1 /* This Source Code Form is subject to the terms of the Mozilla Public
2  * License, v. 2.0. If a copy of the MPL was not distributed with this
3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
4 
5 #include "KungFuDeathGripChecker.h"
6 #include "CustomMatchers.h"
7 
registerMatchers(MatchFinder * AstMatcher)8 void KungFuDeathGripChecker::registerMatchers(MatchFinder *AstMatcher) {
9   AstMatcher->addMatcher(varDecl(allOf(hasType(isRefPtr()), hasLocalStorage(),
10                                        hasInitializer(anything())))
11                              .bind("decl"),
12                          this);
13 }
14 
check(const MatchFinder::MatchResult & Result)15 void KungFuDeathGripChecker::check(const MatchFinder::MatchResult &Result) {
16   const char *Error = "Unused \"kungFuDeathGrip\" %0 objects constructed from "
17                       "%1 are prohibited";
18   const char *Note = "Please switch all accesses to this %0 to go through "
19                      "'%1', or explicitly pass '%1' to `mozilla::Unused`";
20 
21   const VarDecl *D = Result.Nodes.getNodeAs<VarDecl>("decl");
22   if (D->isReferenced()) {
23     return;
24   }
25 
26   // Not interested in parameters.
27   if (isa<ImplicitParamDecl>(D) || isa<ParmVarDecl>(D)) {
28     return;
29   }
30 
31   const Expr *E = IgnoreTrivials(D->getInit());
32   const CXXConstructExpr *CE = dyn_cast<CXXConstructExpr>(E);
33   if (CE && CE->getNumArgs() == 0) {
34     // We don't report an error when we construct and don't use a nsCOMPtr /
35     // nsRefPtr with no arguments. We don't report it because the error is not
36     // related to the current check. In the future it may be reported through a
37     // more generic mechanism.
38     return;
39   }
40 
41   // We don't want to look at the single argument conversion constructors
42   // which are inbetween the declaration and the actual object which we are
43   // assigning into the nsCOMPtr/RefPtr. To do this, we repeatedly
44   // IgnoreTrivials, then look at the expression. If it is one of these
45   // conversion constructors, we ignore it and continue to dig.
46   while ((CE = dyn_cast<CXXConstructExpr>(E)) && CE->getNumArgs() == 1) {
47     E = IgnoreTrivials(CE->getArg(0));
48   }
49 
50   // If the argument expression is an xvalue, we are not taking a copy of
51   // anything.
52   if (E->isXValue()) {
53     return;
54   }
55 
56   // It is possible that the QualType doesn't point to a type yet so we are
57   // not interested.
58   if (E->getType().isNull()) {
59     return;
60   }
61 
62   // We allow taking a kungFuDeathGrip of `this` because it cannot change
63   // beneath us, so calling directly through `this` is OK. This is the same
64   // for local variable declarations.
65   //
66   // We also don't complain about unused RefPtrs which are constructed from
67   // the return value of a new expression, as these are required in order to
68   // immediately destroy the value created (which was presumably created for
69   // its side effects), and are not used as a death grip.
70   if (isa<CXXThisExpr>(E) || isa<DeclRefExpr>(E) || isa<CXXNewExpr>(E)) {
71     return;
72   }
73 
74   // These types are assigned into nsCOMPtr and RefPtr for their side effects,
75   // and not as a kungFuDeathGrip. We don't want to consider RefPtr and nsCOMPtr
76   // types which are initialized with these types as errors.
77   const TagDecl *TD = E->getType()->getAsTagDecl();
78   if (TD && TD->getIdentifier()) {
79     static const char *IgnoreTypes[] = {
80         "already_AddRefed",
81         "nsGetServiceByCID",
82         "nsGetServiceByCIDWithError",
83         "nsGetServiceByContractID",
84         "nsGetServiceByContractIDWithError",
85         "nsCreateInstanceByCID",
86         "nsCreateInstanceByContractID",
87         "nsCreateInstanceFromFactory",
88     };
89 
90     for (uint32_t i = 0; i < sizeof(IgnoreTypes) / sizeof(IgnoreTypes[0]);
91          ++i) {
92       if (TD->getName() == IgnoreTypes[i]) {
93         return;
94       }
95     }
96   }
97 
98   // Report the error
99   const char *ErrThing;
100   const char *NoteThing;
101   if (isa<MemberExpr>(E)) {
102     ErrThing = "members";
103     NoteThing = "member";
104   } else {
105     ErrThing = "temporary values";
106     NoteThing = "value";
107   }
108 
109   // We cannot provide the note if we don't have an initializer
110   diag(D->getBeginLoc(), Error, DiagnosticIDs::Error)
111       << D->getType() << ErrThing;
112   diag(E->getBeginLoc(), Note, DiagnosticIDs::Note)
113       << NoteThing << getNameChecked(D);
114 }
115