1 //===--- ProBoundsArrayToPointerDecayCheck.cpp - clang-tidy----------------===//
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 #include "ProBoundsArrayToPointerDecayCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 
13 using namespace clang::ast_matchers;
14 
15 namespace clang {
16 namespace tidy {
17 namespace cppcoreguidelines {
18 
19 namespace {
20 AST_MATCHER_P(CXXForRangeStmt, hasRangeBeginEndStmt,
21               ast_matchers::internal::Matcher<DeclStmt>, InnerMatcher) {
22   for (const DeclStmt *Stmt : {Node.getBeginStmt(), Node.getEndStmt()})
23     if (Stmt != nullptr && InnerMatcher.matches(*Stmt, Finder, Builder))
24       return true;
25   return false;
26 }
27 
28 AST_MATCHER(Stmt, isInsideOfRangeBeginEndStmt) {
29   return stmt(hasAncestor(cxxForRangeStmt(
30                   hasRangeBeginEndStmt(hasDescendant(equalsNode(&Node))))))
31       .matches(Node, Finder, Builder);
32 }
33 
34 AST_MATCHER_P(Expr, hasParentIgnoringImpCasts,
35               ast_matchers::internal::Matcher<Expr>, InnerMatcher) {
36   const Expr *E = &Node;
37   do {
38     ASTContext::DynTypedNodeList Parents =
39         Finder->getASTContext().getParents(*E);
40     if (Parents.size() != 1)
41       return false;
42     E = Parents[0].get<Expr>();
43     if (!E)
44       return false;
45   } while (isa<ImplicitCastExpr>(E));
46 
47   return InnerMatcher.matches(*E, Finder, Builder);
48 }
49 } // namespace
50 
51 void ProBoundsArrayToPointerDecayCheck::registerMatchers(MatchFinder *Finder) {
52   if (!getLangOpts().CPlusPlus)
53     return;
54 
55   // The only allowed array to pointer decay
56   // 1) just before array subscription
57   // 2) inside a range-for over an array
58   // 3) if it converts a string literal to a pointer
59   Finder->addMatcher(
60       implicitCastExpr(
61           unless(hasParent(arraySubscriptExpr())),
62           unless(hasParentIgnoringImpCasts(explicitCastExpr())),
63           unless(isInsideOfRangeBeginEndStmt()),
64           unless(hasSourceExpression(ignoringParens(stringLiteral()))))
65           .bind("cast"),
66       this);
67 }
68 
69 void ProBoundsArrayToPointerDecayCheck::check(
70     const MatchFinder::MatchResult &Result) {
71   const auto *MatchedCast = Result.Nodes.getNodeAs<ImplicitCastExpr>("cast");
72   if (MatchedCast->getCastKind() != CK_ArrayToPointerDecay)
73     return;
74 
75   diag(MatchedCast->getExprLoc(), "do not implicitly decay an array into a "
76                                   "pointer; consider using gsl::array_view or "
77                                   "an explicit cast instead");
78 }
79 
80 } // namespace cppcoreguidelines
81 } // namespace tidy
82 } // namespace clang
83