /// the other path.  It is opposed to be used in some other way (added to some
88   /// collection, passed as a parameter, etc.).
89   /// \param IsCompletionHandler -- true, if parameter is a completion handler.
90   virtual void handleNeverCalled(const ParmVarDecl *Parameter,
91                                  const Decl *Function, const Stmt *Where,
92                                  NeverCalledReason Reason,
93                                  bool IsCalledDirectly,
94                                  bool IsCompletionHandler) {}
95 
96   /// Called when the block is guaranteed to be called exactly once.
97   /// It means that we can be stricter with what we report on that block.
98   /// \param Block -- block declaration that is known to be called exactly once.
99   virtual void
100   handleBlockThatIsGuaranteedToBeCalledOnce(const BlockDecl *Block) {}
101 
102   /// Called when the block has no guarantees about how many times it can get
103   /// called.
104   /// It means that we should be more lenient with reporting warnings in it.
105   /// \param Block -- block declaration in question.
106   virtual void handleBlockWithNoGuarantees(const BlockDecl *Block) {}
107 };
108 
109 /// Check given CFG for 'called once' parameter violations.
110 ///
111 /// It traverses the function and tracks how such parameters are used.
112 /// It detects two main violations:
113 ///   * parameter is called twice
114 ///   * parameter is not called
115 ///
116 /// \param AC -- context.
117 /// \param Handler -- a handler for found violations.
118 /// \param CheckConventionalParameters -- true, if we want to check parameters
119 /// not explicitly marked as 'called once', but having the same requirements
120 /// according to conventions.
121 void checkCalledOnceParameters(AnalysisDeclContext &AC,
122                                CalledOnceCheckHandler &Handler,
123                                bool CheckConventionalParameters);
124 
125 } // end namespace clang
126 
127 #endif /* LLVM_CLANG_ANALYSIS_ANALYSES_CALLEDONCECHECK_H */
128