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(cxxRecordDecl(hasName("::std::array")).bind("type"))),
53           hasArgument(1, expr().bind("index")))
54           .bind("expr"),
55       this);
56 }
57 
58 void ProBoundsConstantArrayIndexCheck::check(
59     const MatchFinder::MatchResult &Result) {
60   const auto *Matched = Result.Nodes.getNodeAs<Expr>("expr");
61   const auto *IndexExpr = Result.Nodes.getNodeAs<Expr>("index");
62 
63   // This expression can only appear inside ArrayInitLoopExpr, which
64   // is always implicitly generated. ArrayInitIndexExpr is not a
65   // constant, but we shouldn't report a warning for it.
66   if (isa<ArrayInitIndexExpr>(IndexExpr))
67     return;
68 
69   if (IndexExpr->isValueDependent())
70     return; // We check in the specialization.
71 
72   std::optional<llvm::APSInt> Index =
73       IndexExpr->getIntegerConstantExpr(*Result.Context);
74   if (!Index) {
75     SourceRange BaseRange;
76     if (const auto *ArraySubscriptE = dyn_cast<ArraySubscriptExpr>(Matched))
77       BaseRange = ArraySubscriptE->getBase()->getSourceRange();
78     else
79       BaseRange =
80           cast<CXXOperatorCallExpr>(Matched)->getArg(0)->getSourceRange();
81     SourceRange IndexRange = IndexExpr->getSourceRange();
82 
83     auto Diag = diag(Matched->getExprLoc(),
84                      "do not use array subscript when the index is "
85                      "not an integer constant expression");
86     if (!GslHeader.empty()) {
87       Diag << FixItHint::CreateInsertion(BaseRange.getBegin(), "gsl::at(")
88            << FixItHint::CreateReplacement(
89                   SourceRange(BaseRange.getEnd().getLocWithOffset(1),
90                               IndexRange.getBegin().getLocWithOffset(-1)),
91                   ", ")
92            << FixItHint::CreateReplacement(Matched->getEndLoc(), ")")
93            << Inserter.createMainFileIncludeInsertion(GslHeader);
94     }
95     return;
96   }
97 
98   const auto *StdArrayDecl =
99       Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("type");
100 
101   // For static arrays, this is handled in clang-diagnostic-array-bounds.
102   if (!StdArrayDecl)
103     return;
104 
105   if (Index->isSigned() && Index->isNegative()) {
106     diag(Matched->getExprLoc(), "std::array<> index %0 is negative")
107         << toString(*Index, 10);
108     return;
109   }
110 
111   const TemplateArgumentList &TemplateArgs = StdArrayDecl->getTemplateArgs();
112   if (TemplateArgs.size() < 2)
113     return;
114   // First template arg of std::array is the type, second arg is the size.
115   const auto &SizeArg = TemplateArgs[1];
116   if (SizeArg.getKind() != TemplateArgument::Integral)
117     return;
118   llvm::APInt ArraySize = SizeArg.getAsIntegral();
119 
120   // Get uint64_t values, because different bitwidths would lead to an assertion
121   // in APInt::uge.
122   if (Index->getZExtValue() >= ArraySize.getZExtValue()) {
123     diag(Matched->getExprLoc(),
124          "std::array<> index %0 is past the end of the array "
125          "(which contains %1 elements)")
126         << toString(*Index, 10) << toString(ArraySize, 10, false);
127   }
128 }
129 
130 } // namespace clang::tidy::cppcoreguidelines
131