compilerplugins/clang/externvar.cxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  */
   9
  10 #ifndef LO_CLANG_SHARED_PLUGINS
  11
  12 #include "check.hxx"
  13 #include "plugin.hxx"
  14
  15 // Find variable declarations at namespace scope that need not have external
  16 // linkage.
  17
  18 namespace {
  19
  20 // It looks like Clang wrongly implements DR 4
  21 // (<http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#4>) and treats
  22 // a variable declared in an 'extern "..." {...}'-style linkage-specification as
  23 // if it contained the 'extern' specifier:
  24 bool hasExternalLinkage(VarDecl const * decl) {
  25     if (decl->getLinkageAndVisibility().getLinkage() != ExternalLinkage) {
  26         return false;
  27     }
  28     for (auto ctx = decl->getLexicalDeclContext();
  29          ctx->getDeclKind() != Decl::TranslationUnit;
  30          ctx = ctx->getLexicalParent())
  31     {
  32         if (auto ls = dyn_cast<LinkageSpecDecl>(ctx)) {
  33             if (!ls->hasBraces()) {
  34                 return true;
  35             }
  36             if (auto prev = decl->getPreviousDecl()) {
  37                 return hasExternalLinkage(prev);
  38             }
  39             return !decl->isInAnonymousNamespace();
  40         }
  41     }
  42     return true;
  43 }
  44
  45 class ExternVar: public loplugin::FilteringPlugin<ExternVar>
  46 {
  47 public:
  48     explicit ExternVar(loplugin::InstantiationData const & data): FilteringPlugin(data)
  49     {}
  50
  51     void run() override
  52     { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
  53
  54     bool VisitVarDecl(VarDecl const * decl) {
  55         if (ignoreLocation(decl)) {
  56             return true;
  57         }
  58         if (decl->isStaticDataMember()) {
  59             return true;
  60         }
  61         if (!(decl->isFirstDecl()
  62               && compiler.getSourceManager().isInMainFile(decl->getLocation())
  63               && hasExternalLinkage(decl)))
  64         {
  65             return true;
  66         }
  67         auto def = decl->getDefinition();
  68         if (def == nullptr) {
  69             // Code like
  70             //
  71             //   namespace { extern int v; }
  72             //   int f() { return sizeof(v); }
  73             //
  74             // is already handled by Clang itself with an error "variable 'v' is
  75             // not needed and will not be emitted"
  76             return true;
  77         }
  78         if (loplugin::DeclCheck(def).Var("_pRawDllMain").GlobalNamespace()) {
  79             return true;
  80         }
  81         SourceLocation argLoc;
  82         if (compiler.getSourceManager().isMacroArgExpansion(def->getLocation(), &argLoc)
  83             && (Lexer::getImmediateMacroName(
  84                     argLoc, compiler.getSourceManager(), compiler.getLangOpts())
  85                 == "DEFINE_GUID"))
  86         {
  87             return true;
  88         }
  89         report(
  90             DiagnosticsEngine::Warning,
  91             "variable with external linkage not declared in an include file",
  92             def->getLocation())
  93             << def->getSourceRange();
  94         report(
  95             DiagnosticsEngine::Note,
  96             ("should either have internal linkage or be declared in an include"
  97              " file"),
  98             def->getLocation())
  99             << def->getSourceRange();
 100         for (auto prev = def;;) {
 101             prev = prev->getPreviousDecl();
 102             if (prev == nullptr) {
 103                 break;
 104             }
 105             report(
 106                 DiagnosticsEngine::Note, "previously declared here",
 107                 prev->getLocation())
 108                 << prev->getSourceRange();
 109         }
 110         return true;
 111     }
 112 };
 113
 114 loplugin::Plugin::Registration<ExternVar> externvar("externvar");
 115
 116 }
 117
 118 #endif // LO_CLANG_SHARED_PLUGINS
 119
 120 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */