new loplugin:unusedvariablemore

collection of heuristics to look for local variables that are never read
from i.e. do not contribute to the surrounding logic

This is an expensive plugin, since it walks up the parent tree,
so it is off by default.

Change-Id: Ib8ba292241bd16adf299e8bba4502cb473513a06
Reviewed-on: https://gerrit.libreoffice.org/52450
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 405 insertions, 0 deletions

diff --git a/compilerplugins/clang/test/unusedvariablemore.cxx b/compilerplugins/clang/test/unusedvariablemore.cxx
new file mode 100644
index 000000000000..712bcf403614
--- /dev/null
+++ b/compilerplugins/clang/test/unusedvariablemore.cxx
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <sal/config.h>
+#include <sal/types.h>
+#include <map>
+
+struct SAL_WARN_UNUSED Point
+{
+};
+struct SAL_WARN_UNUSED Rectangle
+{
+    Rectangle();
+    Rectangle(int width, int height);
+    Rectangle& Union(const Rectangle&) { return *this; }
+    Rectangle& Intersection(const Rectangle&);
+    Rectangle& operator+=(const Point& rPt);
+};
+
+void func1()
+{
+    Rectangle aTmp1; // expected-error {{unused variable 'aTmp1' [loplugin:unusedvariablemore]}}
+    aTmp1.Union(Rectangle(10, 10));
+}
+
+void func2()
+{
+    Rectangle aViewArea(
+        10, 10); // expected-error@-1 {{unused variable 'aViewArea' [loplugin:unusedvariablemore]}}
+    aViewArea += Point();
+    aViewArea.Intersection(Rectangle(0, 0));
+}
+
+//---------------------------------------------------------------------
+// Negative tests
+//---------------------------------------------------------------------
+
+Rectangle func3(const Rectangle& rRect)
+{
+    Rectangle aTmpRect(Rectangle(10, 10));
+    return aTmpRect.Union(rRect);
+}
+
+void func4()
+{
+    std::map<int, int> aMimeTypeMap;
+    aMimeTypeMap[1] = 0;
+    int aExportMimeType(aMimeTypeMap[0]);
+    (void)aExportMimeType;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/compilerplugins/clang/unusedvariablemore.cxx b/compilerplugins/clang/unusedvariablemore.cxx
new file mode 100644
index 000000000000..6d8cf871e013
--- /dev/null
+++ b/compilerplugins/clang/unusedvariablemore.cxx
@@ -0,0 +1,347 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * Based on LLVM/Clang.
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ */
+
+#include <config_global.h>
+#include "plugin.hxx"
+#include "compat.hxx"
+#include "check.hxx"
+#include <unordered_set>
+#include <unordered_map>
+
+namespace loplugin
+{
+/*
+  This is a compile check. The results of this plugin need to be checked by hand, since it is a collection of heuristics.
+
+  Check for unused variable where
+  (*) we never call methods that return information from the variable.
+  (*) we never pass the variable to anything else
+
+  Classes which are safe to be warned about need to be marked using
+  SAL_WARN_UNUSED (see e.g. OUString). For external classes such as std::vector
+  that cannot be edited there is a manual list.
+
+  This is an expensive plugin, since it walks up the parent tree,
+  so it is off by default.
+*/
+
+class UnusedVariableMore : public RecursiveASTVisitor<UnusedVariableMore>, public Plugin
+{
+public:
+    explicit UnusedVariableMore(const InstantiationData& data);
+    virtual void run() override;
+    bool VisitVarDecl(VarDecl const*);
+    bool VisitDeclRefExpr(DeclRefExpr const*);
+    bool VisitFunctionDecl(FunctionDecl const*);
+
+private:
+    bool checkifUnused(Stmt const*, VarDecl const*);
+    bool isOkForParameter(const QualType&);
+
+    std::unordered_set<VarDecl const*> interestingSet;
+    // used to dump the last place that said the usage was unused, for debug purposes
+    std::unordered_map<VarDecl const*, Stmt const*> interestingDebugMap;
+};
+
+UnusedVariableMore::UnusedVariableMore(const InstantiationData& data)
+    : Plugin(data)
+{
+}
+
+static bool startswith(const std::string& rStr, const char* pSubStr)
+{
+    return rStr.compare(0, strlen(pSubStr), pSubStr) == 0;
+}
+
+void UnusedVariableMore::run()
+{
+    std::string fn(compiler.getSourceManager()
+                       .getFileEntryForID(compiler.getSourceManager().getMainFileID())
+                       ->getName());
+    loplugin::normalizeDotDotInFilePath(fn);
+
+    // ignore QA folders
+    if (startswith(fn, SRCDIR "/sal/qa/"))
+        return;
+    if (startswith(fn, SRCDIR "/i18npool/qa/"))
+        return;
+    if (startswith(fn, SRCDIR "/sc/qa/"))
+        return;
+
+    // vector of shared_ptr used to delay destruction
+    if (fn == SRCDIR "/cppuhelper/source/servicemanager.cxx")
+        return;
+    if (fn == SRCDIR "/i18nlangtag/source/languagetag/languagetag.cxx")
+        return;
+    if (fn == SRCDIR "/vcl/workben/outdevgrind.cxx")
+        return;
+    // unordered_set of Reference to delay destruction
+    if (fn == SRCDIR "/stoc/source/servicemanager/servicemanager.cxx")
+        return;
+    // TODO "operator >>" fooling me here
+    if (fn == SRCDIR "/editeng/source/accessibility/AccessibleEditableTextPara.cxx")
+        return;
+    // some weird stuff
+    if (fn == SRCDIR "/sfx2/source/dialog/dinfdlg.cxx")
+        return;
+    // std::vector< Reference< XInterface > > keep alive
+    if (fn == SRCDIR "/dbaccess/source/core/dataaccess/databasedocument.cxx")
+        return;
+    // template magic
+    if (fn == SRCDIR "/sc/source/core/tool/scmatrix.cxx")
+        return;
+    // storing local copy of Link<>
+    if (fn == SRCDIR "/sc/source/ui/miscdlgs/simpref.cxx")
+        return;
+    // Using an SwPaM to do stuff
+    if (fn == SRCDIR "/sw/source/core/crsr/bookmrk.cxx")
+        return;
+    // index variable in for loop?
+    if (fn == SRCDIR "/sw/source/uibase/docvw/edtwin.cxx")
+        return;
+    // TODO "operator >>" fooling me here
+    if (fn == SRCDIR "/sw/source/filter/ww8/ww8par.cxx")
+        return;
+    // TODO "operator >>" fooling me here
+    if (fn == SRCDIR "/sc/source/filter/excel/xistream.cxx")
+        return;
+
+    TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+
+    for (VarDecl const* varDecl : interestingSet)
+    {
+        report(DiagnosticsEngine::Warning, "unused variable %0", varDecl->getLocation())
+            << varDecl->getDeclName();
+        auto it = interestingDebugMap.find(varDecl);
+        if (it != interestingDebugMap.end())
+            it->second->dump();
+    }
+}
+
+bool isWarnUnusedType(QualType type)
+{
+    if (auto const t = type->getAs<TypedefType>())
+    {
+        if (t->getDecl()->hasAttr<WarnUnusedAttr>())
+        {
+            return true;
+        }
+    }
+    if (auto const t = type->getAs<RecordType>())
+    {
+        if (t->getDecl()->hasAttr<WarnUnusedAttr>())
+        {
+            return true;
+        }
+    }
+    return loplugin::isExtraWarnUnusedType(type);
+}
+
+bool UnusedVariableMore::VisitVarDecl(VarDecl const* var)
+{
+    if (ignoreLocation(var))
+        return true;
+    if (var->isDefinedOutsideFunctionOrMethod())
+        return true;
+    if (isa<ParmVarDecl>(var))
+        return true;
+    if (!isWarnUnusedType(var->getType()))
+        return true;
+
+    // some false +
+    auto dc = loplugin::TypeCheck(var->getType());
+    if (dc.Class("ZCodec").GlobalNamespace())
+        return true;
+    if (dc.Class("ScopedVclPtrInstance").GlobalNamespace())
+        return true;
+    if (dc.Class("VclPtrInstance").GlobalNamespace())
+        return true;
+    if (dc.Class("Config").GlobalNamespace())
+        return true;
+    // I think these classes modify global state somehow
+    if (dc.Class("SvtHistoryOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtSecurityOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtViewOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtUserOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtFontOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtMenuOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtPathOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtPrintWarningOptions").GlobalNamespace())
+        return true;
+    if (dc.Class("SvtSysLocaleOptions").GlobalNamespace())
+        return true;
+
+    interestingSet.insert(var);
+    return true;
+}
+
+bool UnusedVariableMore::VisitDeclRefExpr(DeclRefExpr const* declRefExpr)
+{
+    if (ignoreLocation(declRefExpr))
+        return true;
+    auto varDecl = dyn_cast<VarDecl>(declRefExpr->getDecl());
+    if (!varDecl)
+        return true;
+    if (interestingSet.find(varDecl) == interestingSet.end())
+        return true;
+    if (!checkifUnused(declRefExpr, varDecl))
+        interestingSet.erase(varDecl);
+    return true;
+}
+
+// Walk up from a statement that contains a DeclRefExpr, checking if the usage means that the
+// related VarDecl is unused.
+bool UnusedVariableMore::checkifUnused(Stmt const* stmt, VarDecl const* varDecl)
+{
+    const Stmt* parent = getParentStmt(stmt);
+    if (!parent)
+    {
+        // check if we're inside a CXXCtorInitializer
+        auto parentsRange = compiler.getASTContext().getParents(*stmt);
+        if (parentsRange.begin() != parentsRange.end())
+        {
+            auto parentDecl = parentsRange.begin()->get<Decl>();
+            if (parentDecl && (isa<CXXConstructorDecl>(parentDecl) || isa<VarDecl>(parentDecl)))
+                return false;
+        }
+        interestingDebugMap[varDecl] = stmt;
+        return true;
+    }
+
+    if (isa<ReturnStmt>(parent))
+        return false;
+    if (isa<IfStmt>(parent))
+        return false;
+    if (isa<SwitchStmt>(parent))
+        return false;
+    if (isa<InitListExpr>(parent))
+        return false;
+    if (isa<CXXConstructExpr>(parent))
+        return false;
+    if (isa<BinaryOperator>(parent))
+        return false;
+    if (isa<UnaryOperator>(parent))
+        return false;
+    if (isa<ConditionalOperator>(parent))
+        return false;
+    if (isa<ArraySubscriptExpr>(parent))
+        return false;
+    if (isa<CXXBindTemporaryExpr>(parent))
+        return checkifUnused(parent, varDecl);
+    if (isa<MaterializeTemporaryExpr>(parent))
+        return checkifUnused(parent, varDecl);
+
+    if (isa<CompoundStmt>(parent))
+    {
+        interestingDebugMap[varDecl] = parent;
+        return true;
+    }
+
+    // check for cast to void
+    if (auto explicitCastExpr = dyn_cast<ExplicitCastExpr>(parent))
+    {
+        if (loplugin::TypeCheck(explicitCastExpr->getTypeAsWritten()).Void())
+            return false;
+    }
+
+    if (isa<MemberExpr>(parent))
+        return checkifUnused(parent, varDecl);
+    if (isa<ExprWithCleanups>(parent))
+        return checkifUnused(parent, varDecl);
+    if (isa<CastExpr>(parent))
+        return checkifUnused(parent, varDecl);
+    if (isa<ParenExpr>(parent))
+        return checkifUnused(parent, varDecl);
+
+    if (auto operatorCallExpr = dyn_cast<CXXOperatorCallExpr>(parent))
+    {
+        const CXXMethodDecl* calleeMethodDecl
+            = dyn_cast_or_null<CXXMethodDecl>(operatorCallExpr->getDirectCallee());
+        if (calleeMethodDecl)
+        {
+            if (calleeMethodDecl->getNumParams() == 0)
+                return checkifUnused(parent, varDecl);
+            if (operatorCallExpr->getArg(0) == stmt)
+                return checkifUnused(parent, varDecl);
+        }
+    }
+    if (auto memberCallExpr = dyn_cast<CXXMemberCallExpr>(parent))
+    {
+        const MemberExpr* memberExpr = dyn_cast<MemberExpr>(stmt);
+        if (memberExpr && memberCallExpr->getImplicitObjectArgument() == memberExpr->getBase())
+        {
+            // if we are calling a method on the varDecl, walk up
+            if (!checkifUnused(parent, varDecl))
+                return false;
+            // check if we are passing something to the var by non-const ref, in which case it is updating something else for us
+            const FunctionDecl* calleeFunctionDecl = memberCallExpr->getDirectCallee();
+            if (calleeFunctionDecl)
+            {
+                if (calleeFunctionDecl->isVariadic())
+                    return false;
+                for (unsigned i = 0; i < memberCallExpr->getNumArgs(); ++i)
+                {
+                    if (i >= calleeFunctionDecl->getNumParams()) // can happen in template code
+                    {
+                        interestingDebugMap[varDecl] = parent;
+                        return true;
+                    }
+                    if (!isOkForParameter(calleeFunctionDecl->getParamDecl(i)->getType()))
+                        return false;
+                }
+            }
+            interestingDebugMap[varDecl] = parent;
+            return true;
+        }
+    }
+    if (isa<CallExpr>(parent))
+        return false;
+
+    interestingDebugMap[varDecl] = parent;
+    return true;
+}
+
+bool UnusedVariableMore::isOkForParameter(const QualType& qt)
+{
+    if (qt->isIntegralOrEnumerationType())
+        return true;
+    auto const type = loplugin::TypeCheck(qt);
+    if (type.Pointer())
+    {
+        return bool(type.Pointer().Const());
+    }
+    else if (type.LvalueReference())
+    {
+        return bool(type.LvalueReference().Const());
+    }
+    return false;
+}
+
+bool UnusedVariableMore::VisitFunctionDecl(FunctionDecl const* functionDecl)
+{
+    if (ignoreLocation(functionDecl))
+        return true;
+    //functionDecl->dump();
+    return true;
+}
+
+static Plugin::Registration<UnusedVariableMore> X("unusedvariablemore", false);
+
+} // namespace
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */