1 //===--- ProBoundsConstantArrayIndexCheck.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 "ProBoundsConstantArrayIndexCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include "clang/Frontend/CompilerInstance.h"
13 #include "clang/Lex/Preprocessor.h"
14 #include <optional>
15 
16 using namespace clang::ast_matchers;
17 
18 namespace clang::tidy::cppcoreguidelines {
19 
20 ProBoundsConstantArrayIndexCheck::ProBoundsConstantArrayIndexCheck(
21     StringRef Name, ClangTidyContext *Context)
22     : ClangTidyCheck(Name, Context), GslHeader(Options.get("GslHeader", "")),
23       Inserter(Options.getLocalOrGlobal("IncludeStyle",
24                                         utils::IncludeSorter::IS_LLVM),
25                areDiagsSelfContained()) {}
26 
27 void ProBoundsConstantArrayIndexCheck::storeOptions(
28     ClangTidyOptions::OptionMap &Opts) {
29   Options.store(Opts, "GslHeader", GslHeader);
30   Options.store(Opts, "IncludeStyle", Inserter.getStyle());
31 }
32 
33 void ProBoundsConstantArrayIndexCheck::registerPPCallbacks(
34     const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
35   Inserter.registerPreprocessor(PP);
36 }
37 
38 void ProBoundsConstantArrayIndexCheck::registerMatchers(MatchFinder *Finder) {
39   // Note: if a struct contains an array member, the compiler-generated
40   // constructor has an arraySubscriptExpr.
41   Finder->addMatcher(arraySubscriptExpr(hasBase(ignoringImpCasts(hasType(
42                                             constantArrayType().bind("type")))),
43                                         hasIndex(expr().bind("index")),
44                                         unless(hasAncestor(decl(isImplicit()))))
45                          .bind("expr"),
46                      this);
47 
48   Finder->addMatcher(
49       cxxOperatorCallExpr(
50           hasOverloadedOperatorName("[]"),
51           hasArgument(
52               0, hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
53                      cxxRecordDecl(hasName("::std::array")).bind("type")))))),
54           hasArgument(1, expr().bind("index")))
55           .bind("expr"),
56       this);
57 }
58 
59 void ProBoundsConstantArrayIndexCheck::check(
60     const MatchFinder::MatchResult &Result) {
61   const auto *Matched = Result.Nodes.getNodeAs<Expr>("expr");
62   const auto *IndexExpr = Result.Nodes.getNodeAs<Expr>("index");
63 
64   // This expression can only appear inside ArrayInitLoopExpr, which
65   // is always implicitly generated. ArrayInitIndexExpr is not a
66   // constant, but we shouldn't report a warning for it.
67   if (isa<ArrayInitIndexExpr>(IndexExpr))
68     return;
69 
70   if (IndexExpr->isValueDependent())
71     return; // We check in the specialization.
72 
73   std::optional<llvm::APSInt> Index =
74       IndexExpr->getIntegerConstantExpr(*Result.Context);
75   if (!Index) {
76     SourceRange BaseRange;
77     if (const auto *ArraySubscriptE = dyn_cast<ArraySubscriptExpr>(Matched))
78       BaseRange = ArraySubscriptE->getBase()->getSourceRange();
79     else
80       BaseRange =
81           cast<CXXOperatorCallExpr>(Matched)->getArg(0)->getSourceRange();
82     SourceRange IndexRange = IndexExpr->getSourceRange();
83 
84     auto Diag = diag(Matched->getExprLoc(),
85                      "do not use array subscript when the index is "
86                      "not an integer constant expression");
87     if (!GslHeader.empty()) {
88       Diag << FixItHint::CreateInsertion(BaseRange.getBegin(), "gsl::at(")
89            << FixItHint::CreateReplacement(
90                   SourceRange(BaseRange.getEnd().getLocWithOffset(1),
91                               IndexRange.getBegin().getLocWithOffset(-1)),
92                   ", ")
93            << FixItHint::CreateReplacement(Matched->getEndLoc(), ")")
94            << Inserter.createMainFileIncludeInsertion(GslHeader);
95     }
96     return;
97   }
98 
99   const auto *StdArrayDecl =
100       Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("type");
101 
102   // For static arrays, this is handled in clang-diagnostic-array-bounds.
103   if (!StdArrayDecl)
104     return;
105 
106   if (Index->isSigned() && Index->isNegative()) {
107     diag(Matched->getExprLoc(), "std::array<> index %0 is negative")
108         << toString(*Index, 10);
109     return;
110   }
111 
112   const TemplateArgumentList &TemplateArgs = StdArrayDecl->getTemplateArgs();
113   if (TemplateArgs.size() < 2)
114     return;
115   // First template arg of std::array is the type, second arg is the size.
116   const auto &SizeArg = TemplateArgs[1];
117   if (SizeArg.getKind() != TemplateArgument::Integral)
118     return;
119   llvm::APInt ArraySize = SizeArg.getAsIntegral();
120 
121   // Get uint64_t values, because different bitwidths would lead to an assertion
122   // in APInt::uge.
123   if (Index->getZExtValue() >= ArraySize.getZExtValue()) {
124     diag(Matched->getExprLoc(),
125          "std::array<> index %0 is past the end of the array "
126          "(which contains %1 elements)")
127         << toString(*Index, 10) << toString(ArraySize, 10, false);
128   }
129 }
130 
131 } // namespace clang::tidy::cppcoreguidelines
132