compilerplugins/clang/unusedvariablecheck.cxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * Based on LLVM/Clang.
   6  *
   7  * This file is distributed under the University of Illinois Open Source
   8  * License. See LICENSE.TXT for details.
   9  *
  10  */
  11
  12 #ifndef LO_CLANG_SHARED_PLUGINS
  13
  14 #include <config_global.h>
  15
  16 #include "compat.hxx"
  17 #include "check.hxx"
  18 #include "unusedvariablecheck.hxx"
  19 #include "plugin.hxx"
  20
  21 namespace loplugin
  22 {
  23
  24 /*
  25 This is a compile check.
  26
  27 Check for unused classes where the compiler cannot decide (e.g. because of
  28 non-trivial or extern ctors) if a variable is unused if only its ctor/dtor
  29 are called and nothing else. For example std::vector is a class where
  30 the ctor may call further functions, but an unused std::string variable
  31 does nothing. On the other hand, std::scoped_lock instances are used
  32 for their dtors and so are not unused even if not otherwise accessed.
  33
  34 Classes which are safe to be warned about need to be marked using
  35 SAL_WARN_UNUSED (see e.g. OUString). For external classes such as std::vector
  36 that cannot be edited there is a manual list below.
  37 */
  38
  39 UnusedVariableCheck::UnusedVariableCheck( const InstantiationData& data )
  40     : FilteringPlugin( data )
  41     {
  42     }
  43
  44 void UnusedVariableCheck::run()
  45     {
  46     TraverseDecl( compiler.getASTContext().getTranslationUnitDecl());
  47     }
  48
  49 bool UnusedVariableCheck::VisitVarDecl( const VarDecl* var )
  50     {
  51     if( ignoreLocation( var ))
  52         return true;
  53     if( var->isReferenced() || var->isUsed())
  54         return true;
  55     if( var->isDefinedOutsideFunctionOrMethod())
  56         return true;
  57
  58     auto type = var->getType();
  59     bool check = loplugin::isExtraWarnUnusedType(type);
  60
  61     if (!check)
  62         check = isUnusedSmartPointer(var);
  63
  64
  65     // this chunk of logic generates false+, which is why we don't leave it on
  66 /*
  67     if (!check && type->isRecordType())
  68     {
  69         auto recordDecl
  70             = dyn_cast_or_null<CXXRecordDecl>(type->getAs<RecordType>()->getDecl());
  71         if (recordDecl && recordDecl->hasDefinition() && recordDecl->hasTrivialDestructor())
  72             check = true;
  73     }
  74 */
  75     if(check)
  76         {
  77             if( const ParmVarDecl* param = dyn_cast< ParmVarDecl >( var ))
  78                 {
  79                 if( !param->getDeclName())
  80                     return true; // unnamed parameter -> unused
  81                 // If this declaration does not have a body, then the parameter is indeed not used,
  82                 // so ignore.
  83                 auto const parent = param->getParentFunctionOrMethod();
  84                 if( const FunctionDecl* func = dyn_cast_or_null< FunctionDecl >( parent))
  85                     if( !func->doesThisDeclarationHaveABody() || func->getBody() == nullptr)
  86                         return true;
  87                 if (auto const d = dyn_cast_or_null<ObjCMethodDecl>(parent)) {
  88                     if (!d->hasBody()) {
  89                         return true;
  90                     }
  91                 }
  92                 report( DiagnosticsEngine::Warning, "unused parameter %0",
  93                     var->getLocation()) << var->getDeclName();
  94                 }
  95             else
  96                 report( DiagnosticsEngine::Warning, "unused variable %0",
  97                     var->getLocation()) << var->getDeclName();
  98         }
  99     return true;
 100     }
 101
 102 bool UnusedVariableCheck::isUnusedSmartPointer( const VarDecl* var )
 103     {
 104         // if we have a var of smart-pointer type, and that var is both uninitialised and
 105         // not referenced, then we can remove it
 106         if (!isSmartPointerType(var->getType()))
 107             return false;
 108
 109         if (!var->hasInit())
 110             return true;
 111
 112         auto cxxConstructExpr = dyn_cast<CXXConstructExpr>(var->getInit());
 113         if (!cxxConstructExpr)
 114             return false;
 115         return
 116             cxxConstructExpr->getNumArgs() == 0 || cxxConstructExpr->getArg(0)->isDefaultArgument();
 117     }
 118
 119 static Plugin::Registration< UnusedVariableCheck > unusedvariablecheck( "unusedvariablecheck" );
 120
 121 } // namespace
 122
 123 #endif // LO_CLANG_SHARED_PLUGINS
 124
 125 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */